xref: /freebsd/contrib/llvm-project/clang/lib/Sema/SemaTemplate.cpp (revision 9e5787d2284e187abb5b654d924394a65772e004)
1 //===------- SemaTemplate.cpp - Semantic Analysis for C++ Templates -------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //===----------------------------------------------------------------------===//
7 //
8 //  This file implements semantic analysis for C++ templates.
9 //===----------------------------------------------------------------------===//
10 
11 #include "TreeTransform.h"
12 #include "clang/AST/ASTConsumer.h"
13 #include "clang/AST/ASTContext.h"
14 #include "clang/AST/DeclFriend.h"
15 #include "clang/AST/DeclTemplate.h"
16 #include "clang/AST/Expr.h"
17 #include "clang/AST/ExprCXX.h"
18 #include "clang/AST/RecursiveASTVisitor.h"
19 #include "clang/AST/TypeVisitor.h"
20 #include "clang/Basic/Builtins.h"
21 #include "clang/Basic/LangOptions.h"
22 #include "clang/Basic/PartialDiagnostic.h"
23 #include "clang/Basic/Stack.h"
24 #include "clang/Basic/TargetInfo.h"
25 #include "clang/Sema/DeclSpec.h"
26 #include "clang/Sema/Lookup.h"
27 #include "clang/Sema/Overload.h"
28 #include "clang/Sema/ParsedTemplate.h"
29 #include "clang/Sema/Scope.h"
30 #include "clang/Sema/SemaInternal.h"
31 #include "clang/Sema/Template.h"
32 #include "clang/Sema/TemplateDeduction.h"
33 #include "llvm/ADT/SmallBitVector.h"
34 #include "llvm/ADT/SmallString.h"
35 #include "llvm/ADT/StringExtras.h"
36 
37 #include <iterator>
38 using namespace clang;
39 using namespace sema;
40 
41 // Exported for use by Parser.
42 SourceRange
43 clang::getTemplateParamsRange(TemplateParameterList const * const *Ps,
44                               unsigned N) {
45   if (!N) return SourceRange();
46   return SourceRange(Ps[0]->getTemplateLoc(), Ps[N-1]->getRAngleLoc());
47 }
48 
49 unsigned Sema::getTemplateDepth(Scope *S) const {
50   unsigned Depth = 0;
51 
52   // Each template parameter scope represents one level of template parameter
53   // depth.
54   for (Scope *TempParamScope = S->getTemplateParamParent(); TempParamScope;
55        TempParamScope = TempParamScope->getParent()->getTemplateParamParent()) {
56     ++Depth;
57   }
58 
59   // Note that there are template parameters with the given depth.
60   auto ParamsAtDepth = [&](unsigned D) { Depth = std::max(Depth, D + 1); };
61 
62   // Look for parameters of an enclosing generic lambda. We don't create a
63   // template parameter scope for these.
64   for (FunctionScopeInfo *FSI : getFunctionScopes()) {
65     if (auto *LSI = dyn_cast<LambdaScopeInfo>(FSI)) {
66       if (!LSI->TemplateParams.empty()) {
67         ParamsAtDepth(LSI->AutoTemplateParameterDepth);
68         break;
69       }
70       if (LSI->GLTemplateParameterList) {
71         ParamsAtDepth(LSI->GLTemplateParameterList->getDepth());
72         break;
73       }
74     }
75   }
76 
77   // Look for parameters of an enclosing terse function template. We don't
78   // create a template parameter scope for these either.
79   for (const InventedTemplateParameterInfo &Info :
80        getInventedParameterInfos()) {
81     if (!Info.TemplateParams.empty()) {
82       ParamsAtDepth(Info.AutoTemplateParameterDepth);
83       break;
84     }
85   }
86 
87   return Depth;
88 }
89 
90 /// \brief Determine whether the declaration found is acceptable as the name
91 /// of a template and, if so, return that template declaration. Otherwise,
92 /// returns null.
93 ///
94 /// Note that this may return an UnresolvedUsingValueDecl if AllowDependent
95 /// is true. In all other cases it will return a TemplateDecl (or null).
96 NamedDecl *Sema::getAsTemplateNameDecl(NamedDecl *D,
97                                        bool AllowFunctionTemplates,
98                                        bool AllowDependent) {
99   D = D->getUnderlyingDecl();
100 
101   if (isa<TemplateDecl>(D)) {
102     if (!AllowFunctionTemplates && isa<FunctionTemplateDecl>(D))
103       return nullptr;
104 
105     return D;
106   }
107 
108   if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
109     // C++ [temp.local]p1:
110     //   Like normal (non-template) classes, class templates have an
111     //   injected-class-name (Clause 9). The injected-class-name
112     //   can be used with or without a template-argument-list. When
113     //   it is used without a template-argument-list, it is
114     //   equivalent to the injected-class-name followed by the
115     //   template-parameters of the class template enclosed in
116     //   <>. When it is used with a template-argument-list, it
117     //   refers to the specified class template specialization,
118     //   which could be the current specialization or another
119     //   specialization.
120     if (Record->isInjectedClassName()) {
121       Record = cast<CXXRecordDecl>(Record->getDeclContext());
122       if (Record->getDescribedClassTemplate())
123         return Record->getDescribedClassTemplate();
124 
125       if (ClassTemplateSpecializationDecl *Spec
126             = dyn_cast<ClassTemplateSpecializationDecl>(Record))
127         return Spec->getSpecializedTemplate();
128     }
129 
130     return nullptr;
131   }
132 
133   // 'using Dependent::foo;' can resolve to a template name.
134   // 'using typename Dependent::foo;' cannot (not even if 'foo' is an
135   // injected-class-name).
136   if (AllowDependent && isa<UnresolvedUsingValueDecl>(D))
137     return D;
138 
139   return nullptr;
140 }
141 
142 void Sema::FilterAcceptableTemplateNames(LookupResult &R,
143                                          bool AllowFunctionTemplates,
144                                          bool AllowDependent) {
145   LookupResult::Filter filter = R.makeFilter();
146   while (filter.hasNext()) {
147     NamedDecl *Orig = filter.next();
148     if (!getAsTemplateNameDecl(Orig, AllowFunctionTemplates, AllowDependent))
149       filter.erase();
150   }
151   filter.done();
152 }
153 
154 bool Sema::hasAnyAcceptableTemplateNames(LookupResult &R,
155                                          bool AllowFunctionTemplates,
156                                          bool AllowDependent,
157                                          bool AllowNonTemplateFunctions) {
158   for (LookupResult::iterator I = R.begin(), IEnd = R.end(); I != IEnd; ++I) {
159     if (getAsTemplateNameDecl(*I, AllowFunctionTemplates, AllowDependent))
160       return true;
161     if (AllowNonTemplateFunctions &&
162         isa<FunctionDecl>((*I)->getUnderlyingDecl()))
163       return true;
164   }
165 
166   return false;
167 }
168 
169 TemplateNameKind Sema::isTemplateName(Scope *S,
170                                       CXXScopeSpec &SS,
171                                       bool hasTemplateKeyword,
172                                       const UnqualifiedId &Name,
173                                       ParsedType ObjectTypePtr,
174                                       bool EnteringContext,
175                                       TemplateTy &TemplateResult,
176                                       bool &MemberOfUnknownSpecialization,
177                                       bool Disambiguation) {
178   assert(getLangOpts().CPlusPlus && "No template names in C!");
179 
180   DeclarationName TName;
181   MemberOfUnknownSpecialization = false;
182 
183   switch (Name.getKind()) {
184   case UnqualifiedIdKind::IK_Identifier:
185     TName = DeclarationName(Name.Identifier);
186     break;
187 
188   case UnqualifiedIdKind::IK_OperatorFunctionId:
189     TName = Context.DeclarationNames.getCXXOperatorName(
190                                               Name.OperatorFunctionId.Operator);
191     break;
192 
193   case UnqualifiedIdKind::IK_LiteralOperatorId:
194     TName = Context.DeclarationNames.getCXXLiteralOperatorName(Name.Identifier);
195     break;
196 
197   default:
198     return TNK_Non_template;
199   }
200 
201   QualType ObjectType = ObjectTypePtr.get();
202 
203   AssumedTemplateKind AssumedTemplate;
204   LookupResult R(*this, TName, Name.getBeginLoc(), LookupOrdinaryName);
205   if (LookupTemplateName(R, S, SS, ObjectType, EnteringContext,
206                          MemberOfUnknownSpecialization, SourceLocation(),
207                          &AssumedTemplate,
208                          /*AllowTypoCorrection=*/!Disambiguation))
209     return TNK_Non_template;
210 
211   if (AssumedTemplate != AssumedTemplateKind::None) {
212     TemplateResult = TemplateTy::make(Context.getAssumedTemplateName(TName));
213     // Let the parser know whether we found nothing or found functions; if we
214     // found nothing, we want to more carefully check whether this is actually
215     // a function template name versus some other kind of undeclared identifier.
216     return AssumedTemplate == AssumedTemplateKind::FoundNothing
217                ? TNK_Undeclared_template
218                : TNK_Function_template;
219   }
220 
221   if (R.empty())
222     return TNK_Non_template;
223 
224   NamedDecl *D = nullptr;
225   if (R.isAmbiguous()) {
226     // If we got an ambiguity involving a non-function template, treat this
227     // as a template name, and pick an arbitrary template for error recovery.
228     bool AnyFunctionTemplates = false;
229     for (NamedDecl *FoundD : R) {
230       if (NamedDecl *FoundTemplate = getAsTemplateNameDecl(FoundD)) {
231         if (isa<FunctionTemplateDecl>(FoundTemplate))
232           AnyFunctionTemplates = true;
233         else {
234           D = FoundTemplate;
235           break;
236         }
237       }
238     }
239 
240     // If we didn't find any templates at all, this isn't a template name.
241     // Leave the ambiguity for a later lookup to diagnose.
242     if (!D && !AnyFunctionTemplates) {
243       R.suppressDiagnostics();
244       return TNK_Non_template;
245     }
246 
247     // If the only templates were function templates, filter out the rest.
248     // We'll diagnose the ambiguity later.
249     if (!D)
250       FilterAcceptableTemplateNames(R);
251   }
252 
253   // At this point, we have either picked a single template name declaration D
254   // or we have a non-empty set of results R containing either one template name
255   // declaration or a set of function templates.
256 
257   TemplateName Template;
258   TemplateNameKind TemplateKind;
259 
260   unsigned ResultCount = R.end() - R.begin();
261   if (!D && ResultCount > 1) {
262     // We assume that we'll preserve the qualifier from a function
263     // template name in other ways.
264     Template = Context.getOverloadedTemplateName(R.begin(), R.end());
265     TemplateKind = TNK_Function_template;
266 
267     // We'll do this lookup again later.
268     R.suppressDiagnostics();
269   } else {
270     if (!D) {
271       D = getAsTemplateNameDecl(*R.begin());
272       assert(D && "unambiguous result is not a template name");
273     }
274 
275     if (isa<UnresolvedUsingValueDecl>(D)) {
276       // We don't yet know whether this is a template-name or not.
277       MemberOfUnknownSpecialization = true;
278       return TNK_Non_template;
279     }
280 
281     TemplateDecl *TD = cast<TemplateDecl>(D);
282 
283     if (SS.isSet() && !SS.isInvalid()) {
284       NestedNameSpecifier *Qualifier = SS.getScopeRep();
285       Template = Context.getQualifiedTemplateName(Qualifier,
286                                                   hasTemplateKeyword, TD);
287     } else {
288       Template = TemplateName(TD);
289     }
290 
291     if (isa<FunctionTemplateDecl>(TD)) {
292       TemplateKind = TNK_Function_template;
293 
294       // We'll do this lookup again later.
295       R.suppressDiagnostics();
296     } else {
297       assert(isa<ClassTemplateDecl>(TD) || isa<TemplateTemplateParmDecl>(TD) ||
298              isa<TypeAliasTemplateDecl>(TD) || isa<VarTemplateDecl>(TD) ||
299              isa<BuiltinTemplateDecl>(TD) || isa<ConceptDecl>(TD));
300       TemplateKind =
301           isa<VarTemplateDecl>(TD) ? TNK_Var_template :
302           isa<ConceptDecl>(TD) ? TNK_Concept_template :
303           TNK_Type_template;
304     }
305   }
306 
307   TemplateResult = TemplateTy::make(Template);
308   return TemplateKind;
309 }
310 
311 bool Sema::isDeductionGuideName(Scope *S, const IdentifierInfo &Name,
312                                 SourceLocation NameLoc,
313                                 ParsedTemplateTy *Template) {
314   CXXScopeSpec SS;
315   bool MemberOfUnknownSpecialization = false;
316 
317   // We could use redeclaration lookup here, but we don't need to: the
318   // syntactic form of a deduction guide is enough to identify it even
319   // if we can't look up the template name at all.
320   LookupResult R(*this, DeclarationName(&Name), NameLoc, LookupOrdinaryName);
321   if (LookupTemplateName(R, S, SS, /*ObjectType*/ QualType(),
322                          /*EnteringContext*/ false,
323                          MemberOfUnknownSpecialization))
324     return false;
325 
326   if (R.empty()) return false;
327   if (R.isAmbiguous()) {
328     // FIXME: Diagnose an ambiguity if we find at least one template.
329     R.suppressDiagnostics();
330     return false;
331   }
332 
333   // We only treat template-names that name type templates as valid deduction
334   // guide names.
335   TemplateDecl *TD = R.getAsSingle<TemplateDecl>();
336   if (!TD || !getAsTypeTemplateDecl(TD))
337     return false;
338 
339   if (Template)
340     *Template = TemplateTy::make(TemplateName(TD));
341   return true;
342 }
343 
344 bool Sema::DiagnoseUnknownTemplateName(const IdentifierInfo &II,
345                                        SourceLocation IILoc,
346                                        Scope *S,
347                                        const CXXScopeSpec *SS,
348                                        TemplateTy &SuggestedTemplate,
349                                        TemplateNameKind &SuggestedKind) {
350   // We can't recover unless there's a dependent scope specifier preceding the
351   // template name.
352   // FIXME: Typo correction?
353   if (!SS || !SS->isSet() || !isDependentScopeSpecifier(*SS) ||
354       computeDeclContext(*SS))
355     return false;
356 
357   // The code is missing a 'template' keyword prior to the dependent template
358   // name.
359   NestedNameSpecifier *Qualifier = (NestedNameSpecifier*)SS->getScopeRep();
360   Diag(IILoc, diag::err_template_kw_missing)
361     << Qualifier << II.getName()
362     << FixItHint::CreateInsertion(IILoc, "template ");
363   SuggestedTemplate
364     = TemplateTy::make(Context.getDependentTemplateName(Qualifier, &II));
365   SuggestedKind = TNK_Dependent_template_name;
366   return true;
367 }
368 
369 bool Sema::LookupTemplateName(LookupResult &Found,
370                               Scope *S, CXXScopeSpec &SS,
371                               QualType ObjectType,
372                               bool EnteringContext,
373                               bool &MemberOfUnknownSpecialization,
374                               RequiredTemplateKind RequiredTemplate,
375                               AssumedTemplateKind *ATK,
376                               bool AllowTypoCorrection) {
377   if (ATK)
378     *ATK = AssumedTemplateKind::None;
379 
380   if (SS.isInvalid())
381     return true;
382 
383   Found.setTemplateNameLookup(true);
384 
385   // Determine where to perform name lookup
386   MemberOfUnknownSpecialization = false;
387   DeclContext *LookupCtx = nullptr;
388   bool IsDependent = false;
389   if (!ObjectType.isNull()) {
390     // This nested-name-specifier occurs in a member access expression, e.g.,
391     // x->B::f, and we are looking into the type of the object.
392     assert(SS.isEmpty() && "ObjectType and scope specifier cannot coexist");
393     LookupCtx = computeDeclContext(ObjectType);
394     IsDependent = !LookupCtx && ObjectType->isDependentType();
395     assert((IsDependent || !ObjectType->isIncompleteType() ||
396             ObjectType->castAs<TagType>()->isBeingDefined()) &&
397            "Caller should have completed object type");
398 
399     // Template names cannot appear inside an Objective-C class or object type
400     // or a vector type.
401     //
402     // FIXME: This is wrong. For example:
403     //
404     //   template<typename T> using Vec = T __attribute__((ext_vector_type(4)));
405     //   Vec<int> vi;
406     //   vi.Vec<int>::~Vec<int>();
407     //
408     // ... should be accepted but we will not treat 'Vec' as a template name
409     // here. The right thing to do would be to check if the name is a valid
410     // vector component name, and look up a template name if not. And similarly
411     // for lookups into Objective-C class and object types, where the same
412     // problem can arise.
413     if (ObjectType->isObjCObjectOrInterfaceType() ||
414         ObjectType->isVectorType()) {
415       Found.clear();
416       return false;
417     }
418   } else if (SS.isNotEmpty()) {
419     // This nested-name-specifier occurs after another nested-name-specifier,
420     // so long into the context associated with the prior nested-name-specifier.
421     LookupCtx = computeDeclContext(SS, EnteringContext);
422     IsDependent = !LookupCtx && isDependentScopeSpecifier(SS);
423 
424     // The declaration context must be complete.
425     if (LookupCtx && RequireCompleteDeclContext(SS, LookupCtx))
426       return true;
427   }
428 
429   bool ObjectTypeSearchedInScope = false;
430   bool AllowFunctionTemplatesInLookup = true;
431   if (LookupCtx) {
432     // Perform "qualified" name lookup into the declaration context we
433     // computed, which is either the type of the base of a member access
434     // expression or the declaration context associated with a prior
435     // nested-name-specifier.
436     LookupQualifiedName(Found, LookupCtx);
437 
438     // FIXME: The C++ standard does not clearly specify what happens in the
439     // case where the object type is dependent, and implementations vary. In
440     // Clang, we treat a name after a . or -> as a template-name if lookup
441     // finds a non-dependent member or member of the current instantiation that
442     // is a type template, or finds no such members and lookup in the context
443     // of the postfix-expression finds a type template. In the latter case, the
444     // name is nonetheless dependent, and we may resolve it to a member of an
445     // unknown specialization when we come to instantiate the template.
446     IsDependent |= Found.wasNotFoundInCurrentInstantiation();
447   }
448 
449   if (SS.isEmpty() && (ObjectType.isNull() || Found.empty())) {
450     // C++ [basic.lookup.classref]p1:
451     //   In a class member access expression (5.2.5), if the . or -> token is
452     //   immediately followed by an identifier followed by a <, the
453     //   identifier must be looked up to determine whether the < is the
454     //   beginning of a template argument list (14.2) or a less-than operator.
455     //   The identifier is first looked up in the class of the object
456     //   expression. If the identifier is not found, it is then looked up in
457     //   the context of the entire postfix-expression and shall name a class
458     //   template.
459     if (S)
460       LookupName(Found, S);
461 
462     if (!ObjectType.isNull()) {
463       //  FIXME: We should filter out all non-type templates here, particularly
464       //  variable templates and concepts. But the exclusion of alias templates
465       //  and template template parameters is a wording defect.
466       AllowFunctionTemplatesInLookup = false;
467       ObjectTypeSearchedInScope = true;
468     }
469 
470     IsDependent |= Found.wasNotFoundInCurrentInstantiation();
471   }
472 
473   if (Found.isAmbiguous())
474     return false;
475 
476   if (ATK && SS.isEmpty() && ObjectType.isNull() &&
477       !RequiredTemplate.hasTemplateKeyword()) {
478     // C++2a [temp.names]p2:
479     //   A name is also considered to refer to a template if it is an
480     //   unqualified-id followed by a < and name lookup finds either one or more
481     //   functions or finds nothing.
482     //
483     // To keep our behavior consistent, we apply the "finds nothing" part in
484     // all language modes, and diagnose the empty lookup in ActOnCallExpr if we
485     // successfully form a call to an undeclared template-id.
486     bool AllFunctions =
487         getLangOpts().CPlusPlus20 &&
488         std::all_of(Found.begin(), Found.end(), [](NamedDecl *ND) {
489           return isa<FunctionDecl>(ND->getUnderlyingDecl());
490         });
491     if (AllFunctions || (Found.empty() && !IsDependent)) {
492       // If lookup found any functions, or if this is a name that can only be
493       // used for a function, then strongly assume this is a function
494       // template-id.
495       *ATK = (Found.empty() && Found.getLookupName().isIdentifier())
496                  ? AssumedTemplateKind::FoundNothing
497                  : AssumedTemplateKind::FoundFunctions;
498       Found.clear();
499       return false;
500     }
501   }
502 
503   if (Found.empty() && !IsDependent && AllowTypoCorrection) {
504     // If we did not find any names, and this is not a disambiguation, attempt
505     // to correct any typos.
506     DeclarationName Name = Found.getLookupName();
507     Found.clear();
508     // Simple filter callback that, for keywords, only accepts the C++ *_cast
509     DefaultFilterCCC FilterCCC{};
510     FilterCCC.WantTypeSpecifiers = false;
511     FilterCCC.WantExpressionKeywords = false;
512     FilterCCC.WantRemainingKeywords = false;
513     FilterCCC.WantCXXNamedCasts = true;
514     if (TypoCorrection Corrected =
515             CorrectTypo(Found.getLookupNameInfo(), Found.getLookupKind(), S,
516                         &SS, FilterCCC, CTK_ErrorRecovery, LookupCtx)) {
517       if (auto *ND = Corrected.getFoundDecl())
518         Found.addDecl(ND);
519       FilterAcceptableTemplateNames(Found);
520       if (Found.isAmbiguous()) {
521         Found.clear();
522       } else if (!Found.empty()) {
523         Found.setLookupName(Corrected.getCorrection());
524         if (LookupCtx) {
525           std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
526           bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
527                                   Name.getAsString() == CorrectedStr;
528           diagnoseTypo(Corrected, PDiag(diag::err_no_member_template_suggest)
529                                     << Name << LookupCtx << DroppedSpecifier
530                                     << SS.getRange());
531         } else {
532           diagnoseTypo(Corrected, PDiag(diag::err_no_template_suggest) << Name);
533         }
534       }
535     }
536   }
537 
538   NamedDecl *ExampleLookupResult =
539       Found.empty() ? nullptr : Found.getRepresentativeDecl();
540   FilterAcceptableTemplateNames(Found, AllowFunctionTemplatesInLookup);
541   if (Found.empty()) {
542     if (IsDependent) {
543       MemberOfUnknownSpecialization = true;
544       return false;
545     }
546 
547     // If a 'template' keyword was used, a lookup that finds only non-template
548     // names is an error.
549     if (ExampleLookupResult && RequiredTemplate) {
550       Diag(Found.getNameLoc(), diag::err_template_kw_refers_to_non_template)
551           << Found.getLookupName() << SS.getRange()
552           << RequiredTemplate.hasTemplateKeyword()
553           << RequiredTemplate.getTemplateKeywordLoc();
554       Diag(ExampleLookupResult->getUnderlyingDecl()->getLocation(),
555            diag::note_template_kw_refers_to_non_template)
556           << Found.getLookupName();
557       return true;
558     }
559 
560     return false;
561   }
562 
563   if (S && !ObjectType.isNull() && !ObjectTypeSearchedInScope &&
564       !getLangOpts().CPlusPlus11) {
565     // C++03 [basic.lookup.classref]p1:
566     //   [...] If the lookup in the class of the object expression finds a
567     //   template, the name is also looked up in the context of the entire
568     //   postfix-expression and [...]
569     //
570     // Note: C++11 does not perform this second lookup.
571     LookupResult FoundOuter(*this, Found.getLookupName(), Found.getNameLoc(),
572                             LookupOrdinaryName);
573     FoundOuter.setTemplateNameLookup(true);
574     LookupName(FoundOuter, S);
575     // FIXME: We silently accept an ambiguous lookup here, in violation of
576     // [basic.lookup]/1.
577     FilterAcceptableTemplateNames(FoundOuter, /*AllowFunctionTemplates=*/false);
578 
579     NamedDecl *OuterTemplate;
580     if (FoundOuter.empty()) {
581       //   - if the name is not found, the name found in the class of the
582       //     object expression is used, otherwise
583     } else if (FoundOuter.isAmbiguous() || !FoundOuter.isSingleResult() ||
584                !(OuterTemplate =
585                      getAsTemplateNameDecl(FoundOuter.getFoundDecl()))) {
586       //   - if the name is found in the context of the entire
587       //     postfix-expression and does not name a class template, the name
588       //     found in the class of the object expression is used, otherwise
589       FoundOuter.clear();
590     } else if (!Found.isSuppressingDiagnostics()) {
591       //   - if the name found is a class template, it must refer to the same
592       //     entity as the one found in the class of the object expression,
593       //     otherwise the program is ill-formed.
594       if (!Found.isSingleResult() ||
595           getAsTemplateNameDecl(Found.getFoundDecl())->getCanonicalDecl() !=
596               OuterTemplate->getCanonicalDecl()) {
597         Diag(Found.getNameLoc(),
598              diag::ext_nested_name_member_ref_lookup_ambiguous)
599           << Found.getLookupName()
600           << ObjectType;
601         Diag(Found.getRepresentativeDecl()->getLocation(),
602              diag::note_ambig_member_ref_object_type)
603           << ObjectType;
604         Diag(FoundOuter.getFoundDecl()->getLocation(),
605              diag::note_ambig_member_ref_scope);
606 
607         // Recover by taking the template that we found in the object
608         // expression's type.
609       }
610     }
611   }
612 
613   return false;
614 }
615 
616 void Sema::diagnoseExprIntendedAsTemplateName(Scope *S, ExprResult TemplateName,
617                                               SourceLocation Less,
618                                               SourceLocation Greater) {
619   if (TemplateName.isInvalid())
620     return;
621 
622   DeclarationNameInfo NameInfo;
623   CXXScopeSpec SS;
624   LookupNameKind LookupKind;
625 
626   DeclContext *LookupCtx = nullptr;
627   NamedDecl *Found = nullptr;
628   bool MissingTemplateKeyword = false;
629 
630   // Figure out what name we looked up.
631   if (auto *DRE = dyn_cast<DeclRefExpr>(TemplateName.get())) {
632     NameInfo = DRE->getNameInfo();
633     SS.Adopt(DRE->getQualifierLoc());
634     LookupKind = LookupOrdinaryName;
635     Found = DRE->getFoundDecl();
636   } else if (auto *ME = dyn_cast<MemberExpr>(TemplateName.get())) {
637     NameInfo = ME->getMemberNameInfo();
638     SS.Adopt(ME->getQualifierLoc());
639     LookupKind = LookupMemberName;
640     LookupCtx = ME->getBase()->getType()->getAsCXXRecordDecl();
641     Found = ME->getMemberDecl();
642   } else if (auto *DSDRE =
643                  dyn_cast<DependentScopeDeclRefExpr>(TemplateName.get())) {
644     NameInfo = DSDRE->getNameInfo();
645     SS.Adopt(DSDRE->getQualifierLoc());
646     MissingTemplateKeyword = true;
647   } else if (auto *DSME =
648                  dyn_cast<CXXDependentScopeMemberExpr>(TemplateName.get())) {
649     NameInfo = DSME->getMemberNameInfo();
650     SS.Adopt(DSME->getQualifierLoc());
651     MissingTemplateKeyword = true;
652   } else {
653     llvm_unreachable("unexpected kind of potential template name");
654   }
655 
656   // If this is a dependent-scope lookup, diagnose that the 'template' keyword
657   // was missing.
658   if (MissingTemplateKeyword) {
659     Diag(NameInfo.getBeginLoc(), diag::err_template_kw_missing)
660         << "" << NameInfo.getName().getAsString() << SourceRange(Less, Greater);
661     return;
662   }
663 
664   // Try to correct the name by looking for templates and C++ named casts.
665   struct TemplateCandidateFilter : CorrectionCandidateCallback {
666     Sema &S;
667     TemplateCandidateFilter(Sema &S) : S(S) {
668       WantTypeSpecifiers = false;
669       WantExpressionKeywords = false;
670       WantRemainingKeywords = false;
671       WantCXXNamedCasts = true;
672     };
673     bool ValidateCandidate(const TypoCorrection &Candidate) override {
674       if (auto *ND = Candidate.getCorrectionDecl())
675         return S.getAsTemplateNameDecl(ND);
676       return Candidate.isKeyword();
677     }
678 
679     std::unique_ptr<CorrectionCandidateCallback> clone() override {
680       return std::make_unique<TemplateCandidateFilter>(*this);
681     }
682   };
683 
684   DeclarationName Name = NameInfo.getName();
685   TemplateCandidateFilter CCC(*this);
686   if (TypoCorrection Corrected = CorrectTypo(NameInfo, LookupKind, S, &SS, CCC,
687                                              CTK_ErrorRecovery, LookupCtx)) {
688     auto *ND = Corrected.getFoundDecl();
689     if (ND)
690       ND = getAsTemplateNameDecl(ND);
691     if (ND || Corrected.isKeyword()) {
692       if (LookupCtx) {
693         std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
694         bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
695                                 Name.getAsString() == CorrectedStr;
696         diagnoseTypo(Corrected,
697                      PDiag(diag::err_non_template_in_member_template_id_suggest)
698                          << Name << LookupCtx << DroppedSpecifier
699                          << SS.getRange(), false);
700       } else {
701         diagnoseTypo(Corrected,
702                      PDiag(diag::err_non_template_in_template_id_suggest)
703                          << Name, false);
704       }
705       if (Found)
706         Diag(Found->getLocation(),
707              diag::note_non_template_in_template_id_found);
708       return;
709     }
710   }
711 
712   Diag(NameInfo.getLoc(), diag::err_non_template_in_template_id)
713     << Name << SourceRange(Less, Greater);
714   if (Found)
715     Diag(Found->getLocation(), diag::note_non_template_in_template_id_found);
716 }
717 
718 /// ActOnDependentIdExpression - Handle a dependent id-expression that
719 /// was just parsed.  This is only possible with an explicit scope
720 /// specifier naming a dependent type.
721 ExprResult
722 Sema::ActOnDependentIdExpression(const CXXScopeSpec &SS,
723                                  SourceLocation TemplateKWLoc,
724                                  const DeclarationNameInfo &NameInfo,
725                                  bool isAddressOfOperand,
726                            const TemplateArgumentListInfo *TemplateArgs) {
727   DeclContext *DC = getFunctionLevelDeclContext();
728 
729   // C++11 [expr.prim.general]p12:
730   //   An id-expression that denotes a non-static data member or non-static
731   //   member function of a class can only be used:
732   //   (...)
733   //   - if that id-expression denotes a non-static data member and it
734   //     appears in an unevaluated operand.
735   //
736   // If this might be the case, form a DependentScopeDeclRefExpr instead of a
737   // CXXDependentScopeMemberExpr. The former can instantiate to either
738   // DeclRefExpr or MemberExpr depending on lookup results, while the latter is
739   // always a MemberExpr.
740   bool MightBeCxx11UnevalField =
741       getLangOpts().CPlusPlus11 && isUnevaluatedContext();
742 
743   // Check if the nested name specifier is an enum type.
744   bool IsEnum = false;
745   if (NestedNameSpecifier *NNS = SS.getScopeRep())
746     IsEnum = dyn_cast_or_null<EnumType>(NNS->getAsType());
747 
748   if (!MightBeCxx11UnevalField && !isAddressOfOperand && !IsEnum &&
749       isa<CXXMethodDecl>(DC) && cast<CXXMethodDecl>(DC)->isInstance()) {
750     QualType ThisType = cast<CXXMethodDecl>(DC)->getThisType();
751 
752     // Since the 'this' expression is synthesized, we don't need to
753     // perform the double-lookup check.
754     NamedDecl *FirstQualifierInScope = nullptr;
755 
756     return CXXDependentScopeMemberExpr::Create(
757         Context, /*This*/ nullptr, ThisType, /*IsArrow*/ true,
758         /*Op*/ SourceLocation(), SS.getWithLocInContext(Context), TemplateKWLoc,
759         FirstQualifierInScope, NameInfo, TemplateArgs);
760   }
761 
762   return BuildDependentDeclRefExpr(SS, TemplateKWLoc, NameInfo, TemplateArgs);
763 }
764 
765 ExprResult
766 Sema::BuildDependentDeclRefExpr(const CXXScopeSpec &SS,
767                                 SourceLocation TemplateKWLoc,
768                                 const DeclarationNameInfo &NameInfo,
769                                 const TemplateArgumentListInfo *TemplateArgs) {
770   // DependentScopeDeclRefExpr::Create requires a valid QualifierLoc
771   NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
772   if (!QualifierLoc)
773     return ExprError();
774 
775   return DependentScopeDeclRefExpr::Create(
776       Context, QualifierLoc, TemplateKWLoc, NameInfo, TemplateArgs);
777 }
778 
779 
780 /// Determine whether we would be unable to instantiate this template (because
781 /// it either has no definition, or is in the process of being instantiated).
782 bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
783                                           NamedDecl *Instantiation,
784                                           bool InstantiatedFromMember,
785                                           const NamedDecl *Pattern,
786                                           const NamedDecl *PatternDef,
787                                           TemplateSpecializationKind TSK,
788                                           bool Complain /*= true*/) {
789   assert(isa<TagDecl>(Instantiation) || isa<FunctionDecl>(Instantiation) ||
790          isa<VarDecl>(Instantiation));
791 
792   bool IsEntityBeingDefined = false;
793   if (const TagDecl *TD = dyn_cast_or_null<TagDecl>(PatternDef))
794     IsEntityBeingDefined = TD->isBeingDefined();
795 
796   if (PatternDef && !IsEntityBeingDefined) {
797     NamedDecl *SuggestedDef = nullptr;
798     if (!hasVisibleDefinition(const_cast<NamedDecl*>(PatternDef), &SuggestedDef,
799                               /*OnlyNeedComplete*/false)) {
800       // If we're allowed to diagnose this and recover, do so.
801       bool Recover = Complain && !isSFINAEContext();
802       if (Complain)
803         diagnoseMissingImport(PointOfInstantiation, SuggestedDef,
804                               Sema::MissingImportKind::Definition, Recover);
805       return !Recover;
806     }
807     return false;
808   }
809 
810   if (!Complain || (PatternDef && PatternDef->isInvalidDecl()))
811     return true;
812 
813   llvm::Optional<unsigned> Note;
814   QualType InstantiationTy;
815   if (TagDecl *TD = dyn_cast<TagDecl>(Instantiation))
816     InstantiationTy = Context.getTypeDeclType(TD);
817   if (PatternDef) {
818     Diag(PointOfInstantiation,
819          diag::err_template_instantiate_within_definition)
820       << /*implicit|explicit*/(TSK != TSK_ImplicitInstantiation)
821       << InstantiationTy;
822     // Not much point in noting the template declaration here, since
823     // we're lexically inside it.
824     Instantiation->setInvalidDecl();
825   } else if (InstantiatedFromMember) {
826     if (isa<FunctionDecl>(Instantiation)) {
827       Diag(PointOfInstantiation,
828            diag::err_explicit_instantiation_undefined_member)
829         << /*member function*/ 1 << Instantiation->getDeclName()
830         << Instantiation->getDeclContext();
831       Note = diag::note_explicit_instantiation_here;
832     } else {
833       assert(isa<TagDecl>(Instantiation) && "Must be a TagDecl!");
834       Diag(PointOfInstantiation,
835            diag::err_implicit_instantiate_member_undefined)
836         << InstantiationTy;
837       Note = diag::note_member_declared_at;
838     }
839   } else {
840     if (isa<FunctionDecl>(Instantiation)) {
841       Diag(PointOfInstantiation,
842            diag::err_explicit_instantiation_undefined_func_template)
843         << Pattern;
844       Note = diag::note_explicit_instantiation_here;
845     } else if (isa<TagDecl>(Instantiation)) {
846       Diag(PointOfInstantiation, diag::err_template_instantiate_undefined)
847         << (TSK != TSK_ImplicitInstantiation)
848         << InstantiationTy;
849       Note = diag::note_template_decl_here;
850     } else {
851       assert(isa<VarDecl>(Instantiation) && "Must be a VarDecl!");
852       if (isa<VarTemplateSpecializationDecl>(Instantiation)) {
853         Diag(PointOfInstantiation,
854              diag::err_explicit_instantiation_undefined_var_template)
855           << Instantiation;
856         Instantiation->setInvalidDecl();
857       } else
858         Diag(PointOfInstantiation,
859              diag::err_explicit_instantiation_undefined_member)
860           << /*static data member*/ 2 << Instantiation->getDeclName()
861           << Instantiation->getDeclContext();
862       Note = diag::note_explicit_instantiation_here;
863     }
864   }
865   if (Note) // Diagnostics were emitted.
866     Diag(Pattern->getLocation(), Note.getValue());
867 
868   // In general, Instantiation isn't marked invalid to get more than one
869   // error for multiple undefined instantiations. But the code that does
870   // explicit declaration -> explicit definition conversion can't handle
871   // invalid declarations, so mark as invalid in that case.
872   if (TSK == TSK_ExplicitInstantiationDeclaration)
873     Instantiation->setInvalidDecl();
874   return true;
875 }
876 
877 /// DiagnoseTemplateParameterShadow - Produce a diagnostic complaining
878 /// that the template parameter 'PrevDecl' is being shadowed by a new
879 /// declaration at location Loc. Returns true to indicate that this is
880 /// an error, and false otherwise.
881 void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl) {
882   assert(PrevDecl->isTemplateParameter() && "Not a template parameter");
883 
884   // C++ [temp.local]p4:
885   //   A template-parameter shall not be redeclared within its
886   //   scope (including nested scopes).
887   //
888   // Make this a warning when MSVC compatibility is requested.
889   unsigned DiagId = getLangOpts().MSVCCompat ? diag::ext_template_param_shadow
890                                              : diag::err_template_param_shadow;
891   Diag(Loc, DiagId) << cast<NamedDecl>(PrevDecl)->getDeclName();
892   Diag(PrevDecl->getLocation(), diag::note_template_param_here);
893 }
894 
895 /// AdjustDeclIfTemplate - If the given decl happens to be a template, reset
896 /// the parameter D to reference the templated declaration and return a pointer
897 /// to the template declaration. Otherwise, do nothing to D and return null.
898 TemplateDecl *Sema::AdjustDeclIfTemplate(Decl *&D) {
899   if (TemplateDecl *Temp = dyn_cast_or_null<TemplateDecl>(D)) {
900     D = Temp->getTemplatedDecl();
901     return Temp;
902   }
903   return nullptr;
904 }
905 
906 ParsedTemplateArgument ParsedTemplateArgument::getTemplatePackExpansion(
907                                              SourceLocation EllipsisLoc) const {
908   assert(Kind == Template &&
909          "Only template template arguments can be pack expansions here");
910   assert(getAsTemplate().get().containsUnexpandedParameterPack() &&
911          "Template template argument pack expansion without packs");
912   ParsedTemplateArgument Result(*this);
913   Result.EllipsisLoc = EllipsisLoc;
914   return Result;
915 }
916 
917 static TemplateArgumentLoc translateTemplateArgument(Sema &SemaRef,
918                                             const ParsedTemplateArgument &Arg) {
919 
920   switch (Arg.getKind()) {
921   case ParsedTemplateArgument::Type: {
922     TypeSourceInfo *DI;
923     QualType T = SemaRef.GetTypeFromParser(Arg.getAsType(), &DI);
924     if (!DI)
925       DI = SemaRef.Context.getTrivialTypeSourceInfo(T, Arg.getLocation());
926     return TemplateArgumentLoc(TemplateArgument(T), DI);
927   }
928 
929   case ParsedTemplateArgument::NonType: {
930     Expr *E = static_cast<Expr *>(Arg.getAsExpr());
931     return TemplateArgumentLoc(TemplateArgument(E), E);
932   }
933 
934   case ParsedTemplateArgument::Template: {
935     TemplateName Template = Arg.getAsTemplate().get();
936     TemplateArgument TArg;
937     if (Arg.getEllipsisLoc().isValid())
938       TArg = TemplateArgument(Template, Optional<unsigned int>());
939     else
940       TArg = Template;
941     return TemplateArgumentLoc(TArg,
942                                Arg.getScopeSpec().getWithLocInContext(
943                                                               SemaRef.Context),
944                                Arg.getLocation(),
945                                Arg.getEllipsisLoc());
946   }
947   }
948 
949   llvm_unreachable("Unhandled parsed template argument");
950 }
951 
952 /// Translates template arguments as provided by the parser
953 /// into template arguments used by semantic analysis.
954 void Sema::translateTemplateArguments(const ASTTemplateArgsPtr &TemplateArgsIn,
955                                       TemplateArgumentListInfo &TemplateArgs) {
956  for (unsigned I = 0, Last = TemplateArgsIn.size(); I != Last; ++I)
957    TemplateArgs.addArgument(translateTemplateArgument(*this,
958                                                       TemplateArgsIn[I]));
959 }
960 
961 static void maybeDiagnoseTemplateParameterShadow(Sema &SemaRef, Scope *S,
962                                                  SourceLocation Loc,
963                                                  IdentifierInfo *Name) {
964   NamedDecl *PrevDecl = SemaRef.LookupSingleName(
965       S, Name, Loc, Sema::LookupOrdinaryName, Sema::ForVisibleRedeclaration);
966   if (PrevDecl && PrevDecl->isTemplateParameter())
967     SemaRef.DiagnoseTemplateParameterShadow(Loc, PrevDecl);
968 }
969 
970 /// Convert a parsed type into a parsed template argument. This is mostly
971 /// trivial, except that we may have parsed a C++17 deduced class template
972 /// specialization type, in which case we should form a template template
973 /// argument instead of a type template argument.
974 ParsedTemplateArgument Sema::ActOnTemplateTypeArgument(TypeResult ParsedType) {
975   TypeSourceInfo *TInfo;
976   QualType T = GetTypeFromParser(ParsedType.get(), &TInfo);
977   if (T.isNull())
978     return ParsedTemplateArgument();
979   assert(TInfo && "template argument with no location");
980 
981   // If we might have formed a deduced template specialization type, convert
982   // it to a template template argument.
983   if (getLangOpts().CPlusPlus17) {
984     TypeLoc TL = TInfo->getTypeLoc();
985     SourceLocation EllipsisLoc;
986     if (auto PET = TL.getAs<PackExpansionTypeLoc>()) {
987       EllipsisLoc = PET.getEllipsisLoc();
988       TL = PET.getPatternLoc();
989     }
990 
991     CXXScopeSpec SS;
992     if (auto ET = TL.getAs<ElaboratedTypeLoc>()) {
993       SS.Adopt(ET.getQualifierLoc());
994       TL = ET.getNamedTypeLoc();
995     }
996 
997     if (auto DTST = TL.getAs<DeducedTemplateSpecializationTypeLoc>()) {
998       TemplateName Name = DTST.getTypePtr()->getTemplateName();
999       if (SS.isSet())
1000         Name = Context.getQualifiedTemplateName(SS.getScopeRep(),
1001                                                 /*HasTemplateKeyword*/ false,
1002                                                 Name.getAsTemplateDecl());
1003       ParsedTemplateArgument Result(SS, TemplateTy::make(Name),
1004                                     DTST.getTemplateNameLoc());
1005       if (EllipsisLoc.isValid())
1006         Result = Result.getTemplatePackExpansion(EllipsisLoc);
1007       return Result;
1008     }
1009   }
1010 
1011   // This is a normal type template argument. Note, if the type template
1012   // argument is an injected-class-name for a template, it has a dual nature
1013   // and can be used as either a type or a template. We handle that in
1014   // convertTypeTemplateArgumentToTemplate.
1015   return ParsedTemplateArgument(ParsedTemplateArgument::Type,
1016                                 ParsedType.get().getAsOpaquePtr(),
1017                                 TInfo->getTypeLoc().getBeginLoc());
1018 }
1019 
1020 /// ActOnTypeParameter - Called when a C++ template type parameter
1021 /// (e.g., "typename T") has been parsed. Typename specifies whether
1022 /// the keyword "typename" was used to declare the type parameter
1023 /// (otherwise, "class" was used), and KeyLoc is the location of the
1024 /// "class" or "typename" keyword. ParamName is the name of the
1025 /// parameter (NULL indicates an unnamed template parameter) and
1026 /// ParamNameLoc is the location of the parameter name (if any).
1027 /// If the type parameter has a default argument, it will be added
1028 /// later via ActOnTypeParameterDefault.
1029 NamedDecl *Sema::ActOnTypeParameter(Scope *S, bool Typename,
1030                                     SourceLocation EllipsisLoc,
1031                                     SourceLocation KeyLoc,
1032                                     IdentifierInfo *ParamName,
1033                                     SourceLocation ParamNameLoc,
1034                                     unsigned Depth, unsigned Position,
1035                                     SourceLocation EqualLoc,
1036                                     ParsedType DefaultArg,
1037                                     bool HasTypeConstraint) {
1038   assert(S->isTemplateParamScope() &&
1039          "Template type parameter not in template parameter scope!");
1040 
1041   bool IsParameterPack = EllipsisLoc.isValid();
1042   TemplateTypeParmDecl *Param
1043     = TemplateTypeParmDecl::Create(Context, Context.getTranslationUnitDecl(),
1044                                    KeyLoc, ParamNameLoc, Depth, Position,
1045                                    ParamName, Typename, IsParameterPack,
1046                                    HasTypeConstraint);
1047   Param->setAccess(AS_public);
1048 
1049   if (Param->isParameterPack())
1050     if (auto *LSI = getEnclosingLambda())
1051       LSI->LocalPacks.push_back(Param);
1052 
1053   if (ParamName) {
1054     maybeDiagnoseTemplateParameterShadow(*this, S, ParamNameLoc, ParamName);
1055 
1056     // Add the template parameter into the current scope.
1057     S->AddDecl(Param);
1058     IdResolver.AddDecl(Param);
1059   }
1060 
1061   // C++0x [temp.param]p9:
1062   //   A default template-argument may be specified for any kind of
1063   //   template-parameter that is not a template parameter pack.
1064   if (DefaultArg && IsParameterPack) {
1065     Diag(EqualLoc, diag::err_template_param_pack_default_arg);
1066     DefaultArg = nullptr;
1067   }
1068 
1069   // Handle the default argument, if provided.
1070   if (DefaultArg) {
1071     TypeSourceInfo *DefaultTInfo;
1072     GetTypeFromParser(DefaultArg, &DefaultTInfo);
1073 
1074     assert(DefaultTInfo && "expected source information for type");
1075 
1076     // Check for unexpanded parameter packs.
1077     if (DiagnoseUnexpandedParameterPack(ParamNameLoc, DefaultTInfo,
1078                                         UPPC_DefaultArgument))
1079       return Param;
1080 
1081     // Check the template argument itself.
1082     if (CheckTemplateArgument(Param, DefaultTInfo)) {
1083       Param->setInvalidDecl();
1084       return Param;
1085     }
1086 
1087     Param->setDefaultArgument(DefaultTInfo);
1088   }
1089 
1090   return Param;
1091 }
1092 
1093 /// Convert the parser's template argument list representation into our form.
1094 static TemplateArgumentListInfo
1095 makeTemplateArgumentListInfo(Sema &S, TemplateIdAnnotation &TemplateId) {
1096   TemplateArgumentListInfo TemplateArgs(TemplateId.LAngleLoc,
1097                                         TemplateId.RAngleLoc);
1098   ASTTemplateArgsPtr TemplateArgsPtr(TemplateId.getTemplateArgs(),
1099                                      TemplateId.NumArgs);
1100   S.translateTemplateArguments(TemplateArgsPtr, TemplateArgs);
1101   return TemplateArgs;
1102 }
1103 
1104 bool Sema::ActOnTypeConstraint(const CXXScopeSpec &SS,
1105                                TemplateIdAnnotation *TypeConstr,
1106                                TemplateTypeParmDecl *ConstrainedParameter,
1107                                SourceLocation EllipsisLoc) {
1108   ConceptDecl *CD =
1109       cast<ConceptDecl>(TypeConstr->Template.get().getAsTemplateDecl());
1110 
1111   // C++2a [temp.param]p4:
1112   //     [...] The concept designated by a type-constraint shall be a type
1113   //     concept ([temp.concept]).
1114   if (!CD->isTypeConcept()) {
1115     Diag(TypeConstr->TemplateNameLoc,
1116          diag::err_type_constraint_non_type_concept);
1117     return true;
1118   }
1119 
1120   bool WereArgsSpecified = TypeConstr->LAngleLoc.isValid();
1121 
1122   if (!WereArgsSpecified &&
1123       CD->getTemplateParameters()->getMinRequiredArguments() > 1) {
1124     Diag(TypeConstr->TemplateNameLoc,
1125          diag::err_type_constraint_missing_arguments) << CD;
1126     return true;
1127   }
1128 
1129   TemplateArgumentListInfo TemplateArgs;
1130   if (TypeConstr->LAngleLoc.isValid()) {
1131     TemplateArgs =
1132         makeTemplateArgumentListInfo(*this, *TypeConstr);
1133   }
1134   return AttachTypeConstraint(
1135       SS.isSet() ? SS.getWithLocInContext(Context) : NestedNameSpecifierLoc(),
1136       DeclarationNameInfo(DeclarationName(TypeConstr->Name),
1137                           TypeConstr->TemplateNameLoc), CD,
1138       TypeConstr->LAngleLoc.isValid() ? &TemplateArgs : nullptr,
1139       ConstrainedParameter, EllipsisLoc);
1140 }
1141 
1142 template<typename ArgumentLocAppender>
1143 static ExprResult formImmediatelyDeclaredConstraint(
1144     Sema &S, NestedNameSpecifierLoc NS, DeclarationNameInfo NameInfo,
1145     ConceptDecl *NamedConcept, SourceLocation LAngleLoc,
1146     SourceLocation RAngleLoc, QualType ConstrainedType,
1147     SourceLocation ParamNameLoc, ArgumentLocAppender Appender,
1148     SourceLocation EllipsisLoc) {
1149 
1150   TemplateArgumentListInfo ConstraintArgs;
1151   ConstraintArgs.addArgument(
1152     S.getTrivialTemplateArgumentLoc(TemplateArgument(ConstrainedType),
1153                                     /*NTTPType=*/QualType(), ParamNameLoc));
1154 
1155   ConstraintArgs.setRAngleLoc(RAngleLoc);
1156   ConstraintArgs.setLAngleLoc(LAngleLoc);
1157   Appender(ConstraintArgs);
1158 
1159   // C++2a [temp.param]p4:
1160   //     [...] This constraint-expression E is called the immediately-declared
1161   //     constraint of T. [...]
1162   CXXScopeSpec SS;
1163   SS.Adopt(NS);
1164   ExprResult ImmediatelyDeclaredConstraint = S.CheckConceptTemplateId(
1165       SS, /*TemplateKWLoc=*/SourceLocation(), NameInfo,
1166       /*FoundDecl=*/NamedConcept, NamedConcept, &ConstraintArgs);
1167   if (ImmediatelyDeclaredConstraint.isInvalid() || !EllipsisLoc.isValid())
1168     return ImmediatelyDeclaredConstraint;
1169 
1170   // C++2a [temp.param]p4:
1171   //     [...] If T is not a pack, then E is E', otherwise E is (E' && ...).
1172   //
1173   // We have the following case:
1174   //
1175   // template<typename T> concept C1 = true;
1176   // template<C1... T> struct s1;
1177   //
1178   // The constraint: (C1<T> && ...)
1179   return S.BuildCXXFoldExpr(/*LParenLoc=*/SourceLocation(),
1180                             ImmediatelyDeclaredConstraint.get(), BO_LAnd,
1181                             EllipsisLoc, /*RHS=*/nullptr,
1182                             /*RParenLoc=*/SourceLocation(),
1183                             /*NumExpansions=*/None);
1184 }
1185 
1186 /// Attach a type-constraint to a template parameter.
1187 /// \returns true if an error occured. This can happen if the
1188 /// immediately-declared constraint could not be formed (e.g. incorrect number
1189 /// of arguments for the named concept).
1190 bool Sema::AttachTypeConstraint(NestedNameSpecifierLoc NS,
1191                                 DeclarationNameInfo NameInfo,
1192                                 ConceptDecl *NamedConcept,
1193                                 const TemplateArgumentListInfo *TemplateArgs,
1194                                 TemplateTypeParmDecl *ConstrainedParameter,
1195                                 SourceLocation EllipsisLoc) {
1196   // C++2a [temp.param]p4:
1197   //     [...] If Q is of the form C<A1, ..., An>, then let E' be
1198   //     C<T, A1, ..., An>. Otherwise, let E' be C<T>. [...]
1199   const ASTTemplateArgumentListInfo *ArgsAsWritten =
1200     TemplateArgs ? ASTTemplateArgumentListInfo::Create(Context,
1201                                                        *TemplateArgs) : nullptr;
1202 
1203   QualType ParamAsArgument(ConstrainedParameter->getTypeForDecl(), 0);
1204 
1205   ExprResult ImmediatelyDeclaredConstraint =
1206       formImmediatelyDeclaredConstraint(
1207           *this, NS, NameInfo, NamedConcept,
1208           TemplateArgs ? TemplateArgs->getLAngleLoc() : SourceLocation(),
1209           TemplateArgs ? TemplateArgs->getRAngleLoc() : SourceLocation(),
1210           ParamAsArgument, ConstrainedParameter->getLocation(),
1211           [&] (TemplateArgumentListInfo &ConstraintArgs) {
1212             if (TemplateArgs)
1213               for (const auto &ArgLoc : TemplateArgs->arguments())
1214                 ConstraintArgs.addArgument(ArgLoc);
1215           }, EllipsisLoc);
1216   if (ImmediatelyDeclaredConstraint.isInvalid())
1217     return true;
1218 
1219   ConstrainedParameter->setTypeConstraint(NS, NameInfo,
1220                                           /*FoundDecl=*/NamedConcept,
1221                                           NamedConcept, ArgsAsWritten,
1222                                           ImmediatelyDeclaredConstraint.get());
1223   return false;
1224 }
1225 
1226 bool Sema::AttachTypeConstraint(AutoTypeLoc TL, NonTypeTemplateParmDecl *NTTP,
1227                                 SourceLocation EllipsisLoc) {
1228   if (NTTP->getType() != TL.getType() ||
1229       TL.getAutoKeyword() != AutoTypeKeyword::Auto) {
1230     Diag(NTTP->getTypeSourceInfo()->getTypeLoc().getBeginLoc(),
1231          diag::err_unsupported_placeholder_constraint)
1232        << NTTP->getTypeSourceInfo()->getTypeLoc().getSourceRange();
1233     return true;
1234   }
1235   // FIXME: Concepts: This should be the type of the placeholder, but this is
1236   // unclear in the wording right now.
1237   DeclRefExpr *Ref = BuildDeclRefExpr(NTTP, NTTP->getType(), VK_RValue,
1238                                       NTTP->getLocation());
1239   if (!Ref)
1240     return true;
1241   ExprResult ImmediatelyDeclaredConstraint =
1242       formImmediatelyDeclaredConstraint(
1243           *this, TL.getNestedNameSpecifierLoc(), TL.getConceptNameInfo(),
1244           TL.getNamedConcept(), TL.getLAngleLoc(), TL.getRAngleLoc(),
1245           BuildDecltypeType(Ref, NTTP->getLocation()), NTTP->getLocation(),
1246           [&] (TemplateArgumentListInfo &ConstraintArgs) {
1247             for (unsigned I = 0, C = TL.getNumArgs(); I != C; ++I)
1248               ConstraintArgs.addArgument(TL.getArgLoc(I));
1249           }, EllipsisLoc);
1250   if (ImmediatelyDeclaredConstraint.isInvalid() ||
1251      !ImmediatelyDeclaredConstraint.isUsable())
1252     return true;
1253 
1254   NTTP->setPlaceholderTypeConstraint(ImmediatelyDeclaredConstraint.get());
1255   return false;
1256 }
1257 
1258 /// Check that the type of a non-type template parameter is
1259 /// well-formed.
1260 ///
1261 /// \returns the (possibly-promoted) parameter type if valid;
1262 /// otherwise, produces a diagnostic and returns a NULL type.
1263 QualType Sema::CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
1264                                                  SourceLocation Loc) {
1265   if (TSI->getType()->isUndeducedType()) {
1266     // C++17 [temp.dep.expr]p3:
1267     //   An id-expression is type-dependent if it contains
1268     //    - an identifier associated by name lookup with a non-type
1269     //      template-parameter declared with a type that contains a
1270     //      placeholder type (7.1.7.4),
1271     TSI = SubstAutoTypeSourceInfo(TSI, Context.DependentTy);
1272   }
1273 
1274   return CheckNonTypeTemplateParameterType(TSI->getType(), Loc);
1275 }
1276 
1277 QualType Sema::CheckNonTypeTemplateParameterType(QualType T,
1278                                                  SourceLocation Loc) {
1279   // We don't allow variably-modified types as the type of non-type template
1280   // parameters.
1281   if (T->isVariablyModifiedType()) {
1282     Diag(Loc, diag::err_variably_modified_nontype_template_param)
1283       << T;
1284     return QualType();
1285   }
1286 
1287   // C++ [temp.param]p4:
1288   //
1289   // A non-type template-parameter shall have one of the following
1290   // (optionally cv-qualified) types:
1291   //
1292   //       -- integral or enumeration type,
1293   if (T->isIntegralOrEnumerationType() ||
1294       //   -- pointer to object or pointer to function,
1295       T->isPointerType() ||
1296       //   -- reference to object or reference to function,
1297       T->isReferenceType() ||
1298       //   -- pointer to member,
1299       T->isMemberPointerType() ||
1300       //   -- std::nullptr_t.
1301       T->isNullPtrType() ||
1302       // Allow use of auto in template parameter declarations.
1303       T->isUndeducedType()) {
1304     // C++ [temp.param]p5: The top-level cv-qualifiers on the template-parameter
1305     // are ignored when determining its type.
1306     return T.getUnqualifiedType();
1307   }
1308 
1309   // C++ [temp.param]p8:
1310   //
1311   //   A non-type template-parameter of type "array of T" or
1312   //   "function returning T" is adjusted to be of type "pointer to
1313   //   T" or "pointer to function returning T", respectively.
1314   if (T->isArrayType() || T->isFunctionType())
1315     return Context.getDecayedType(T);
1316 
1317   // If T is a dependent type, we can't do the check now, so we
1318   // assume that it is well-formed. Note that stripping off the
1319   // qualifiers here is not really correct if T turns out to be
1320   // an array type, but we'll recompute the type everywhere it's
1321   // used during instantiation, so that should be OK. (Using the
1322   // qualified type is equally wrong.)
1323   if (T->isDependentType())
1324     return T.getUnqualifiedType();
1325 
1326   Diag(Loc, diag::err_template_nontype_parm_bad_type)
1327     << T;
1328 
1329   return QualType();
1330 }
1331 
1332 NamedDecl *Sema::ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
1333                                           unsigned Depth,
1334                                           unsigned Position,
1335                                           SourceLocation EqualLoc,
1336                                           Expr *Default) {
1337   TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
1338 
1339   // Check that we have valid decl-specifiers specified.
1340   auto CheckValidDeclSpecifiers = [this, &D] {
1341     // C++ [temp.param]
1342     // p1
1343     //   template-parameter:
1344     //     ...
1345     //     parameter-declaration
1346     // p2
1347     //   ... A storage class shall not be specified in a template-parameter
1348     //   declaration.
1349     // [dcl.typedef]p1:
1350     //   The typedef specifier [...] shall not be used in the decl-specifier-seq
1351     //   of a parameter-declaration
1352     const DeclSpec &DS = D.getDeclSpec();
1353     auto EmitDiag = [this](SourceLocation Loc) {
1354       Diag(Loc, diag::err_invalid_decl_specifier_in_nontype_parm)
1355           << FixItHint::CreateRemoval(Loc);
1356     };
1357     if (DS.getStorageClassSpec() != DeclSpec::SCS_unspecified)
1358       EmitDiag(DS.getStorageClassSpecLoc());
1359 
1360     if (DS.getThreadStorageClassSpec() != TSCS_unspecified)
1361       EmitDiag(DS.getThreadStorageClassSpecLoc());
1362 
1363     // [dcl.inline]p1:
1364     //   The inline specifier can be applied only to the declaration or
1365     //   definition of a variable or function.
1366 
1367     if (DS.isInlineSpecified())
1368       EmitDiag(DS.getInlineSpecLoc());
1369 
1370     // [dcl.constexpr]p1:
1371     //   The constexpr specifier shall be applied only to the definition of a
1372     //   variable or variable template or the declaration of a function or
1373     //   function template.
1374 
1375     if (DS.hasConstexprSpecifier())
1376       EmitDiag(DS.getConstexprSpecLoc());
1377 
1378     // [dcl.fct.spec]p1:
1379     //   Function-specifiers can be used only in function declarations.
1380 
1381     if (DS.isVirtualSpecified())
1382       EmitDiag(DS.getVirtualSpecLoc());
1383 
1384     if (DS.hasExplicitSpecifier())
1385       EmitDiag(DS.getExplicitSpecLoc());
1386 
1387     if (DS.isNoreturnSpecified())
1388       EmitDiag(DS.getNoreturnSpecLoc());
1389   };
1390 
1391   CheckValidDeclSpecifiers();
1392 
1393   if (TInfo->getType()->isUndeducedType()) {
1394     Diag(D.getIdentifierLoc(),
1395          diag::warn_cxx14_compat_template_nontype_parm_auto_type)
1396       << QualType(TInfo->getType()->getContainedAutoType(), 0);
1397   }
1398 
1399   assert(S->isTemplateParamScope() &&
1400          "Non-type template parameter not in template parameter scope!");
1401   bool Invalid = false;
1402 
1403   QualType T = CheckNonTypeTemplateParameterType(TInfo, D.getIdentifierLoc());
1404   if (T.isNull()) {
1405     T = Context.IntTy; // Recover with an 'int' type.
1406     Invalid = true;
1407   }
1408 
1409   CheckFunctionOrTemplateParamDeclarator(S, D);
1410 
1411   IdentifierInfo *ParamName = D.getIdentifier();
1412   bool IsParameterPack = D.hasEllipsis();
1413   NonTypeTemplateParmDecl *Param = NonTypeTemplateParmDecl::Create(
1414       Context, Context.getTranslationUnitDecl(), D.getBeginLoc(),
1415       D.getIdentifierLoc(), Depth, Position, ParamName, T, IsParameterPack,
1416       TInfo);
1417   Param->setAccess(AS_public);
1418 
1419   if (AutoTypeLoc TL = TInfo->getTypeLoc().getContainedAutoTypeLoc())
1420     if (TL.isConstrained())
1421       if (AttachTypeConstraint(TL, Param, D.getEllipsisLoc()))
1422         Invalid = true;
1423 
1424   if (Invalid)
1425     Param->setInvalidDecl();
1426 
1427   if (Param->isParameterPack())
1428     if (auto *LSI = getEnclosingLambda())
1429       LSI->LocalPacks.push_back(Param);
1430 
1431   if (ParamName) {
1432     maybeDiagnoseTemplateParameterShadow(*this, S, D.getIdentifierLoc(),
1433                                          ParamName);
1434 
1435     // Add the template parameter into the current scope.
1436     S->AddDecl(Param);
1437     IdResolver.AddDecl(Param);
1438   }
1439 
1440   // C++0x [temp.param]p9:
1441   //   A default template-argument may be specified for any kind of
1442   //   template-parameter that is not a template parameter pack.
1443   if (Default && IsParameterPack) {
1444     Diag(EqualLoc, diag::err_template_param_pack_default_arg);
1445     Default = nullptr;
1446   }
1447 
1448   // Check the well-formedness of the default template argument, if provided.
1449   if (Default) {
1450     // Check for unexpanded parameter packs.
1451     if (DiagnoseUnexpandedParameterPack(Default, UPPC_DefaultArgument))
1452       return Param;
1453 
1454     TemplateArgument Converted;
1455     ExprResult DefaultRes =
1456         CheckTemplateArgument(Param, Param->getType(), Default, Converted);
1457     if (DefaultRes.isInvalid()) {
1458       Param->setInvalidDecl();
1459       return Param;
1460     }
1461     Default = DefaultRes.get();
1462 
1463     Param->setDefaultArgument(Default);
1464   }
1465 
1466   return Param;
1467 }
1468 
1469 /// ActOnTemplateTemplateParameter - Called when a C++ template template
1470 /// parameter (e.g. T in template <template \<typename> class T> class array)
1471 /// has been parsed. S is the current scope.
1472 NamedDecl *Sema::ActOnTemplateTemplateParameter(Scope* S,
1473                                            SourceLocation TmpLoc,
1474                                            TemplateParameterList *Params,
1475                                            SourceLocation EllipsisLoc,
1476                                            IdentifierInfo *Name,
1477                                            SourceLocation NameLoc,
1478                                            unsigned Depth,
1479                                            unsigned Position,
1480                                            SourceLocation EqualLoc,
1481                                            ParsedTemplateArgument Default) {
1482   assert(S->isTemplateParamScope() &&
1483          "Template template parameter not in template parameter scope!");
1484 
1485   // Construct the parameter object.
1486   bool IsParameterPack = EllipsisLoc.isValid();
1487   TemplateTemplateParmDecl *Param =
1488     TemplateTemplateParmDecl::Create(Context, Context.getTranslationUnitDecl(),
1489                                      NameLoc.isInvalid()? TmpLoc : NameLoc,
1490                                      Depth, Position, IsParameterPack,
1491                                      Name, Params);
1492   Param->setAccess(AS_public);
1493 
1494   if (Param->isParameterPack())
1495     if (auto *LSI = getEnclosingLambda())
1496       LSI->LocalPacks.push_back(Param);
1497 
1498   // If the template template parameter has a name, then link the identifier
1499   // into the scope and lookup mechanisms.
1500   if (Name) {
1501     maybeDiagnoseTemplateParameterShadow(*this, S, NameLoc, Name);
1502 
1503     S->AddDecl(Param);
1504     IdResolver.AddDecl(Param);
1505   }
1506 
1507   if (Params->size() == 0) {
1508     Diag(Param->getLocation(), diag::err_template_template_parm_no_parms)
1509     << SourceRange(Params->getLAngleLoc(), Params->getRAngleLoc());
1510     Param->setInvalidDecl();
1511   }
1512 
1513   // C++0x [temp.param]p9:
1514   //   A default template-argument may be specified for any kind of
1515   //   template-parameter that is not a template parameter pack.
1516   if (IsParameterPack && !Default.isInvalid()) {
1517     Diag(EqualLoc, diag::err_template_param_pack_default_arg);
1518     Default = ParsedTemplateArgument();
1519   }
1520 
1521   if (!Default.isInvalid()) {
1522     // Check only that we have a template template argument. We don't want to
1523     // try to check well-formedness now, because our template template parameter
1524     // might have dependent types in its template parameters, which we wouldn't
1525     // be able to match now.
1526     //
1527     // If none of the template template parameter's template arguments mention
1528     // other template parameters, we could actually perform more checking here.
1529     // However, it isn't worth doing.
1530     TemplateArgumentLoc DefaultArg = translateTemplateArgument(*this, Default);
1531     if (DefaultArg.getArgument().getAsTemplate().isNull()) {
1532       Diag(DefaultArg.getLocation(), diag::err_template_arg_not_valid_template)
1533         << DefaultArg.getSourceRange();
1534       return Param;
1535     }
1536 
1537     // Check for unexpanded parameter packs.
1538     if (DiagnoseUnexpandedParameterPack(DefaultArg.getLocation(),
1539                                         DefaultArg.getArgument().getAsTemplate(),
1540                                         UPPC_DefaultArgument))
1541       return Param;
1542 
1543     Param->setDefaultArgument(Context, DefaultArg);
1544   }
1545 
1546   return Param;
1547 }
1548 
1549 /// ActOnTemplateParameterList - Builds a TemplateParameterList, optionally
1550 /// constrained by RequiresClause, that contains the template parameters in
1551 /// Params.
1552 TemplateParameterList *
1553 Sema::ActOnTemplateParameterList(unsigned Depth,
1554                                  SourceLocation ExportLoc,
1555                                  SourceLocation TemplateLoc,
1556                                  SourceLocation LAngleLoc,
1557                                  ArrayRef<NamedDecl *> Params,
1558                                  SourceLocation RAngleLoc,
1559                                  Expr *RequiresClause) {
1560   if (ExportLoc.isValid())
1561     Diag(ExportLoc, diag::warn_template_export_unsupported);
1562 
1563   return TemplateParameterList::Create(
1564       Context, TemplateLoc, LAngleLoc,
1565       llvm::makeArrayRef(Params.data(), Params.size()),
1566       RAngleLoc, RequiresClause);
1567 }
1568 
1569 static void SetNestedNameSpecifier(Sema &S, TagDecl *T,
1570                                    const CXXScopeSpec &SS) {
1571   if (SS.isSet())
1572     T->setQualifierInfo(SS.getWithLocInContext(S.Context));
1573 }
1574 
1575 DeclResult Sema::CheckClassTemplate(
1576     Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
1577     CXXScopeSpec &SS, IdentifierInfo *Name, SourceLocation NameLoc,
1578     const ParsedAttributesView &Attr, TemplateParameterList *TemplateParams,
1579     AccessSpecifier AS, SourceLocation ModulePrivateLoc,
1580     SourceLocation FriendLoc, unsigned NumOuterTemplateParamLists,
1581     TemplateParameterList **OuterTemplateParamLists, SkipBodyInfo *SkipBody) {
1582   assert(TemplateParams && TemplateParams->size() > 0 &&
1583          "No template parameters");
1584   assert(TUK != TUK_Reference && "Can only declare or define class templates");
1585   bool Invalid = false;
1586 
1587   // Check that we can declare a template here.
1588   if (CheckTemplateDeclScope(S, TemplateParams))
1589     return true;
1590 
1591   TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForTypeSpec(TagSpec);
1592   assert(Kind != TTK_Enum && "can't build template of enumerated type");
1593 
1594   // There is no such thing as an unnamed class template.
1595   if (!Name) {
1596     Diag(KWLoc, diag::err_template_unnamed_class);
1597     return true;
1598   }
1599 
1600   // Find any previous declaration with this name. For a friend with no
1601   // scope explicitly specified, we only look for tag declarations (per
1602   // C++11 [basic.lookup.elab]p2).
1603   DeclContext *SemanticContext;
1604   LookupResult Previous(*this, Name, NameLoc,
1605                         (SS.isEmpty() && TUK == TUK_Friend)
1606                           ? LookupTagName : LookupOrdinaryName,
1607                         forRedeclarationInCurContext());
1608   if (SS.isNotEmpty() && !SS.isInvalid()) {
1609     SemanticContext = computeDeclContext(SS, true);
1610     if (!SemanticContext) {
1611       // FIXME: Horrible, horrible hack! We can't currently represent this
1612       // in the AST, and historically we have just ignored such friend
1613       // class templates, so don't complain here.
1614       Diag(NameLoc, TUK == TUK_Friend
1615                         ? diag::warn_template_qualified_friend_ignored
1616                         : diag::err_template_qualified_declarator_no_match)
1617           << SS.getScopeRep() << SS.getRange();
1618       return TUK != TUK_Friend;
1619     }
1620 
1621     if (RequireCompleteDeclContext(SS, SemanticContext))
1622       return true;
1623 
1624     // If we're adding a template to a dependent context, we may need to
1625     // rebuilding some of the types used within the template parameter list,
1626     // now that we know what the current instantiation is.
1627     if (SemanticContext->isDependentContext()) {
1628       ContextRAII SavedContext(*this, SemanticContext);
1629       if (RebuildTemplateParamsInCurrentInstantiation(TemplateParams))
1630         Invalid = true;
1631     } else if (TUK != TUK_Friend && TUK != TUK_Reference)
1632       diagnoseQualifiedDeclaration(SS, SemanticContext, Name, NameLoc, false);
1633 
1634     LookupQualifiedName(Previous, SemanticContext);
1635   } else {
1636     SemanticContext = CurContext;
1637 
1638     // C++14 [class.mem]p14:
1639     //   If T is the name of a class, then each of the following shall have a
1640     //   name different from T:
1641     //    -- every member template of class T
1642     if (TUK != TUK_Friend &&
1643         DiagnoseClassNameShadow(SemanticContext,
1644                                 DeclarationNameInfo(Name, NameLoc)))
1645       return true;
1646 
1647     LookupName(Previous, S);
1648   }
1649 
1650   if (Previous.isAmbiguous())
1651     return true;
1652 
1653   NamedDecl *PrevDecl = nullptr;
1654   if (Previous.begin() != Previous.end())
1655     PrevDecl = (*Previous.begin())->getUnderlyingDecl();
1656 
1657   if (PrevDecl && PrevDecl->isTemplateParameter()) {
1658     // Maybe we will complain about the shadowed template parameter.
1659     DiagnoseTemplateParameterShadow(NameLoc, PrevDecl);
1660     // Just pretend that we didn't see the previous declaration.
1661     PrevDecl = nullptr;
1662   }
1663 
1664   // If there is a previous declaration with the same name, check
1665   // whether this is a valid redeclaration.
1666   ClassTemplateDecl *PrevClassTemplate =
1667       dyn_cast_or_null<ClassTemplateDecl>(PrevDecl);
1668 
1669   // We may have found the injected-class-name of a class template,
1670   // class template partial specialization, or class template specialization.
1671   // In these cases, grab the template that is being defined or specialized.
1672   if (!PrevClassTemplate && PrevDecl && isa<CXXRecordDecl>(PrevDecl) &&
1673       cast<CXXRecordDecl>(PrevDecl)->isInjectedClassName()) {
1674     PrevDecl = cast<CXXRecordDecl>(PrevDecl->getDeclContext());
1675     PrevClassTemplate
1676       = cast<CXXRecordDecl>(PrevDecl)->getDescribedClassTemplate();
1677     if (!PrevClassTemplate && isa<ClassTemplateSpecializationDecl>(PrevDecl)) {
1678       PrevClassTemplate
1679         = cast<ClassTemplateSpecializationDecl>(PrevDecl)
1680             ->getSpecializedTemplate();
1681     }
1682   }
1683 
1684   if (TUK == TUK_Friend) {
1685     // C++ [namespace.memdef]p3:
1686     //   [...] When looking for a prior declaration of a class or a function
1687     //   declared as a friend, and when the name of the friend class or
1688     //   function is neither a qualified name nor a template-id, scopes outside
1689     //   the innermost enclosing namespace scope are not considered.
1690     if (!SS.isSet()) {
1691       DeclContext *OutermostContext = CurContext;
1692       while (!OutermostContext->isFileContext())
1693         OutermostContext = OutermostContext->getLookupParent();
1694 
1695       if (PrevDecl &&
1696           (OutermostContext->Equals(PrevDecl->getDeclContext()) ||
1697            OutermostContext->Encloses(PrevDecl->getDeclContext()))) {
1698         SemanticContext = PrevDecl->getDeclContext();
1699       } else {
1700         // Declarations in outer scopes don't matter. However, the outermost
1701         // context we computed is the semantic context for our new
1702         // declaration.
1703         PrevDecl = PrevClassTemplate = nullptr;
1704         SemanticContext = OutermostContext;
1705 
1706         // Check that the chosen semantic context doesn't already contain a
1707         // declaration of this name as a non-tag type.
1708         Previous.clear(LookupOrdinaryName);
1709         DeclContext *LookupContext = SemanticContext;
1710         while (LookupContext->isTransparentContext())
1711           LookupContext = LookupContext->getLookupParent();
1712         LookupQualifiedName(Previous, LookupContext);
1713 
1714         if (Previous.isAmbiguous())
1715           return true;
1716 
1717         if (Previous.begin() != Previous.end())
1718           PrevDecl = (*Previous.begin())->getUnderlyingDecl();
1719       }
1720     }
1721   } else if (PrevDecl &&
1722              !isDeclInScope(Previous.getRepresentativeDecl(), SemanticContext,
1723                             S, SS.isValid()))
1724     PrevDecl = PrevClassTemplate = nullptr;
1725 
1726   if (auto *Shadow = dyn_cast_or_null<UsingShadowDecl>(
1727           PrevDecl ? Previous.getRepresentativeDecl() : nullptr)) {
1728     if (SS.isEmpty() &&
1729         !(PrevClassTemplate &&
1730           PrevClassTemplate->getDeclContext()->getRedeclContext()->Equals(
1731               SemanticContext->getRedeclContext()))) {
1732       Diag(KWLoc, diag::err_using_decl_conflict_reverse);
1733       Diag(Shadow->getTargetDecl()->getLocation(),
1734            diag::note_using_decl_target);
1735       Diag(Shadow->getUsingDecl()->getLocation(), diag::note_using_decl) << 0;
1736       // Recover by ignoring the old declaration.
1737       PrevDecl = PrevClassTemplate = nullptr;
1738     }
1739   }
1740 
1741   if (PrevClassTemplate) {
1742     // Ensure that the template parameter lists are compatible. Skip this check
1743     // for a friend in a dependent context: the template parameter list itself
1744     // could be dependent.
1745     if (!(TUK == TUK_Friend && CurContext->isDependentContext()) &&
1746         !TemplateParameterListsAreEqual(TemplateParams,
1747                                    PrevClassTemplate->getTemplateParameters(),
1748                                         /*Complain=*/true,
1749                                         TPL_TemplateMatch))
1750       return true;
1751 
1752     // C++ [temp.class]p4:
1753     //   In a redeclaration, partial specialization, explicit
1754     //   specialization or explicit instantiation of a class template,
1755     //   the class-key shall agree in kind with the original class
1756     //   template declaration (7.1.5.3).
1757     RecordDecl *PrevRecordDecl = PrevClassTemplate->getTemplatedDecl();
1758     if (!isAcceptableTagRedeclaration(PrevRecordDecl, Kind,
1759                                       TUK == TUK_Definition,  KWLoc, Name)) {
1760       Diag(KWLoc, diag::err_use_with_wrong_tag)
1761         << Name
1762         << FixItHint::CreateReplacement(KWLoc, PrevRecordDecl->getKindName());
1763       Diag(PrevRecordDecl->getLocation(), diag::note_previous_use);
1764       Kind = PrevRecordDecl->getTagKind();
1765     }
1766 
1767     // Check for redefinition of this class template.
1768     if (TUK == TUK_Definition) {
1769       if (TagDecl *Def = PrevRecordDecl->getDefinition()) {
1770         // If we have a prior definition that is not visible, treat this as
1771         // simply making that previous definition visible.
1772         NamedDecl *Hidden = nullptr;
1773         if (SkipBody && !hasVisibleDefinition(Def, &Hidden)) {
1774           SkipBody->ShouldSkip = true;
1775           SkipBody->Previous = Def;
1776           auto *Tmpl = cast<CXXRecordDecl>(Hidden)->getDescribedClassTemplate();
1777           assert(Tmpl && "original definition of a class template is not a "
1778                          "class template?");
1779           makeMergedDefinitionVisible(Hidden);
1780           makeMergedDefinitionVisible(Tmpl);
1781         } else {
1782           Diag(NameLoc, diag::err_redefinition) << Name;
1783           Diag(Def->getLocation(), diag::note_previous_definition);
1784           // FIXME: Would it make sense to try to "forget" the previous
1785           // definition, as part of error recovery?
1786           return true;
1787         }
1788       }
1789     }
1790   } else if (PrevDecl) {
1791     // C++ [temp]p5:
1792     //   A class template shall not have the same name as any other
1793     //   template, class, function, object, enumeration, enumerator,
1794     //   namespace, or type in the same scope (3.3), except as specified
1795     //   in (14.5.4).
1796     Diag(NameLoc, diag::err_redefinition_different_kind) << Name;
1797     Diag(PrevDecl->getLocation(), diag::note_previous_definition);
1798     return true;
1799   }
1800 
1801   // Check the template parameter list of this declaration, possibly
1802   // merging in the template parameter list from the previous class
1803   // template declaration. Skip this check for a friend in a dependent
1804   // context, because the template parameter list might be dependent.
1805   if (!(TUK == TUK_Friend && CurContext->isDependentContext()) &&
1806       CheckTemplateParameterList(
1807           TemplateParams,
1808           PrevClassTemplate
1809               ? PrevClassTemplate->getMostRecentDecl()->getTemplateParameters()
1810               : nullptr,
1811           (SS.isSet() && SemanticContext && SemanticContext->isRecord() &&
1812            SemanticContext->isDependentContext())
1813               ? TPC_ClassTemplateMember
1814               : TUK == TUK_Friend ? TPC_FriendClassTemplate : TPC_ClassTemplate,
1815           SkipBody))
1816     Invalid = true;
1817 
1818   if (SS.isSet()) {
1819     // If the name of the template was qualified, we must be defining the
1820     // template out-of-line.
1821     if (!SS.isInvalid() && !Invalid && !PrevClassTemplate) {
1822       Diag(NameLoc, TUK == TUK_Friend ? diag::err_friend_decl_does_not_match
1823                                       : diag::err_member_decl_does_not_match)
1824         << Name << SemanticContext << /*IsDefinition*/true << SS.getRange();
1825       Invalid = true;
1826     }
1827   }
1828 
1829   // If this is a templated friend in a dependent context we should not put it
1830   // on the redecl chain. In some cases, the templated friend can be the most
1831   // recent declaration tricking the template instantiator to make substitutions
1832   // there.
1833   // FIXME: Figure out how to combine with shouldLinkDependentDeclWithPrevious
1834   bool ShouldAddRedecl
1835     = !(TUK == TUK_Friend && CurContext->isDependentContext());
1836 
1837   CXXRecordDecl *NewClass =
1838     CXXRecordDecl::Create(Context, Kind, SemanticContext, KWLoc, NameLoc, Name,
1839                           PrevClassTemplate && ShouldAddRedecl ?
1840                             PrevClassTemplate->getTemplatedDecl() : nullptr,
1841                           /*DelayTypeCreation=*/true);
1842   SetNestedNameSpecifier(*this, NewClass, SS);
1843   if (NumOuterTemplateParamLists > 0)
1844     NewClass->setTemplateParameterListsInfo(
1845         Context, llvm::makeArrayRef(OuterTemplateParamLists,
1846                                     NumOuterTemplateParamLists));
1847 
1848   // Add alignment attributes if necessary; these attributes are checked when
1849   // the ASTContext lays out the structure.
1850   if (TUK == TUK_Definition && (!SkipBody || !SkipBody->ShouldSkip)) {
1851     AddAlignmentAttributesForRecord(NewClass);
1852     AddMsStructLayoutForRecord(NewClass);
1853   }
1854 
1855   ClassTemplateDecl *NewTemplate
1856     = ClassTemplateDecl::Create(Context, SemanticContext, NameLoc,
1857                                 DeclarationName(Name), TemplateParams,
1858                                 NewClass);
1859 
1860   if (ShouldAddRedecl)
1861     NewTemplate->setPreviousDecl(PrevClassTemplate);
1862 
1863   NewClass->setDescribedClassTemplate(NewTemplate);
1864 
1865   if (ModulePrivateLoc.isValid())
1866     NewTemplate->setModulePrivate();
1867 
1868   // Build the type for the class template declaration now.
1869   QualType T = NewTemplate->getInjectedClassNameSpecialization();
1870   T = Context.getInjectedClassNameType(NewClass, T);
1871   assert(T->isDependentType() && "Class template type is not dependent?");
1872   (void)T;
1873 
1874   // If we are providing an explicit specialization of a member that is a
1875   // class template, make a note of that.
1876   if (PrevClassTemplate &&
1877       PrevClassTemplate->getInstantiatedFromMemberTemplate())
1878     PrevClassTemplate->setMemberSpecialization();
1879 
1880   // Set the access specifier.
1881   if (!Invalid && TUK != TUK_Friend && NewTemplate->getDeclContext()->isRecord())
1882     SetMemberAccessSpecifier(NewTemplate, PrevClassTemplate, AS);
1883 
1884   // Set the lexical context of these templates
1885   NewClass->setLexicalDeclContext(CurContext);
1886   NewTemplate->setLexicalDeclContext(CurContext);
1887 
1888   if (TUK == TUK_Definition && (!SkipBody || !SkipBody->ShouldSkip))
1889     NewClass->startDefinition();
1890 
1891   ProcessDeclAttributeList(S, NewClass, Attr);
1892 
1893   if (PrevClassTemplate)
1894     mergeDeclAttributes(NewClass, PrevClassTemplate->getTemplatedDecl());
1895 
1896   AddPushedVisibilityAttribute(NewClass);
1897   inferGslOwnerPointerAttribute(NewClass);
1898 
1899   if (TUK != TUK_Friend) {
1900     // Per C++ [basic.scope.temp]p2, skip the template parameter scopes.
1901     Scope *Outer = S;
1902     while ((Outer->getFlags() & Scope::TemplateParamScope) != 0)
1903       Outer = Outer->getParent();
1904     PushOnScopeChains(NewTemplate, Outer);
1905   } else {
1906     if (PrevClassTemplate && PrevClassTemplate->getAccess() != AS_none) {
1907       NewTemplate->setAccess(PrevClassTemplate->getAccess());
1908       NewClass->setAccess(PrevClassTemplate->getAccess());
1909     }
1910 
1911     NewTemplate->setObjectOfFriendDecl();
1912 
1913     // Friend templates are visible in fairly strange ways.
1914     if (!CurContext->isDependentContext()) {
1915       DeclContext *DC = SemanticContext->getRedeclContext();
1916       DC->makeDeclVisibleInContext(NewTemplate);
1917       if (Scope *EnclosingScope = getScopeForDeclContext(S, DC))
1918         PushOnScopeChains(NewTemplate, EnclosingScope,
1919                           /* AddToContext = */ false);
1920     }
1921 
1922     FriendDecl *Friend = FriendDecl::Create(
1923         Context, CurContext, NewClass->getLocation(), NewTemplate, FriendLoc);
1924     Friend->setAccess(AS_public);
1925     CurContext->addDecl(Friend);
1926   }
1927 
1928   if (PrevClassTemplate)
1929     CheckRedeclarationModuleOwnership(NewTemplate, PrevClassTemplate);
1930 
1931   if (Invalid) {
1932     NewTemplate->setInvalidDecl();
1933     NewClass->setInvalidDecl();
1934   }
1935 
1936   ActOnDocumentableDecl(NewTemplate);
1937 
1938   if (SkipBody && SkipBody->ShouldSkip)
1939     return SkipBody->Previous;
1940 
1941   return NewTemplate;
1942 }
1943 
1944 namespace {
1945 /// Tree transform to "extract" a transformed type from a class template's
1946 /// constructor to a deduction guide.
1947 class ExtractTypeForDeductionGuide
1948   : public TreeTransform<ExtractTypeForDeductionGuide> {
1949   llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs;
1950 
1951 public:
1952   typedef TreeTransform<ExtractTypeForDeductionGuide> Base;
1953   ExtractTypeForDeductionGuide(
1954       Sema &SemaRef,
1955       llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs)
1956       : Base(SemaRef), MaterializedTypedefs(MaterializedTypedefs) {}
1957 
1958   TypeSourceInfo *transform(TypeSourceInfo *TSI) { return TransformType(TSI); }
1959 
1960   QualType TransformTypedefType(TypeLocBuilder &TLB, TypedefTypeLoc TL) {
1961     ASTContext &Context = SemaRef.getASTContext();
1962     TypedefNameDecl *OrigDecl = TL.getTypedefNameDecl();
1963     TypeLocBuilder InnerTLB;
1964     QualType Transformed =
1965         TransformType(InnerTLB, OrigDecl->getTypeSourceInfo()->getTypeLoc());
1966     TypeSourceInfo *TSI =
1967         TransformType(InnerTLB.getTypeSourceInfo(Context, Transformed));
1968 
1969     TypedefNameDecl *Decl = nullptr;
1970 
1971     if (isa<TypeAliasDecl>(OrigDecl))
1972       Decl = TypeAliasDecl::Create(
1973           Context, Context.getTranslationUnitDecl(), OrigDecl->getBeginLoc(),
1974           OrigDecl->getLocation(), OrigDecl->getIdentifier(), TSI);
1975     else {
1976       assert(isa<TypedefDecl>(OrigDecl) && "Not a Type alias or typedef");
1977       Decl = TypedefDecl::Create(
1978           Context, Context.getTranslationUnitDecl(), OrigDecl->getBeginLoc(),
1979           OrigDecl->getLocation(), OrigDecl->getIdentifier(), TSI);
1980     }
1981 
1982     MaterializedTypedefs.push_back(Decl);
1983 
1984     QualType TDTy = Context.getTypedefType(Decl);
1985     TypedefTypeLoc TypedefTL = TLB.push<TypedefTypeLoc>(TDTy);
1986     TypedefTL.setNameLoc(TL.getNameLoc());
1987 
1988     return TDTy;
1989   }
1990 };
1991 
1992 /// Transform to convert portions of a constructor declaration into the
1993 /// corresponding deduction guide, per C++1z [over.match.class.deduct]p1.
1994 struct ConvertConstructorToDeductionGuideTransform {
1995   ConvertConstructorToDeductionGuideTransform(Sema &S,
1996                                               ClassTemplateDecl *Template)
1997       : SemaRef(S), Template(Template) {}
1998 
1999   Sema &SemaRef;
2000   ClassTemplateDecl *Template;
2001 
2002   DeclContext *DC = Template->getDeclContext();
2003   CXXRecordDecl *Primary = Template->getTemplatedDecl();
2004   DeclarationName DeductionGuideName =
2005       SemaRef.Context.DeclarationNames.getCXXDeductionGuideName(Template);
2006 
2007   QualType DeducedType = SemaRef.Context.getTypeDeclType(Primary);
2008 
2009   // Index adjustment to apply to convert depth-1 template parameters into
2010   // depth-0 template parameters.
2011   unsigned Depth1IndexAdjustment = Template->getTemplateParameters()->size();
2012 
2013   /// Transform a constructor declaration into a deduction guide.
2014   NamedDecl *transformConstructor(FunctionTemplateDecl *FTD,
2015                                   CXXConstructorDecl *CD) {
2016     SmallVector<TemplateArgument, 16> SubstArgs;
2017 
2018     LocalInstantiationScope Scope(SemaRef);
2019 
2020     // C++ [over.match.class.deduct]p1:
2021     // -- For each constructor of the class template designated by the
2022     //    template-name, a function template with the following properties:
2023 
2024     //    -- The template parameters are the template parameters of the class
2025     //       template followed by the template parameters (including default
2026     //       template arguments) of the constructor, if any.
2027     TemplateParameterList *TemplateParams = Template->getTemplateParameters();
2028     if (FTD) {
2029       TemplateParameterList *InnerParams = FTD->getTemplateParameters();
2030       SmallVector<NamedDecl *, 16> AllParams;
2031       AllParams.reserve(TemplateParams->size() + InnerParams->size());
2032       AllParams.insert(AllParams.begin(),
2033                        TemplateParams->begin(), TemplateParams->end());
2034       SubstArgs.reserve(InnerParams->size());
2035 
2036       // Later template parameters could refer to earlier ones, so build up
2037       // a list of substituted template arguments as we go.
2038       for (NamedDecl *Param : *InnerParams) {
2039         MultiLevelTemplateArgumentList Args;
2040         Args.setKind(TemplateSubstitutionKind::Rewrite);
2041         Args.addOuterTemplateArguments(SubstArgs);
2042         Args.addOuterRetainedLevel();
2043         NamedDecl *NewParam = transformTemplateParameter(Param, Args);
2044         if (!NewParam)
2045           return nullptr;
2046         AllParams.push_back(NewParam);
2047         SubstArgs.push_back(SemaRef.Context.getCanonicalTemplateArgument(
2048             SemaRef.Context.getInjectedTemplateArg(NewParam)));
2049       }
2050       TemplateParams = TemplateParameterList::Create(
2051           SemaRef.Context, InnerParams->getTemplateLoc(),
2052           InnerParams->getLAngleLoc(), AllParams, InnerParams->getRAngleLoc(),
2053           /*FIXME: RequiresClause*/ nullptr);
2054     }
2055 
2056     // If we built a new template-parameter-list, track that we need to
2057     // substitute references to the old parameters into references to the
2058     // new ones.
2059     MultiLevelTemplateArgumentList Args;
2060     Args.setKind(TemplateSubstitutionKind::Rewrite);
2061     if (FTD) {
2062       Args.addOuterTemplateArguments(SubstArgs);
2063       Args.addOuterRetainedLevel();
2064     }
2065 
2066     FunctionProtoTypeLoc FPTL = CD->getTypeSourceInfo()->getTypeLoc()
2067                                    .getAsAdjusted<FunctionProtoTypeLoc>();
2068     assert(FPTL && "no prototype for constructor declaration");
2069 
2070     // Transform the type of the function, adjusting the return type and
2071     // replacing references to the old parameters with references to the
2072     // new ones.
2073     TypeLocBuilder TLB;
2074     SmallVector<ParmVarDecl*, 8> Params;
2075     SmallVector<TypedefNameDecl *, 4> MaterializedTypedefs;
2076     QualType NewType = transformFunctionProtoType(TLB, FPTL, Params, Args,
2077                                                   MaterializedTypedefs);
2078     if (NewType.isNull())
2079       return nullptr;
2080     TypeSourceInfo *NewTInfo = TLB.getTypeSourceInfo(SemaRef.Context, NewType);
2081 
2082     return buildDeductionGuide(TemplateParams, CD->getExplicitSpecifier(),
2083                                NewTInfo, CD->getBeginLoc(), CD->getLocation(),
2084                                CD->getEndLoc(), MaterializedTypedefs);
2085   }
2086 
2087   /// Build a deduction guide with the specified parameter types.
2088   NamedDecl *buildSimpleDeductionGuide(MutableArrayRef<QualType> ParamTypes) {
2089     SourceLocation Loc = Template->getLocation();
2090 
2091     // Build the requested type.
2092     FunctionProtoType::ExtProtoInfo EPI;
2093     EPI.HasTrailingReturn = true;
2094     QualType Result = SemaRef.BuildFunctionType(DeducedType, ParamTypes, Loc,
2095                                                 DeductionGuideName, EPI);
2096     TypeSourceInfo *TSI = SemaRef.Context.getTrivialTypeSourceInfo(Result, Loc);
2097 
2098     FunctionProtoTypeLoc FPTL =
2099         TSI->getTypeLoc().castAs<FunctionProtoTypeLoc>();
2100 
2101     // Build the parameters, needed during deduction / substitution.
2102     SmallVector<ParmVarDecl*, 4> Params;
2103     for (auto T : ParamTypes) {
2104       ParmVarDecl *NewParam = ParmVarDecl::Create(
2105           SemaRef.Context, DC, Loc, Loc, nullptr, T,
2106           SemaRef.Context.getTrivialTypeSourceInfo(T, Loc), SC_None, nullptr);
2107       NewParam->setScopeInfo(0, Params.size());
2108       FPTL.setParam(Params.size(), NewParam);
2109       Params.push_back(NewParam);
2110     }
2111 
2112     return buildDeductionGuide(Template->getTemplateParameters(),
2113                                ExplicitSpecifier(), TSI, Loc, Loc, Loc);
2114   }
2115 
2116 private:
2117   /// Transform a constructor template parameter into a deduction guide template
2118   /// parameter, rebuilding any internal references to earlier parameters and
2119   /// renumbering as we go.
2120   NamedDecl *transformTemplateParameter(NamedDecl *TemplateParam,
2121                                         MultiLevelTemplateArgumentList &Args) {
2122     if (auto *TTP = dyn_cast<TemplateTypeParmDecl>(TemplateParam)) {
2123       // TemplateTypeParmDecl's index cannot be changed after creation, so
2124       // substitute it directly.
2125       auto *NewTTP = TemplateTypeParmDecl::Create(
2126           SemaRef.Context, DC, TTP->getBeginLoc(), TTP->getLocation(),
2127           /*Depth*/ 0, Depth1IndexAdjustment + TTP->getIndex(),
2128           TTP->getIdentifier(), TTP->wasDeclaredWithTypename(),
2129           TTP->isParameterPack(), TTP->hasTypeConstraint(),
2130           TTP->isExpandedParameterPack() ?
2131           llvm::Optional<unsigned>(TTP->getNumExpansionParameters()) : None);
2132       if (const auto *TC = TTP->getTypeConstraint()) {
2133         TemplateArgumentListInfo TransformedArgs;
2134         const auto *ArgsAsWritten = TC->getTemplateArgsAsWritten();
2135         if (!ArgsAsWritten ||
2136             SemaRef.Subst(ArgsAsWritten->getTemplateArgs(),
2137                           ArgsAsWritten->NumTemplateArgs, TransformedArgs,
2138                           Args))
2139           SemaRef.AttachTypeConstraint(
2140               TC->getNestedNameSpecifierLoc(), TC->getConceptNameInfo(),
2141               TC->getNamedConcept(), ArgsAsWritten ? &TransformedArgs : nullptr,
2142               NewTTP,
2143               NewTTP->isParameterPack()
2144                  ? cast<CXXFoldExpr>(TC->getImmediatelyDeclaredConstraint())
2145                      ->getEllipsisLoc()
2146                  : SourceLocation());
2147       }
2148       if (TTP->hasDefaultArgument()) {
2149         TypeSourceInfo *InstantiatedDefaultArg =
2150             SemaRef.SubstType(TTP->getDefaultArgumentInfo(), Args,
2151                               TTP->getDefaultArgumentLoc(), TTP->getDeclName());
2152         if (InstantiatedDefaultArg)
2153           NewTTP->setDefaultArgument(InstantiatedDefaultArg);
2154       }
2155       SemaRef.CurrentInstantiationScope->InstantiatedLocal(TemplateParam,
2156                                                            NewTTP);
2157       return NewTTP;
2158     }
2159 
2160     if (auto *TTP = dyn_cast<TemplateTemplateParmDecl>(TemplateParam))
2161       return transformTemplateParameterImpl(TTP, Args);
2162 
2163     return transformTemplateParameterImpl(
2164         cast<NonTypeTemplateParmDecl>(TemplateParam), Args);
2165   }
2166   template<typename TemplateParmDecl>
2167   TemplateParmDecl *
2168   transformTemplateParameterImpl(TemplateParmDecl *OldParam,
2169                                  MultiLevelTemplateArgumentList &Args) {
2170     // Ask the template instantiator to do the heavy lifting for us, then adjust
2171     // the index of the parameter once it's done.
2172     auto *NewParam =
2173         cast<TemplateParmDecl>(SemaRef.SubstDecl(OldParam, DC, Args));
2174     assert(NewParam->getDepth() == 0 && "unexpected template param depth");
2175     NewParam->setPosition(NewParam->getPosition() + Depth1IndexAdjustment);
2176     return NewParam;
2177   }
2178 
2179   QualType transformFunctionProtoType(
2180       TypeLocBuilder &TLB, FunctionProtoTypeLoc TL,
2181       SmallVectorImpl<ParmVarDecl *> &Params,
2182       MultiLevelTemplateArgumentList &Args,
2183       SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs) {
2184     SmallVector<QualType, 4> ParamTypes;
2185     const FunctionProtoType *T = TL.getTypePtr();
2186 
2187     //    -- The types of the function parameters are those of the constructor.
2188     for (auto *OldParam : TL.getParams()) {
2189       ParmVarDecl *NewParam =
2190           transformFunctionTypeParam(OldParam, Args, MaterializedTypedefs);
2191       if (!NewParam)
2192         return QualType();
2193       ParamTypes.push_back(NewParam->getType());
2194       Params.push_back(NewParam);
2195     }
2196 
2197     //    -- The return type is the class template specialization designated by
2198     //       the template-name and template arguments corresponding to the
2199     //       template parameters obtained from the class template.
2200     //
2201     // We use the injected-class-name type of the primary template instead.
2202     // This has the convenient property that it is different from any type that
2203     // the user can write in a deduction-guide (because they cannot enter the
2204     // context of the template), so implicit deduction guides can never collide
2205     // with explicit ones.
2206     QualType ReturnType = DeducedType;
2207     TLB.pushTypeSpec(ReturnType).setNameLoc(Primary->getLocation());
2208 
2209     // Resolving a wording defect, we also inherit the variadicness of the
2210     // constructor.
2211     FunctionProtoType::ExtProtoInfo EPI;
2212     EPI.Variadic = T->isVariadic();
2213     EPI.HasTrailingReturn = true;
2214 
2215     QualType Result = SemaRef.BuildFunctionType(
2216         ReturnType, ParamTypes, TL.getBeginLoc(), DeductionGuideName, EPI);
2217     if (Result.isNull())
2218       return QualType();
2219 
2220     FunctionProtoTypeLoc NewTL = TLB.push<FunctionProtoTypeLoc>(Result);
2221     NewTL.setLocalRangeBegin(TL.getLocalRangeBegin());
2222     NewTL.setLParenLoc(TL.getLParenLoc());
2223     NewTL.setRParenLoc(TL.getRParenLoc());
2224     NewTL.setExceptionSpecRange(SourceRange());
2225     NewTL.setLocalRangeEnd(TL.getLocalRangeEnd());
2226     for (unsigned I = 0, E = NewTL.getNumParams(); I != E; ++I)
2227       NewTL.setParam(I, Params[I]);
2228 
2229     return Result;
2230   }
2231 
2232   ParmVarDecl *transformFunctionTypeParam(
2233       ParmVarDecl *OldParam, MultiLevelTemplateArgumentList &Args,
2234       llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs) {
2235     TypeSourceInfo *OldDI = OldParam->getTypeSourceInfo();
2236     TypeSourceInfo *NewDI;
2237     if (auto PackTL = OldDI->getTypeLoc().getAs<PackExpansionTypeLoc>()) {
2238       // Expand out the one and only element in each inner pack.
2239       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, 0);
2240       NewDI =
2241           SemaRef.SubstType(PackTL.getPatternLoc(), Args,
2242                             OldParam->getLocation(), OldParam->getDeclName());
2243       if (!NewDI) return nullptr;
2244       NewDI =
2245           SemaRef.CheckPackExpansion(NewDI, PackTL.getEllipsisLoc(),
2246                                      PackTL.getTypePtr()->getNumExpansions());
2247     } else
2248       NewDI = SemaRef.SubstType(OldDI, Args, OldParam->getLocation(),
2249                                 OldParam->getDeclName());
2250     if (!NewDI)
2251       return nullptr;
2252 
2253     // Extract the type. This (for instance) replaces references to typedef
2254     // members of the current instantiations with the definitions of those
2255     // typedefs, avoiding triggering instantiation of the deduced type during
2256     // deduction.
2257     NewDI = ExtractTypeForDeductionGuide(SemaRef, MaterializedTypedefs)
2258                 .transform(NewDI);
2259 
2260     // Resolving a wording defect, we also inherit default arguments from the
2261     // constructor.
2262     ExprResult NewDefArg;
2263     if (OldParam->hasDefaultArg()) {
2264       // We don't care what the value is (we won't use it); just create a
2265       // placeholder to indicate there is a default argument.
2266       QualType ParamTy = NewDI->getType();
2267       NewDefArg = new (SemaRef.Context)
2268           OpaqueValueExpr(OldParam->getDefaultArg()->getBeginLoc(),
2269                           ParamTy.getNonLValueExprType(SemaRef.Context),
2270                           ParamTy->isLValueReferenceType() ? VK_LValue :
2271                           ParamTy->isRValueReferenceType() ? VK_XValue :
2272                           VK_RValue);
2273     }
2274 
2275     ParmVarDecl *NewParam = ParmVarDecl::Create(SemaRef.Context, DC,
2276                                                 OldParam->getInnerLocStart(),
2277                                                 OldParam->getLocation(),
2278                                                 OldParam->getIdentifier(),
2279                                                 NewDI->getType(),
2280                                                 NewDI,
2281                                                 OldParam->getStorageClass(),
2282                                                 NewDefArg.get());
2283     NewParam->setScopeInfo(OldParam->getFunctionScopeDepth(),
2284                            OldParam->getFunctionScopeIndex());
2285     SemaRef.CurrentInstantiationScope->InstantiatedLocal(OldParam, NewParam);
2286     return NewParam;
2287   }
2288 
2289   FunctionTemplateDecl *buildDeductionGuide(
2290       TemplateParameterList *TemplateParams, ExplicitSpecifier ES,
2291       TypeSourceInfo *TInfo, SourceLocation LocStart, SourceLocation Loc,
2292       SourceLocation LocEnd,
2293       llvm::ArrayRef<TypedefNameDecl *> MaterializedTypedefs = {}) {
2294     DeclarationNameInfo Name(DeductionGuideName, Loc);
2295     ArrayRef<ParmVarDecl *> Params =
2296         TInfo->getTypeLoc().castAs<FunctionProtoTypeLoc>().getParams();
2297 
2298     // Build the implicit deduction guide template.
2299     auto *Guide =
2300         CXXDeductionGuideDecl::Create(SemaRef.Context, DC, LocStart, ES, Name,
2301                                       TInfo->getType(), TInfo, LocEnd);
2302     Guide->setImplicit();
2303     Guide->setParams(Params);
2304 
2305     for (auto *Param : Params)
2306       Param->setDeclContext(Guide);
2307     for (auto *TD : MaterializedTypedefs)
2308       TD->setDeclContext(Guide);
2309 
2310     auto *GuideTemplate = FunctionTemplateDecl::Create(
2311         SemaRef.Context, DC, Loc, DeductionGuideName, TemplateParams, Guide);
2312     GuideTemplate->setImplicit();
2313     Guide->setDescribedFunctionTemplate(GuideTemplate);
2314 
2315     if (isa<CXXRecordDecl>(DC)) {
2316       Guide->setAccess(AS_public);
2317       GuideTemplate->setAccess(AS_public);
2318     }
2319 
2320     DC->addDecl(GuideTemplate);
2321     return GuideTemplate;
2322   }
2323 };
2324 }
2325 
2326 void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
2327                                           SourceLocation Loc) {
2328   if (CXXRecordDecl *DefRecord =
2329           cast<CXXRecordDecl>(Template->getTemplatedDecl())->getDefinition()) {
2330     TemplateDecl *DescribedTemplate = DefRecord->getDescribedClassTemplate();
2331     Template = DescribedTemplate ? DescribedTemplate : Template;
2332   }
2333 
2334   DeclContext *DC = Template->getDeclContext();
2335   if (DC->isDependentContext())
2336     return;
2337 
2338   ConvertConstructorToDeductionGuideTransform Transform(
2339       *this, cast<ClassTemplateDecl>(Template));
2340   if (!isCompleteType(Loc, Transform.DeducedType))
2341     return;
2342 
2343   // Check whether we've already declared deduction guides for this template.
2344   // FIXME: Consider storing a flag on the template to indicate this.
2345   auto Existing = DC->lookup(Transform.DeductionGuideName);
2346   for (auto *D : Existing)
2347     if (D->isImplicit())
2348       return;
2349 
2350   // In case we were expanding a pack when we attempted to declare deduction
2351   // guides, turn off pack expansion for everything we're about to do.
2352   ArgumentPackSubstitutionIndexRAII SubstIndex(*this, -1);
2353   // Create a template instantiation record to track the "instantiation" of
2354   // constructors into deduction guides.
2355   // FIXME: Add a kind for this to give more meaningful diagnostics. But can
2356   // this substitution process actually fail?
2357   InstantiatingTemplate BuildingDeductionGuides(*this, Loc, Template);
2358   if (BuildingDeductionGuides.isInvalid())
2359     return;
2360 
2361   // Convert declared constructors into deduction guide templates.
2362   // FIXME: Skip constructors for which deduction must necessarily fail (those
2363   // for which some class template parameter without a default argument never
2364   // appears in a deduced context).
2365   bool AddedAny = false;
2366   for (NamedDecl *D : LookupConstructors(Transform.Primary)) {
2367     D = D->getUnderlyingDecl();
2368     if (D->isInvalidDecl() || D->isImplicit())
2369       continue;
2370     D = cast<NamedDecl>(D->getCanonicalDecl());
2371 
2372     auto *FTD = dyn_cast<FunctionTemplateDecl>(D);
2373     auto *CD =
2374         dyn_cast_or_null<CXXConstructorDecl>(FTD ? FTD->getTemplatedDecl() : D);
2375     // Class-scope explicit specializations (MS extension) do not result in
2376     // deduction guides.
2377     if (!CD || (!FTD && CD->isFunctionTemplateSpecialization()))
2378       continue;
2379 
2380     Transform.transformConstructor(FTD, CD);
2381     AddedAny = true;
2382   }
2383 
2384   // C++17 [over.match.class.deduct]
2385   //    --  If C is not defined or does not declare any constructors, an
2386   //    additional function template derived as above from a hypothetical
2387   //    constructor C().
2388   if (!AddedAny)
2389     Transform.buildSimpleDeductionGuide(None);
2390 
2391   //    -- An additional function template derived as above from a hypothetical
2392   //    constructor C(C), called the copy deduction candidate.
2393   cast<CXXDeductionGuideDecl>(
2394       cast<FunctionTemplateDecl>(
2395           Transform.buildSimpleDeductionGuide(Transform.DeducedType))
2396           ->getTemplatedDecl())
2397       ->setIsCopyDeductionCandidate();
2398 }
2399 
2400 /// Diagnose the presence of a default template argument on a
2401 /// template parameter, which is ill-formed in certain contexts.
2402 ///
2403 /// \returns true if the default template argument should be dropped.
2404 static bool DiagnoseDefaultTemplateArgument(Sema &S,
2405                                             Sema::TemplateParamListContext TPC,
2406                                             SourceLocation ParamLoc,
2407                                             SourceRange DefArgRange) {
2408   switch (TPC) {
2409   case Sema::TPC_ClassTemplate:
2410   case Sema::TPC_VarTemplate:
2411   case Sema::TPC_TypeAliasTemplate:
2412     return false;
2413 
2414   case Sema::TPC_FunctionTemplate:
2415   case Sema::TPC_FriendFunctionTemplateDefinition:
2416     // C++ [temp.param]p9:
2417     //   A default template-argument shall not be specified in a
2418     //   function template declaration or a function template
2419     //   definition [...]
2420     //   If a friend function template declaration specifies a default
2421     //   template-argument, that declaration shall be a definition and shall be
2422     //   the only declaration of the function template in the translation unit.
2423     // (C++98/03 doesn't have this wording; see DR226).
2424     S.Diag(ParamLoc, S.getLangOpts().CPlusPlus11 ?
2425          diag::warn_cxx98_compat_template_parameter_default_in_function_template
2426            : diag::ext_template_parameter_default_in_function_template)
2427       << DefArgRange;
2428     return false;
2429 
2430   case Sema::TPC_ClassTemplateMember:
2431     // C++0x [temp.param]p9:
2432     //   A default template-argument shall not be specified in the
2433     //   template-parameter-lists of the definition of a member of a
2434     //   class template that appears outside of the member's class.
2435     S.Diag(ParamLoc, diag::err_template_parameter_default_template_member)
2436       << DefArgRange;
2437     return true;
2438 
2439   case Sema::TPC_FriendClassTemplate:
2440   case Sema::TPC_FriendFunctionTemplate:
2441     // C++ [temp.param]p9:
2442     //   A default template-argument shall not be specified in a
2443     //   friend template declaration.
2444     S.Diag(ParamLoc, diag::err_template_parameter_default_friend_template)
2445       << DefArgRange;
2446     return true;
2447 
2448     // FIXME: C++0x [temp.param]p9 allows default template-arguments
2449     // for friend function templates if there is only a single
2450     // declaration (and it is a definition). Strange!
2451   }
2452 
2453   llvm_unreachable("Invalid TemplateParamListContext!");
2454 }
2455 
2456 /// Check for unexpanded parameter packs within the template parameters
2457 /// of a template template parameter, recursively.
2458 static bool DiagnoseUnexpandedParameterPacks(Sema &S,
2459                                              TemplateTemplateParmDecl *TTP) {
2460   // A template template parameter which is a parameter pack is also a pack
2461   // expansion.
2462   if (TTP->isParameterPack())
2463     return false;
2464 
2465   TemplateParameterList *Params = TTP->getTemplateParameters();
2466   for (unsigned I = 0, N = Params->size(); I != N; ++I) {
2467     NamedDecl *P = Params->getParam(I);
2468     if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(P)) {
2469       if (!TTP->isParameterPack())
2470         if (const TypeConstraint *TC = TTP->getTypeConstraint())
2471           if (TC->hasExplicitTemplateArgs())
2472             for (auto &ArgLoc : TC->getTemplateArgsAsWritten()->arguments())
2473               if (S.DiagnoseUnexpandedParameterPack(ArgLoc,
2474                                                     Sema::UPPC_TypeConstraint))
2475                 return true;
2476       continue;
2477     }
2478 
2479     if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(P)) {
2480       if (!NTTP->isParameterPack() &&
2481           S.DiagnoseUnexpandedParameterPack(NTTP->getLocation(),
2482                                             NTTP->getTypeSourceInfo(),
2483                                       Sema::UPPC_NonTypeTemplateParameterType))
2484         return true;
2485 
2486       continue;
2487     }
2488 
2489     if (TemplateTemplateParmDecl *InnerTTP
2490                                         = dyn_cast<TemplateTemplateParmDecl>(P))
2491       if (DiagnoseUnexpandedParameterPacks(S, InnerTTP))
2492         return true;
2493   }
2494 
2495   return false;
2496 }
2497 
2498 /// Checks the validity of a template parameter list, possibly
2499 /// considering the template parameter list from a previous
2500 /// declaration.
2501 ///
2502 /// If an "old" template parameter list is provided, it must be
2503 /// equivalent (per TemplateParameterListsAreEqual) to the "new"
2504 /// template parameter list.
2505 ///
2506 /// \param NewParams Template parameter list for a new template
2507 /// declaration. This template parameter list will be updated with any
2508 /// default arguments that are carried through from the previous
2509 /// template parameter list.
2510 ///
2511 /// \param OldParams If provided, template parameter list from a
2512 /// previous declaration of the same template. Default template
2513 /// arguments will be merged from the old template parameter list to
2514 /// the new template parameter list.
2515 ///
2516 /// \param TPC Describes the context in which we are checking the given
2517 /// template parameter list.
2518 ///
2519 /// \param SkipBody If we might have already made a prior merged definition
2520 /// of this template visible, the corresponding body-skipping information.
2521 /// Default argument redefinition is not an error when skipping such a body,
2522 /// because (under the ODR) we can assume the default arguments are the same
2523 /// as the prior merged definition.
2524 ///
2525 /// \returns true if an error occurred, false otherwise.
2526 bool Sema::CheckTemplateParameterList(TemplateParameterList *NewParams,
2527                                       TemplateParameterList *OldParams,
2528                                       TemplateParamListContext TPC,
2529                                       SkipBodyInfo *SkipBody) {
2530   bool Invalid = false;
2531 
2532   // C++ [temp.param]p10:
2533   //   The set of default template-arguments available for use with a
2534   //   template declaration or definition is obtained by merging the
2535   //   default arguments from the definition (if in scope) and all
2536   //   declarations in scope in the same way default function
2537   //   arguments are (8.3.6).
2538   bool SawDefaultArgument = false;
2539   SourceLocation PreviousDefaultArgLoc;
2540 
2541   // Dummy initialization to avoid warnings.
2542   TemplateParameterList::iterator OldParam = NewParams->end();
2543   if (OldParams)
2544     OldParam = OldParams->begin();
2545 
2546   bool RemoveDefaultArguments = false;
2547   for (TemplateParameterList::iterator NewParam = NewParams->begin(),
2548                                     NewParamEnd = NewParams->end();
2549        NewParam != NewParamEnd; ++NewParam) {
2550     // Variables used to diagnose redundant default arguments
2551     bool RedundantDefaultArg = false;
2552     SourceLocation OldDefaultLoc;
2553     SourceLocation NewDefaultLoc;
2554 
2555     // Variable used to diagnose missing default arguments
2556     bool MissingDefaultArg = false;
2557 
2558     // Variable used to diagnose non-final parameter packs
2559     bool SawParameterPack = false;
2560 
2561     if (TemplateTypeParmDecl *NewTypeParm
2562           = dyn_cast<TemplateTypeParmDecl>(*NewParam)) {
2563       // Check the presence of a default argument here.
2564       if (NewTypeParm->hasDefaultArgument() &&
2565           DiagnoseDefaultTemplateArgument(*this, TPC,
2566                                           NewTypeParm->getLocation(),
2567                NewTypeParm->getDefaultArgumentInfo()->getTypeLoc()
2568                                                        .getSourceRange()))
2569         NewTypeParm->removeDefaultArgument();
2570 
2571       // Merge default arguments for template type parameters.
2572       TemplateTypeParmDecl *OldTypeParm
2573           = OldParams? cast<TemplateTypeParmDecl>(*OldParam) : nullptr;
2574       if (NewTypeParm->isParameterPack()) {
2575         assert(!NewTypeParm->hasDefaultArgument() &&
2576                "Parameter packs can't have a default argument!");
2577         SawParameterPack = true;
2578       } else if (OldTypeParm && hasVisibleDefaultArgument(OldTypeParm) &&
2579                  NewTypeParm->hasDefaultArgument() &&
2580                  (!SkipBody || !SkipBody->ShouldSkip)) {
2581         OldDefaultLoc = OldTypeParm->getDefaultArgumentLoc();
2582         NewDefaultLoc = NewTypeParm->getDefaultArgumentLoc();
2583         SawDefaultArgument = true;
2584         RedundantDefaultArg = true;
2585         PreviousDefaultArgLoc = NewDefaultLoc;
2586       } else if (OldTypeParm && OldTypeParm->hasDefaultArgument()) {
2587         // Merge the default argument from the old declaration to the
2588         // new declaration.
2589         NewTypeParm->setInheritedDefaultArgument(Context, OldTypeParm);
2590         PreviousDefaultArgLoc = OldTypeParm->getDefaultArgumentLoc();
2591       } else if (NewTypeParm->hasDefaultArgument()) {
2592         SawDefaultArgument = true;
2593         PreviousDefaultArgLoc = NewTypeParm->getDefaultArgumentLoc();
2594       } else if (SawDefaultArgument)
2595         MissingDefaultArg = true;
2596     } else if (NonTypeTemplateParmDecl *NewNonTypeParm
2597                = dyn_cast<NonTypeTemplateParmDecl>(*NewParam)) {
2598       // Check for unexpanded parameter packs.
2599       if (!NewNonTypeParm->isParameterPack() &&
2600           DiagnoseUnexpandedParameterPack(NewNonTypeParm->getLocation(),
2601                                           NewNonTypeParm->getTypeSourceInfo(),
2602                                           UPPC_NonTypeTemplateParameterType)) {
2603         Invalid = true;
2604         continue;
2605       }
2606 
2607       // Check the presence of a default argument here.
2608       if (NewNonTypeParm->hasDefaultArgument() &&
2609           DiagnoseDefaultTemplateArgument(*this, TPC,
2610                                           NewNonTypeParm->getLocation(),
2611                     NewNonTypeParm->getDefaultArgument()->getSourceRange())) {
2612         NewNonTypeParm->removeDefaultArgument();
2613       }
2614 
2615       // Merge default arguments for non-type template parameters
2616       NonTypeTemplateParmDecl *OldNonTypeParm
2617         = OldParams? cast<NonTypeTemplateParmDecl>(*OldParam) : nullptr;
2618       if (NewNonTypeParm->isParameterPack()) {
2619         assert(!NewNonTypeParm->hasDefaultArgument() &&
2620                "Parameter packs can't have a default argument!");
2621         if (!NewNonTypeParm->isPackExpansion())
2622           SawParameterPack = true;
2623       } else if (OldNonTypeParm && hasVisibleDefaultArgument(OldNonTypeParm) &&
2624                  NewNonTypeParm->hasDefaultArgument() &&
2625                  (!SkipBody || !SkipBody->ShouldSkip)) {
2626         OldDefaultLoc = OldNonTypeParm->getDefaultArgumentLoc();
2627         NewDefaultLoc = NewNonTypeParm->getDefaultArgumentLoc();
2628         SawDefaultArgument = true;
2629         RedundantDefaultArg = true;
2630         PreviousDefaultArgLoc = NewDefaultLoc;
2631       } else if (OldNonTypeParm && OldNonTypeParm->hasDefaultArgument()) {
2632         // Merge the default argument from the old declaration to the
2633         // new declaration.
2634         NewNonTypeParm->setInheritedDefaultArgument(Context, OldNonTypeParm);
2635         PreviousDefaultArgLoc = OldNonTypeParm->getDefaultArgumentLoc();
2636       } else if (NewNonTypeParm->hasDefaultArgument()) {
2637         SawDefaultArgument = true;
2638         PreviousDefaultArgLoc = NewNonTypeParm->getDefaultArgumentLoc();
2639       } else if (SawDefaultArgument)
2640         MissingDefaultArg = true;
2641     } else {
2642       TemplateTemplateParmDecl *NewTemplateParm
2643         = cast<TemplateTemplateParmDecl>(*NewParam);
2644 
2645       // Check for unexpanded parameter packs, recursively.
2646       if (::DiagnoseUnexpandedParameterPacks(*this, NewTemplateParm)) {
2647         Invalid = true;
2648         continue;
2649       }
2650 
2651       // Check the presence of a default argument here.
2652       if (NewTemplateParm->hasDefaultArgument() &&
2653           DiagnoseDefaultTemplateArgument(*this, TPC,
2654                                           NewTemplateParm->getLocation(),
2655                      NewTemplateParm->getDefaultArgument().getSourceRange()))
2656         NewTemplateParm->removeDefaultArgument();
2657 
2658       // Merge default arguments for template template parameters
2659       TemplateTemplateParmDecl *OldTemplateParm
2660         = OldParams? cast<TemplateTemplateParmDecl>(*OldParam) : nullptr;
2661       if (NewTemplateParm->isParameterPack()) {
2662         assert(!NewTemplateParm->hasDefaultArgument() &&
2663                "Parameter packs can't have a default argument!");
2664         if (!NewTemplateParm->isPackExpansion())
2665           SawParameterPack = true;
2666       } else if (OldTemplateParm &&
2667                  hasVisibleDefaultArgument(OldTemplateParm) &&
2668                  NewTemplateParm->hasDefaultArgument() &&
2669                  (!SkipBody || !SkipBody->ShouldSkip)) {
2670         OldDefaultLoc = OldTemplateParm->getDefaultArgument().getLocation();
2671         NewDefaultLoc = NewTemplateParm->getDefaultArgument().getLocation();
2672         SawDefaultArgument = true;
2673         RedundantDefaultArg = true;
2674         PreviousDefaultArgLoc = NewDefaultLoc;
2675       } else if (OldTemplateParm && OldTemplateParm->hasDefaultArgument()) {
2676         // Merge the default argument from the old declaration to the
2677         // new declaration.
2678         NewTemplateParm->setInheritedDefaultArgument(Context, OldTemplateParm);
2679         PreviousDefaultArgLoc
2680           = OldTemplateParm->getDefaultArgument().getLocation();
2681       } else if (NewTemplateParm->hasDefaultArgument()) {
2682         SawDefaultArgument = true;
2683         PreviousDefaultArgLoc
2684           = NewTemplateParm->getDefaultArgument().getLocation();
2685       } else if (SawDefaultArgument)
2686         MissingDefaultArg = true;
2687     }
2688 
2689     // C++11 [temp.param]p11:
2690     //   If a template parameter of a primary class template or alias template
2691     //   is a template parameter pack, it shall be the last template parameter.
2692     if (SawParameterPack && (NewParam + 1) != NewParamEnd &&
2693         (TPC == TPC_ClassTemplate || TPC == TPC_VarTemplate ||
2694          TPC == TPC_TypeAliasTemplate)) {
2695       Diag((*NewParam)->getLocation(),
2696            diag::err_template_param_pack_must_be_last_template_parameter);
2697       Invalid = true;
2698     }
2699 
2700     if (RedundantDefaultArg) {
2701       // C++ [temp.param]p12:
2702       //   A template-parameter shall not be given default arguments
2703       //   by two different declarations in the same scope.
2704       Diag(NewDefaultLoc, diag::err_template_param_default_arg_redefinition);
2705       Diag(OldDefaultLoc, diag::note_template_param_prev_default_arg);
2706       Invalid = true;
2707     } else if (MissingDefaultArg && TPC != TPC_FunctionTemplate) {
2708       // C++ [temp.param]p11:
2709       //   If a template-parameter of a class template has a default
2710       //   template-argument, each subsequent template-parameter shall either
2711       //   have a default template-argument supplied or be a template parameter
2712       //   pack.
2713       Diag((*NewParam)->getLocation(),
2714            diag::err_template_param_default_arg_missing);
2715       Diag(PreviousDefaultArgLoc, diag::note_template_param_prev_default_arg);
2716       Invalid = true;
2717       RemoveDefaultArguments = true;
2718     }
2719 
2720     // If we have an old template parameter list that we're merging
2721     // in, move on to the next parameter.
2722     if (OldParams)
2723       ++OldParam;
2724   }
2725 
2726   // We were missing some default arguments at the end of the list, so remove
2727   // all of the default arguments.
2728   if (RemoveDefaultArguments) {
2729     for (TemplateParameterList::iterator NewParam = NewParams->begin(),
2730                                       NewParamEnd = NewParams->end();
2731          NewParam != NewParamEnd; ++NewParam) {
2732       if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(*NewParam))
2733         TTP->removeDefaultArgument();
2734       else if (NonTypeTemplateParmDecl *NTTP
2735                                 = dyn_cast<NonTypeTemplateParmDecl>(*NewParam))
2736         NTTP->removeDefaultArgument();
2737       else
2738         cast<TemplateTemplateParmDecl>(*NewParam)->removeDefaultArgument();
2739     }
2740   }
2741 
2742   return Invalid;
2743 }
2744 
2745 namespace {
2746 
2747 /// A class which looks for a use of a certain level of template
2748 /// parameter.
2749 struct DependencyChecker : RecursiveASTVisitor<DependencyChecker> {
2750   typedef RecursiveASTVisitor<DependencyChecker> super;
2751 
2752   unsigned Depth;
2753 
2754   // Whether we're looking for a use of a template parameter that makes the
2755   // overall construct type-dependent / a dependent type. This is strictly
2756   // best-effort for now; we may fail to match at all for a dependent type
2757   // in some cases if this is set.
2758   bool IgnoreNonTypeDependent;
2759 
2760   bool Match;
2761   SourceLocation MatchLoc;
2762 
2763   DependencyChecker(unsigned Depth, bool IgnoreNonTypeDependent)
2764       : Depth(Depth), IgnoreNonTypeDependent(IgnoreNonTypeDependent),
2765         Match(false) {}
2766 
2767   DependencyChecker(TemplateParameterList *Params, bool IgnoreNonTypeDependent)
2768       : IgnoreNonTypeDependent(IgnoreNonTypeDependent), Match(false) {
2769     NamedDecl *ND = Params->getParam(0);
2770     if (TemplateTypeParmDecl *PD = dyn_cast<TemplateTypeParmDecl>(ND)) {
2771       Depth = PD->getDepth();
2772     } else if (NonTypeTemplateParmDecl *PD =
2773                  dyn_cast<NonTypeTemplateParmDecl>(ND)) {
2774       Depth = PD->getDepth();
2775     } else {
2776       Depth = cast<TemplateTemplateParmDecl>(ND)->getDepth();
2777     }
2778   }
2779 
2780   bool Matches(unsigned ParmDepth, SourceLocation Loc = SourceLocation()) {
2781     if (ParmDepth >= Depth) {
2782       Match = true;
2783       MatchLoc = Loc;
2784       return true;
2785     }
2786     return false;
2787   }
2788 
2789   bool TraverseStmt(Stmt *S, DataRecursionQueue *Q = nullptr) {
2790     // Prune out non-type-dependent expressions if requested. This can
2791     // sometimes result in us failing to find a template parameter reference
2792     // (if a value-dependent expression creates a dependent type), but this
2793     // mode is best-effort only.
2794     if (auto *E = dyn_cast_or_null<Expr>(S))
2795       if (IgnoreNonTypeDependent && !E->isTypeDependent())
2796         return true;
2797     return super::TraverseStmt(S, Q);
2798   }
2799 
2800   bool TraverseTypeLoc(TypeLoc TL) {
2801     if (IgnoreNonTypeDependent && !TL.isNull() &&
2802         !TL.getType()->isDependentType())
2803       return true;
2804     return super::TraverseTypeLoc(TL);
2805   }
2806 
2807   bool VisitTemplateTypeParmTypeLoc(TemplateTypeParmTypeLoc TL) {
2808     return !Matches(TL.getTypePtr()->getDepth(), TL.getNameLoc());
2809   }
2810 
2811   bool VisitTemplateTypeParmType(const TemplateTypeParmType *T) {
2812     // For a best-effort search, keep looking until we find a location.
2813     return IgnoreNonTypeDependent || !Matches(T->getDepth());
2814   }
2815 
2816   bool TraverseTemplateName(TemplateName N) {
2817     if (TemplateTemplateParmDecl *PD =
2818           dyn_cast_or_null<TemplateTemplateParmDecl>(N.getAsTemplateDecl()))
2819       if (Matches(PD->getDepth()))
2820         return false;
2821     return super::TraverseTemplateName(N);
2822   }
2823 
2824   bool VisitDeclRefExpr(DeclRefExpr *E) {
2825     if (NonTypeTemplateParmDecl *PD =
2826           dyn_cast<NonTypeTemplateParmDecl>(E->getDecl()))
2827       if (Matches(PD->getDepth(), E->getExprLoc()))
2828         return false;
2829     return super::VisitDeclRefExpr(E);
2830   }
2831 
2832   bool VisitSubstTemplateTypeParmType(const SubstTemplateTypeParmType *T) {
2833     return TraverseType(T->getReplacementType());
2834   }
2835 
2836   bool
2837   VisitSubstTemplateTypeParmPackType(const SubstTemplateTypeParmPackType *T) {
2838     return TraverseTemplateArgument(T->getArgumentPack());
2839   }
2840 
2841   bool TraverseInjectedClassNameType(const InjectedClassNameType *T) {
2842     return TraverseType(T->getInjectedSpecializationType());
2843   }
2844 };
2845 } // end anonymous namespace
2846 
2847 /// Determines whether a given type depends on the given parameter
2848 /// list.
2849 static bool
2850 DependsOnTemplateParameters(QualType T, TemplateParameterList *Params) {
2851   if (!Params->size())
2852     return false;
2853 
2854   DependencyChecker Checker(Params, /*IgnoreNonTypeDependent*/false);
2855   Checker.TraverseType(T);
2856   return Checker.Match;
2857 }
2858 
2859 // Find the source range corresponding to the named type in the given
2860 // nested-name-specifier, if any.
2861 static SourceRange getRangeOfTypeInNestedNameSpecifier(ASTContext &Context,
2862                                                        QualType T,
2863                                                        const CXXScopeSpec &SS) {
2864   NestedNameSpecifierLoc NNSLoc(SS.getScopeRep(), SS.location_data());
2865   while (NestedNameSpecifier *NNS = NNSLoc.getNestedNameSpecifier()) {
2866     if (const Type *CurType = NNS->getAsType()) {
2867       if (Context.hasSameUnqualifiedType(T, QualType(CurType, 0)))
2868         return NNSLoc.getTypeLoc().getSourceRange();
2869     } else
2870       break;
2871 
2872     NNSLoc = NNSLoc.getPrefix();
2873   }
2874 
2875   return SourceRange();
2876 }
2877 
2878 /// Match the given template parameter lists to the given scope
2879 /// specifier, returning the template parameter list that applies to the
2880 /// name.
2881 ///
2882 /// \param DeclStartLoc the start of the declaration that has a scope
2883 /// specifier or a template parameter list.
2884 ///
2885 /// \param DeclLoc The location of the declaration itself.
2886 ///
2887 /// \param SS the scope specifier that will be matched to the given template
2888 /// parameter lists. This scope specifier precedes a qualified name that is
2889 /// being declared.
2890 ///
2891 /// \param TemplateId The template-id following the scope specifier, if there
2892 /// is one. Used to check for a missing 'template<>'.
2893 ///
2894 /// \param ParamLists the template parameter lists, from the outermost to the
2895 /// innermost template parameter lists.
2896 ///
2897 /// \param IsFriend Whether to apply the slightly different rules for
2898 /// matching template parameters to scope specifiers in friend
2899 /// declarations.
2900 ///
2901 /// \param IsMemberSpecialization will be set true if the scope specifier
2902 /// denotes a fully-specialized type, and therefore this is a declaration of
2903 /// a member specialization.
2904 ///
2905 /// \returns the template parameter list, if any, that corresponds to the
2906 /// name that is preceded by the scope specifier @p SS. This template
2907 /// parameter list may have template parameters (if we're declaring a
2908 /// template) or may have no template parameters (if we're declaring a
2909 /// template specialization), or may be NULL (if what we're declaring isn't
2910 /// itself a template).
2911 TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
2912     SourceLocation DeclStartLoc, SourceLocation DeclLoc, const CXXScopeSpec &SS,
2913     TemplateIdAnnotation *TemplateId,
2914     ArrayRef<TemplateParameterList *> ParamLists, bool IsFriend,
2915     bool &IsMemberSpecialization, bool &Invalid, bool SuppressDiagnostic) {
2916   IsMemberSpecialization = false;
2917   Invalid = false;
2918 
2919   // The sequence of nested types to which we will match up the template
2920   // parameter lists. We first build this list by starting with the type named
2921   // by the nested-name-specifier and walking out until we run out of types.
2922   SmallVector<QualType, 4> NestedTypes;
2923   QualType T;
2924   if (SS.getScopeRep()) {
2925     if (CXXRecordDecl *Record
2926               = dyn_cast_or_null<CXXRecordDecl>(computeDeclContext(SS, true)))
2927       T = Context.getTypeDeclType(Record);
2928     else
2929       T = QualType(SS.getScopeRep()->getAsType(), 0);
2930   }
2931 
2932   // If we found an explicit specialization that prevents us from needing
2933   // 'template<>' headers, this will be set to the location of that
2934   // explicit specialization.
2935   SourceLocation ExplicitSpecLoc;
2936 
2937   while (!T.isNull()) {
2938     NestedTypes.push_back(T);
2939 
2940     // Retrieve the parent of a record type.
2941     if (CXXRecordDecl *Record = T->getAsCXXRecordDecl()) {
2942       // If this type is an explicit specialization, we're done.
2943       if (ClassTemplateSpecializationDecl *Spec
2944           = dyn_cast<ClassTemplateSpecializationDecl>(Record)) {
2945         if (!isa<ClassTemplatePartialSpecializationDecl>(Spec) &&
2946             Spec->getSpecializationKind() == TSK_ExplicitSpecialization) {
2947           ExplicitSpecLoc = Spec->getLocation();
2948           break;
2949         }
2950       } else if (Record->getTemplateSpecializationKind()
2951                                                 == TSK_ExplicitSpecialization) {
2952         ExplicitSpecLoc = Record->getLocation();
2953         break;
2954       }
2955 
2956       if (TypeDecl *Parent = dyn_cast<TypeDecl>(Record->getParent()))
2957         T = Context.getTypeDeclType(Parent);
2958       else
2959         T = QualType();
2960       continue;
2961     }
2962 
2963     if (const TemplateSpecializationType *TST
2964                                      = T->getAs<TemplateSpecializationType>()) {
2965       if (TemplateDecl *Template = TST->getTemplateName().getAsTemplateDecl()) {
2966         if (TypeDecl *Parent = dyn_cast<TypeDecl>(Template->getDeclContext()))
2967           T = Context.getTypeDeclType(Parent);
2968         else
2969           T = QualType();
2970         continue;
2971       }
2972     }
2973 
2974     // Look one step prior in a dependent template specialization type.
2975     if (const DependentTemplateSpecializationType *DependentTST
2976                           = T->getAs<DependentTemplateSpecializationType>()) {
2977       if (NestedNameSpecifier *NNS = DependentTST->getQualifier())
2978         T = QualType(NNS->getAsType(), 0);
2979       else
2980         T = QualType();
2981       continue;
2982     }
2983 
2984     // Look one step prior in a dependent name type.
2985     if (const DependentNameType *DependentName = T->getAs<DependentNameType>()){
2986       if (NestedNameSpecifier *NNS = DependentName->getQualifier())
2987         T = QualType(NNS->getAsType(), 0);
2988       else
2989         T = QualType();
2990       continue;
2991     }
2992 
2993     // Retrieve the parent of an enumeration type.
2994     if (const EnumType *EnumT = T->getAs<EnumType>()) {
2995       // FIXME: Forward-declared enums require a TSK_ExplicitSpecialization
2996       // check here.
2997       EnumDecl *Enum = EnumT->getDecl();
2998 
2999       // Get to the parent type.
3000       if (TypeDecl *Parent = dyn_cast<TypeDecl>(Enum->getParent()))
3001         T = Context.getTypeDeclType(Parent);
3002       else
3003         T = QualType();
3004       continue;
3005     }
3006 
3007     T = QualType();
3008   }
3009   // Reverse the nested types list, since we want to traverse from the outermost
3010   // to the innermost while checking template-parameter-lists.
3011   std::reverse(NestedTypes.begin(), NestedTypes.end());
3012 
3013   // C++0x [temp.expl.spec]p17:
3014   //   A member or a member template may be nested within many
3015   //   enclosing class templates. In an explicit specialization for
3016   //   such a member, the member declaration shall be preceded by a
3017   //   template<> for each enclosing class template that is
3018   //   explicitly specialized.
3019   bool SawNonEmptyTemplateParameterList = false;
3020 
3021   auto CheckExplicitSpecialization = [&](SourceRange Range, bool Recovery) {
3022     if (SawNonEmptyTemplateParameterList) {
3023       if (!SuppressDiagnostic)
3024         Diag(DeclLoc, diag::err_specialize_member_of_template)
3025           << !Recovery << Range;
3026       Invalid = true;
3027       IsMemberSpecialization = false;
3028       return true;
3029     }
3030 
3031     return false;
3032   };
3033 
3034   auto DiagnoseMissingExplicitSpecialization = [&] (SourceRange Range) {
3035     // Check that we can have an explicit specialization here.
3036     if (CheckExplicitSpecialization(Range, true))
3037       return true;
3038 
3039     // We don't have a template header, but we should.
3040     SourceLocation ExpectedTemplateLoc;
3041     if (!ParamLists.empty())
3042       ExpectedTemplateLoc = ParamLists[0]->getTemplateLoc();
3043     else
3044       ExpectedTemplateLoc = DeclStartLoc;
3045 
3046     if (!SuppressDiagnostic)
3047       Diag(DeclLoc, diag::err_template_spec_needs_header)
3048         << Range
3049         << FixItHint::CreateInsertion(ExpectedTemplateLoc, "template<> ");
3050     return false;
3051   };
3052 
3053   unsigned ParamIdx = 0;
3054   for (unsigned TypeIdx = 0, NumTypes = NestedTypes.size(); TypeIdx != NumTypes;
3055        ++TypeIdx) {
3056     T = NestedTypes[TypeIdx];
3057 
3058     // Whether we expect a 'template<>' header.
3059     bool NeedEmptyTemplateHeader = false;
3060 
3061     // Whether we expect a template header with parameters.
3062     bool NeedNonemptyTemplateHeader = false;
3063 
3064     // For a dependent type, the set of template parameters that we
3065     // expect to see.
3066     TemplateParameterList *ExpectedTemplateParams = nullptr;
3067 
3068     // C++0x [temp.expl.spec]p15:
3069     //   A member or a member template may be nested within many enclosing
3070     //   class templates. In an explicit specialization for such a member, the
3071     //   member declaration shall be preceded by a template<> for each
3072     //   enclosing class template that is explicitly specialized.
3073     if (CXXRecordDecl *Record = T->getAsCXXRecordDecl()) {
3074       if (ClassTemplatePartialSpecializationDecl *Partial
3075             = dyn_cast<ClassTemplatePartialSpecializationDecl>(Record)) {
3076         ExpectedTemplateParams = Partial->getTemplateParameters();
3077         NeedNonemptyTemplateHeader = true;
3078       } else if (Record->isDependentType()) {
3079         if (Record->getDescribedClassTemplate()) {
3080           ExpectedTemplateParams = Record->getDescribedClassTemplate()
3081                                                       ->getTemplateParameters();
3082           NeedNonemptyTemplateHeader = true;
3083         }
3084       } else if (ClassTemplateSpecializationDecl *Spec
3085                      = dyn_cast<ClassTemplateSpecializationDecl>(Record)) {
3086         // C++0x [temp.expl.spec]p4:
3087         //   Members of an explicitly specialized class template are defined
3088         //   in the same manner as members of normal classes, and not using
3089         //   the template<> syntax.
3090         if (Spec->getSpecializationKind() != TSK_ExplicitSpecialization)
3091           NeedEmptyTemplateHeader = true;
3092         else
3093           continue;
3094       } else if (Record->getTemplateSpecializationKind()) {
3095         if (Record->getTemplateSpecializationKind()
3096                                                 != TSK_ExplicitSpecialization &&
3097             TypeIdx == NumTypes - 1)
3098           IsMemberSpecialization = true;
3099 
3100         continue;
3101       }
3102     } else if (const TemplateSpecializationType *TST
3103                                      = T->getAs<TemplateSpecializationType>()) {
3104       if (TemplateDecl *Template = TST->getTemplateName().getAsTemplateDecl()) {
3105         ExpectedTemplateParams = Template->getTemplateParameters();
3106         NeedNonemptyTemplateHeader = true;
3107       }
3108     } else if (T->getAs<DependentTemplateSpecializationType>()) {
3109       // FIXME:  We actually could/should check the template arguments here
3110       // against the corresponding template parameter list.
3111       NeedNonemptyTemplateHeader = false;
3112     }
3113 
3114     // C++ [temp.expl.spec]p16:
3115     //   In an explicit specialization declaration for a member of a class
3116     //   template or a member template that ap- pears in namespace scope, the
3117     //   member template and some of its enclosing class templates may remain
3118     //   unspecialized, except that the declaration shall not explicitly
3119     //   specialize a class member template if its en- closing class templates
3120     //   are not explicitly specialized as well.
3121     if (ParamIdx < ParamLists.size()) {
3122       if (ParamLists[ParamIdx]->size() == 0) {
3123         if (CheckExplicitSpecialization(ParamLists[ParamIdx]->getSourceRange(),
3124                                         false))
3125           return nullptr;
3126       } else
3127         SawNonEmptyTemplateParameterList = true;
3128     }
3129 
3130     if (NeedEmptyTemplateHeader) {
3131       // If we're on the last of the types, and we need a 'template<>' header
3132       // here, then it's a member specialization.
3133       if (TypeIdx == NumTypes - 1)
3134         IsMemberSpecialization = true;
3135 
3136       if (ParamIdx < ParamLists.size()) {
3137         if (ParamLists[ParamIdx]->size() > 0) {
3138           // The header has template parameters when it shouldn't. Complain.
3139           if (!SuppressDiagnostic)
3140             Diag(ParamLists[ParamIdx]->getTemplateLoc(),
3141                  diag::err_template_param_list_matches_nontemplate)
3142               << T
3143               << SourceRange(ParamLists[ParamIdx]->getLAngleLoc(),
3144                              ParamLists[ParamIdx]->getRAngleLoc())
3145               << getRangeOfTypeInNestedNameSpecifier(Context, T, SS);
3146           Invalid = true;
3147           return nullptr;
3148         }
3149 
3150         // Consume this template header.
3151         ++ParamIdx;
3152         continue;
3153       }
3154 
3155       if (!IsFriend)
3156         if (DiagnoseMissingExplicitSpecialization(
3157                 getRangeOfTypeInNestedNameSpecifier(Context, T, SS)))
3158           return nullptr;
3159 
3160       continue;
3161     }
3162 
3163     if (NeedNonemptyTemplateHeader) {
3164       // In friend declarations we can have template-ids which don't
3165       // depend on the corresponding template parameter lists.  But
3166       // assume that empty parameter lists are supposed to match this
3167       // template-id.
3168       if (IsFriend && T->isDependentType()) {
3169         if (ParamIdx < ParamLists.size() &&
3170             DependsOnTemplateParameters(T, ParamLists[ParamIdx]))
3171           ExpectedTemplateParams = nullptr;
3172         else
3173           continue;
3174       }
3175 
3176       if (ParamIdx < ParamLists.size()) {
3177         // Check the template parameter list, if we can.
3178         if (ExpectedTemplateParams &&
3179             !TemplateParameterListsAreEqual(ParamLists[ParamIdx],
3180                                             ExpectedTemplateParams,
3181                                             !SuppressDiagnostic, TPL_TemplateMatch))
3182           Invalid = true;
3183 
3184         if (!Invalid &&
3185             CheckTemplateParameterList(ParamLists[ParamIdx], nullptr,
3186                                        TPC_ClassTemplateMember))
3187           Invalid = true;
3188 
3189         ++ParamIdx;
3190         continue;
3191       }
3192 
3193       if (!SuppressDiagnostic)
3194         Diag(DeclLoc, diag::err_template_spec_needs_template_parameters)
3195           << T
3196           << getRangeOfTypeInNestedNameSpecifier(Context, T, SS);
3197       Invalid = true;
3198       continue;
3199     }
3200   }
3201 
3202   // If there were at least as many template-ids as there were template
3203   // parameter lists, then there are no template parameter lists remaining for
3204   // the declaration itself.
3205   if (ParamIdx >= ParamLists.size()) {
3206     if (TemplateId && !IsFriend) {
3207       // We don't have a template header for the declaration itself, but we
3208       // should.
3209       DiagnoseMissingExplicitSpecialization(SourceRange(TemplateId->LAngleLoc,
3210                                                         TemplateId->RAngleLoc));
3211 
3212       // Fabricate an empty template parameter list for the invented header.
3213       return TemplateParameterList::Create(Context, SourceLocation(),
3214                                            SourceLocation(), None,
3215                                            SourceLocation(), nullptr);
3216     }
3217 
3218     return nullptr;
3219   }
3220 
3221   // If there were too many template parameter lists, complain about that now.
3222   if (ParamIdx < ParamLists.size() - 1) {
3223     bool HasAnyExplicitSpecHeader = false;
3224     bool AllExplicitSpecHeaders = true;
3225     for (unsigned I = ParamIdx, E = ParamLists.size() - 1; I != E; ++I) {
3226       if (ParamLists[I]->size() == 0)
3227         HasAnyExplicitSpecHeader = true;
3228       else
3229         AllExplicitSpecHeaders = false;
3230     }
3231 
3232     if (!SuppressDiagnostic)
3233       Diag(ParamLists[ParamIdx]->getTemplateLoc(),
3234            AllExplicitSpecHeaders ? diag::warn_template_spec_extra_headers
3235                                   : diag::err_template_spec_extra_headers)
3236           << SourceRange(ParamLists[ParamIdx]->getTemplateLoc(),
3237                          ParamLists[ParamLists.size() - 2]->getRAngleLoc());
3238 
3239     // If there was a specialization somewhere, such that 'template<>' is
3240     // not required, and there were any 'template<>' headers, note where the
3241     // specialization occurred.
3242     if (ExplicitSpecLoc.isValid() && HasAnyExplicitSpecHeader &&
3243         !SuppressDiagnostic)
3244       Diag(ExplicitSpecLoc,
3245            diag::note_explicit_template_spec_does_not_need_header)
3246         << NestedTypes.back();
3247 
3248     // We have a template parameter list with no corresponding scope, which
3249     // means that the resulting template declaration can't be instantiated
3250     // properly (we'll end up with dependent nodes when we shouldn't).
3251     if (!AllExplicitSpecHeaders)
3252       Invalid = true;
3253   }
3254 
3255   // C++ [temp.expl.spec]p16:
3256   //   In an explicit specialization declaration for a member of a class
3257   //   template or a member template that ap- pears in namespace scope, the
3258   //   member template and some of its enclosing class templates may remain
3259   //   unspecialized, except that the declaration shall not explicitly
3260   //   specialize a class member template if its en- closing class templates
3261   //   are not explicitly specialized as well.
3262   if (ParamLists.back()->size() == 0 &&
3263       CheckExplicitSpecialization(ParamLists[ParamIdx]->getSourceRange(),
3264                                   false))
3265     return nullptr;
3266 
3267   // Return the last template parameter list, which corresponds to the
3268   // entity being declared.
3269   return ParamLists.back();
3270 }
3271 
3272 void Sema::NoteAllFoundTemplates(TemplateName Name) {
3273   if (TemplateDecl *Template = Name.getAsTemplateDecl()) {
3274     Diag(Template->getLocation(), diag::note_template_declared_here)
3275         << (isa<FunctionTemplateDecl>(Template)
3276                 ? 0
3277                 : isa<ClassTemplateDecl>(Template)
3278                       ? 1
3279                       : isa<VarTemplateDecl>(Template)
3280                             ? 2
3281                             : isa<TypeAliasTemplateDecl>(Template) ? 3 : 4)
3282         << Template->getDeclName();
3283     return;
3284   }
3285 
3286   if (OverloadedTemplateStorage *OST = Name.getAsOverloadedTemplate()) {
3287     for (OverloadedTemplateStorage::iterator I = OST->begin(),
3288                                           IEnd = OST->end();
3289          I != IEnd; ++I)
3290       Diag((*I)->getLocation(), diag::note_template_declared_here)
3291         << 0 << (*I)->getDeclName();
3292 
3293     return;
3294   }
3295 }
3296 
3297 static QualType
3298 checkBuiltinTemplateIdType(Sema &SemaRef, BuiltinTemplateDecl *BTD,
3299                            const SmallVectorImpl<TemplateArgument> &Converted,
3300                            SourceLocation TemplateLoc,
3301                            TemplateArgumentListInfo &TemplateArgs) {
3302   ASTContext &Context = SemaRef.getASTContext();
3303   switch (BTD->getBuiltinTemplateKind()) {
3304   case BTK__make_integer_seq: {
3305     // Specializations of __make_integer_seq<S, T, N> are treated like
3306     // S<T, 0, ..., N-1>.
3307 
3308     // C++14 [inteseq.intseq]p1:
3309     //   T shall be an integer type.
3310     if (!Converted[1].getAsType()->isIntegralType(Context)) {
3311       SemaRef.Diag(TemplateArgs[1].getLocation(),
3312                    diag::err_integer_sequence_integral_element_type);
3313       return QualType();
3314     }
3315 
3316     // C++14 [inteseq.make]p1:
3317     //   If N is negative the program is ill-formed.
3318     TemplateArgument NumArgsArg = Converted[2];
3319     llvm::APSInt NumArgs = NumArgsArg.getAsIntegral();
3320     if (NumArgs < 0) {
3321       SemaRef.Diag(TemplateArgs[2].getLocation(),
3322                    diag::err_integer_sequence_negative_length);
3323       return QualType();
3324     }
3325 
3326     QualType ArgTy = NumArgsArg.getIntegralType();
3327     TemplateArgumentListInfo SyntheticTemplateArgs;
3328     // The type argument gets reused as the first template argument in the
3329     // synthetic template argument list.
3330     SyntheticTemplateArgs.addArgument(TemplateArgs[1]);
3331     // Expand N into 0 ... N-1.
3332     for (llvm::APSInt I(NumArgs.getBitWidth(), NumArgs.isUnsigned());
3333          I < NumArgs; ++I) {
3334       TemplateArgument TA(Context, I, ArgTy);
3335       SyntheticTemplateArgs.addArgument(SemaRef.getTrivialTemplateArgumentLoc(
3336           TA, ArgTy, TemplateArgs[2].getLocation()));
3337     }
3338     // The first template argument will be reused as the template decl that
3339     // our synthetic template arguments will be applied to.
3340     return SemaRef.CheckTemplateIdType(Converted[0].getAsTemplate(),
3341                                        TemplateLoc, SyntheticTemplateArgs);
3342   }
3343 
3344   case BTK__type_pack_element:
3345     // Specializations of
3346     //    __type_pack_element<Index, T_1, ..., T_N>
3347     // are treated like T_Index.
3348     assert(Converted.size() == 2 &&
3349       "__type_pack_element should be given an index and a parameter pack");
3350 
3351     // If the Index is out of bounds, the program is ill-formed.
3352     TemplateArgument IndexArg = Converted[0], Ts = Converted[1];
3353     llvm::APSInt Index = IndexArg.getAsIntegral();
3354     assert(Index >= 0 && "the index used with __type_pack_element should be of "
3355                          "type std::size_t, and hence be non-negative");
3356     if (Index >= Ts.pack_size()) {
3357       SemaRef.Diag(TemplateArgs[0].getLocation(),
3358                    diag::err_type_pack_element_out_of_bounds);
3359       return QualType();
3360     }
3361 
3362     // We simply return the type at index `Index`.
3363     auto Nth = std::next(Ts.pack_begin(), Index.getExtValue());
3364     return Nth->getAsType();
3365   }
3366   llvm_unreachable("unexpected BuiltinTemplateDecl!");
3367 }
3368 
3369 /// Determine whether this alias template is "enable_if_t".
3370 static bool isEnableIfAliasTemplate(TypeAliasTemplateDecl *AliasTemplate) {
3371   return AliasTemplate->getName().equals("enable_if_t");
3372 }
3373 
3374 /// Collect all of the separable terms in the given condition, which
3375 /// might be a conjunction.
3376 ///
3377 /// FIXME: The right answer is to convert the logical expression into
3378 /// disjunctive normal form, so we can find the first failed term
3379 /// within each possible clause.
3380 static void collectConjunctionTerms(Expr *Clause,
3381                                     SmallVectorImpl<Expr *> &Terms) {
3382   if (auto BinOp = dyn_cast<BinaryOperator>(Clause->IgnoreParenImpCasts())) {
3383     if (BinOp->getOpcode() == BO_LAnd) {
3384       collectConjunctionTerms(BinOp->getLHS(), Terms);
3385       collectConjunctionTerms(BinOp->getRHS(), Terms);
3386     }
3387 
3388     return;
3389   }
3390 
3391   Terms.push_back(Clause);
3392 }
3393 
3394 // The ranges-v3 library uses an odd pattern of a top-level "||" with
3395 // a left-hand side that is value-dependent but never true. Identify
3396 // the idiom and ignore that term.
3397 static Expr *lookThroughRangesV3Condition(Preprocessor &PP, Expr *Cond) {
3398   // Top-level '||'.
3399   auto *BinOp = dyn_cast<BinaryOperator>(Cond->IgnoreParenImpCasts());
3400   if (!BinOp) return Cond;
3401 
3402   if (BinOp->getOpcode() != BO_LOr) return Cond;
3403 
3404   // With an inner '==' that has a literal on the right-hand side.
3405   Expr *LHS = BinOp->getLHS();
3406   auto *InnerBinOp = dyn_cast<BinaryOperator>(LHS->IgnoreParenImpCasts());
3407   if (!InnerBinOp) return Cond;
3408 
3409   if (InnerBinOp->getOpcode() != BO_EQ ||
3410       !isa<IntegerLiteral>(InnerBinOp->getRHS()))
3411     return Cond;
3412 
3413   // If the inner binary operation came from a macro expansion named
3414   // CONCEPT_REQUIRES or CONCEPT_REQUIRES_, return the right-hand side
3415   // of the '||', which is the real, user-provided condition.
3416   SourceLocation Loc = InnerBinOp->getExprLoc();
3417   if (!Loc.isMacroID()) return Cond;
3418 
3419   StringRef MacroName = PP.getImmediateMacroName(Loc);
3420   if (MacroName == "CONCEPT_REQUIRES" || MacroName == "CONCEPT_REQUIRES_")
3421     return BinOp->getRHS();
3422 
3423   return Cond;
3424 }
3425 
3426 namespace {
3427 
3428 // A PrinterHelper that prints more helpful diagnostics for some sub-expressions
3429 // within failing boolean expression, such as substituting template parameters
3430 // for actual types.
3431 class FailedBooleanConditionPrinterHelper : public PrinterHelper {
3432 public:
3433   explicit FailedBooleanConditionPrinterHelper(const PrintingPolicy &P)
3434       : Policy(P) {}
3435 
3436   bool handledStmt(Stmt *E, raw_ostream &OS) override {
3437     const auto *DR = dyn_cast<DeclRefExpr>(E);
3438     if (DR && DR->getQualifier()) {
3439       // If this is a qualified name, expand the template arguments in nested
3440       // qualifiers.
3441       DR->getQualifier()->print(OS, Policy, true);
3442       // Then print the decl itself.
3443       const ValueDecl *VD = DR->getDecl();
3444       OS << VD->getName();
3445       if (const auto *IV = dyn_cast<VarTemplateSpecializationDecl>(VD)) {
3446         // This is a template variable, print the expanded template arguments.
3447         printTemplateArgumentList(OS, IV->getTemplateArgs().asArray(), Policy);
3448       }
3449       return true;
3450     }
3451     return false;
3452   }
3453 
3454 private:
3455   const PrintingPolicy Policy;
3456 };
3457 
3458 } // end anonymous namespace
3459 
3460 std::pair<Expr *, std::string>
3461 Sema::findFailedBooleanCondition(Expr *Cond) {
3462   Cond = lookThroughRangesV3Condition(PP, Cond);
3463 
3464   // Separate out all of the terms in a conjunction.
3465   SmallVector<Expr *, 4> Terms;
3466   collectConjunctionTerms(Cond, Terms);
3467 
3468   // Determine which term failed.
3469   Expr *FailedCond = nullptr;
3470   for (Expr *Term : Terms) {
3471     Expr *TermAsWritten = Term->IgnoreParenImpCasts();
3472 
3473     // Literals are uninteresting.
3474     if (isa<CXXBoolLiteralExpr>(TermAsWritten) ||
3475         isa<IntegerLiteral>(TermAsWritten))
3476       continue;
3477 
3478     // The initialization of the parameter from the argument is
3479     // a constant-evaluated context.
3480     EnterExpressionEvaluationContext ConstantEvaluated(
3481       *this, Sema::ExpressionEvaluationContext::ConstantEvaluated);
3482 
3483     bool Succeeded;
3484     if (Term->EvaluateAsBooleanCondition(Succeeded, Context) &&
3485         !Succeeded) {
3486       FailedCond = TermAsWritten;
3487       break;
3488     }
3489   }
3490   if (!FailedCond)
3491     FailedCond = Cond->IgnoreParenImpCasts();
3492 
3493   std::string Description;
3494   {
3495     llvm::raw_string_ostream Out(Description);
3496     PrintingPolicy Policy = getPrintingPolicy();
3497     Policy.PrintCanonicalTypes = true;
3498     FailedBooleanConditionPrinterHelper Helper(Policy);
3499     FailedCond->printPretty(Out, &Helper, Policy, 0, "\n", nullptr);
3500   }
3501   return { FailedCond, Description };
3502 }
3503 
3504 QualType Sema::CheckTemplateIdType(TemplateName Name,
3505                                    SourceLocation TemplateLoc,
3506                                    TemplateArgumentListInfo &TemplateArgs) {
3507   DependentTemplateName *DTN
3508     = Name.getUnderlying().getAsDependentTemplateName();
3509   if (DTN && DTN->isIdentifier())
3510     // When building a template-id where the template-name is dependent,
3511     // assume the template is a type template. Either our assumption is
3512     // correct, or the code is ill-formed and will be diagnosed when the
3513     // dependent name is substituted.
3514     return Context.getDependentTemplateSpecializationType(ETK_None,
3515                                                           DTN->getQualifier(),
3516                                                           DTN->getIdentifier(),
3517                                                           TemplateArgs);
3518 
3519   if (Name.getAsAssumedTemplateName() &&
3520       resolveAssumedTemplateNameAsType(/*Scope*/nullptr, Name, TemplateLoc))
3521     return QualType();
3522 
3523   TemplateDecl *Template = Name.getAsTemplateDecl();
3524   if (!Template || isa<FunctionTemplateDecl>(Template) ||
3525       isa<VarTemplateDecl>(Template) || isa<ConceptDecl>(Template)) {
3526     // We might have a substituted template template parameter pack. If so,
3527     // build a template specialization type for it.
3528     if (Name.getAsSubstTemplateTemplateParmPack())
3529       return Context.getTemplateSpecializationType(Name, TemplateArgs);
3530 
3531     Diag(TemplateLoc, diag::err_template_id_not_a_type)
3532       << Name;
3533     NoteAllFoundTemplates(Name);
3534     return QualType();
3535   }
3536 
3537   // Check that the template argument list is well-formed for this
3538   // template.
3539   SmallVector<TemplateArgument, 4> Converted;
3540   if (CheckTemplateArgumentList(Template, TemplateLoc, TemplateArgs,
3541                                 false, Converted,
3542                                 /*UpdateArgsWithConversion=*/true))
3543     return QualType();
3544 
3545   QualType CanonType;
3546 
3547   bool InstantiationDependent = false;
3548   if (TypeAliasTemplateDecl *AliasTemplate =
3549           dyn_cast<TypeAliasTemplateDecl>(Template)) {
3550 
3551     // Find the canonical type for this type alias template specialization.
3552     TypeAliasDecl *Pattern = AliasTemplate->getTemplatedDecl();
3553     if (Pattern->isInvalidDecl())
3554       return QualType();
3555 
3556     TemplateArgumentList StackTemplateArgs(TemplateArgumentList::OnStack,
3557                                            Converted);
3558 
3559     // Only substitute for the innermost template argument list.
3560     MultiLevelTemplateArgumentList TemplateArgLists;
3561     TemplateArgLists.addOuterTemplateArguments(&StackTemplateArgs);
3562     TemplateArgLists.addOuterRetainedLevels(
3563         AliasTemplate->getTemplateParameters()->getDepth());
3564 
3565     LocalInstantiationScope Scope(*this);
3566     InstantiatingTemplate Inst(*this, TemplateLoc, Template);
3567     if (Inst.isInvalid())
3568       return QualType();
3569 
3570     CanonType = SubstType(Pattern->getUnderlyingType(),
3571                           TemplateArgLists, AliasTemplate->getLocation(),
3572                           AliasTemplate->getDeclName());
3573     if (CanonType.isNull()) {
3574       // If this was enable_if and we failed to find the nested type
3575       // within enable_if in a SFINAE context, dig out the specific
3576       // enable_if condition that failed and present that instead.
3577       if (isEnableIfAliasTemplate(AliasTemplate)) {
3578         if (auto DeductionInfo = isSFINAEContext()) {
3579           if (*DeductionInfo &&
3580               (*DeductionInfo)->hasSFINAEDiagnostic() &&
3581               (*DeductionInfo)->peekSFINAEDiagnostic().second.getDiagID() ==
3582                 diag::err_typename_nested_not_found_enable_if &&
3583               TemplateArgs[0].getArgument().getKind()
3584                 == TemplateArgument::Expression) {
3585             Expr *FailedCond;
3586             std::string FailedDescription;
3587             std::tie(FailedCond, FailedDescription) =
3588               findFailedBooleanCondition(TemplateArgs[0].getSourceExpression());
3589 
3590             // Remove the old SFINAE diagnostic.
3591             PartialDiagnosticAt OldDiag =
3592               {SourceLocation(), PartialDiagnostic::NullDiagnostic()};
3593             (*DeductionInfo)->takeSFINAEDiagnostic(OldDiag);
3594 
3595             // Add a new SFINAE diagnostic specifying which condition
3596             // failed.
3597             (*DeductionInfo)->addSFINAEDiagnostic(
3598               OldDiag.first,
3599               PDiag(diag::err_typename_nested_not_found_requirement)
3600                 << FailedDescription
3601                 << FailedCond->getSourceRange());
3602           }
3603         }
3604       }
3605 
3606       return QualType();
3607     }
3608   } else if (Name.isDependent() ||
3609              TemplateSpecializationType::anyDependentTemplateArguments(
3610                TemplateArgs, InstantiationDependent)) {
3611     // This class template specialization is a dependent
3612     // type. Therefore, its canonical type is another class template
3613     // specialization type that contains all of the converted
3614     // arguments in canonical form. This ensures that, e.g., A<T> and
3615     // A<T, T> have identical types when A is declared as:
3616     //
3617     //   template<typename T, typename U = T> struct A;
3618     CanonType = Context.getCanonicalTemplateSpecializationType(Name, Converted);
3619 
3620     // This might work out to be a current instantiation, in which
3621     // case the canonical type needs to be the InjectedClassNameType.
3622     //
3623     // TODO: in theory this could be a simple hashtable lookup; most
3624     // changes to CurContext don't change the set of current
3625     // instantiations.
3626     if (isa<ClassTemplateDecl>(Template)) {
3627       for (DeclContext *Ctx = CurContext; Ctx; Ctx = Ctx->getLookupParent()) {
3628         // If we get out to a namespace, we're done.
3629         if (Ctx->isFileContext()) break;
3630 
3631         // If this isn't a record, keep looking.
3632         CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(Ctx);
3633         if (!Record) continue;
3634 
3635         // Look for one of the two cases with InjectedClassNameTypes
3636         // and check whether it's the same template.
3637         if (!isa<ClassTemplatePartialSpecializationDecl>(Record) &&
3638             !Record->getDescribedClassTemplate())
3639           continue;
3640 
3641         // Fetch the injected class name type and check whether its
3642         // injected type is equal to the type we just built.
3643         QualType ICNT = Context.getTypeDeclType(Record);
3644         QualType Injected = cast<InjectedClassNameType>(ICNT)
3645           ->getInjectedSpecializationType();
3646 
3647         if (CanonType != Injected->getCanonicalTypeInternal())
3648           continue;
3649 
3650         // If so, the canonical type of this TST is the injected
3651         // class name type of the record we just found.
3652         assert(ICNT.isCanonical());
3653         CanonType = ICNT;
3654         break;
3655       }
3656     }
3657   } else if (ClassTemplateDecl *ClassTemplate
3658                = dyn_cast<ClassTemplateDecl>(Template)) {
3659     // Find the class template specialization declaration that
3660     // corresponds to these arguments.
3661     void *InsertPos = nullptr;
3662     ClassTemplateSpecializationDecl *Decl
3663       = ClassTemplate->findSpecialization(Converted, InsertPos);
3664     if (!Decl) {
3665       // This is the first time we have referenced this class template
3666       // specialization. Create the canonical declaration and add it to
3667       // the set of specializations.
3668       Decl = ClassTemplateSpecializationDecl::Create(
3669           Context, ClassTemplate->getTemplatedDecl()->getTagKind(),
3670           ClassTemplate->getDeclContext(),
3671           ClassTemplate->getTemplatedDecl()->getBeginLoc(),
3672           ClassTemplate->getLocation(), ClassTemplate, Converted, nullptr);
3673       ClassTemplate->AddSpecialization(Decl, InsertPos);
3674       if (ClassTemplate->isOutOfLine())
3675         Decl->setLexicalDeclContext(ClassTemplate->getLexicalDeclContext());
3676     }
3677 
3678     if (Decl->getSpecializationKind() == TSK_Undeclared) {
3679       MultiLevelTemplateArgumentList TemplateArgLists;
3680       TemplateArgLists.addOuterTemplateArguments(Converted);
3681       InstantiateAttrsForDecl(TemplateArgLists, ClassTemplate->getTemplatedDecl(),
3682                               Decl);
3683     }
3684 
3685     // Diagnose uses of this specialization.
3686     (void)DiagnoseUseOfDecl(Decl, TemplateLoc);
3687 
3688     CanonType = Context.getTypeDeclType(Decl);
3689     assert(isa<RecordType>(CanonType) &&
3690            "type of non-dependent specialization is not a RecordType");
3691   } else if (auto *BTD = dyn_cast<BuiltinTemplateDecl>(Template)) {
3692     CanonType = checkBuiltinTemplateIdType(*this, BTD, Converted, TemplateLoc,
3693                                            TemplateArgs);
3694   }
3695 
3696   // Build the fully-sugared type for this class template
3697   // specialization, which refers back to the class template
3698   // specialization we created or found.
3699   return Context.getTemplateSpecializationType(Name, TemplateArgs, CanonType);
3700 }
3701 
3702 void Sema::ActOnUndeclaredTypeTemplateName(Scope *S, TemplateTy &ParsedName,
3703                                            TemplateNameKind &TNK,
3704                                            SourceLocation NameLoc,
3705                                            IdentifierInfo *&II) {
3706   assert(TNK == TNK_Undeclared_template && "not an undeclared template name");
3707 
3708   TemplateName Name = ParsedName.get();
3709   auto *ATN = Name.getAsAssumedTemplateName();
3710   assert(ATN && "not an assumed template name");
3711   II = ATN->getDeclName().getAsIdentifierInfo();
3712 
3713   if (!resolveAssumedTemplateNameAsType(S, Name, NameLoc, /*Diagnose*/false)) {
3714     // Resolved to a type template name.
3715     ParsedName = TemplateTy::make(Name);
3716     TNK = TNK_Type_template;
3717   }
3718 }
3719 
3720 bool Sema::resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
3721                                             SourceLocation NameLoc,
3722                                             bool Diagnose) {
3723   // We assumed this undeclared identifier to be an (ADL-only) function
3724   // template name, but it was used in a context where a type was required.
3725   // Try to typo-correct it now.
3726   AssumedTemplateStorage *ATN = Name.getAsAssumedTemplateName();
3727   assert(ATN && "not an assumed template name");
3728 
3729   LookupResult R(*this, ATN->getDeclName(), NameLoc, LookupOrdinaryName);
3730   struct CandidateCallback : CorrectionCandidateCallback {
3731     bool ValidateCandidate(const TypoCorrection &TC) override {
3732       return TC.getCorrectionDecl() &&
3733              getAsTypeTemplateDecl(TC.getCorrectionDecl());
3734     }
3735     std::unique_ptr<CorrectionCandidateCallback> clone() override {
3736       return std::make_unique<CandidateCallback>(*this);
3737     }
3738   } FilterCCC;
3739 
3740   TypoCorrection Corrected =
3741       CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, nullptr,
3742                   FilterCCC, CTK_ErrorRecovery);
3743   if (Corrected && Corrected.getFoundDecl()) {
3744     diagnoseTypo(Corrected, PDiag(diag::err_no_template_suggest)
3745                                 << ATN->getDeclName());
3746     Name = TemplateName(Corrected.getCorrectionDeclAs<TemplateDecl>());
3747     return false;
3748   }
3749 
3750   if (Diagnose)
3751     Diag(R.getNameLoc(), diag::err_no_template) << R.getLookupName();
3752   return true;
3753 }
3754 
3755 TypeResult Sema::ActOnTemplateIdType(
3756     Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
3757     TemplateTy TemplateD, IdentifierInfo *TemplateII,
3758     SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
3759     ASTTemplateArgsPtr TemplateArgsIn, SourceLocation RAngleLoc,
3760     bool IsCtorOrDtorName, bool IsClassName) {
3761   if (SS.isInvalid())
3762     return true;
3763 
3764   if (!IsCtorOrDtorName && !IsClassName && SS.isSet()) {
3765     DeclContext *LookupCtx = computeDeclContext(SS, /*EnteringContext*/false);
3766 
3767     // C++ [temp.res]p3:
3768     //   A qualified-id that refers to a type and in which the
3769     //   nested-name-specifier depends on a template-parameter (14.6.2)
3770     //   shall be prefixed by the keyword typename to indicate that the
3771     //   qualified-id denotes a type, forming an
3772     //   elaborated-type-specifier (7.1.5.3).
3773     if (!LookupCtx && isDependentScopeSpecifier(SS)) {
3774       Diag(SS.getBeginLoc(), diag::err_typename_missing_template)
3775         << SS.getScopeRep() << TemplateII->getName();
3776       // Recover as if 'typename' were specified.
3777       // FIXME: This is not quite correct recovery as we don't transform SS
3778       // into the corresponding dependent form (and we don't diagnose missing
3779       // 'template' keywords within SS as a result).
3780       return ActOnTypenameType(nullptr, SourceLocation(), SS, TemplateKWLoc,
3781                                TemplateD, TemplateII, TemplateIILoc, LAngleLoc,
3782                                TemplateArgsIn, RAngleLoc);
3783     }
3784 
3785     // Per C++ [class.qual]p2, if the template-id was an injected-class-name,
3786     // it's not actually allowed to be used as a type in most cases. Because
3787     // we annotate it before we know whether it's valid, we have to check for
3788     // this case here.
3789     auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
3790     if (LookupRD && LookupRD->getIdentifier() == TemplateII) {
3791       Diag(TemplateIILoc,
3792            TemplateKWLoc.isInvalid()
3793                ? diag::err_out_of_line_qualified_id_type_names_constructor
3794                : diag::ext_out_of_line_qualified_id_type_names_constructor)
3795         << TemplateII << 0 /*injected-class-name used as template name*/
3796         << 1 /*if any keyword was present, it was 'template'*/;
3797     }
3798   }
3799 
3800   TemplateName Template = TemplateD.get();
3801   if (Template.getAsAssumedTemplateName() &&
3802       resolveAssumedTemplateNameAsType(S, Template, TemplateIILoc))
3803     return true;
3804 
3805   // Translate the parser's template argument list in our AST format.
3806   TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
3807   translateTemplateArguments(TemplateArgsIn, TemplateArgs);
3808 
3809   if (DependentTemplateName *DTN = Template.getAsDependentTemplateName()) {
3810     QualType T
3811       = Context.getDependentTemplateSpecializationType(ETK_None,
3812                                                        DTN->getQualifier(),
3813                                                        DTN->getIdentifier(),
3814                                                        TemplateArgs);
3815     // Build type-source information.
3816     TypeLocBuilder TLB;
3817     DependentTemplateSpecializationTypeLoc SpecTL
3818       = TLB.push<DependentTemplateSpecializationTypeLoc>(T);
3819     SpecTL.setElaboratedKeywordLoc(SourceLocation());
3820     SpecTL.setQualifierLoc(SS.getWithLocInContext(Context));
3821     SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
3822     SpecTL.setTemplateNameLoc(TemplateIILoc);
3823     SpecTL.setLAngleLoc(LAngleLoc);
3824     SpecTL.setRAngleLoc(RAngleLoc);
3825     for (unsigned I = 0, N = SpecTL.getNumArgs(); I != N; ++I)
3826       SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
3827     return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
3828   }
3829 
3830   QualType Result = CheckTemplateIdType(Template, TemplateIILoc, TemplateArgs);
3831   if (Result.isNull())
3832     return true;
3833 
3834   // Build type-source information.
3835   TypeLocBuilder TLB;
3836   TemplateSpecializationTypeLoc SpecTL
3837     = TLB.push<TemplateSpecializationTypeLoc>(Result);
3838   SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
3839   SpecTL.setTemplateNameLoc(TemplateIILoc);
3840   SpecTL.setLAngleLoc(LAngleLoc);
3841   SpecTL.setRAngleLoc(RAngleLoc);
3842   for (unsigned i = 0, e = SpecTL.getNumArgs(); i != e; ++i)
3843     SpecTL.setArgLocInfo(i, TemplateArgs[i].getLocInfo());
3844 
3845   // NOTE: avoid constructing an ElaboratedTypeLoc if this is a
3846   // constructor or destructor name (in such a case, the scope specifier
3847   // will be attached to the enclosing Decl or Expr node).
3848   if (SS.isNotEmpty() && !IsCtorOrDtorName) {
3849     // Create an elaborated-type-specifier containing the nested-name-specifier.
3850     Result = Context.getElaboratedType(ETK_None, SS.getScopeRep(), Result);
3851     ElaboratedTypeLoc ElabTL = TLB.push<ElaboratedTypeLoc>(Result);
3852     ElabTL.setElaboratedKeywordLoc(SourceLocation());
3853     ElabTL.setQualifierLoc(SS.getWithLocInContext(Context));
3854   }
3855 
3856   return CreateParsedType(Result, TLB.getTypeSourceInfo(Context, Result));
3857 }
3858 
3859 TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
3860                                         TypeSpecifierType TagSpec,
3861                                         SourceLocation TagLoc,
3862                                         CXXScopeSpec &SS,
3863                                         SourceLocation TemplateKWLoc,
3864                                         TemplateTy TemplateD,
3865                                         SourceLocation TemplateLoc,
3866                                         SourceLocation LAngleLoc,
3867                                         ASTTemplateArgsPtr TemplateArgsIn,
3868                                         SourceLocation RAngleLoc) {
3869   if (SS.isInvalid())
3870     return TypeResult(true);
3871 
3872   TemplateName Template = TemplateD.get();
3873 
3874   // Translate the parser's template argument list in our AST format.
3875   TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
3876   translateTemplateArguments(TemplateArgsIn, TemplateArgs);
3877 
3878   // Determine the tag kind
3879   TagTypeKind TagKind = TypeWithKeyword::getTagTypeKindForTypeSpec(TagSpec);
3880   ElaboratedTypeKeyword Keyword
3881     = TypeWithKeyword::getKeywordForTagTypeKind(TagKind);
3882 
3883   if (DependentTemplateName *DTN = Template.getAsDependentTemplateName()) {
3884     QualType T = Context.getDependentTemplateSpecializationType(Keyword,
3885                                                           DTN->getQualifier(),
3886                                                           DTN->getIdentifier(),
3887                                                                 TemplateArgs);
3888 
3889     // Build type-source information.
3890     TypeLocBuilder TLB;
3891     DependentTemplateSpecializationTypeLoc SpecTL
3892       = TLB.push<DependentTemplateSpecializationTypeLoc>(T);
3893     SpecTL.setElaboratedKeywordLoc(TagLoc);
3894     SpecTL.setQualifierLoc(SS.getWithLocInContext(Context));
3895     SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
3896     SpecTL.setTemplateNameLoc(TemplateLoc);
3897     SpecTL.setLAngleLoc(LAngleLoc);
3898     SpecTL.setRAngleLoc(RAngleLoc);
3899     for (unsigned I = 0, N = SpecTL.getNumArgs(); I != N; ++I)
3900       SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
3901     return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
3902   }
3903 
3904   if (TypeAliasTemplateDecl *TAT =
3905         dyn_cast_or_null<TypeAliasTemplateDecl>(Template.getAsTemplateDecl())) {
3906     // C++0x [dcl.type.elab]p2:
3907     //   If the identifier resolves to a typedef-name or the simple-template-id
3908     //   resolves to an alias template specialization, the
3909     //   elaborated-type-specifier is ill-formed.
3910     Diag(TemplateLoc, diag::err_tag_reference_non_tag)
3911         << TAT << NTK_TypeAliasTemplate << TagKind;
3912     Diag(TAT->getLocation(), diag::note_declared_at);
3913   }
3914 
3915   QualType Result = CheckTemplateIdType(Template, TemplateLoc, TemplateArgs);
3916   if (Result.isNull())
3917     return TypeResult(true);
3918 
3919   // Check the tag kind
3920   if (const RecordType *RT = Result->getAs<RecordType>()) {
3921     RecordDecl *D = RT->getDecl();
3922 
3923     IdentifierInfo *Id = D->getIdentifier();
3924     assert(Id && "templated class must have an identifier");
3925 
3926     if (!isAcceptableTagRedeclaration(D, TagKind, TUK == TUK_Definition,
3927                                       TagLoc, Id)) {
3928       Diag(TagLoc, diag::err_use_with_wrong_tag)
3929         << Result
3930         << FixItHint::CreateReplacement(SourceRange(TagLoc), D->getKindName());
3931       Diag(D->getLocation(), diag::note_previous_use);
3932     }
3933   }
3934 
3935   // Provide source-location information for the template specialization.
3936   TypeLocBuilder TLB;
3937   TemplateSpecializationTypeLoc SpecTL
3938     = TLB.push<TemplateSpecializationTypeLoc>(Result);
3939   SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
3940   SpecTL.setTemplateNameLoc(TemplateLoc);
3941   SpecTL.setLAngleLoc(LAngleLoc);
3942   SpecTL.setRAngleLoc(RAngleLoc);
3943   for (unsigned i = 0, e = SpecTL.getNumArgs(); i != e; ++i)
3944     SpecTL.setArgLocInfo(i, TemplateArgs[i].getLocInfo());
3945 
3946   // Construct an elaborated type containing the nested-name-specifier (if any)
3947   // and tag keyword.
3948   Result = Context.getElaboratedType(Keyword, SS.getScopeRep(), Result);
3949   ElaboratedTypeLoc ElabTL = TLB.push<ElaboratedTypeLoc>(Result);
3950   ElabTL.setElaboratedKeywordLoc(TagLoc);
3951   ElabTL.setQualifierLoc(SS.getWithLocInContext(Context));
3952   return CreateParsedType(Result, TLB.getTypeSourceInfo(Context, Result));
3953 }
3954 
3955 static bool CheckTemplateSpecializationScope(Sema &S, NamedDecl *Specialized,
3956                                              NamedDecl *PrevDecl,
3957                                              SourceLocation Loc,
3958                                              bool IsPartialSpecialization);
3959 
3960 static TemplateSpecializationKind getTemplateSpecializationKind(Decl *D);
3961 
3962 static bool isTemplateArgumentTemplateParameter(
3963     const TemplateArgument &Arg, unsigned Depth, unsigned Index) {
3964   switch (Arg.getKind()) {
3965   case TemplateArgument::Null:
3966   case TemplateArgument::NullPtr:
3967   case TemplateArgument::Integral:
3968   case TemplateArgument::Declaration:
3969   case TemplateArgument::Pack:
3970   case TemplateArgument::TemplateExpansion:
3971     return false;
3972 
3973   case TemplateArgument::Type: {
3974     QualType Type = Arg.getAsType();
3975     const TemplateTypeParmType *TPT =
3976         Arg.getAsType()->getAs<TemplateTypeParmType>();
3977     return TPT && !Type.hasQualifiers() &&
3978            TPT->getDepth() == Depth && TPT->getIndex() == Index;
3979   }
3980 
3981   case TemplateArgument::Expression: {
3982     DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Arg.getAsExpr());
3983     if (!DRE || !DRE->getDecl())
3984       return false;
3985     const NonTypeTemplateParmDecl *NTTP =
3986         dyn_cast<NonTypeTemplateParmDecl>(DRE->getDecl());
3987     return NTTP && NTTP->getDepth() == Depth && NTTP->getIndex() == Index;
3988   }
3989 
3990   case TemplateArgument::Template:
3991     const TemplateTemplateParmDecl *TTP =
3992         dyn_cast_or_null<TemplateTemplateParmDecl>(
3993             Arg.getAsTemplateOrTemplatePattern().getAsTemplateDecl());
3994     return TTP && TTP->getDepth() == Depth && TTP->getIndex() == Index;
3995   }
3996   llvm_unreachable("unexpected kind of template argument");
3997 }
3998 
3999 static bool isSameAsPrimaryTemplate(TemplateParameterList *Params,
4000                                     ArrayRef<TemplateArgument> Args) {
4001   if (Params->size() != Args.size())
4002     return false;
4003 
4004   unsigned Depth = Params->getDepth();
4005 
4006   for (unsigned I = 0, N = Args.size(); I != N; ++I) {
4007     TemplateArgument Arg = Args[I];
4008 
4009     // If the parameter is a pack expansion, the argument must be a pack
4010     // whose only element is a pack expansion.
4011     if (Params->getParam(I)->isParameterPack()) {
4012       if (Arg.getKind() != TemplateArgument::Pack || Arg.pack_size() != 1 ||
4013           !Arg.pack_begin()->isPackExpansion())
4014         return false;
4015       Arg = Arg.pack_begin()->getPackExpansionPattern();
4016     }
4017 
4018     if (!isTemplateArgumentTemplateParameter(Arg, Depth, I))
4019       return false;
4020   }
4021 
4022   return true;
4023 }
4024 
4025 template<typename PartialSpecDecl>
4026 static void checkMoreSpecializedThanPrimary(Sema &S, PartialSpecDecl *Partial) {
4027   if (Partial->getDeclContext()->isDependentContext())
4028     return;
4029 
4030   // FIXME: Get the TDK from deduction in order to provide better diagnostics
4031   // for non-substitution-failure issues?
4032   TemplateDeductionInfo Info(Partial->getLocation());
4033   if (S.isMoreSpecializedThanPrimary(Partial, Info))
4034     return;
4035 
4036   auto *Template = Partial->getSpecializedTemplate();
4037   S.Diag(Partial->getLocation(),
4038          diag::ext_partial_spec_not_more_specialized_than_primary)
4039       << isa<VarTemplateDecl>(Template);
4040 
4041   if (Info.hasSFINAEDiagnostic()) {
4042     PartialDiagnosticAt Diag = {SourceLocation(),
4043                                 PartialDiagnostic::NullDiagnostic()};
4044     Info.takeSFINAEDiagnostic(Diag);
4045     SmallString<128> SFINAEArgString;
4046     Diag.second.EmitToString(S.getDiagnostics(), SFINAEArgString);
4047     S.Diag(Diag.first,
4048            diag::note_partial_spec_not_more_specialized_than_primary)
4049       << SFINAEArgString;
4050   }
4051 
4052   S.Diag(Template->getLocation(), diag::note_template_decl_here);
4053   SmallVector<const Expr *, 3> PartialAC, TemplateAC;
4054   Template->getAssociatedConstraints(TemplateAC);
4055   Partial->getAssociatedConstraints(PartialAC);
4056   S.MaybeEmitAmbiguousAtomicConstraintsDiagnostic(Partial, PartialAC, Template,
4057                                                   TemplateAC);
4058 }
4059 
4060 static void
4061 noteNonDeducibleParameters(Sema &S, TemplateParameterList *TemplateParams,
4062                            const llvm::SmallBitVector &DeducibleParams) {
4063   for (unsigned I = 0, N = DeducibleParams.size(); I != N; ++I) {
4064     if (!DeducibleParams[I]) {
4065       NamedDecl *Param = TemplateParams->getParam(I);
4066       if (Param->getDeclName())
4067         S.Diag(Param->getLocation(), diag::note_non_deducible_parameter)
4068             << Param->getDeclName();
4069       else
4070         S.Diag(Param->getLocation(), diag::note_non_deducible_parameter)
4071             << "(anonymous)";
4072     }
4073   }
4074 }
4075 
4076 
4077 template<typename PartialSpecDecl>
4078 static void checkTemplatePartialSpecialization(Sema &S,
4079                                                PartialSpecDecl *Partial) {
4080   // C++1z [temp.class.spec]p8: (DR1495)
4081   //   - The specialization shall be more specialized than the primary
4082   //     template (14.5.5.2).
4083   checkMoreSpecializedThanPrimary(S, Partial);
4084 
4085   // C++ [temp.class.spec]p8: (DR1315)
4086   //   - Each template-parameter shall appear at least once in the
4087   //     template-id outside a non-deduced context.
4088   // C++1z [temp.class.spec.match]p3 (P0127R2)
4089   //   If the template arguments of a partial specialization cannot be
4090   //   deduced because of the structure of its template-parameter-list
4091   //   and the template-id, the program is ill-formed.
4092   auto *TemplateParams = Partial->getTemplateParameters();
4093   llvm::SmallBitVector DeducibleParams(TemplateParams->size());
4094   S.MarkUsedTemplateParameters(Partial->getTemplateArgs(), true,
4095                                TemplateParams->getDepth(), DeducibleParams);
4096 
4097   if (!DeducibleParams.all()) {
4098     unsigned NumNonDeducible = DeducibleParams.size() - DeducibleParams.count();
4099     S.Diag(Partial->getLocation(), diag::ext_partial_specs_not_deducible)
4100       << isa<VarTemplatePartialSpecializationDecl>(Partial)
4101       << (NumNonDeducible > 1)
4102       << SourceRange(Partial->getLocation(),
4103                      Partial->getTemplateArgsAsWritten()->RAngleLoc);
4104     noteNonDeducibleParameters(S, TemplateParams, DeducibleParams);
4105   }
4106 }
4107 
4108 void Sema::CheckTemplatePartialSpecialization(
4109     ClassTemplatePartialSpecializationDecl *Partial) {
4110   checkTemplatePartialSpecialization(*this, Partial);
4111 }
4112 
4113 void Sema::CheckTemplatePartialSpecialization(
4114     VarTemplatePartialSpecializationDecl *Partial) {
4115   checkTemplatePartialSpecialization(*this, Partial);
4116 }
4117 
4118 void Sema::CheckDeductionGuideTemplate(FunctionTemplateDecl *TD) {
4119   // C++1z [temp.param]p11:
4120   //   A template parameter of a deduction guide template that does not have a
4121   //   default-argument shall be deducible from the parameter-type-list of the
4122   //   deduction guide template.
4123   auto *TemplateParams = TD->getTemplateParameters();
4124   llvm::SmallBitVector DeducibleParams(TemplateParams->size());
4125   MarkDeducedTemplateParameters(TD, DeducibleParams);
4126   for (unsigned I = 0; I != TemplateParams->size(); ++I) {
4127     // A parameter pack is deducible (to an empty pack).
4128     auto *Param = TemplateParams->getParam(I);
4129     if (Param->isParameterPack() || hasVisibleDefaultArgument(Param))
4130       DeducibleParams[I] = true;
4131   }
4132 
4133   if (!DeducibleParams.all()) {
4134     unsigned NumNonDeducible = DeducibleParams.size() - DeducibleParams.count();
4135     Diag(TD->getLocation(), diag::err_deduction_guide_template_not_deducible)
4136       << (NumNonDeducible > 1);
4137     noteNonDeducibleParameters(*this, TemplateParams, DeducibleParams);
4138   }
4139 }
4140 
4141 DeclResult Sema::ActOnVarTemplateSpecialization(
4142     Scope *S, Declarator &D, TypeSourceInfo *DI, SourceLocation TemplateKWLoc,
4143     TemplateParameterList *TemplateParams, StorageClass SC,
4144     bool IsPartialSpecialization) {
4145   // D must be variable template id.
4146   assert(D.getName().getKind() == UnqualifiedIdKind::IK_TemplateId &&
4147          "Variable template specialization is declared with a template it.");
4148 
4149   TemplateIdAnnotation *TemplateId = D.getName().TemplateId;
4150   TemplateArgumentListInfo TemplateArgs =
4151       makeTemplateArgumentListInfo(*this, *TemplateId);
4152   SourceLocation TemplateNameLoc = D.getIdentifierLoc();
4153   SourceLocation LAngleLoc = TemplateId->LAngleLoc;
4154   SourceLocation RAngleLoc = TemplateId->RAngleLoc;
4155 
4156   TemplateName Name = TemplateId->Template.get();
4157 
4158   // The template-id must name a variable template.
4159   VarTemplateDecl *VarTemplate =
4160       dyn_cast_or_null<VarTemplateDecl>(Name.getAsTemplateDecl());
4161   if (!VarTemplate) {
4162     NamedDecl *FnTemplate;
4163     if (auto *OTS = Name.getAsOverloadedTemplate())
4164       FnTemplate = *OTS->begin();
4165     else
4166       FnTemplate = dyn_cast_or_null<FunctionTemplateDecl>(Name.getAsTemplateDecl());
4167     if (FnTemplate)
4168       return Diag(D.getIdentifierLoc(), diag::err_var_spec_no_template_but_method)
4169                << FnTemplate->getDeclName();
4170     return Diag(D.getIdentifierLoc(), diag::err_var_spec_no_template)
4171              << IsPartialSpecialization;
4172   }
4173 
4174   // Check for unexpanded parameter packs in any of the template arguments.
4175   for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
4176     if (DiagnoseUnexpandedParameterPack(TemplateArgs[I],
4177                                         UPPC_PartialSpecialization))
4178       return true;
4179 
4180   // Check that the template argument list is well-formed for this
4181   // template.
4182   SmallVector<TemplateArgument, 4> Converted;
4183   if (CheckTemplateArgumentList(VarTemplate, TemplateNameLoc, TemplateArgs,
4184                                 false, Converted,
4185                                 /*UpdateArgsWithConversion=*/true))
4186     return true;
4187 
4188   // Find the variable template (partial) specialization declaration that
4189   // corresponds to these arguments.
4190   if (IsPartialSpecialization) {
4191     if (CheckTemplatePartialSpecializationArgs(TemplateNameLoc, VarTemplate,
4192                                                TemplateArgs.size(), Converted))
4193       return true;
4194 
4195     // FIXME: Move these checks to CheckTemplatePartialSpecializationArgs so we
4196     // also do them during instantiation.
4197     bool InstantiationDependent;
4198     if (!Name.isDependent() &&
4199         !TemplateSpecializationType::anyDependentTemplateArguments(
4200             TemplateArgs.arguments(),
4201             InstantiationDependent)) {
4202       Diag(TemplateNameLoc, diag::err_partial_spec_fully_specialized)
4203           << VarTemplate->getDeclName();
4204       IsPartialSpecialization = false;
4205     }
4206 
4207     if (isSameAsPrimaryTemplate(VarTemplate->getTemplateParameters(),
4208                                 Converted) &&
4209         (!Context.getLangOpts().CPlusPlus20 ||
4210          !TemplateParams->hasAssociatedConstraints())) {
4211       // C++ [temp.class.spec]p9b3:
4212       //
4213       //   -- The argument list of the specialization shall not be identical
4214       //      to the implicit argument list of the primary template.
4215       Diag(TemplateNameLoc, diag::err_partial_spec_args_match_primary_template)
4216         << /*variable template*/ 1
4217         << /*is definition*/(SC != SC_Extern && !CurContext->isRecord())
4218         << FixItHint::CreateRemoval(SourceRange(LAngleLoc, RAngleLoc));
4219       // FIXME: Recover from this by treating the declaration as a redeclaration
4220       // of the primary template.
4221       return true;
4222     }
4223   }
4224 
4225   void *InsertPos = nullptr;
4226   VarTemplateSpecializationDecl *PrevDecl = nullptr;
4227 
4228   if (IsPartialSpecialization)
4229     PrevDecl = VarTemplate->findPartialSpecialization(Converted, TemplateParams,
4230                                                       InsertPos);
4231   else
4232     PrevDecl = VarTemplate->findSpecialization(Converted, InsertPos);
4233 
4234   VarTemplateSpecializationDecl *Specialization = nullptr;
4235 
4236   // Check whether we can declare a variable template specialization in
4237   // the current scope.
4238   if (CheckTemplateSpecializationScope(*this, VarTemplate, PrevDecl,
4239                                        TemplateNameLoc,
4240                                        IsPartialSpecialization))
4241     return true;
4242 
4243   if (PrevDecl && PrevDecl->getSpecializationKind() == TSK_Undeclared) {
4244     // Since the only prior variable template specialization with these
4245     // arguments was referenced but not declared,  reuse that
4246     // declaration node as our own, updating its source location and
4247     // the list of outer template parameters to reflect our new declaration.
4248     Specialization = PrevDecl;
4249     Specialization->setLocation(TemplateNameLoc);
4250     PrevDecl = nullptr;
4251   } else if (IsPartialSpecialization) {
4252     // Create a new class template partial specialization declaration node.
4253     VarTemplatePartialSpecializationDecl *PrevPartial =
4254         cast_or_null<VarTemplatePartialSpecializationDecl>(PrevDecl);
4255     VarTemplatePartialSpecializationDecl *Partial =
4256         VarTemplatePartialSpecializationDecl::Create(
4257             Context, VarTemplate->getDeclContext(), TemplateKWLoc,
4258             TemplateNameLoc, TemplateParams, VarTemplate, DI->getType(), DI, SC,
4259             Converted, TemplateArgs);
4260 
4261     if (!PrevPartial)
4262       VarTemplate->AddPartialSpecialization(Partial, InsertPos);
4263     Specialization = Partial;
4264 
4265     // If we are providing an explicit specialization of a member variable
4266     // template specialization, make a note of that.
4267     if (PrevPartial && PrevPartial->getInstantiatedFromMember())
4268       PrevPartial->setMemberSpecialization();
4269 
4270     CheckTemplatePartialSpecialization(Partial);
4271   } else {
4272     // Create a new class template specialization declaration node for
4273     // this explicit specialization or friend declaration.
4274     Specialization = VarTemplateSpecializationDecl::Create(
4275         Context, VarTemplate->getDeclContext(), TemplateKWLoc, TemplateNameLoc,
4276         VarTemplate, DI->getType(), DI, SC, Converted);
4277     Specialization->setTemplateArgsInfo(TemplateArgs);
4278 
4279     if (!PrevDecl)
4280       VarTemplate->AddSpecialization(Specialization, InsertPos);
4281   }
4282 
4283   // C++ [temp.expl.spec]p6:
4284   //   If a template, a member template or the member of a class template is
4285   //   explicitly specialized then that specialization shall be declared
4286   //   before the first use of that specialization that would cause an implicit
4287   //   instantiation to take place, in every translation unit in which such a
4288   //   use occurs; no diagnostic is required.
4289   if (PrevDecl && PrevDecl->getPointOfInstantiation().isValid()) {
4290     bool Okay = false;
4291     for (Decl *Prev = PrevDecl; Prev; Prev = Prev->getPreviousDecl()) {
4292       // Is there any previous explicit specialization declaration?
4293       if (getTemplateSpecializationKind(Prev) == TSK_ExplicitSpecialization) {
4294         Okay = true;
4295         break;
4296       }
4297     }
4298 
4299     if (!Okay) {
4300       SourceRange Range(TemplateNameLoc, RAngleLoc);
4301       Diag(TemplateNameLoc, diag::err_specialization_after_instantiation)
4302           << Name << Range;
4303 
4304       Diag(PrevDecl->getPointOfInstantiation(),
4305            diag::note_instantiation_required_here)
4306           << (PrevDecl->getTemplateSpecializationKind() !=
4307               TSK_ImplicitInstantiation);
4308       return true;
4309     }
4310   }
4311 
4312   Specialization->setTemplateKeywordLoc(TemplateKWLoc);
4313   Specialization->setLexicalDeclContext(CurContext);
4314 
4315   // Add the specialization into its lexical context, so that it can
4316   // be seen when iterating through the list of declarations in that
4317   // context. However, specializations are not found by name lookup.
4318   CurContext->addDecl(Specialization);
4319 
4320   // Note that this is an explicit specialization.
4321   Specialization->setSpecializationKind(TSK_ExplicitSpecialization);
4322 
4323   if (PrevDecl) {
4324     // Check that this isn't a redefinition of this specialization,
4325     // merging with previous declarations.
4326     LookupResult PrevSpec(*this, GetNameForDeclarator(D), LookupOrdinaryName,
4327                           forRedeclarationInCurContext());
4328     PrevSpec.addDecl(PrevDecl);
4329     D.setRedeclaration(CheckVariableDeclaration(Specialization, PrevSpec));
4330   } else if (Specialization->isStaticDataMember() &&
4331              Specialization->isOutOfLine()) {
4332     Specialization->setAccess(VarTemplate->getAccess());
4333   }
4334 
4335   return Specialization;
4336 }
4337 
4338 namespace {
4339 /// A partial specialization whose template arguments have matched
4340 /// a given template-id.
4341 struct PartialSpecMatchResult {
4342   VarTemplatePartialSpecializationDecl *Partial;
4343   TemplateArgumentList *Args;
4344 };
4345 } // end anonymous namespace
4346 
4347 DeclResult
4348 Sema::CheckVarTemplateId(VarTemplateDecl *Template, SourceLocation TemplateLoc,
4349                          SourceLocation TemplateNameLoc,
4350                          const TemplateArgumentListInfo &TemplateArgs) {
4351   assert(Template && "A variable template id without template?");
4352 
4353   // Check that the template argument list is well-formed for this template.
4354   SmallVector<TemplateArgument, 4> Converted;
4355   if (CheckTemplateArgumentList(
4356           Template, TemplateNameLoc,
4357           const_cast<TemplateArgumentListInfo &>(TemplateArgs), false,
4358           Converted, /*UpdateArgsWithConversion=*/true))
4359     return true;
4360 
4361   // Find the variable template specialization declaration that
4362   // corresponds to these arguments.
4363   void *InsertPos = nullptr;
4364   if (VarTemplateSpecializationDecl *Spec = Template->findSpecialization(
4365           Converted, InsertPos)) {
4366     checkSpecializationVisibility(TemplateNameLoc, Spec);
4367     // If we already have a variable template specialization, return it.
4368     return Spec;
4369   }
4370 
4371   // This is the first time we have referenced this variable template
4372   // specialization. Create the canonical declaration and add it to
4373   // the set of specializations, based on the closest partial specialization
4374   // that it represents. That is,
4375   VarDecl *InstantiationPattern = Template->getTemplatedDecl();
4376   TemplateArgumentList TemplateArgList(TemplateArgumentList::OnStack,
4377                                        Converted);
4378   TemplateArgumentList *InstantiationArgs = &TemplateArgList;
4379   bool AmbiguousPartialSpec = false;
4380   typedef PartialSpecMatchResult MatchResult;
4381   SmallVector<MatchResult, 4> Matched;
4382   SourceLocation PointOfInstantiation = TemplateNameLoc;
4383   TemplateSpecCandidateSet FailedCandidates(PointOfInstantiation,
4384                                             /*ForTakingAddress=*/false);
4385 
4386   // 1. Attempt to find the closest partial specialization that this
4387   // specializes, if any.
4388   // If any of the template arguments is dependent, then this is probably
4389   // a placeholder for an incomplete declarative context; which must be
4390   // complete by instantiation time. Thus, do not search through the partial
4391   // specializations yet.
4392   // TODO: Unify with InstantiateClassTemplateSpecialization()?
4393   //       Perhaps better after unification of DeduceTemplateArguments() and
4394   //       getMoreSpecializedPartialSpecialization().
4395   bool InstantiationDependent = false;
4396   if (!TemplateSpecializationType::anyDependentTemplateArguments(
4397           TemplateArgs, InstantiationDependent)) {
4398 
4399     SmallVector<VarTemplatePartialSpecializationDecl *, 4> PartialSpecs;
4400     Template->getPartialSpecializations(PartialSpecs);
4401 
4402     for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I) {
4403       VarTemplatePartialSpecializationDecl *Partial = PartialSpecs[I];
4404       TemplateDeductionInfo Info(FailedCandidates.getLocation());
4405 
4406       if (TemplateDeductionResult Result =
4407               DeduceTemplateArguments(Partial, TemplateArgList, Info)) {
4408         // Store the failed-deduction information for use in diagnostics, later.
4409         // TODO: Actually use the failed-deduction info?
4410         FailedCandidates.addCandidate().set(
4411             DeclAccessPair::make(Template, AS_public), Partial,
4412             MakeDeductionFailureInfo(Context, Result, Info));
4413         (void)Result;
4414       } else {
4415         Matched.push_back(PartialSpecMatchResult());
4416         Matched.back().Partial = Partial;
4417         Matched.back().Args = Info.take();
4418       }
4419     }
4420 
4421     if (Matched.size() >= 1) {
4422       SmallVector<MatchResult, 4>::iterator Best = Matched.begin();
4423       if (Matched.size() == 1) {
4424         //   -- If exactly one matching specialization is found, the
4425         //      instantiation is generated from that specialization.
4426         // We don't need to do anything for this.
4427       } else {
4428         //   -- If more than one matching specialization is found, the
4429         //      partial order rules (14.5.4.2) are used to determine
4430         //      whether one of the specializations is more specialized
4431         //      than the others. If none of the specializations is more
4432         //      specialized than all of the other matching
4433         //      specializations, then the use of the variable template is
4434         //      ambiguous and the program is ill-formed.
4435         for (SmallVector<MatchResult, 4>::iterator P = Best + 1,
4436                                                    PEnd = Matched.end();
4437              P != PEnd; ++P) {
4438           if (getMoreSpecializedPartialSpecialization(P->Partial, Best->Partial,
4439                                                       PointOfInstantiation) ==
4440               P->Partial)
4441             Best = P;
4442         }
4443 
4444         // Determine if the best partial specialization is more specialized than
4445         // the others.
4446         for (SmallVector<MatchResult, 4>::iterator P = Matched.begin(),
4447                                                    PEnd = Matched.end();
4448              P != PEnd; ++P) {
4449           if (P != Best && getMoreSpecializedPartialSpecialization(
4450                                P->Partial, Best->Partial,
4451                                PointOfInstantiation) != Best->Partial) {
4452             AmbiguousPartialSpec = true;
4453             break;
4454           }
4455         }
4456       }
4457 
4458       // Instantiate using the best variable template partial specialization.
4459       InstantiationPattern = Best->Partial;
4460       InstantiationArgs = Best->Args;
4461     } else {
4462       //   -- If no match is found, the instantiation is generated
4463       //      from the primary template.
4464       // InstantiationPattern = Template->getTemplatedDecl();
4465     }
4466   }
4467 
4468   // 2. Create the canonical declaration.
4469   // Note that we do not instantiate a definition until we see an odr-use
4470   // in DoMarkVarDeclReferenced().
4471   // FIXME: LateAttrs et al.?
4472   VarTemplateSpecializationDecl *Decl = BuildVarTemplateInstantiation(
4473       Template, InstantiationPattern, *InstantiationArgs, TemplateArgs,
4474       Converted, TemplateNameLoc, InsertPos /*, LateAttrs, StartingScope*/);
4475   if (!Decl)
4476     return true;
4477 
4478   if (AmbiguousPartialSpec) {
4479     // Partial ordering did not produce a clear winner. Complain.
4480     Decl->setInvalidDecl();
4481     Diag(PointOfInstantiation, diag::err_partial_spec_ordering_ambiguous)
4482         << Decl;
4483 
4484     // Print the matching partial specializations.
4485     for (MatchResult P : Matched)
4486       Diag(P.Partial->getLocation(), diag::note_partial_spec_match)
4487           << getTemplateArgumentBindingsText(P.Partial->getTemplateParameters(),
4488                                              *P.Args);
4489     return true;
4490   }
4491 
4492   if (VarTemplatePartialSpecializationDecl *D =
4493           dyn_cast<VarTemplatePartialSpecializationDecl>(InstantiationPattern))
4494     Decl->setInstantiationOf(D, InstantiationArgs);
4495 
4496   checkSpecializationVisibility(TemplateNameLoc, Decl);
4497 
4498   assert(Decl && "No variable template specialization?");
4499   return Decl;
4500 }
4501 
4502 ExprResult
4503 Sema::CheckVarTemplateId(const CXXScopeSpec &SS,
4504                          const DeclarationNameInfo &NameInfo,
4505                          VarTemplateDecl *Template, SourceLocation TemplateLoc,
4506                          const TemplateArgumentListInfo *TemplateArgs) {
4507 
4508   DeclResult Decl = CheckVarTemplateId(Template, TemplateLoc, NameInfo.getLoc(),
4509                                        *TemplateArgs);
4510   if (Decl.isInvalid())
4511     return ExprError();
4512 
4513   VarDecl *Var = cast<VarDecl>(Decl.get());
4514   if (!Var->getTemplateSpecializationKind())
4515     Var->setTemplateSpecializationKind(TSK_ImplicitInstantiation,
4516                                        NameInfo.getLoc());
4517 
4518   // Build an ordinary singleton decl ref.
4519   return BuildDeclarationNameExpr(SS, NameInfo, Var,
4520                                   /*FoundD=*/nullptr, TemplateArgs);
4521 }
4522 
4523 void Sema::diagnoseMissingTemplateArguments(TemplateName Name,
4524                                             SourceLocation Loc) {
4525   Diag(Loc, diag::err_template_missing_args)
4526     << (int)getTemplateNameKindForDiagnostics(Name) << Name;
4527   if (TemplateDecl *TD = Name.getAsTemplateDecl()) {
4528     Diag(TD->getLocation(), diag::note_template_decl_here)
4529       << TD->getTemplateParameters()->getSourceRange();
4530   }
4531 }
4532 
4533 ExprResult
4534 Sema::CheckConceptTemplateId(const CXXScopeSpec &SS,
4535                              SourceLocation TemplateKWLoc,
4536                              const DeclarationNameInfo &ConceptNameInfo,
4537                              NamedDecl *FoundDecl,
4538                              ConceptDecl *NamedConcept,
4539                              const TemplateArgumentListInfo *TemplateArgs) {
4540   assert(NamedConcept && "A concept template id without a template?");
4541 
4542   llvm::SmallVector<TemplateArgument, 4> Converted;
4543   if (CheckTemplateArgumentList(NamedConcept, ConceptNameInfo.getLoc(),
4544                            const_cast<TemplateArgumentListInfo&>(*TemplateArgs),
4545                                 /*PartialTemplateArgs=*/false, Converted,
4546                                 /*UpdateArgsWithConversion=*/false))
4547     return ExprError();
4548 
4549   ConstraintSatisfaction Satisfaction;
4550   bool AreArgsDependent = false;
4551   for (TemplateArgument &Arg : Converted) {
4552     if (Arg.isDependent()) {
4553       AreArgsDependent = true;
4554       break;
4555     }
4556   }
4557   if (!AreArgsDependent &&
4558       CheckConstraintSatisfaction(NamedConcept,
4559                                   {NamedConcept->getConstraintExpr()},
4560                                   Converted,
4561                                   SourceRange(SS.isSet() ? SS.getBeginLoc() :
4562                                                        ConceptNameInfo.getLoc(),
4563                                                 TemplateArgs->getRAngleLoc()),
4564                                     Satisfaction))
4565       return ExprError();
4566 
4567   return ConceptSpecializationExpr::Create(Context,
4568       SS.isSet() ? SS.getWithLocInContext(Context) : NestedNameSpecifierLoc{},
4569       TemplateKWLoc, ConceptNameInfo, FoundDecl, NamedConcept,
4570       ASTTemplateArgumentListInfo::Create(Context, *TemplateArgs), Converted,
4571       AreArgsDependent ? nullptr : &Satisfaction);
4572 }
4573 
4574 ExprResult Sema::BuildTemplateIdExpr(const CXXScopeSpec &SS,
4575                                      SourceLocation TemplateKWLoc,
4576                                      LookupResult &R,
4577                                      bool RequiresADL,
4578                                  const TemplateArgumentListInfo *TemplateArgs) {
4579   // FIXME: Can we do any checking at this point? I guess we could check the
4580   // template arguments that we have against the template name, if the template
4581   // name refers to a single template. That's not a terribly common case,
4582   // though.
4583   // foo<int> could identify a single function unambiguously
4584   // This approach does NOT work, since f<int>(1);
4585   // gets resolved prior to resorting to overload resolution
4586   // i.e., template<class T> void f(double);
4587   //       vs template<class T, class U> void f(U);
4588 
4589   // These should be filtered out by our callers.
4590   assert(!R.isAmbiguous() && "ambiguous lookup when building templateid");
4591 
4592   // Non-function templates require a template argument list.
4593   if (auto *TD = R.getAsSingle<TemplateDecl>()) {
4594     if (!TemplateArgs && !isa<FunctionTemplateDecl>(TD)) {
4595       diagnoseMissingTemplateArguments(TemplateName(TD), R.getNameLoc());
4596       return ExprError();
4597     }
4598   }
4599 
4600   auto AnyDependentArguments = [&]() -> bool {
4601     bool InstantiationDependent;
4602     return TemplateArgs &&
4603            TemplateSpecializationType::anyDependentTemplateArguments(
4604                *TemplateArgs, InstantiationDependent);
4605   };
4606 
4607   // In C++1y, check variable template ids.
4608   if (R.getAsSingle<VarTemplateDecl>() && !AnyDependentArguments()) {
4609     return CheckVarTemplateId(SS, R.getLookupNameInfo(),
4610                               R.getAsSingle<VarTemplateDecl>(),
4611                               TemplateKWLoc, TemplateArgs);
4612   }
4613 
4614   if (R.getAsSingle<ConceptDecl>()) {
4615     return CheckConceptTemplateId(SS, TemplateKWLoc, R.getLookupNameInfo(),
4616                                   R.getFoundDecl(),
4617                                   R.getAsSingle<ConceptDecl>(), TemplateArgs);
4618   }
4619 
4620   // We don't want lookup warnings at this point.
4621   R.suppressDiagnostics();
4622 
4623   UnresolvedLookupExpr *ULE
4624     = UnresolvedLookupExpr::Create(Context, R.getNamingClass(),
4625                                    SS.getWithLocInContext(Context),
4626                                    TemplateKWLoc,
4627                                    R.getLookupNameInfo(),
4628                                    RequiresADL, TemplateArgs,
4629                                    R.begin(), R.end());
4630 
4631   return ULE;
4632 }
4633 
4634 // We actually only call this from template instantiation.
4635 ExprResult
4636 Sema::BuildQualifiedTemplateIdExpr(CXXScopeSpec &SS,
4637                                    SourceLocation TemplateKWLoc,
4638                                    const DeclarationNameInfo &NameInfo,
4639                              const TemplateArgumentListInfo *TemplateArgs) {
4640 
4641   assert(TemplateArgs || TemplateKWLoc.isValid());
4642   DeclContext *DC;
4643   if (!(DC = computeDeclContext(SS, false)) ||
4644       DC->isDependentContext() ||
4645       RequireCompleteDeclContext(SS, DC))
4646     return BuildDependentDeclRefExpr(SS, TemplateKWLoc, NameInfo, TemplateArgs);
4647 
4648   bool MemberOfUnknownSpecialization;
4649   LookupResult R(*this, NameInfo, LookupOrdinaryName);
4650   if (LookupTemplateName(R, (Scope *)nullptr, SS, QualType(),
4651                          /*Entering*/false, MemberOfUnknownSpecialization,
4652                          TemplateKWLoc))
4653     return ExprError();
4654 
4655   if (R.isAmbiguous())
4656     return ExprError();
4657 
4658   if (R.empty()) {
4659     Diag(NameInfo.getLoc(), diag::err_no_member)
4660       << NameInfo.getName() << DC << SS.getRange();
4661     return ExprError();
4662   }
4663 
4664   if (ClassTemplateDecl *Temp = R.getAsSingle<ClassTemplateDecl>()) {
4665     Diag(NameInfo.getLoc(), diag::err_template_kw_refers_to_class_template)
4666       << SS.getScopeRep()
4667       << NameInfo.getName().getAsString() << SS.getRange();
4668     Diag(Temp->getLocation(), diag::note_referenced_class_template);
4669     return ExprError();
4670   }
4671 
4672   return BuildTemplateIdExpr(SS, TemplateKWLoc, R, /*ADL*/ false, TemplateArgs);
4673 }
4674 
4675 /// Form a template name from a name that is syntactically required to name a
4676 /// template, either due to use of the 'template' keyword or because a name in
4677 /// this syntactic context is assumed to name a template (C++ [temp.names]p2-4).
4678 ///
4679 /// This action forms a template name given the name of the template and its
4680 /// optional scope specifier. This is used when the 'template' keyword is used
4681 /// or when the parsing context unambiguously treats a following '<' as
4682 /// introducing a template argument list. Note that this may produce a
4683 /// non-dependent template name if we can perform the lookup now and identify
4684 /// the named template.
4685 ///
4686 /// For example, given "x.MetaFun::template apply", the scope specifier
4687 /// \p SS will be "MetaFun::", \p TemplateKWLoc contains the location
4688 /// of the "template" keyword, and "apply" is the \p Name.
4689 TemplateNameKind Sema::ActOnTemplateName(Scope *S,
4690                                          CXXScopeSpec &SS,
4691                                          SourceLocation TemplateKWLoc,
4692                                          const UnqualifiedId &Name,
4693                                          ParsedType ObjectType,
4694                                          bool EnteringContext,
4695                                          TemplateTy &Result,
4696                                          bool AllowInjectedClassName) {
4697   if (TemplateKWLoc.isValid() && S && !S->getTemplateParamParent())
4698     Diag(TemplateKWLoc,
4699          getLangOpts().CPlusPlus11 ?
4700            diag::warn_cxx98_compat_template_outside_of_template :
4701            diag::ext_template_outside_of_template)
4702       << FixItHint::CreateRemoval(TemplateKWLoc);
4703 
4704   if (SS.isInvalid())
4705     return TNK_Non_template;
4706 
4707   // Figure out where isTemplateName is going to look.
4708   DeclContext *LookupCtx = nullptr;
4709   if (SS.isNotEmpty())
4710     LookupCtx = computeDeclContext(SS, EnteringContext);
4711   else if (ObjectType)
4712     LookupCtx = computeDeclContext(GetTypeFromParser(ObjectType));
4713 
4714   // C++0x [temp.names]p5:
4715   //   If a name prefixed by the keyword template is not the name of
4716   //   a template, the program is ill-formed. [Note: the keyword
4717   //   template may not be applied to non-template members of class
4718   //   templates. -end note ] [ Note: as is the case with the
4719   //   typename prefix, the template prefix is allowed in cases
4720   //   where it is not strictly necessary; i.e., when the
4721   //   nested-name-specifier or the expression on the left of the ->
4722   //   or . is not dependent on a template-parameter, or the use
4723   //   does not appear in the scope of a template. -end note]
4724   //
4725   // Note: C++03 was more strict here, because it banned the use of
4726   // the "template" keyword prior to a template-name that was not a
4727   // dependent name. C++ DR468 relaxed this requirement (the
4728   // "template" keyword is now permitted). We follow the C++0x
4729   // rules, even in C++03 mode with a warning, retroactively applying the DR.
4730   bool MemberOfUnknownSpecialization;
4731   TemplateNameKind TNK = isTemplateName(S, SS, TemplateKWLoc.isValid(), Name,
4732                                         ObjectType, EnteringContext, Result,
4733                                         MemberOfUnknownSpecialization);
4734   if (TNK != TNK_Non_template) {
4735     // We resolved this to a (non-dependent) template name. Return it.
4736     auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
4737     if (!AllowInjectedClassName && SS.isNotEmpty() && LookupRD &&
4738         Name.getKind() == UnqualifiedIdKind::IK_Identifier &&
4739         Name.Identifier && LookupRD->getIdentifier() == Name.Identifier) {
4740       // C++14 [class.qual]p2:
4741       //   In a lookup in which function names are not ignored and the
4742       //   nested-name-specifier nominates a class C, if the name specified
4743       //   [...] is the injected-class-name of C, [...] the name is instead
4744       //   considered to name the constructor
4745       //
4746       // We don't get here if naming the constructor would be valid, so we
4747       // just reject immediately and recover by treating the
4748       // injected-class-name as naming the template.
4749       Diag(Name.getBeginLoc(),
4750            diag::ext_out_of_line_qualified_id_type_names_constructor)
4751           << Name.Identifier
4752           << 0 /*injected-class-name used as template name*/
4753           << TemplateKWLoc.isValid();
4754     }
4755     return TNK;
4756   }
4757 
4758   if (!MemberOfUnknownSpecialization) {
4759     // Didn't find a template name, and the lookup wasn't dependent.
4760     // Do the lookup again to determine if this is a "nothing found" case or
4761     // a "not a template" case. FIXME: Refactor isTemplateName so we don't
4762     // need to do this.
4763     DeclarationNameInfo DNI = GetNameFromUnqualifiedId(Name);
4764     LookupResult R(*this, DNI.getName(), Name.getBeginLoc(),
4765                    LookupOrdinaryName);
4766     bool MOUS;
4767     // Tell LookupTemplateName that we require a template so that it diagnoses
4768     // cases where it finds a non-template.
4769     RequiredTemplateKind RTK = TemplateKWLoc.isValid()
4770                                    ? RequiredTemplateKind(TemplateKWLoc)
4771                                    : TemplateNameIsRequired;
4772     if (!LookupTemplateName(R, S, SS, ObjectType.get(), EnteringContext, MOUS,
4773                             RTK, nullptr, /*AllowTypoCorrection=*/false) &&
4774         !R.isAmbiguous()) {
4775       if (LookupCtx)
4776         Diag(Name.getBeginLoc(), diag::err_no_member)
4777             << DNI.getName() << LookupCtx << SS.getRange();
4778       else
4779         Diag(Name.getBeginLoc(), diag::err_undeclared_use)
4780             << DNI.getName() << SS.getRange();
4781     }
4782     return TNK_Non_template;
4783   }
4784 
4785   NestedNameSpecifier *Qualifier = SS.getScopeRep();
4786 
4787   switch (Name.getKind()) {
4788   case UnqualifiedIdKind::IK_Identifier:
4789     Result = TemplateTy::make(
4790         Context.getDependentTemplateName(Qualifier, Name.Identifier));
4791     return TNK_Dependent_template_name;
4792 
4793   case UnqualifiedIdKind::IK_OperatorFunctionId:
4794     Result = TemplateTy::make(Context.getDependentTemplateName(
4795         Qualifier, Name.OperatorFunctionId.Operator));
4796     return TNK_Function_template;
4797 
4798   case UnqualifiedIdKind::IK_LiteralOperatorId:
4799     // This is a kind of template name, but can never occur in a dependent
4800     // scope (literal operators can only be declared at namespace scope).
4801     break;
4802 
4803   default:
4804     break;
4805   }
4806 
4807   // This name cannot possibly name a dependent template. Diagnose this now
4808   // rather than building a dependent template name that can never be valid.
4809   Diag(Name.getBeginLoc(),
4810        diag::err_template_kw_refers_to_dependent_non_template)
4811       << GetNameFromUnqualifiedId(Name).getName() << Name.getSourceRange()
4812       << TemplateKWLoc.isValid() << TemplateKWLoc;
4813   return TNK_Non_template;
4814 }
4815 
4816 bool Sema::CheckTemplateTypeArgument(TemplateTypeParmDecl *Param,
4817                                      TemplateArgumentLoc &AL,
4818                           SmallVectorImpl<TemplateArgument> &Converted) {
4819   const TemplateArgument &Arg = AL.getArgument();
4820   QualType ArgType;
4821   TypeSourceInfo *TSI = nullptr;
4822 
4823   // Check template type parameter.
4824   switch(Arg.getKind()) {
4825   case TemplateArgument::Type:
4826     // C++ [temp.arg.type]p1:
4827     //   A template-argument for a template-parameter which is a
4828     //   type shall be a type-id.
4829     ArgType = Arg.getAsType();
4830     TSI = AL.getTypeSourceInfo();
4831     break;
4832   case TemplateArgument::Template:
4833   case TemplateArgument::TemplateExpansion: {
4834     // We have a template type parameter but the template argument
4835     // is a template without any arguments.
4836     SourceRange SR = AL.getSourceRange();
4837     TemplateName Name = Arg.getAsTemplateOrTemplatePattern();
4838     diagnoseMissingTemplateArguments(Name, SR.getEnd());
4839     return true;
4840   }
4841   case TemplateArgument::Expression: {
4842     // We have a template type parameter but the template argument is an
4843     // expression; see if maybe it is missing the "typename" keyword.
4844     CXXScopeSpec SS;
4845     DeclarationNameInfo NameInfo;
4846 
4847    if (DependentScopeDeclRefExpr *ArgExpr =
4848                dyn_cast<DependentScopeDeclRefExpr>(Arg.getAsExpr())) {
4849       SS.Adopt(ArgExpr->getQualifierLoc());
4850       NameInfo = ArgExpr->getNameInfo();
4851     } else if (CXXDependentScopeMemberExpr *ArgExpr =
4852                dyn_cast<CXXDependentScopeMemberExpr>(Arg.getAsExpr())) {
4853       if (ArgExpr->isImplicitAccess()) {
4854         SS.Adopt(ArgExpr->getQualifierLoc());
4855         NameInfo = ArgExpr->getMemberNameInfo();
4856       }
4857     }
4858 
4859     if (auto *II = NameInfo.getName().getAsIdentifierInfo()) {
4860       LookupResult Result(*this, NameInfo, LookupOrdinaryName);
4861       LookupParsedName(Result, CurScope, &SS);
4862 
4863       if (Result.getAsSingle<TypeDecl>() ||
4864           Result.getResultKind() ==
4865               LookupResult::NotFoundInCurrentInstantiation) {
4866         assert(SS.getScopeRep() && "dependent scope expr must has a scope!");
4867         // Suggest that the user add 'typename' before the NNS.
4868         SourceLocation Loc = AL.getSourceRange().getBegin();
4869         Diag(Loc, getLangOpts().MSVCCompat
4870                       ? diag::ext_ms_template_type_arg_missing_typename
4871                       : diag::err_template_arg_must_be_type_suggest)
4872             << FixItHint::CreateInsertion(Loc, "typename ");
4873         Diag(Param->getLocation(), diag::note_template_param_here);
4874 
4875         // Recover by synthesizing a type using the location information that we
4876         // already have.
4877         ArgType =
4878             Context.getDependentNameType(ETK_Typename, SS.getScopeRep(), II);
4879         TypeLocBuilder TLB;
4880         DependentNameTypeLoc TL = TLB.push<DependentNameTypeLoc>(ArgType);
4881         TL.setElaboratedKeywordLoc(SourceLocation(/*synthesized*/));
4882         TL.setQualifierLoc(SS.getWithLocInContext(Context));
4883         TL.setNameLoc(NameInfo.getLoc());
4884         TSI = TLB.getTypeSourceInfo(Context, ArgType);
4885 
4886         // Overwrite our input TemplateArgumentLoc so that we can recover
4887         // properly.
4888         AL = TemplateArgumentLoc(TemplateArgument(ArgType),
4889                                  TemplateArgumentLocInfo(TSI));
4890 
4891         break;
4892       }
4893     }
4894     // fallthrough
4895     LLVM_FALLTHROUGH;
4896   }
4897   default: {
4898     // We have a template type parameter but the template argument
4899     // is not a type.
4900     SourceRange SR = AL.getSourceRange();
4901     Diag(SR.getBegin(), diag::err_template_arg_must_be_type) << SR;
4902     Diag(Param->getLocation(), diag::note_template_param_here);
4903 
4904     return true;
4905   }
4906   }
4907 
4908   if (CheckTemplateArgument(Param, TSI))
4909     return true;
4910 
4911   // Add the converted template type argument.
4912   ArgType = Context.getCanonicalType(ArgType);
4913 
4914   // Objective-C ARC:
4915   //   If an explicitly-specified template argument type is a lifetime type
4916   //   with no lifetime qualifier, the __strong lifetime qualifier is inferred.
4917   if (getLangOpts().ObjCAutoRefCount &&
4918       ArgType->isObjCLifetimeType() &&
4919       !ArgType.getObjCLifetime()) {
4920     Qualifiers Qs;
4921     Qs.setObjCLifetime(Qualifiers::OCL_Strong);
4922     ArgType = Context.getQualifiedType(ArgType, Qs);
4923   }
4924 
4925   Converted.push_back(TemplateArgument(ArgType));
4926   return false;
4927 }
4928 
4929 /// Substitute template arguments into the default template argument for
4930 /// the given template type parameter.
4931 ///
4932 /// \param SemaRef the semantic analysis object for which we are performing
4933 /// the substitution.
4934 ///
4935 /// \param Template the template that we are synthesizing template arguments
4936 /// for.
4937 ///
4938 /// \param TemplateLoc the location of the template name that started the
4939 /// template-id we are checking.
4940 ///
4941 /// \param RAngleLoc the location of the right angle bracket ('>') that
4942 /// terminates the template-id.
4943 ///
4944 /// \param Param the template template parameter whose default we are
4945 /// substituting into.
4946 ///
4947 /// \param Converted the list of template arguments provided for template
4948 /// parameters that precede \p Param in the template parameter list.
4949 /// \returns the substituted template argument, or NULL if an error occurred.
4950 static TypeSourceInfo *
4951 SubstDefaultTemplateArgument(Sema &SemaRef,
4952                              TemplateDecl *Template,
4953                              SourceLocation TemplateLoc,
4954                              SourceLocation RAngleLoc,
4955                              TemplateTypeParmDecl *Param,
4956                              SmallVectorImpl<TemplateArgument> &Converted) {
4957   TypeSourceInfo *ArgType = Param->getDefaultArgumentInfo();
4958 
4959   // If the argument type is dependent, instantiate it now based
4960   // on the previously-computed template arguments.
4961   if (ArgType->getType()->isInstantiationDependentType()) {
4962     Sema::InstantiatingTemplate Inst(SemaRef, TemplateLoc,
4963                                      Param, Template, Converted,
4964                                      SourceRange(TemplateLoc, RAngleLoc));
4965     if (Inst.isInvalid())
4966       return nullptr;
4967 
4968     TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack, Converted);
4969 
4970     // Only substitute for the innermost template argument list.
4971     MultiLevelTemplateArgumentList TemplateArgLists;
4972     TemplateArgLists.addOuterTemplateArguments(&TemplateArgs);
4973     for (unsigned i = 0, e = Param->getDepth(); i != e; ++i)
4974       TemplateArgLists.addOuterTemplateArguments(None);
4975 
4976     Sema::ContextRAII SavedContext(SemaRef, Template->getDeclContext());
4977     ArgType =
4978         SemaRef.SubstType(ArgType, TemplateArgLists,
4979                           Param->getDefaultArgumentLoc(), Param->getDeclName());
4980   }
4981 
4982   return ArgType;
4983 }
4984 
4985 /// Substitute template arguments into the default template argument for
4986 /// the given non-type template parameter.
4987 ///
4988 /// \param SemaRef the semantic analysis object for which we are performing
4989 /// the substitution.
4990 ///
4991 /// \param Template the template that we are synthesizing template arguments
4992 /// for.
4993 ///
4994 /// \param TemplateLoc the location of the template name that started the
4995 /// template-id we are checking.
4996 ///
4997 /// \param RAngleLoc the location of the right angle bracket ('>') that
4998 /// terminates the template-id.
4999 ///
5000 /// \param Param the non-type template parameter whose default we are
5001 /// substituting into.
5002 ///
5003 /// \param Converted the list of template arguments provided for template
5004 /// parameters that precede \p Param in the template parameter list.
5005 ///
5006 /// \returns the substituted template argument, or NULL if an error occurred.
5007 static ExprResult
5008 SubstDefaultTemplateArgument(Sema &SemaRef,
5009                              TemplateDecl *Template,
5010                              SourceLocation TemplateLoc,
5011                              SourceLocation RAngleLoc,
5012                              NonTypeTemplateParmDecl *Param,
5013                         SmallVectorImpl<TemplateArgument> &Converted) {
5014   Sema::InstantiatingTemplate Inst(SemaRef, TemplateLoc,
5015                                    Param, Template, Converted,
5016                                    SourceRange(TemplateLoc, RAngleLoc));
5017   if (Inst.isInvalid())
5018     return ExprError();
5019 
5020   TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack, Converted);
5021 
5022   // Only substitute for the innermost template argument list.
5023   MultiLevelTemplateArgumentList TemplateArgLists;
5024   TemplateArgLists.addOuterTemplateArguments(&TemplateArgs);
5025   for (unsigned i = 0, e = Param->getDepth(); i != e; ++i)
5026     TemplateArgLists.addOuterTemplateArguments(None);
5027 
5028   Sema::ContextRAII SavedContext(SemaRef, Template->getDeclContext());
5029   EnterExpressionEvaluationContext ConstantEvaluated(
5030       SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
5031   return SemaRef.SubstExpr(Param->getDefaultArgument(), TemplateArgLists);
5032 }
5033 
5034 /// Substitute template arguments into the default template argument for
5035 /// the given template template parameter.
5036 ///
5037 /// \param SemaRef the semantic analysis object for which we are performing
5038 /// the substitution.
5039 ///
5040 /// \param Template the template that we are synthesizing template arguments
5041 /// for.
5042 ///
5043 /// \param TemplateLoc the location of the template name that started the
5044 /// template-id we are checking.
5045 ///
5046 /// \param RAngleLoc the location of the right angle bracket ('>') that
5047 /// terminates the template-id.
5048 ///
5049 /// \param Param the template template parameter whose default we are
5050 /// substituting into.
5051 ///
5052 /// \param Converted the list of template arguments provided for template
5053 /// parameters that precede \p Param in the template parameter list.
5054 ///
5055 /// \param QualifierLoc Will be set to the nested-name-specifier (with
5056 /// source-location information) that precedes the template name.
5057 ///
5058 /// \returns the substituted template argument, or NULL if an error occurred.
5059 static TemplateName
5060 SubstDefaultTemplateArgument(Sema &SemaRef,
5061                              TemplateDecl *Template,
5062                              SourceLocation TemplateLoc,
5063                              SourceLocation RAngleLoc,
5064                              TemplateTemplateParmDecl *Param,
5065                        SmallVectorImpl<TemplateArgument> &Converted,
5066                              NestedNameSpecifierLoc &QualifierLoc) {
5067   Sema::InstantiatingTemplate Inst(
5068       SemaRef, TemplateLoc, TemplateParameter(Param), Template, Converted,
5069       SourceRange(TemplateLoc, RAngleLoc));
5070   if (Inst.isInvalid())
5071     return TemplateName();
5072 
5073   TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack, Converted);
5074 
5075   // Only substitute for the innermost template argument list.
5076   MultiLevelTemplateArgumentList TemplateArgLists;
5077   TemplateArgLists.addOuterTemplateArguments(&TemplateArgs);
5078   for (unsigned i = 0, e = Param->getDepth(); i != e; ++i)
5079     TemplateArgLists.addOuterTemplateArguments(None);
5080 
5081   Sema::ContextRAII SavedContext(SemaRef, Template->getDeclContext());
5082   // Substitute into the nested-name-specifier first,
5083   QualifierLoc = Param->getDefaultArgument().getTemplateQualifierLoc();
5084   if (QualifierLoc) {
5085     QualifierLoc =
5086         SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc, TemplateArgLists);
5087     if (!QualifierLoc)
5088       return TemplateName();
5089   }
5090 
5091   return SemaRef.SubstTemplateName(
5092              QualifierLoc,
5093              Param->getDefaultArgument().getArgument().getAsTemplate(),
5094              Param->getDefaultArgument().getTemplateNameLoc(),
5095              TemplateArgLists);
5096 }
5097 
5098 /// If the given template parameter has a default template
5099 /// argument, substitute into that default template argument and
5100 /// return the corresponding template argument.
5101 TemplateArgumentLoc
5102 Sema::SubstDefaultTemplateArgumentIfAvailable(TemplateDecl *Template,
5103                                               SourceLocation TemplateLoc,
5104                                               SourceLocation RAngleLoc,
5105                                               Decl *Param,
5106                                               SmallVectorImpl<TemplateArgument>
5107                                                 &Converted,
5108                                               bool &HasDefaultArg) {
5109   HasDefaultArg = false;
5110 
5111   if (TemplateTypeParmDecl *TypeParm = dyn_cast<TemplateTypeParmDecl>(Param)) {
5112     if (!hasVisibleDefaultArgument(TypeParm))
5113       return TemplateArgumentLoc();
5114 
5115     HasDefaultArg = true;
5116     TypeSourceInfo *DI = SubstDefaultTemplateArgument(*this, Template,
5117                                                       TemplateLoc,
5118                                                       RAngleLoc,
5119                                                       TypeParm,
5120                                                       Converted);
5121     if (DI)
5122       return TemplateArgumentLoc(TemplateArgument(DI->getType()), DI);
5123 
5124     return TemplateArgumentLoc();
5125   }
5126 
5127   if (NonTypeTemplateParmDecl *NonTypeParm
5128         = dyn_cast<NonTypeTemplateParmDecl>(Param)) {
5129     if (!hasVisibleDefaultArgument(NonTypeParm))
5130       return TemplateArgumentLoc();
5131 
5132     HasDefaultArg = true;
5133     ExprResult Arg = SubstDefaultTemplateArgument(*this, Template,
5134                                                   TemplateLoc,
5135                                                   RAngleLoc,
5136                                                   NonTypeParm,
5137                                                   Converted);
5138     if (Arg.isInvalid())
5139       return TemplateArgumentLoc();
5140 
5141     Expr *ArgE = Arg.getAs<Expr>();
5142     return TemplateArgumentLoc(TemplateArgument(ArgE), ArgE);
5143   }
5144 
5145   TemplateTemplateParmDecl *TempTempParm
5146     = cast<TemplateTemplateParmDecl>(Param);
5147   if (!hasVisibleDefaultArgument(TempTempParm))
5148     return TemplateArgumentLoc();
5149 
5150   HasDefaultArg = true;
5151   NestedNameSpecifierLoc QualifierLoc;
5152   TemplateName TName = SubstDefaultTemplateArgument(*this, Template,
5153                                                     TemplateLoc,
5154                                                     RAngleLoc,
5155                                                     TempTempParm,
5156                                                     Converted,
5157                                                     QualifierLoc);
5158   if (TName.isNull())
5159     return TemplateArgumentLoc();
5160 
5161   return TemplateArgumentLoc(TemplateArgument(TName),
5162                 TempTempParm->getDefaultArgument().getTemplateQualifierLoc(),
5163                 TempTempParm->getDefaultArgument().getTemplateNameLoc());
5164 }
5165 
5166 /// Convert a template-argument that we parsed as a type into a template, if
5167 /// possible. C++ permits injected-class-names to perform dual service as
5168 /// template template arguments and as template type arguments.
5169 static TemplateArgumentLoc convertTypeTemplateArgumentToTemplate(TypeLoc TLoc) {
5170   // Extract and step over any surrounding nested-name-specifier.
5171   NestedNameSpecifierLoc QualLoc;
5172   if (auto ETLoc = TLoc.getAs<ElaboratedTypeLoc>()) {
5173     if (ETLoc.getTypePtr()->getKeyword() != ETK_None)
5174       return TemplateArgumentLoc();
5175 
5176     QualLoc = ETLoc.getQualifierLoc();
5177     TLoc = ETLoc.getNamedTypeLoc();
5178   }
5179 
5180   // If this type was written as an injected-class-name, it can be used as a
5181   // template template argument.
5182   if (auto InjLoc = TLoc.getAs<InjectedClassNameTypeLoc>())
5183     return TemplateArgumentLoc(InjLoc.getTypePtr()->getTemplateName(),
5184                                QualLoc, InjLoc.getNameLoc());
5185 
5186   // If this type was written as an injected-class-name, it may have been
5187   // converted to a RecordType during instantiation. If the RecordType is
5188   // *not* wrapped in a TemplateSpecializationType and denotes a class
5189   // template specialization, it must have come from an injected-class-name.
5190   if (auto RecLoc = TLoc.getAs<RecordTypeLoc>())
5191     if (auto *CTSD =
5192             dyn_cast<ClassTemplateSpecializationDecl>(RecLoc.getDecl()))
5193       return TemplateArgumentLoc(TemplateName(CTSD->getSpecializedTemplate()),
5194                                  QualLoc, RecLoc.getNameLoc());
5195 
5196   return TemplateArgumentLoc();
5197 }
5198 
5199 /// Check that the given template argument corresponds to the given
5200 /// template parameter.
5201 ///
5202 /// \param Param The template parameter against which the argument will be
5203 /// checked.
5204 ///
5205 /// \param Arg The template argument, which may be updated due to conversions.
5206 ///
5207 /// \param Template The template in which the template argument resides.
5208 ///
5209 /// \param TemplateLoc The location of the template name for the template
5210 /// whose argument list we're matching.
5211 ///
5212 /// \param RAngleLoc The location of the right angle bracket ('>') that closes
5213 /// the template argument list.
5214 ///
5215 /// \param ArgumentPackIndex The index into the argument pack where this
5216 /// argument will be placed. Only valid if the parameter is a parameter pack.
5217 ///
5218 /// \param Converted The checked, converted argument will be added to the
5219 /// end of this small vector.
5220 ///
5221 /// \param CTAK Describes how we arrived at this particular template argument:
5222 /// explicitly written, deduced, etc.
5223 ///
5224 /// \returns true on error, false otherwise.
5225 bool Sema::CheckTemplateArgument(NamedDecl *Param,
5226                                  TemplateArgumentLoc &Arg,
5227                                  NamedDecl *Template,
5228                                  SourceLocation TemplateLoc,
5229                                  SourceLocation RAngleLoc,
5230                                  unsigned ArgumentPackIndex,
5231                             SmallVectorImpl<TemplateArgument> &Converted,
5232                                  CheckTemplateArgumentKind CTAK) {
5233   // Check template type parameters.
5234   if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(Param))
5235     return CheckTemplateTypeArgument(TTP, Arg, Converted);
5236 
5237   // Check non-type template parameters.
5238   if (NonTypeTemplateParmDecl *NTTP =dyn_cast<NonTypeTemplateParmDecl>(Param)) {
5239     // Do substitution on the type of the non-type template parameter
5240     // with the template arguments we've seen thus far.  But if the
5241     // template has a dependent context then we cannot substitute yet.
5242     QualType NTTPType = NTTP->getType();
5243     if (NTTP->isParameterPack() && NTTP->isExpandedParameterPack())
5244       NTTPType = NTTP->getExpansionType(ArgumentPackIndex);
5245 
5246     if (NTTPType->isInstantiationDependentType() &&
5247         !isa<TemplateTemplateParmDecl>(Template) &&
5248         !Template->getDeclContext()->isDependentContext()) {
5249       // Do substitution on the type of the non-type template parameter.
5250       InstantiatingTemplate Inst(*this, TemplateLoc, Template,
5251                                  NTTP, Converted,
5252                                  SourceRange(TemplateLoc, RAngleLoc));
5253       if (Inst.isInvalid())
5254         return true;
5255 
5256       TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack,
5257                                         Converted);
5258 
5259       // If the parameter is a pack expansion, expand this slice of the pack.
5260       if (auto *PET = NTTPType->getAs<PackExpansionType>()) {
5261         Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this,
5262                                                            ArgumentPackIndex);
5263         NTTPType = SubstType(PET->getPattern(),
5264                              MultiLevelTemplateArgumentList(TemplateArgs),
5265                              NTTP->getLocation(),
5266                              NTTP->getDeclName());
5267       } else {
5268         NTTPType = SubstType(NTTPType,
5269                              MultiLevelTemplateArgumentList(TemplateArgs),
5270                              NTTP->getLocation(),
5271                              NTTP->getDeclName());
5272       }
5273 
5274       // If that worked, check the non-type template parameter type
5275       // for validity.
5276       if (!NTTPType.isNull())
5277         NTTPType = CheckNonTypeTemplateParameterType(NTTPType,
5278                                                      NTTP->getLocation());
5279       if (NTTPType.isNull())
5280         return true;
5281     }
5282 
5283     switch (Arg.getArgument().getKind()) {
5284     case TemplateArgument::Null:
5285       llvm_unreachable("Should never see a NULL template argument here");
5286 
5287     case TemplateArgument::Expression: {
5288       TemplateArgument Result;
5289       unsigned CurSFINAEErrors = NumSFINAEErrors;
5290       ExprResult Res =
5291         CheckTemplateArgument(NTTP, NTTPType, Arg.getArgument().getAsExpr(),
5292                               Result, CTAK);
5293       if (Res.isInvalid())
5294         return true;
5295       // If the current template argument causes an error, give up now.
5296       if (CurSFINAEErrors < NumSFINAEErrors)
5297         return true;
5298 
5299       // If the resulting expression is new, then use it in place of the
5300       // old expression in the template argument.
5301       if (Res.get() != Arg.getArgument().getAsExpr()) {
5302         TemplateArgument TA(Res.get());
5303         Arg = TemplateArgumentLoc(TA, Res.get());
5304       }
5305 
5306       Converted.push_back(Result);
5307       break;
5308     }
5309 
5310     case TemplateArgument::Declaration:
5311     case TemplateArgument::Integral:
5312     case TemplateArgument::NullPtr:
5313       // We've already checked this template argument, so just copy
5314       // it to the list of converted arguments.
5315       Converted.push_back(Arg.getArgument());
5316       break;
5317 
5318     case TemplateArgument::Template:
5319     case TemplateArgument::TemplateExpansion:
5320       // We were given a template template argument. It may not be ill-formed;
5321       // see below.
5322       if (DependentTemplateName *DTN
5323             = Arg.getArgument().getAsTemplateOrTemplatePattern()
5324                                               .getAsDependentTemplateName()) {
5325         // We have a template argument such as \c T::template X, which we
5326         // parsed as a template template argument. However, since we now
5327         // know that we need a non-type template argument, convert this
5328         // template name into an expression.
5329 
5330         DeclarationNameInfo NameInfo(DTN->getIdentifier(),
5331                                      Arg.getTemplateNameLoc());
5332 
5333         CXXScopeSpec SS;
5334         SS.Adopt(Arg.getTemplateQualifierLoc());
5335         // FIXME: the template-template arg was a DependentTemplateName,
5336         // so it was provided with a template keyword. However, its source
5337         // location is not stored in the template argument structure.
5338         SourceLocation TemplateKWLoc;
5339         ExprResult E = DependentScopeDeclRefExpr::Create(
5340             Context, SS.getWithLocInContext(Context), TemplateKWLoc, NameInfo,
5341             nullptr);
5342 
5343         // If we parsed the template argument as a pack expansion, create a
5344         // pack expansion expression.
5345         if (Arg.getArgument().getKind() == TemplateArgument::TemplateExpansion){
5346           E = ActOnPackExpansion(E.get(), Arg.getTemplateEllipsisLoc());
5347           if (E.isInvalid())
5348             return true;
5349         }
5350 
5351         TemplateArgument Result;
5352         E = CheckTemplateArgument(NTTP, NTTPType, E.get(), Result);
5353         if (E.isInvalid())
5354           return true;
5355 
5356         Converted.push_back(Result);
5357         break;
5358       }
5359 
5360       // We have a template argument that actually does refer to a class
5361       // template, alias template, or template template parameter, and
5362       // therefore cannot be a non-type template argument.
5363       Diag(Arg.getLocation(), diag::err_template_arg_must_be_expr)
5364         << Arg.getSourceRange();
5365 
5366       Diag(Param->getLocation(), diag::note_template_param_here);
5367       return true;
5368 
5369     case TemplateArgument::Type: {
5370       // We have a non-type template parameter but the template
5371       // argument is a type.
5372 
5373       // C++ [temp.arg]p2:
5374       //   In a template-argument, an ambiguity between a type-id and
5375       //   an expression is resolved to a type-id, regardless of the
5376       //   form of the corresponding template-parameter.
5377       //
5378       // We warn specifically about this case, since it can be rather
5379       // confusing for users.
5380       QualType T = Arg.getArgument().getAsType();
5381       SourceRange SR = Arg.getSourceRange();
5382       if (T->isFunctionType())
5383         Diag(SR.getBegin(), diag::err_template_arg_nontype_ambig) << SR << T;
5384       else
5385         Diag(SR.getBegin(), diag::err_template_arg_must_be_expr) << SR;
5386       Diag(Param->getLocation(), diag::note_template_param_here);
5387       return true;
5388     }
5389 
5390     case TemplateArgument::Pack:
5391       llvm_unreachable("Caller must expand template argument packs");
5392     }
5393 
5394     return false;
5395   }
5396 
5397 
5398   // Check template template parameters.
5399   TemplateTemplateParmDecl *TempParm = cast<TemplateTemplateParmDecl>(Param);
5400 
5401   TemplateParameterList *Params = TempParm->getTemplateParameters();
5402   if (TempParm->isExpandedParameterPack())
5403     Params = TempParm->getExpansionTemplateParameters(ArgumentPackIndex);
5404 
5405   // Substitute into the template parameter list of the template
5406   // template parameter, since previously-supplied template arguments
5407   // may appear within the template template parameter.
5408   //
5409   // FIXME: Skip this if the parameters aren't instantiation-dependent.
5410   {
5411     // Set up a template instantiation context.
5412     LocalInstantiationScope Scope(*this);
5413     InstantiatingTemplate Inst(*this, TemplateLoc, Template,
5414                                TempParm, Converted,
5415                                SourceRange(TemplateLoc, RAngleLoc));
5416     if (Inst.isInvalid())
5417       return true;
5418 
5419     TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack, Converted);
5420     Params = SubstTemplateParams(Params, CurContext,
5421                                  MultiLevelTemplateArgumentList(TemplateArgs));
5422     if (!Params)
5423       return true;
5424   }
5425 
5426   // C++1z [temp.local]p1: (DR1004)
5427   //   When [the injected-class-name] is used [...] as a template-argument for
5428   //   a template template-parameter [...] it refers to the class template
5429   //   itself.
5430   if (Arg.getArgument().getKind() == TemplateArgument::Type) {
5431     TemplateArgumentLoc ConvertedArg = convertTypeTemplateArgumentToTemplate(
5432         Arg.getTypeSourceInfo()->getTypeLoc());
5433     if (!ConvertedArg.getArgument().isNull())
5434       Arg = ConvertedArg;
5435   }
5436 
5437   switch (Arg.getArgument().getKind()) {
5438   case TemplateArgument::Null:
5439     llvm_unreachable("Should never see a NULL template argument here");
5440 
5441   case TemplateArgument::Template:
5442   case TemplateArgument::TemplateExpansion:
5443     if (CheckTemplateTemplateArgument(TempParm, Params, Arg))
5444       return true;
5445 
5446     Converted.push_back(Arg.getArgument());
5447     break;
5448 
5449   case TemplateArgument::Expression:
5450   case TemplateArgument::Type:
5451     // We have a template template parameter but the template
5452     // argument does not refer to a template.
5453     Diag(Arg.getLocation(), diag::err_template_arg_must_be_template)
5454       << getLangOpts().CPlusPlus11;
5455     return true;
5456 
5457   case TemplateArgument::Declaration:
5458     llvm_unreachable("Declaration argument with template template parameter");
5459   case TemplateArgument::Integral:
5460     llvm_unreachable("Integral argument with template template parameter");
5461   case TemplateArgument::NullPtr:
5462     llvm_unreachable("Null pointer argument with template template parameter");
5463 
5464   case TemplateArgument::Pack:
5465     llvm_unreachable("Caller must expand template argument packs");
5466   }
5467 
5468   return false;
5469 }
5470 
5471 /// Check whether the template parameter is a pack expansion, and if so,
5472 /// determine the number of parameters produced by that expansion. For instance:
5473 ///
5474 /// \code
5475 /// template<typename ...Ts> struct A {
5476 ///   template<Ts ...NTs, template<Ts> class ...TTs, typename ...Us> struct B;
5477 /// };
5478 /// \endcode
5479 ///
5480 /// In \c A<int,int>::B, \c NTs and \c TTs have expanded pack size 2, and \c Us
5481 /// is not a pack expansion, so returns an empty Optional.
5482 static Optional<unsigned> getExpandedPackSize(NamedDecl *Param) {
5483   if (TemplateTypeParmDecl *TTP
5484         = dyn_cast<TemplateTypeParmDecl>(Param)) {
5485     if (TTP->isExpandedParameterPack())
5486       return TTP->getNumExpansionParameters();
5487   }
5488 
5489   if (NonTypeTemplateParmDecl *NTTP
5490         = dyn_cast<NonTypeTemplateParmDecl>(Param)) {
5491     if (NTTP->isExpandedParameterPack())
5492       return NTTP->getNumExpansionTypes();
5493   }
5494 
5495   if (TemplateTemplateParmDecl *TTP
5496         = dyn_cast<TemplateTemplateParmDecl>(Param)) {
5497     if (TTP->isExpandedParameterPack())
5498       return TTP->getNumExpansionTemplateParameters();
5499   }
5500 
5501   return None;
5502 }
5503 
5504 /// Diagnose a missing template argument.
5505 template<typename TemplateParmDecl>
5506 static bool diagnoseMissingArgument(Sema &S, SourceLocation Loc,
5507                                     TemplateDecl *TD,
5508                                     const TemplateParmDecl *D,
5509                                     TemplateArgumentListInfo &Args) {
5510   // Dig out the most recent declaration of the template parameter; there may be
5511   // declarations of the template that are more recent than TD.
5512   D = cast<TemplateParmDecl>(cast<TemplateDecl>(TD->getMostRecentDecl())
5513                                  ->getTemplateParameters()
5514                                  ->getParam(D->getIndex()));
5515 
5516   // If there's a default argument that's not visible, diagnose that we're
5517   // missing a module import.
5518   llvm::SmallVector<Module*, 8> Modules;
5519   if (D->hasDefaultArgument() && !S.hasVisibleDefaultArgument(D, &Modules)) {
5520     S.diagnoseMissingImport(Loc, cast<NamedDecl>(TD),
5521                             D->getDefaultArgumentLoc(), Modules,
5522                             Sema::MissingImportKind::DefaultArgument,
5523                             /*Recover*/true);
5524     return true;
5525   }
5526 
5527   // FIXME: If there's a more recent default argument that *is* visible,
5528   // diagnose that it was declared too late.
5529 
5530   TemplateParameterList *Params = TD->getTemplateParameters();
5531 
5532   S.Diag(Loc, diag::err_template_arg_list_different_arity)
5533     << /*not enough args*/0
5534     << (int)S.getTemplateNameKindForDiagnostics(TemplateName(TD))
5535     << TD;
5536   S.Diag(TD->getLocation(), diag::note_template_decl_here)
5537     << Params->getSourceRange();
5538   return true;
5539 }
5540 
5541 /// Check that the given template argument list is well-formed
5542 /// for specializing the given template.
5543 bool Sema::CheckTemplateArgumentList(
5544     TemplateDecl *Template, SourceLocation TemplateLoc,
5545     TemplateArgumentListInfo &TemplateArgs, bool PartialTemplateArgs,
5546     SmallVectorImpl<TemplateArgument> &Converted,
5547     bool UpdateArgsWithConversions, bool *ConstraintsNotSatisfied) {
5548 
5549   if (ConstraintsNotSatisfied)
5550     *ConstraintsNotSatisfied = false;
5551 
5552   // Make a copy of the template arguments for processing.  Only make the
5553   // changes at the end when successful in matching the arguments to the
5554   // template.
5555   TemplateArgumentListInfo NewArgs = TemplateArgs;
5556 
5557   // Make sure we get the template parameter list from the most
5558   // recentdeclaration, since that is the only one that has is guaranteed to
5559   // have all the default template argument information.
5560   TemplateParameterList *Params =
5561       cast<TemplateDecl>(Template->getMostRecentDecl())
5562           ->getTemplateParameters();
5563 
5564   SourceLocation RAngleLoc = NewArgs.getRAngleLoc();
5565 
5566   // C++ [temp.arg]p1:
5567   //   [...] The type and form of each template-argument specified in
5568   //   a template-id shall match the type and form specified for the
5569   //   corresponding parameter declared by the template in its
5570   //   template-parameter-list.
5571   bool isTemplateTemplateParameter = isa<TemplateTemplateParmDecl>(Template);
5572   SmallVector<TemplateArgument, 2> ArgumentPack;
5573   unsigned ArgIdx = 0, NumArgs = NewArgs.size();
5574   LocalInstantiationScope InstScope(*this, true);
5575   for (TemplateParameterList::iterator Param = Params->begin(),
5576                                        ParamEnd = Params->end();
5577        Param != ParamEnd; /* increment in loop */) {
5578     // If we have an expanded parameter pack, make sure we don't have too
5579     // many arguments.
5580     if (Optional<unsigned> Expansions = getExpandedPackSize(*Param)) {
5581       if (*Expansions == ArgumentPack.size()) {
5582         // We're done with this parameter pack. Pack up its arguments and add
5583         // them to the list.
5584         Converted.push_back(
5585             TemplateArgument::CreatePackCopy(Context, ArgumentPack));
5586         ArgumentPack.clear();
5587 
5588         // This argument is assigned to the next parameter.
5589         ++Param;
5590         continue;
5591       } else if (ArgIdx == NumArgs && !PartialTemplateArgs) {
5592         // Not enough arguments for this parameter pack.
5593         Diag(TemplateLoc, diag::err_template_arg_list_different_arity)
5594           << /*not enough args*/0
5595           << (int)getTemplateNameKindForDiagnostics(TemplateName(Template))
5596           << Template;
5597         Diag(Template->getLocation(), diag::note_template_decl_here)
5598           << Params->getSourceRange();
5599         return true;
5600       }
5601     }
5602 
5603     if (ArgIdx < NumArgs) {
5604       // Check the template argument we were given.
5605       if (CheckTemplateArgument(*Param, NewArgs[ArgIdx], Template,
5606                                 TemplateLoc, RAngleLoc,
5607                                 ArgumentPack.size(), Converted))
5608         return true;
5609 
5610       bool PackExpansionIntoNonPack =
5611           NewArgs[ArgIdx].getArgument().isPackExpansion() &&
5612           (!(*Param)->isTemplateParameterPack() || getExpandedPackSize(*Param));
5613       if (PackExpansionIntoNonPack && (isa<TypeAliasTemplateDecl>(Template) ||
5614                                        isa<ConceptDecl>(Template))) {
5615         // Core issue 1430: we have a pack expansion as an argument to an
5616         // alias template, and it's not part of a parameter pack. This
5617         // can't be canonicalized, so reject it now.
5618         // As for concepts - we cannot normalize constraints where this
5619         // situation exists.
5620         Diag(NewArgs[ArgIdx].getLocation(),
5621              diag::err_template_expansion_into_fixed_list)
5622           << (isa<ConceptDecl>(Template) ? 1 : 0)
5623           << NewArgs[ArgIdx].getSourceRange();
5624         Diag((*Param)->getLocation(), diag::note_template_param_here);
5625         return true;
5626       }
5627 
5628       // We're now done with this argument.
5629       ++ArgIdx;
5630 
5631       if ((*Param)->isTemplateParameterPack()) {
5632         // The template parameter was a template parameter pack, so take the
5633         // deduced argument and place it on the argument pack. Note that we
5634         // stay on the same template parameter so that we can deduce more
5635         // arguments.
5636         ArgumentPack.push_back(Converted.pop_back_val());
5637       } else {
5638         // Move to the next template parameter.
5639         ++Param;
5640       }
5641 
5642       // If we just saw a pack expansion into a non-pack, then directly convert
5643       // the remaining arguments, because we don't know what parameters they'll
5644       // match up with.
5645       if (PackExpansionIntoNonPack) {
5646         if (!ArgumentPack.empty()) {
5647           // If we were part way through filling in an expanded parameter pack,
5648           // fall back to just producing individual arguments.
5649           Converted.insert(Converted.end(),
5650                            ArgumentPack.begin(), ArgumentPack.end());
5651           ArgumentPack.clear();
5652         }
5653 
5654         while (ArgIdx < NumArgs) {
5655           Converted.push_back(NewArgs[ArgIdx].getArgument());
5656           ++ArgIdx;
5657         }
5658 
5659         return false;
5660       }
5661 
5662       continue;
5663     }
5664 
5665     // If we're checking a partial template argument list, we're done.
5666     if (PartialTemplateArgs) {
5667       if ((*Param)->isTemplateParameterPack() && !ArgumentPack.empty())
5668         Converted.push_back(
5669             TemplateArgument::CreatePackCopy(Context, ArgumentPack));
5670       return false;
5671     }
5672 
5673     // If we have a template parameter pack with no more corresponding
5674     // arguments, just break out now and we'll fill in the argument pack below.
5675     if ((*Param)->isTemplateParameterPack()) {
5676       assert(!getExpandedPackSize(*Param) &&
5677              "Should have dealt with this already");
5678 
5679       // A non-expanded parameter pack before the end of the parameter list
5680       // only occurs for an ill-formed template parameter list, unless we've
5681       // got a partial argument list for a function template, so just bail out.
5682       if (Param + 1 != ParamEnd)
5683         return true;
5684 
5685       Converted.push_back(
5686           TemplateArgument::CreatePackCopy(Context, ArgumentPack));
5687       ArgumentPack.clear();
5688 
5689       ++Param;
5690       continue;
5691     }
5692 
5693     // Check whether we have a default argument.
5694     TemplateArgumentLoc Arg;
5695 
5696     // Retrieve the default template argument from the template
5697     // parameter. For each kind of template parameter, we substitute the
5698     // template arguments provided thus far and any "outer" template arguments
5699     // (when the template parameter was part of a nested template) into
5700     // the default argument.
5701     if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(*Param)) {
5702       if (!hasVisibleDefaultArgument(TTP))
5703         return diagnoseMissingArgument(*this, TemplateLoc, Template, TTP,
5704                                        NewArgs);
5705 
5706       TypeSourceInfo *ArgType = SubstDefaultTemplateArgument(*this,
5707                                                              Template,
5708                                                              TemplateLoc,
5709                                                              RAngleLoc,
5710                                                              TTP,
5711                                                              Converted);
5712       if (!ArgType)
5713         return true;
5714 
5715       Arg = TemplateArgumentLoc(TemplateArgument(ArgType->getType()),
5716                                 ArgType);
5717     } else if (NonTypeTemplateParmDecl *NTTP
5718                  = dyn_cast<NonTypeTemplateParmDecl>(*Param)) {
5719       if (!hasVisibleDefaultArgument(NTTP))
5720         return diagnoseMissingArgument(*this, TemplateLoc, Template, NTTP,
5721                                        NewArgs);
5722 
5723       ExprResult E = SubstDefaultTemplateArgument(*this, Template,
5724                                                               TemplateLoc,
5725                                                               RAngleLoc,
5726                                                               NTTP,
5727                                                               Converted);
5728       if (E.isInvalid())
5729         return true;
5730 
5731       Expr *Ex = E.getAs<Expr>();
5732       Arg = TemplateArgumentLoc(TemplateArgument(Ex), Ex);
5733     } else {
5734       TemplateTemplateParmDecl *TempParm
5735         = cast<TemplateTemplateParmDecl>(*Param);
5736 
5737       if (!hasVisibleDefaultArgument(TempParm))
5738         return diagnoseMissingArgument(*this, TemplateLoc, Template, TempParm,
5739                                        NewArgs);
5740 
5741       NestedNameSpecifierLoc QualifierLoc;
5742       TemplateName Name = SubstDefaultTemplateArgument(*this, Template,
5743                                                        TemplateLoc,
5744                                                        RAngleLoc,
5745                                                        TempParm,
5746                                                        Converted,
5747                                                        QualifierLoc);
5748       if (Name.isNull())
5749         return true;
5750 
5751       Arg = TemplateArgumentLoc(TemplateArgument(Name), QualifierLoc,
5752                            TempParm->getDefaultArgument().getTemplateNameLoc());
5753     }
5754 
5755     // Introduce an instantiation record that describes where we are using
5756     // the default template argument. We're not actually instantiating a
5757     // template here, we just create this object to put a note into the
5758     // context stack.
5759     InstantiatingTemplate Inst(*this, RAngleLoc, Template, *Param, Converted,
5760                                SourceRange(TemplateLoc, RAngleLoc));
5761     if (Inst.isInvalid())
5762       return true;
5763 
5764     // Check the default template argument.
5765     if (CheckTemplateArgument(*Param, Arg, Template, TemplateLoc,
5766                               RAngleLoc, 0, Converted))
5767       return true;
5768 
5769     // Core issue 150 (assumed resolution): if this is a template template
5770     // parameter, keep track of the default template arguments from the
5771     // template definition.
5772     if (isTemplateTemplateParameter)
5773       NewArgs.addArgument(Arg);
5774 
5775     // Move to the next template parameter and argument.
5776     ++Param;
5777     ++ArgIdx;
5778   }
5779 
5780   // If we're performing a partial argument substitution, allow any trailing
5781   // pack expansions; they might be empty. This can happen even if
5782   // PartialTemplateArgs is false (the list of arguments is complete but
5783   // still dependent).
5784   if (ArgIdx < NumArgs && CurrentInstantiationScope &&
5785       CurrentInstantiationScope->getPartiallySubstitutedPack()) {
5786     while (ArgIdx < NumArgs && NewArgs[ArgIdx].getArgument().isPackExpansion())
5787       Converted.push_back(NewArgs[ArgIdx++].getArgument());
5788   }
5789 
5790   // If we have any leftover arguments, then there were too many arguments.
5791   // Complain and fail.
5792   if (ArgIdx < NumArgs) {
5793     Diag(TemplateLoc, diag::err_template_arg_list_different_arity)
5794         << /*too many args*/1
5795         << (int)getTemplateNameKindForDiagnostics(TemplateName(Template))
5796         << Template
5797         << SourceRange(NewArgs[ArgIdx].getLocation(), NewArgs.getRAngleLoc());
5798     Diag(Template->getLocation(), diag::note_template_decl_here)
5799         << Params->getSourceRange();
5800     return true;
5801   }
5802 
5803   // No problems found with the new argument list, propagate changes back
5804   // to caller.
5805   if (UpdateArgsWithConversions)
5806     TemplateArgs = std::move(NewArgs);
5807 
5808   if (!PartialTemplateArgs &&
5809       EnsureTemplateArgumentListConstraints(
5810         Template, Converted, SourceRange(TemplateLoc,
5811                                          TemplateArgs.getRAngleLoc()))) {
5812     if (ConstraintsNotSatisfied)
5813       *ConstraintsNotSatisfied = true;
5814     return true;
5815   }
5816 
5817   return false;
5818 }
5819 
5820 namespace {
5821   class UnnamedLocalNoLinkageFinder
5822     : public TypeVisitor<UnnamedLocalNoLinkageFinder, bool>
5823   {
5824     Sema &S;
5825     SourceRange SR;
5826 
5827     typedef TypeVisitor<UnnamedLocalNoLinkageFinder, bool> inherited;
5828 
5829   public:
5830     UnnamedLocalNoLinkageFinder(Sema &S, SourceRange SR) : S(S), SR(SR) { }
5831 
5832     bool Visit(QualType T) {
5833       return T.isNull() ? false : inherited::Visit(T.getTypePtr());
5834     }
5835 
5836 #define TYPE(Class, Parent) \
5837     bool Visit##Class##Type(const Class##Type *);
5838 #define ABSTRACT_TYPE(Class, Parent) \
5839     bool Visit##Class##Type(const Class##Type *) { return false; }
5840 #define NON_CANONICAL_TYPE(Class, Parent) \
5841     bool Visit##Class##Type(const Class##Type *) { return false; }
5842 #include "clang/AST/TypeNodes.inc"
5843 
5844     bool VisitTagDecl(const TagDecl *Tag);
5845     bool VisitNestedNameSpecifier(NestedNameSpecifier *NNS);
5846   };
5847 } // end anonymous namespace
5848 
5849 bool UnnamedLocalNoLinkageFinder::VisitBuiltinType(const BuiltinType*) {
5850   return false;
5851 }
5852 
5853 bool UnnamedLocalNoLinkageFinder::VisitComplexType(const ComplexType* T) {
5854   return Visit(T->getElementType());
5855 }
5856 
5857 bool UnnamedLocalNoLinkageFinder::VisitPointerType(const PointerType* T) {
5858   return Visit(T->getPointeeType());
5859 }
5860 
5861 bool UnnamedLocalNoLinkageFinder::VisitBlockPointerType(
5862                                                     const BlockPointerType* T) {
5863   return Visit(T->getPointeeType());
5864 }
5865 
5866 bool UnnamedLocalNoLinkageFinder::VisitLValueReferenceType(
5867                                                 const LValueReferenceType* T) {
5868   return Visit(T->getPointeeType());
5869 }
5870 
5871 bool UnnamedLocalNoLinkageFinder::VisitRValueReferenceType(
5872                                                 const RValueReferenceType* T) {
5873   return Visit(T->getPointeeType());
5874 }
5875 
5876 bool UnnamedLocalNoLinkageFinder::VisitMemberPointerType(
5877                                                   const MemberPointerType* T) {
5878   return Visit(T->getPointeeType()) || Visit(QualType(T->getClass(), 0));
5879 }
5880 
5881 bool UnnamedLocalNoLinkageFinder::VisitConstantArrayType(
5882                                                   const ConstantArrayType* T) {
5883   return Visit(T->getElementType());
5884 }
5885 
5886 bool UnnamedLocalNoLinkageFinder::VisitIncompleteArrayType(
5887                                                  const IncompleteArrayType* T) {
5888   return Visit(T->getElementType());
5889 }
5890 
5891 bool UnnamedLocalNoLinkageFinder::VisitVariableArrayType(
5892                                                    const VariableArrayType* T) {
5893   return Visit(T->getElementType());
5894 }
5895 
5896 bool UnnamedLocalNoLinkageFinder::VisitDependentSizedArrayType(
5897                                             const DependentSizedArrayType* T) {
5898   return Visit(T->getElementType());
5899 }
5900 
5901 bool UnnamedLocalNoLinkageFinder::VisitDependentSizedExtVectorType(
5902                                          const DependentSizedExtVectorType* T) {
5903   return Visit(T->getElementType());
5904 }
5905 
5906 bool UnnamedLocalNoLinkageFinder::VisitDependentSizedMatrixType(
5907     const DependentSizedMatrixType *T) {
5908   return Visit(T->getElementType());
5909 }
5910 
5911 bool UnnamedLocalNoLinkageFinder::VisitDependentAddressSpaceType(
5912     const DependentAddressSpaceType *T) {
5913   return Visit(T->getPointeeType());
5914 }
5915 
5916 bool UnnamedLocalNoLinkageFinder::VisitVectorType(const VectorType* T) {
5917   return Visit(T->getElementType());
5918 }
5919 
5920 bool UnnamedLocalNoLinkageFinder::VisitDependentVectorType(
5921     const DependentVectorType *T) {
5922   return Visit(T->getElementType());
5923 }
5924 
5925 bool UnnamedLocalNoLinkageFinder::VisitExtVectorType(const ExtVectorType* T) {
5926   return Visit(T->getElementType());
5927 }
5928 
5929 bool UnnamedLocalNoLinkageFinder::VisitConstantMatrixType(
5930     const ConstantMatrixType *T) {
5931   return Visit(T->getElementType());
5932 }
5933 
5934 bool UnnamedLocalNoLinkageFinder::VisitFunctionProtoType(
5935                                                   const FunctionProtoType* T) {
5936   for (const auto &A : T->param_types()) {
5937     if (Visit(A))
5938       return true;
5939   }
5940 
5941   return Visit(T->getReturnType());
5942 }
5943 
5944 bool UnnamedLocalNoLinkageFinder::VisitFunctionNoProtoType(
5945                                                const FunctionNoProtoType* T) {
5946   return Visit(T->getReturnType());
5947 }
5948 
5949 bool UnnamedLocalNoLinkageFinder::VisitUnresolvedUsingType(
5950                                                   const UnresolvedUsingType*) {
5951   return false;
5952 }
5953 
5954 bool UnnamedLocalNoLinkageFinder::VisitTypeOfExprType(const TypeOfExprType*) {
5955   return false;
5956 }
5957 
5958 bool UnnamedLocalNoLinkageFinder::VisitTypeOfType(const TypeOfType* T) {
5959   return Visit(T->getUnderlyingType());
5960 }
5961 
5962 bool UnnamedLocalNoLinkageFinder::VisitDecltypeType(const DecltypeType*) {
5963   return false;
5964 }
5965 
5966 bool UnnamedLocalNoLinkageFinder::VisitUnaryTransformType(
5967                                                     const UnaryTransformType*) {
5968   return false;
5969 }
5970 
5971 bool UnnamedLocalNoLinkageFinder::VisitAutoType(const AutoType *T) {
5972   return Visit(T->getDeducedType());
5973 }
5974 
5975 bool UnnamedLocalNoLinkageFinder::VisitDeducedTemplateSpecializationType(
5976     const DeducedTemplateSpecializationType *T) {
5977   return Visit(T->getDeducedType());
5978 }
5979 
5980 bool UnnamedLocalNoLinkageFinder::VisitRecordType(const RecordType* T) {
5981   return VisitTagDecl(T->getDecl());
5982 }
5983 
5984 bool UnnamedLocalNoLinkageFinder::VisitEnumType(const EnumType* T) {
5985   return VisitTagDecl(T->getDecl());
5986 }
5987 
5988 bool UnnamedLocalNoLinkageFinder::VisitTemplateTypeParmType(
5989                                                  const TemplateTypeParmType*) {
5990   return false;
5991 }
5992 
5993 bool UnnamedLocalNoLinkageFinder::VisitSubstTemplateTypeParmPackType(
5994                                         const SubstTemplateTypeParmPackType *) {
5995   return false;
5996 }
5997 
5998 bool UnnamedLocalNoLinkageFinder::VisitTemplateSpecializationType(
5999                                             const TemplateSpecializationType*) {
6000   return false;
6001 }
6002 
6003 bool UnnamedLocalNoLinkageFinder::VisitInjectedClassNameType(
6004                                               const InjectedClassNameType* T) {
6005   return VisitTagDecl(T->getDecl());
6006 }
6007 
6008 bool UnnamedLocalNoLinkageFinder::VisitDependentNameType(
6009                                                    const DependentNameType* T) {
6010   return VisitNestedNameSpecifier(T->getQualifier());
6011 }
6012 
6013 bool UnnamedLocalNoLinkageFinder::VisitDependentTemplateSpecializationType(
6014                                  const DependentTemplateSpecializationType* T) {
6015   if (auto *Q = T->getQualifier())
6016     return VisitNestedNameSpecifier(Q);
6017   return false;
6018 }
6019 
6020 bool UnnamedLocalNoLinkageFinder::VisitPackExpansionType(
6021                                                    const PackExpansionType* T) {
6022   return Visit(T->getPattern());
6023 }
6024 
6025 bool UnnamedLocalNoLinkageFinder::VisitObjCObjectType(const ObjCObjectType *) {
6026   return false;
6027 }
6028 
6029 bool UnnamedLocalNoLinkageFinder::VisitObjCInterfaceType(
6030                                                    const ObjCInterfaceType *) {
6031   return false;
6032 }
6033 
6034 bool UnnamedLocalNoLinkageFinder::VisitObjCObjectPointerType(
6035                                                 const ObjCObjectPointerType *) {
6036   return false;
6037 }
6038 
6039 bool UnnamedLocalNoLinkageFinder::VisitAtomicType(const AtomicType* T) {
6040   return Visit(T->getValueType());
6041 }
6042 
6043 bool UnnamedLocalNoLinkageFinder::VisitPipeType(const PipeType* T) {
6044   return false;
6045 }
6046 
6047 bool UnnamedLocalNoLinkageFinder::VisitExtIntType(const ExtIntType *T) {
6048   return false;
6049 }
6050 
6051 bool UnnamedLocalNoLinkageFinder::VisitDependentExtIntType(
6052     const DependentExtIntType *T) {
6053   return false;
6054 }
6055 
6056 bool UnnamedLocalNoLinkageFinder::VisitTagDecl(const TagDecl *Tag) {
6057   if (Tag->getDeclContext()->isFunctionOrMethod()) {
6058     S.Diag(SR.getBegin(),
6059            S.getLangOpts().CPlusPlus11 ?
6060              diag::warn_cxx98_compat_template_arg_local_type :
6061              diag::ext_template_arg_local_type)
6062       << S.Context.getTypeDeclType(Tag) << SR;
6063     return true;
6064   }
6065 
6066   if (!Tag->hasNameForLinkage()) {
6067     S.Diag(SR.getBegin(),
6068            S.getLangOpts().CPlusPlus11 ?
6069              diag::warn_cxx98_compat_template_arg_unnamed_type :
6070              diag::ext_template_arg_unnamed_type) << SR;
6071     S.Diag(Tag->getLocation(), diag::note_template_unnamed_type_here);
6072     return true;
6073   }
6074 
6075   return false;
6076 }
6077 
6078 bool UnnamedLocalNoLinkageFinder::VisitNestedNameSpecifier(
6079                                                     NestedNameSpecifier *NNS) {
6080   assert(NNS);
6081   if (NNS->getPrefix() && VisitNestedNameSpecifier(NNS->getPrefix()))
6082     return true;
6083 
6084   switch (NNS->getKind()) {
6085   case NestedNameSpecifier::Identifier:
6086   case NestedNameSpecifier::Namespace:
6087   case NestedNameSpecifier::NamespaceAlias:
6088   case NestedNameSpecifier::Global:
6089   case NestedNameSpecifier::Super:
6090     return false;
6091 
6092   case NestedNameSpecifier::TypeSpec:
6093   case NestedNameSpecifier::TypeSpecWithTemplate:
6094     return Visit(QualType(NNS->getAsType(), 0));
6095   }
6096   llvm_unreachable("Invalid NestedNameSpecifier::Kind!");
6097 }
6098 
6099 /// Check a template argument against its corresponding
6100 /// template type parameter.
6101 ///
6102 /// This routine implements the semantics of C++ [temp.arg.type]. It
6103 /// returns true if an error occurred, and false otherwise.
6104 bool Sema::CheckTemplateArgument(TemplateTypeParmDecl *Param,
6105                                  TypeSourceInfo *ArgInfo) {
6106   assert(ArgInfo && "invalid TypeSourceInfo");
6107   QualType Arg = ArgInfo->getType();
6108   SourceRange SR = ArgInfo->getTypeLoc().getSourceRange();
6109 
6110   if (Arg->isVariablyModifiedType()) {
6111     return Diag(SR.getBegin(), diag::err_variably_modified_template_arg) << Arg;
6112   } else if (Context.hasSameUnqualifiedType(Arg, Context.OverloadTy)) {
6113     return Diag(SR.getBegin(), diag::err_template_arg_overload_type) << SR;
6114   }
6115 
6116   // C++03 [temp.arg.type]p2:
6117   //   A local type, a type with no linkage, an unnamed type or a type
6118   //   compounded from any of these types shall not be used as a
6119   //   template-argument for a template type-parameter.
6120   //
6121   // C++11 allows these, and even in C++03 we allow them as an extension with
6122   // a warning.
6123   if (LangOpts.CPlusPlus11 || Arg->hasUnnamedOrLocalType()) {
6124     UnnamedLocalNoLinkageFinder Finder(*this, SR);
6125     (void)Finder.Visit(Context.getCanonicalType(Arg));
6126   }
6127 
6128   return false;
6129 }
6130 
6131 enum NullPointerValueKind {
6132   NPV_NotNullPointer,
6133   NPV_NullPointer,
6134   NPV_Error
6135 };
6136 
6137 /// Determine whether the given template argument is a null pointer
6138 /// value of the appropriate type.
6139 static NullPointerValueKind
6140 isNullPointerValueTemplateArgument(Sema &S, NonTypeTemplateParmDecl *Param,
6141                                    QualType ParamType, Expr *Arg,
6142                                    Decl *Entity = nullptr) {
6143   if (Arg->isValueDependent() || Arg->isTypeDependent())
6144     return NPV_NotNullPointer;
6145 
6146   // dllimport'd entities aren't constant but are available inside of template
6147   // arguments.
6148   if (Entity && Entity->hasAttr<DLLImportAttr>())
6149     return NPV_NotNullPointer;
6150 
6151   if (!S.isCompleteType(Arg->getExprLoc(), ParamType))
6152     llvm_unreachable(
6153         "Incomplete parameter type in isNullPointerValueTemplateArgument!");
6154 
6155   if (!S.getLangOpts().CPlusPlus11)
6156     return NPV_NotNullPointer;
6157 
6158   // Determine whether we have a constant expression.
6159   ExprResult ArgRV = S.DefaultFunctionArrayConversion(Arg);
6160   if (ArgRV.isInvalid())
6161     return NPV_Error;
6162   Arg = ArgRV.get();
6163 
6164   Expr::EvalResult EvalResult;
6165   SmallVector<PartialDiagnosticAt, 8> Notes;
6166   EvalResult.Diag = &Notes;
6167   if (!Arg->EvaluateAsRValue(EvalResult, S.Context) ||
6168       EvalResult.HasSideEffects) {
6169     SourceLocation DiagLoc = Arg->getExprLoc();
6170 
6171     // If our only note is the usual "invalid subexpression" note, just point
6172     // the caret at its location rather than producing an essentially
6173     // redundant note.
6174     if (Notes.size() == 1 && Notes[0].second.getDiagID() ==
6175         diag::note_invalid_subexpr_in_const_expr) {
6176       DiagLoc = Notes[0].first;
6177       Notes.clear();
6178     }
6179 
6180     S.Diag(DiagLoc, diag::err_template_arg_not_address_constant)
6181       << Arg->getType() << Arg->getSourceRange();
6182     for (unsigned I = 0, N = Notes.size(); I != N; ++I)
6183       S.Diag(Notes[I].first, Notes[I].second);
6184 
6185     S.Diag(Param->getLocation(), diag::note_template_param_here);
6186     return NPV_Error;
6187   }
6188 
6189   // C++11 [temp.arg.nontype]p1:
6190   //   - an address constant expression of type std::nullptr_t
6191   if (Arg->getType()->isNullPtrType())
6192     return NPV_NullPointer;
6193 
6194   //   - a constant expression that evaluates to a null pointer value (4.10); or
6195   //   - a constant expression that evaluates to a null member pointer value
6196   //     (4.11); or
6197   if ((EvalResult.Val.isLValue() && !EvalResult.Val.getLValueBase()) ||
6198       (EvalResult.Val.isMemberPointer() &&
6199        !EvalResult.Val.getMemberPointerDecl())) {
6200     // If our expression has an appropriate type, we've succeeded.
6201     bool ObjCLifetimeConversion;
6202     if (S.Context.hasSameUnqualifiedType(Arg->getType(), ParamType) ||
6203         S.IsQualificationConversion(Arg->getType(), ParamType, false,
6204                                      ObjCLifetimeConversion))
6205       return NPV_NullPointer;
6206 
6207     // The types didn't match, but we know we got a null pointer; complain,
6208     // then recover as if the types were correct.
6209     S.Diag(Arg->getExprLoc(), diag::err_template_arg_wrongtype_null_constant)
6210       << Arg->getType() << ParamType << Arg->getSourceRange();
6211     S.Diag(Param->getLocation(), diag::note_template_param_here);
6212     return NPV_NullPointer;
6213   }
6214 
6215   // If we don't have a null pointer value, but we do have a NULL pointer
6216   // constant, suggest a cast to the appropriate type.
6217   if (Arg->isNullPointerConstant(S.Context, Expr::NPC_NeverValueDependent)) {
6218     std::string Code = "static_cast<" + ParamType.getAsString() + ">(";
6219     S.Diag(Arg->getExprLoc(), diag::err_template_arg_untyped_null_constant)
6220         << ParamType << FixItHint::CreateInsertion(Arg->getBeginLoc(), Code)
6221         << FixItHint::CreateInsertion(S.getLocForEndOfToken(Arg->getEndLoc()),
6222                                       ")");
6223     S.Diag(Param->getLocation(), diag::note_template_param_here);
6224     return NPV_NullPointer;
6225   }
6226 
6227   // FIXME: If we ever want to support general, address-constant expressions
6228   // as non-type template arguments, we should return the ExprResult here to
6229   // be interpreted by the caller.
6230   return NPV_NotNullPointer;
6231 }
6232 
6233 /// Checks whether the given template argument is compatible with its
6234 /// template parameter.
6235 static bool CheckTemplateArgumentIsCompatibleWithParameter(
6236     Sema &S, NonTypeTemplateParmDecl *Param, QualType ParamType, Expr *ArgIn,
6237     Expr *Arg, QualType ArgType) {
6238   bool ObjCLifetimeConversion;
6239   if (ParamType->isPointerType() &&
6240       !ParamType->castAs<PointerType>()->getPointeeType()->isFunctionType() &&
6241       S.IsQualificationConversion(ArgType, ParamType, false,
6242                                   ObjCLifetimeConversion)) {
6243     // For pointer-to-object types, qualification conversions are
6244     // permitted.
6245   } else {
6246     if (const ReferenceType *ParamRef = ParamType->getAs<ReferenceType>()) {
6247       if (!ParamRef->getPointeeType()->isFunctionType()) {
6248         // C++ [temp.arg.nontype]p5b3:
6249         //   For a non-type template-parameter of type reference to
6250         //   object, no conversions apply. The type referred to by the
6251         //   reference may be more cv-qualified than the (otherwise
6252         //   identical) type of the template- argument. The
6253         //   template-parameter is bound directly to the
6254         //   template-argument, which shall be an lvalue.
6255 
6256         // FIXME: Other qualifiers?
6257         unsigned ParamQuals = ParamRef->getPointeeType().getCVRQualifiers();
6258         unsigned ArgQuals = ArgType.getCVRQualifiers();
6259 
6260         if ((ParamQuals | ArgQuals) != ParamQuals) {
6261           S.Diag(Arg->getBeginLoc(),
6262                  diag::err_template_arg_ref_bind_ignores_quals)
6263               << ParamType << Arg->getType() << Arg->getSourceRange();
6264           S.Diag(Param->getLocation(), diag::note_template_param_here);
6265           return true;
6266         }
6267       }
6268     }
6269 
6270     // At this point, the template argument refers to an object or
6271     // function with external linkage. We now need to check whether the
6272     // argument and parameter types are compatible.
6273     if (!S.Context.hasSameUnqualifiedType(ArgType,
6274                                           ParamType.getNonReferenceType())) {
6275       // We can't perform this conversion or binding.
6276       if (ParamType->isReferenceType())
6277         S.Diag(Arg->getBeginLoc(), diag::err_template_arg_no_ref_bind)
6278             << ParamType << ArgIn->getType() << Arg->getSourceRange();
6279       else
6280         S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_convertible)
6281             << ArgIn->getType() << ParamType << Arg->getSourceRange();
6282       S.Diag(Param->getLocation(), diag::note_template_param_here);
6283       return true;
6284     }
6285   }
6286 
6287   return false;
6288 }
6289 
6290 /// Checks whether the given template argument is the address
6291 /// of an object or function according to C++ [temp.arg.nontype]p1.
6292 static bool
6293 CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
6294                                                NonTypeTemplateParmDecl *Param,
6295                                                QualType ParamType,
6296                                                Expr *ArgIn,
6297                                                TemplateArgument &Converted) {
6298   bool Invalid = false;
6299   Expr *Arg = ArgIn;
6300   QualType ArgType = Arg->getType();
6301 
6302   bool AddressTaken = false;
6303   SourceLocation AddrOpLoc;
6304   if (S.getLangOpts().MicrosoftExt) {
6305     // Microsoft Visual C++ strips all casts, allows an arbitrary number of
6306     // dereference and address-of operators.
6307     Arg = Arg->IgnoreParenCasts();
6308 
6309     bool ExtWarnMSTemplateArg = false;
6310     UnaryOperatorKind FirstOpKind;
6311     SourceLocation FirstOpLoc;
6312     while (UnaryOperator *UnOp = dyn_cast<UnaryOperator>(Arg)) {
6313       UnaryOperatorKind UnOpKind = UnOp->getOpcode();
6314       if (UnOpKind == UO_Deref)
6315         ExtWarnMSTemplateArg = true;
6316       if (UnOpKind == UO_AddrOf || UnOpKind == UO_Deref) {
6317         Arg = UnOp->getSubExpr()->IgnoreParenCasts();
6318         if (!AddrOpLoc.isValid()) {
6319           FirstOpKind = UnOpKind;
6320           FirstOpLoc = UnOp->getOperatorLoc();
6321         }
6322       } else
6323         break;
6324     }
6325     if (FirstOpLoc.isValid()) {
6326       if (ExtWarnMSTemplateArg)
6327         S.Diag(ArgIn->getBeginLoc(), diag::ext_ms_deref_template_argument)
6328             << ArgIn->getSourceRange();
6329 
6330       if (FirstOpKind == UO_AddrOf)
6331         AddressTaken = true;
6332       else if (Arg->getType()->isPointerType()) {
6333         // We cannot let pointers get dereferenced here, that is obviously not a
6334         // constant expression.
6335         assert(FirstOpKind == UO_Deref);
6336         S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
6337             << Arg->getSourceRange();
6338       }
6339     }
6340   } else {
6341     // See through any implicit casts we added to fix the type.
6342     Arg = Arg->IgnoreImpCasts();
6343 
6344     // C++ [temp.arg.nontype]p1:
6345     //
6346     //   A template-argument for a non-type, non-template
6347     //   template-parameter shall be one of: [...]
6348     //
6349     //     -- the address of an object or function with external
6350     //        linkage, including function templates and function
6351     //        template-ids but excluding non-static class members,
6352     //        expressed as & id-expression where the & is optional if
6353     //        the name refers to a function or array, or if the
6354     //        corresponding template-parameter is a reference; or
6355 
6356     // In C++98/03 mode, give an extension warning on any extra parentheses.
6357     // See http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#773
6358     bool ExtraParens = false;
6359     while (ParenExpr *Parens = dyn_cast<ParenExpr>(Arg)) {
6360       if (!Invalid && !ExtraParens) {
6361         S.Diag(Arg->getBeginLoc(),
6362                S.getLangOpts().CPlusPlus11
6363                    ? diag::warn_cxx98_compat_template_arg_extra_parens
6364                    : diag::ext_template_arg_extra_parens)
6365             << Arg->getSourceRange();
6366         ExtraParens = true;
6367       }
6368 
6369       Arg = Parens->getSubExpr();
6370     }
6371 
6372     while (SubstNonTypeTemplateParmExpr *subst =
6373                dyn_cast<SubstNonTypeTemplateParmExpr>(Arg))
6374       Arg = subst->getReplacement()->IgnoreImpCasts();
6375 
6376     if (UnaryOperator *UnOp = dyn_cast<UnaryOperator>(Arg)) {
6377       if (UnOp->getOpcode() == UO_AddrOf) {
6378         Arg = UnOp->getSubExpr();
6379         AddressTaken = true;
6380         AddrOpLoc = UnOp->getOperatorLoc();
6381       }
6382     }
6383 
6384     while (SubstNonTypeTemplateParmExpr *subst =
6385                dyn_cast<SubstNonTypeTemplateParmExpr>(Arg))
6386       Arg = subst->getReplacement()->IgnoreImpCasts();
6387   }
6388 
6389   ValueDecl *Entity = nullptr;
6390   if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Arg))
6391     Entity = DRE->getDecl();
6392   else if (CXXUuidofExpr *CUE = dyn_cast<CXXUuidofExpr>(Arg))
6393     Entity = CUE->getGuidDecl();
6394 
6395   // If our parameter has pointer type, check for a null template value.
6396   if (ParamType->isPointerType() || ParamType->isNullPtrType()) {
6397     switch (isNullPointerValueTemplateArgument(S, Param, ParamType, ArgIn,
6398                                                Entity)) {
6399     case NPV_NullPointer:
6400       S.Diag(Arg->getExprLoc(), diag::warn_cxx98_compat_template_arg_null);
6401       Converted = TemplateArgument(S.Context.getCanonicalType(ParamType),
6402                                    /*isNullPtr=*/true);
6403       return false;
6404 
6405     case NPV_Error:
6406       return true;
6407 
6408     case NPV_NotNullPointer:
6409       break;
6410     }
6411   }
6412 
6413   // Stop checking the precise nature of the argument if it is value dependent,
6414   // it should be checked when instantiated.
6415   if (Arg->isValueDependent()) {
6416     Converted = TemplateArgument(ArgIn);
6417     return false;
6418   }
6419 
6420   if (!Entity) {
6421     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
6422         << Arg->getSourceRange();
6423     S.Diag(Param->getLocation(), diag::note_template_param_here);
6424     return true;
6425   }
6426 
6427   // Cannot refer to non-static data members
6428   if (isa<FieldDecl>(Entity) || isa<IndirectFieldDecl>(Entity)) {
6429     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_field)
6430         << Entity << Arg->getSourceRange();
6431     S.Diag(Param->getLocation(), diag::note_template_param_here);
6432     return true;
6433   }
6434 
6435   // Cannot refer to non-static member functions
6436   if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Entity)) {
6437     if (!Method->isStatic()) {
6438       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_method)
6439           << Method << Arg->getSourceRange();
6440       S.Diag(Param->getLocation(), diag::note_template_param_here);
6441       return true;
6442     }
6443   }
6444 
6445   FunctionDecl *Func = dyn_cast<FunctionDecl>(Entity);
6446   VarDecl *Var = dyn_cast<VarDecl>(Entity);
6447   MSGuidDecl *Guid = dyn_cast<MSGuidDecl>(Entity);
6448 
6449   // A non-type template argument must refer to an object or function.
6450   if (!Func && !Var && !Guid) {
6451     // We found something, but we don't know specifically what it is.
6452     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_object_or_func)
6453         << Arg->getSourceRange();
6454     S.Diag(Entity->getLocation(), diag::note_template_arg_refers_here);
6455     return true;
6456   }
6457 
6458   // Address / reference template args must have external linkage in C++98.
6459   if (Entity->getFormalLinkage() == InternalLinkage) {
6460     S.Diag(Arg->getBeginLoc(),
6461            S.getLangOpts().CPlusPlus11
6462                ? diag::warn_cxx98_compat_template_arg_object_internal
6463                : diag::ext_template_arg_object_internal)
6464         << !Func << Entity << Arg->getSourceRange();
6465     S.Diag(Entity->getLocation(), diag::note_template_arg_internal_object)
6466       << !Func;
6467   } else if (!Entity->hasLinkage()) {
6468     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_object_no_linkage)
6469         << !Func << Entity << Arg->getSourceRange();
6470     S.Diag(Entity->getLocation(), diag::note_template_arg_internal_object)
6471       << !Func;
6472     return true;
6473   }
6474 
6475   if (Var) {
6476     // A value of reference type is not an object.
6477     if (Var->getType()->isReferenceType()) {
6478       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_reference_var)
6479           << Var->getType() << Arg->getSourceRange();
6480       S.Diag(Param->getLocation(), diag::note_template_param_here);
6481       return true;
6482     }
6483 
6484     // A template argument must have static storage duration.
6485     if (Var->getTLSKind()) {
6486       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_thread_local)
6487           << Arg->getSourceRange();
6488       S.Diag(Var->getLocation(), diag::note_template_arg_refers_here);
6489       return true;
6490     }
6491   }
6492 
6493   if (AddressTaken && ParamType->isReferenceType()) {
6494     // If we originally had an address-of operator, but the
6495     // parameter has reference type, complain and (if things look
6496     // like they will work) drop the address-of operator.
6497     if (!S.Context.hasSameUnqualifiedType(Entity->getType(),
6498                                           ParamType.getNonReferenceType())) {
6499       S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
6500         << ParamType;
6501       S.Diag(Param->getLocation(), diag::note_template_param_here);
6502       return true;
6503     }
6504 
6505     S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
6506       << ParamType
6507       << FixItHint::CreateRemoval(AddrOpLoc);
6508     S.Diag(Param->getLocation(), diag::note_template_param_here);
6509 
6510     ArgType = Entity->getType();
6511   }
6512 
6513   // If the template parameter has pointer type, either we must have taken the
6514   // address or the argument must decay to a pointer.
6515   if (!AddressTaken && ParamType->isPointerType()) {
6516     if (Func) {
6517       // Function-to-pointer decay.
6518       ArgType = S.Context.getPointerType(Func->getType());
6519     } else if (Entity->getType()->isArrayType()) {
6520       // Array-to-pointer decay.
6521       ArgType = S.Context.getArrayDecayedType(Entity->getType());
6522     } else {
6523       // If the template parameter has pointer type but the address of
6524       // this object was not taken, complain and (possibly) recover by
6525       // taking the address of the entity.
6526       ArgType = S.Context.getPointerType(Entity->getType());
6527       if (!S.Context.hasSameUnqualifiedType(ArgType, ParamType)) {
6528         S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
6529           << ParamType;
6530         S.Diag(Param->getLocation(), diag::note_template_param_here);
6531         return true;
6532       }
6533 
6534       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
6535         << ParamType << FixItHint::CreateInsertion(Arg->getBeginLoc(), "&");
6536 
6537       S.Diag(Param->getLocation(), diag::note_template_param_here);
6538     }
6539   }
6540 
6541   if (CheckTemplateArgumentIsCompatibleWithParameter(S, Param, ParamType, ArgIn,
6542                                                      Arg, ArgType))
6543     return true;
6544 
6545   // Create the template argument.
6546   Converted =
6547       TemplateArgument(cast<ValueDecl>(Entity->getCanonicalDecl()), ParamType);
6548   S.MarkAnyDeclReferenced(Arg->getBeginLoc(), Entity, false);
6549   return false;
6550 }
6551 
6552 /// Checks whether the given template argument is a pointer to
6553 /// member constant according to C++ [temp.arg.nontype]p1.
6554 static bool CheckTemplateArgumentPointerToMember(Sema &S,
6555                                                  NonTypeTemplateParmDecl *Param,
6556                                                  QualType ParamType,
6557                                                  Expr *&ResultArg,
6558                                                  TemplateArgument &Converted) {
6559   bool Invalid = false;
6560 
6561   Expr *Arg = ResultArg;
6562   bool ObjCLifetimeConversion;
6563 
6564   // C++ [temp.arg.nontype]p1:
6565   //
6566   //   A template-argument for a non-type, non-template
6567   //   template-parameter shall be one of: [...]
6568   //
6569   //     -- a pointer to member expressed as described in 5.3.1.
6570   DeclRefExpr *DRE = nullptr;
6571 
6572   // In C++98/03 mode, give an extension warning on any extra parentheses.
6573   // See http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#773
6574   bool ExtraParens = false;
6575   while (ParenExpr *Parens = dyn_cast<ParenExpr>(Arg)) {
6576     if (!Invalid && !ExtraParens) {
6577       S.Diag(Arg->getBeginLoc(),
6578              S.getLangOpts().CPlusPlus11
6579                  ? diag::warn_cxx98_compat_template_arg_extra_parens
6580                  : diag::ext_template_arg_extra_parens)
6581           << Arg->getSourceRange();
6582       ExtraParens = true;
6583     }
6584 
6585     Arg = Parens->getSubExpr();
6586   }
6587 
6588   while (SubstNonTypeTemplateParmExpr *subst =
6589            dyn_cast<SubstNonTypeTemplateParmExpr>(Arg))
6590     Arg = subst->getReplacement()->IgnoreImpCasts();
6591 
6592   // A pointer-to-member constant written &Class::member.
6593   if (UnaryOperator *UnOp = dyn_cast<UnaryOperator>(Arg)) {
6594     if (UnOp->getOpcode() == UO_AddrOf) {
6595       DRE = dyn_cast<DeclRefExpr>(UnOp->getSubExpr());
6596       if (DRE && !DRE->getQualifier())
6597         DRE = nullptr;
6598     }
6599   }
6600   // A constant of pointer-to-member type.
6601   else if ((DRE = dyn_cast<DeclRefExpr>(Arg))) {
6602     ValueDecl *VD = DRE->getDecl();
6603     if (VD->getType()->isMemberPointerType()) {
6604       if (isa<NonTypeTemplateParmDecl>(VD)) {
6605         if (Arg->isTypeDependent() || Arg->isValueDependent()) {
6606           Converted = TemplateArgument(Arg);
6607         } else {
6608           VD = cast<ValueDecl>(VD->getCanonicalDecl());
6609           Converted = TemplateArgument(VD, ParamType);
6610         }
6611         return Invalid;
6612       }
6613     }
6614 
6615     DRE = nullptr;
6616   }
6617 
6618   ValueDecl *Entity = DRE ? DRE->getDecl() : nullptr;
6619 
6620   // Check for a null pointer value.
6621   switch (isNullPointerValueTemplateArgument(S, Param, ParamType, ResultArg,
6622                                              Entity)) {
6623   case NPV_Error:
6624     return true;
6625   case NPV_NullPointer:
6626     S.Diag(ResultArg->getExprLoc(), diag::warn_cxx98_compat_template_arg_null);
6627     Converted = TemplateArgument(S.Context.getCanonicalType(ParamType),
6628                                  /*isNullPtr*/true);
6629     return false;
6630   case NPV_NotNullPointer:
6631     break;
6632   }
6633 
6634   if (S.IsQualificationConversion(ResultArg->getType(),
6635                                   ParamType.getNonReferenceType(), false,
6636                                   ObjCLifetimeConversion)) {
6637     ResultArg = S.ImpCastExprToType(ResultArg, ParamType, CK_NoOp,
6638                                     ResultArg->getValueKind())
6639                     .get();
6640   } else if (!S.Context.hasSameUnqualifiedType(
6641                  ResultArg->getType(), ParamType.getNonReferenceType())) {
6642     // We can't perform this conversion.
6643     S.Diag(ResultArg->getBeginLoc(), diag::err_template_arg_not_convertible)
6644         << ResultArg->getType() << ParamType << ResultArg->getSourceRange();
6645     S.Diag(Param->getLocation(), diag::note_template_param_here);
6646     return true;
6647   }
6648 
6649   if (!DRE)
6650     return S.Diag(Arg->getBeginLoc(),
6651                   diag::err_template_arg_not_pointer_to_member_form)
6652            << Arg->getSourceRange();
6653 
6654   if (isa<FieldDecl>(DRE->getDecl()) ||
6655       isa<IndirectFieldDecl>(DRE->getDecl()) ||
6656       isa<CXXMethodDecl>(DRE->getDecl())) {
6657     assert((isa<FieldDecl>(DRE->getDecl()) ||
6658             isa<IndirectFieldDecl>(DRE->getDecl()) ||
6659             !cast<CXXMethodDecl>(DRE->getDecl())->isStatic()) &&
6660            "Only non-static member pointers can make it here");
6661 
6662     // Okay: this is the address of a non-static member, and therefore
6663     // a member pointer constant.
6664     if (Arg->isTypeDependent() || Arg->isValueDependent()) {
6665       Converted = TemplateArgument(Arg);
6666     } else {
6667       ValueDecl *D = cast<ValueDecl>(DRE->getDecl()->getCanonicalDecl());
6668       Converted = TemplateArgument(D, ParamType);
6669     }
6670     return Invalid;
6671   }
6672 
6673   // We found something else, but we don't know specifically what it is.
6674   S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_pointer_to_member_form)
6675       << Arg->getSourceRange();
6676   S.Diag(DRE->getDecl()->getLocation(), diag::note_template_arg_refers_here);
6677   return true;
6678 }
6679 
6680 /// Check a template argument against its corresponding
6681 /// non-type template parameter.
6682 ///
6683 /// This routine implements the semantics of C++ [temp.arg.nontype].
6684 /// If an error occurred, it returns ExprError(); otherwise, it
6685 /// returns the converted template argument. \p ParamType is the
6686 /// type of the non-type template parameter after it has been instantiated.
6687 ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
6688                                        QualType ParamType, Expr *Arg,
6689                                        TemplateArgument &Converted,
6690                                        CheckTemplateArgumentKind CTAK) {
6691   SourceLocation StartLoc = Arg->getBeginLoc();
6692 
6693   // If the parameter type somehow involves auto, deduce the type now.
6694   if (getLangOpts().CPlusPlus17 && ParamType->isUndeducedType()) {
6695     // During template argument deduction, we allow 'decltype(auto)' to
6696     // match an arbitrary dependent argument.
6697     // FIXME: The language rules don't say what happens in this case.
6698     // FIXME: We get an opaque dependent type out of decltype(auto) if the
6699     // expression is merely instantiation-dependent; is this enough?
6700     if (CTAK == CTAK_Deduced && Arg->isTypeDependent()) {
6701       auto *AT = dyn_cast<AutoType>(ParamType);
6702       if (AT && AT->isDecltypeAuto()) {
6703         Converted = TemplateArgument(Arg);
6704         return Arg;
6705       }
6706     }
6707 
6708     // When checking a deduced template argument, deduce from its type even if
6709     // the type is dependent, in order to check the types of non-type template
6710     // arguments line up properly in partial ordering.
6711     Optional<unsigned> Depth = Param->getDepth() + 1;
6712     Expr *DeductionArg = Arg;
6713     if (auto *PE = dyn_cast<PackExpansionExpr>(DeductionArg))
6714       DeductionArg = PE->getPattern();
6715     if (DeduceAutoType(
6716             Context.getTrivialTypeSourceInfo(ParamType, Param->getLocation()),
6717             DeductionArg, ParamType, Depth,
6718             // We do not check constraints right now because the
6719             // immediately-declared constraint of the auto type is also an
6720             // associated constraint, and will be checked along with the other
6721             // associated constraints after checking the template argument list.
6722             /*IgnoreConstraints=*/true) == DAR_Failed) {
6723       Diag(Arg->getExprLoc(),
6724            diag::err_non_type_template_parm_type_deduction_failure)
6725         << Param->getDeclName() << Param->getType() << Arg->getType()
6726         << Arg->getSourceRange();
6727       Diag(Param->getLocation(), diag::note_template_param_here);
6728       return ExprError();
6729     }
6730     // CheckNonTypeTemplateParameterType will produce a diagnostic if there's
6731     // an error. The error message normally references the parameter
6732     // declaration, but here we'll pass the argument location because that's
6733     // where the parameter type is deduced.
6734     ParamType = CheckNonTypeTemplateParameterType(ParamType, Arg->getExprLoc());
6735     if (ParamType.isNull()) {
6736       Diag(Param->getLocation(), diag::note_template_param_here);
6737       return ExprError();
6738     }
6739   }
6740 
6741   // We should have already dropped all cv-qualifiers by now.
6742   assert(!ParamType.hasQualifiers() &&
6743          "non-type template parameter type cannot be qualified");
6744 
6745   if (CTAK == CTAK_Deduced &&
6746       !Context.hasSameType(ParamType.getNonLValueExprType(Context),
6747                            Arg->getType())) {
6748     // FIXME: If either type is dependent, we skip the check. This isn't
6749     // correct, since during deduction we're supposed to have replaced each
6750     // template parameter with some unique (non-dependent) placeholder.
6751     // FIXME: If the argument type contains 'auto', we carry on and fail the
6752     // type check in order to force specific types to be more specialized than
6753     // 'auto'. It's not clear how partial ordering with 'auto' is supposed to
6754     // work.
6755     if ((ParamType->isDependentType() || Arg->isTypeDependent()) &&
6756         !Arg->getType()->getContainedAutoType()) {
6757       Converted = TemplateArgument(Arg);
6758       return Arg;
6759     }
6760     // FIXME: This attempts to implement C++ [temp.deduct.type]p17. Per DR1770,
6761     // we should actually be checking the type of the template argument in P,
6762     // not the type of the template argument deduced from A, against the
6763     // template parameter type.
6764     Diag(StartLoc, diag::err_deduced_non_type_template_arg_type_mismatch)
6765       << Arg->getType()
6766       << ParamType.getUnqualifiedType();
6767     Diag(Param->getLocation(), diag::note_template_param_here);
6768     return ExprError();
6769   }
6770 
6771   // If either the parameter has a dependent type or the argument is
6772   // type-dependent, there's nothing we can check now. The argument only
6773   // contains an unexpanded pack during partial ordering, and there's
6774   // nothing more we can check in that case.
6775   if (ParamType->isDependentType() || Arg->isTypeDependent() ||
6776       Arg->containsUnexpandedParameterPack()) {
6777     // Force the argument to the type of the parameter to maintain invariants.
6778     auto *PE = dyn_cast<PackExpansionExpr>(Arg);
6779     if (PE)
6780       Arg = PE->getPattern();
6781     ExprResult E = ImpCastExprToType(
6782         Arg, ParamType.getNonLValueExprType(Context), CK_Dependent,
6783         ParamType->isLValueReferenceType() ? VK_LValue :
6784         ParamType->isRValueReferenceType() ? VK_XValue : VK_RValue);
6785     if (E.isInvalid())
6786       return ExprError();
6787     if (PE) {
6788       // Recreate a pack expansion if we unwrapped one.
6789       E = new (Context)
6790           PackExpansionExpr(E.get()->getType(), E.get(), PE->getEllipsisLoc(),
6791                             PE->getNumExpansions());
6792     }
6793     Converted = TemplateArgument(E.get());
6794     return E;
6795   }
6796 
6797   // The initialization of the parameter from the argument is
6798   // a constant-evaluated context.
6799   EnterExpressionEvaluationContext ConstantEvaluated(
6800       *this, Sema::ExpressionEvaluationContext::ConstantEvaluated);
6801 
6802   if (getLangOpts().CPlusPlus17) {
6803     // C++17 [temp.arg.nontype]p1:
6804     //   A template-argument for a non-type template parameter shall be
6805     //   a converted constant expression of the type of the template-parameter.
6806     APValue Value;
6807     ExprResult ArgResult = CheckConvertedConstantExpression(
6808         Arg, ParamType, Value, CCEK_TemplateArg);
6809     if (ArgResult.isInvalid())
6810       return ExprError();
6811 
6812     // For a value-dependent argument, CheckConvertedConstantExpression is
6813     // permitted (and expected) to be unable to determine a value.
6814     if (ArgResult.get()->isValueDependent()) {
6815       Converted = TemplateArgument(ArgResult.get());
6816       return ArgResult;
6817     }
6818 
6819     QualType CanonParamType = Context.getCanonicalType(ParamType);
6820 
6821     // Convert the APValue to a TemplateArgument.
6822     switch (Value.getKind()) {
6823     case APValue::None:
6824       assert(ParamType->isNullPtrType());
6825       Converted = TemplateArgument(CanonParamType, /*isNullPtr*/true);
6826       break;
6827     case APValue::Indeterminate:
6828       llvm_unreachable("result of constant evaluation should be initialized");
6829       break;
6830     case APValue::Int:
6831       assert(ParamType->isIntegralOrEnumerationType());
6832       Converted = TemplateArgument(Context, Value.getInt(), CanonParamType);
6833       break;
6834     case APValue::MemberPointer: {
6835       assert(ParamType->isMemberPointerType());
6836 
6837       // FIXME: We need TemplateArgument representation and mangling for these.
6838       if (!Value.getMemberPointerPath().empty()) {
6839         Diag(Arg->getBeginLoc(),
6840              diag::err_template_arg_member_ptr_base_derived_not_supported)
6841             << Value.getMemberPointerDecl() << ParamType
6842             << Arg->getSourceRange();
6843         return ExprError();
6844       }
6845 
6846       auto *VD = const_cast<ValueDecl*>(Value.getMemberPointerDecl());
6847       Converted = VD ? TemplateArgument(VD, CanonParamType)
6848                      : TemplateArgument(CanonParamType, /*isNullPtr*/true);
6849       break;
6850     }
6851     case APValue::LValue: {
6852       //   For a non-type template-parameter of pointer or reference type,
6853       //   the value of the constant expression shall not refer to
6854       assert(ParamType->isPointerType() || ParamType->isReferenceType() ||
6855              ParamType->isNullPtrType());
6856       // -- a temporary object
6857       // -- a string literal
6858       // -- the result of a typeid expression, or
6859       // -- a predefined __func__ variable
6860       APValue::LValueBase Base = Value.getLValueBase();
6861       auto *VD = const_cast<ValueDecl *>(Base.dyn_cast<const ValueDecl *>());
6862       if (Base && (!VD || isa<LifetimeExtendedTemporaryDecl>(VD))) {
6863         Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
6864             << Arg->getSourceRange();
6865         return ExprError();
6866       }
6867       // -- a subobject
6868       if (Value.hasLValuePath() && Value.getLValuePath().size() == 1 &&
6869           VD && VD->getType()->isArrayType() &&
6870           Value.getLValuePath()[0].getAsArrayIndex() == 0 &&
6871           !Value.isLValueOnePastTheEnd() && ParamType->isPointerType()) {
6872         // Per defect report (no number yet):
6873         //   ... other than a pointer to the first element of a complete array
6874         //       object.
6875       } else if (!Value.hasLValuePath() || Value.getLValuePath().size() ||
6876                  Value.isLValueOnePastTheEnd()) {
6877         Diag(StartLoc, diag::err_non_type_template_arg_subobject)
6878           << Value.getAsString(Context, ParamType);
6879         return ExprError();
6880       }
6881       assert((VD || !ParamType->isReferenceType()) &&
6882              "null reference should not be a constant expression");
6883       assert((!VD || !ParamType->isNullPtrType()) &&
6884              "non-null value of type nullptr_t?");
6885       Converted = VD ? TemplateArgument(VD, CanonParamType)
6886                      : TemplateArgument(CanonParamType, /*isNullPtr*/true);
6887       break;
6888     }
6889     case APValue::AddrLabelDiff:
6890       return Diag(StartLoc, diag::err_non_type_template_arg_addr_label_diff);
6891     case APValue::FixedPoint:
6892     case APValue::Float:
6893     case APValue::ComplexInt:
6894     case APValue::ComplexFloat:
6895     case APValue::Vector:
6896     case APValue::Array:
6897     case APValue::Struct:
6898     case APValue::Union:
6899       llvm_unreachable("invalid kind for template argument");
6900     }
6901 
6902     return ArgResult.get();
6903   }
6904 
6905   // C++ [temp.arg.nontype]p5:
6906   //   The following conversions are performed on each expression used
6907   //   as a non-type template-argument. If a non-type
6908   //   template-argument cannot be converted to the type of the
6909   //   corresponding template-parameter then the program is
6910   //   ill-formed.
6911   if (ParamType->isIntegralOrEnumerationType()) {
6912     // C++11:
6913     //   -- for a non-type template-parameter of integral or
6914     //      enumeration type, conversions permitted in a converted
6915     //      constant expression are applied.
6916     //
6917     // C++98:
6918     //   -- for a non-type template-parameter of integral or
6919     //      enumeration type, integral promotions (4.5) and integral
6920     //      conversions (4.7) are applied.
6921 
6922     if (getLangOpts().CPlusPlus11) {
6923       // C++ [temp.arg.nontype]p1:
6924       //   A template-argument for a non-type, non-template template-parameter
6925       //   shall be one of:
6926       //
6927       //     -- for a non-type template-parameter of integral or enumeration
6928       //        type, a converted constant expression of the type of the
6929       //        template-parameter; or
6930       llvm::APSInt Value;
6931       ExprResult ArgResult =
6932         CheckConvertedConstantExpression(Arg, ParamType, Value,
6933                                          CCEK_TemplateArg);
6934       if (ArgResult.isInvalid())
6935         return ExprError();
6936 
6937       // We can't check arbitrary value-dependent arguments.
6938       if (ArgResult.get()->isValueDependent()) {
6939         Converted = TemplateArgument(ArgResult.get());
6940         return ArgResult;
6941       }
6942 
6943       // Widen the argument value to sizeof(parameter type). This is almost
6944       // always a no-op, except when the parameter type is bool. In
6945       // that case, this may extend the argument from 1 bit to 8 bits.
6946       QualType IntegerType = ParamType;
6947       if (const EnumType *Enum = IntegerType->getAs<EnumType>())
6948         IntegerType = Enum->getDecl()->getIntegerType();
6949       Value = Value.extOrTrunc(IntegerType->isExtIntType()
6950                                    ? Context.getIntWidth(IntegerType)
6951                                    : Context.getTypeSize(IntegerType));
6952 
6953       Converted = TemplateArgument(Context, Value,
6954                                    Context.getCanonicalType(ParamType));
6955       return ArgResult;
6956     }
6957 
6958     ExprResult ArgResult = DefaultLvalueConversion(Arg);
6959     if (ArgResult.isInvalid())
6960       return ExprError();
6961     Arg = ArgResult.get();
6962 
6963     QualType ArgType = Arg->getType();
6964 
6965     // C++ [temp.arg.nontype]p1:
6966     //   A template-argument for a non-type, non-template
6967     //   template-parameter shall be one of:
6968     //
6969     //     -- an integral constant-expression of integral or enumeration
6970     //        type; or
6971     //     -- the name of a non-type template-parameter; or
6972     llvm::APSInt Value;
6973     if (!ArgType->isIntegralOrEnumerationType()) {
6974       Diag(Arg->getBeginLoc(), diag::err_template_arg_not_integral_or_enumeral)
6975           << ArgType << Arg->getSourceRange();
6976       Diag(Param->getLocation(), diag::note_template_param_here);
6977       return ExprError();
6978     } else if (!Arg->isValueDependent()) {
6979       class TmplArgICEDiagnoser : public VerifyICEDiagnoser {
6980         QualType T;
6981 
6982       public:
6983         TmplArgICEDiagnoser(QualType T) : T(T) { }
6984 
6985         void diagnoseNotICE(Sema &S, SourceLocation Loc,
6986                             SourceRange SR) override {
6987           S.Diag(Loc, diag::err_template_arg_not_ice) << T << SR;
6988         }
6989       } Diagnoser(ArgType);
6990 
6991       Arg = VerifyIntegerConstantExpression(Arg, &Value, Diagnoser,
6992                                             false).get();
6993       if (!Arg)
6994         return ExprError();
6995     }
6996 
6997     // From here on out, all we care about is the unqualified form
6998     // of the argument type.
6999     ArgType = ArgType.getUnqualifiedType();
7000 
7001     // Try to convert the argument to the parameter's type.
7002     if (Context.hasSameType(ParamType, ArgType)) {
7003       // Okay: no conversion necessary
7004     } else if (ParamType->isBooleanType()) {
7005       // This is an integral-to-boolean conversion.
7006       Arg = ImpCastExprToType(Arg, ParamType, CK_IntegralToBoolean).get();
7007     } else if (IsIntegralPromotion(Arg, ArgType, ParamType) ||
7008                !ParamType->isEnumeralType()) {
7009       // This is an integral promotion or conversion.
7010       Arg = ImpCastExprToType(Arg, ParamType, CK_IntegralCast).get();
7011     } else {
7012       // We can't perform this conversion.
7013       Diag(Arg->getBeginLoc(), diag::err_template_arg_not_convertible)
7014           << Arg->getType() << ParamType << Arg->getSourceRange();
7015       Diag(Param->getLocation(), diag::note_template_param_here);
7016       return ExprError();
7017     }
7018 
7019     // Add the value of this argument to the list of converted
7020     // arguments. We use the bitwidth and signedness of the template
7021     // parameter.
7022     if (Arg->isValueDependent()) {
7023       // The argument is value-dependent. Create a new
7024       // TemplateArgument with the converted expression.
7025       Converted = TemplateArgument(Arg);
7026       return Arg;
7027     }
7028 
7029     QualType IntegerType = Context.getCanonicalType(ParamType);
7030     if (const EnumType *Enum = IntegerType->getAs<EnumType>())
7031       IntegerType = Context.getCanonicalType(Enum->getDecl()->getIntegerType());
7032 
7033     if (ParamType->isBooleanType()) {
7034       // Value must be zero or one.
7035       Value = Value != 0;
7036       unsigned AllowedBits = Context.getTypeSize(IntegerType);
7037       if (Value.getBitWidth() != AllowedBits)
7038         Value = Value.extOrTrunc(AllowedBits);
7039       Value.setIsSigned(IntegerType->isSignedIntegerOrEnumerationType());
7040     } else {
7041       llvm::APSInt OldValue = Value;
7042 
7043       // Coerce the template argument's value to the value it will have
7044       // based on the template parameter's type.
7045       unsigned AllowedBits = IntegerType->isExtIntType()
7046                                  ? Context.getIntWidth(IntegerType)
7047                                  : Context.getTypeSize(IntegerType);
7048       if (Value.getBitWidth() != AllowedBits)
7049         Value = Value.extOrTrunc(AllowedBits);
7050       Value.setIsSigned(IntegerType->isSignedIntegerOrEnumerationType());
7051 
7052       // Complain if an unsigned parameter received a negative value.
7053       if (IntegerType->isUnsignedIntegerOrEnumerationType()
7054                && (OldValue.isSigned() && OldValue.isNegative())) {
7055         Diag(Arg->getBeginLoc(), diag::warn_template_arg_negative)
7056             << OldValue.toString(10) << Value.toString(10) << Param->getType()
7057             << Arg->getSourceRange();
7058         Diag(Param->getLocation(), diag::note_template_param_here);
7059       }
7060 
7061       // Complain if we overflowed the template parameter's type.
7062       unsigned RequiredBits;
7063       if (IntegerType->isUnsignedIntegerOrEnumerationType())
7064         RequiredBits = OldValue.getActiveBits();
7065       else if (OldValue.isUnsigned())
7066         RequiredBits = OldValue.getActiveBits() + 1;
7067       else
7068         RequiredBits = OldValue.getMinSignedBits();
7069       if (RequiredBits > AllowedBits) {
7070         Diag(Arg->getBeginLoc(), diag::warn_template_arg_too_large)
7071             << OldValue.toString(10) << Value.toString(10) << Param->getType()
7072             << Arg->getSourceRange();
7073         Diag(Param->getLocation(), diag::note_template_param_here);
7074       }
7075     }
7076 
7077     Converted = TemplateArgument(Context, Value,
7078                                  ParamType->isEnumeralType()
7079                                    ? Context.getCanonicalType(ParamType)
7080                                    : IntegerType);
7081     return Arg;
7082   }
7083 
7084   QualType ArgType = Arg->getType();
7085   DeclAccessPair FoundResult; // temporary for ResolveOverloadedFunction
7086 
7087   // Handle pointer-to-function, reference-to-function, and
7088   // pointer-to-member-function all in (roughly) the same way.
7089   if (// -- For a non-type template-parameter of type pointer to
7090       //    function, only the function-to-pointer conversion (4.3) is
7091       //    applied. If the template-argument represents a set of
7092       //    overloaded functions (or a pointer to such), the matching
7093       //    function is selected from the set (13.4).
7094       (ParamType->isPointerType() &&
7095        ParamType->castAs<PointerType>()->getPointeeType()->isFunctionType()) ||
7096       // -- For a non-type template-parameter of type reference to
7097       //    function, no conversions apply. If the template-argument
7098       //    represents a set of overloaded functions, the matching
7099       //    function is selected from the set (13.4).
7100       (ParamType->isReferenceType() &&
7101        ParamType->castAs<ReferenceType>()->getPointeeType()->isFunctionType()) ||
7102       // -- For a non-type template-parameter of type pointer to
7103       //    member function, no conversions apply. If the
7104       //    template-argument represents a set of overloaded member
7105       //    functions, the matching member function is selected from
7106       //    the set (13.4).
7107       (ParamType->isMemberPointerType() &&
7108        ParamType->castAs<MemberPointerType>()->getPointeeType()
7109          ->isFunctionType())) {
7110 
7111     if (Arg->getType() == Context.OverloadTy) {
7112       if (FunctionDecl *Fn = ResolveAddressOfOverloadedFunction(Arg, ParamType,
7113                                                                 true,
7114                                                                 FoundResult)) {
7115         if (DiagnoseUseOfDecl(Fn, Arg->getBeginLoc()))
7116           return ExprError();
7117 
7118         Arg = FixOverloadedFunctionReference(Arg, FoundResult, Fn);
7119         ArgType = Arg->getType();
7120       } else
7121         return ExprError();
7122     }
7123 
7124     if (!ParamType->isMemberPointerType()) {
7125       if (CheckTemplateArgumentAddressOfObjectOrFunction(*this, Param,
7126                                                          ParamType,
7127                                                          Arg, Converted))
7128         return ExprError();
7129       return Arg;
7130     }
7131 
7132     if (CheckTemplateArgumentPointerToMember(*this, Param, ParamType, Arg,
7133                                              Converted))
7134       return ExprError();
7135     return Arg;
7136   }
7137 
7138   if (ParamType->isPointerType()) {
7139     //   -- for a non-type template-parameter of type pointer to
7140     //      object, qualification conversions (4.4) and the
7141     //      array-to-pointer conversion (4.2) are applied.
7142     // C++0x also allows a value of std::nullptr_t.
7143     assert(ParamType->getPointeeType()->isIncompleteOrObjectType() &&
7144            "Only object pointers allowed here");
7145 
7146     if (CheckTemplateArgumentAddressOfObjectOrFunction(*this, Param,
7147                                                        ParamType,
7148                                                        Arg, Converted))
7149       return ExprError();
7150     return Arg;
7151   }
7152 
7153   if (const ReferenceType *ParamRefType = ParamType->getAs<ReferenceType>()) {
7154     //   -- For a non-type template-parameter of type reference to
7155     //      object, no conversions apply. The type referred to by the
7156     //      reference may be more cv-qualified than the (otherwise
7157     //      identical) type of the template-argument. The
7158     //      template-parameter is bound directly to the
7159     //      template-argument, which must be an lvalue.
7160     assert(ParamRefType->getPointeeType()->isIncompleteOrObjectType() &&
7161            "Only object references allowed here");
7162 
7163     if (Arg->getType() == Context.OverloadTy) {
7164       if (FunctionDecl *Fn = ResolveAddressOfOverloadedFunction(Arg,
7165                                                  ParamRefType->getPointeeType(),
7166                                                                 true,
7167                                                                 FoundResult)) {
7168         if (DiagnoseUseOfDecl(Fn, Arg->getBeginLoc()))
7169           return ExprError();
7170 
7171         Arg = FixOverloadedFunctionReference(Arg, FoundResult, Fn);
7172         ArgType = Arg->getType();
7173       } else
7174         return ExprError();
7175     }
7176 
7177     if (CheckTemplateArgumentAddressOfObjectOrFunction(*this, Param,
7178                                                        ParamType,
7179                                                        Arg, Converted))
7180       return ExprError();
7181     return Arg;
7182   }
7183 
7184   // Deal with parameters of type std::nullptr_t.
7185   if (ParamType->isNullPtrType()) {
7186     if (Arg->isTypeDependent() || Arg->isValueDependent()) {
7187       Converted = TemplateArgument(Arg);
7188       return Arg;
7189     }
7190 
7191     switch (isNullPointerValueTemplateArgument(*this, Param, ParamType, Arg)) {
7192     case NPV_NotNullPointer:
7193       Diag(Arg->getExprLoc(), diag::err_template_arg_not_convertible)
7194         << Arg->getType() << ParamType;
7195       Diag(Param->getLocation(), diag::note_template_param_here);
7196       return ExprError();
7197 
7198     case NPV_Error:
7199       return ExprError();
7200 
7201     case NPV_NullPointer:
7202       Diag(Arg->getExprLoc(), diag::warn_cxx98_compat_template_arg_null);
7203       Converted = TemplateArgument(Context.getCanonicalType(ParamType),
7204                                    /*isNullPtr*/true);
7205       return Arg;
7206     }
7207   }
7208 
7209   //     -- For a non-type template-parameter of type pointer to data
7210   //        member, qualification conversions (4.4) are applied.
7211   assert(ParamType->isMemberPointerType() && "Only pointers to members remain");
7212 
7213   if (CheckTemplateArgumentPointerToMember(*this, Param, ParamType, Arg,
7214                                            Converted))
7215     return ExprError();
7216   return Arg;
7217 }
7218 
7219 static void DiagnoseTemplateParameterListArityMismatch(
7220     Sema &S, TemplateParameterList *New, TemplateParameterList *Old,
7221     Sema::TemplateParameterListEqualKind Kind, SourceLocation TemplateArgLoc);
7222 
7223 /// Check a template argument against its corresponding
7224 /// template template parameter.
7225 ///
7226 /// This routine implements the semantics of C++ [temp.arg.template].
7227 /// It returns true if an error occurred, and false otherwise.
7228 bool Sema::CheckTemplateTemplateArgument(TemplateTemplateParmDecl *Param,
7229                                          TemplateParameterList *Params,
7230                                          TemplateArgumentLoc &Arg) {
7231   TemplateName Name = Arg.getArgument().getAsTemplateOrTemplatePattern();
7232   TemplateDecl *Template = Name.getAsTemplateDecl();
7233   if (!Template) {
7234     // Any dependent template name is fine.
7235     assert(Name.isDependent() && "Non-dependent template isn't a declaration?");
7236     return false;
7237   }
7238 
7239   if (Template->isInvalidDecl())
7240     return true;
7241 
7242   // C++0x [temp.arg.template]p1:
7243   //   A template-argument for a template template-parameter shall be
7244   //   the name of a class template or an alias template, expressed as an
7245   //   id-expression. When the template-argument names a class template, only
7246   //   primary class templates are considered when matching the
7247   //   template template argument with the corresponding parameter;
7248   //   partial specializations are not considered even if their
7249   //   parameter lists match that of the template template parameter.
7250   //
7251   // Note that we also allow template template parameters here, which
7252   // will happen when we are dealing with, e.g., class template
7253   // partial specializations.
7254   if (!isa<ClassTemplateDecl>(Template) &&
7255       !isa<TemplateTemplateParmDecl>(Template) &&
7256       !isa<TypeAliasTemplateDecl>(Template) &&
7257       !isa<BuiltinTemplateDecl>(Template)) {
7258     assert(isa<FunctionTemplateDecl>(Template) &&
7259            "Only function templates are possible here");
7260     Diag(Arg.getLocation(), diag::err_template_arg_not_valid_template);
7261     Diag(Template->getLocation(), diag::note_template_arg_refers_here_func)
7262       << Template;
7263   }
7264 
7265   // C++1z [temp.arg.template]p3: (DR 150)
7266   //   A template-argument matches a template template-parameter P when P
7267   //   is at least as specialized as the template-argument A.
7268   // FIXME: We should enable RelaxedTemplateTemplateArgs by default as it is a
7269   //  defect report resolution from C++17 and shouldn't be introduced by
7270   //  concepts.
7271   if (getLangOpts().RelaxedTemplateTemplateArgs) {
7272     // Quick check for the common case:
7273     //   If P contains a parameter pack, then A [...] matches P if each of A's
7274     //   template parameters matches the corresponding template parameter in
7275     //   the template-parameter-list of P.
7276     if (TemplateParameterListsAreEqual(
7277             Template->getTemplateParameters(), Params, false,
7278             TPL_TemplateTemplateArgumentMatch, Arg.getLocation()) &&
7279         // If the argument has no associated constraints, then the parameter is
7280         // definitely at least as specialized as the argument.
7281         // Otherwise - we need a more thorough check.
7282         !Template->hasAssociatedConstraints())
7283       return false;
7284 
7285     if (isTemplateTemplateParameterAtLeastAsSpecializedAs(Params, Template,
7286                                                           Arg.getLocation())) {
7287       // C++2a[temp.func.order]p2
7288       //   [...] If both deductions succeed, the partial ordering selects the
7289       //   more constrained template as described by the rules in
7290       //   [temp.constr.order].
7291       SmallVector<const Expr *, 3> ParamsAC, TemplateAC;
7292       Params->getAssociatedConstraints(ParamsAC);
7293       // C++2a[temp.arg.template]p3
7294       //   [...] In this comparison, if P is unconstrained, the constraints on A
7295       //   are not considered.
7296       if (ParamsAC.empty())
7297         return false;
7298       Template->getAssociatedConstraints(TemplateAC);
7299       bool IsParamAtLeastAsConstrained;
7300       if (IsAtLeastAsConstrained(Param, ParamsAC, Template, TemplateAC,
7301                                  IsParamAtLeastAsConstrained))
7302         return true;
7303       if (!IsParamAtLeastAsConstrained) {
7304         Diag(Arg.getLocation(),
7305              diag::err_template_template_parameter_not_at_least_as_constrained)
7306             << Template << Param << Arg.getSourceRange();
7307         Diag(Param->getLocation(), diag::note_entity_declared_at) << Param;
7308         Diag(Template->getLocation(), diag::note_entity_declared_at)
7309             << Template;
7310         MaybeEmitAmbiguousAtomicConstraintsDiagnostic(Param, ParamsAC, Template,
7311                                                       TemplateAC);
7312         return true;
7313       }
7314       return false;
7315     }
7316     // FIXME: Produce better diagnostics for deduction failures.
7317   }
7318 
7319   return !TemplateParameterListsAreEqual(Template->getTemplateParameters(),
7320                                          Params,
7321                                          true,
7322                                          TPL_TemplateTemplateArgumentMatch,
7323                                          Arg.getLocation());
7324 }
7325 
7326 /// Given a non-type template argument that refers to a
7327 /// declaration and the type of its corresponding non-type template
7328 /// parameter, produce an expression that properly refers to that
7329 /// declaration.
7330 ExprResult
7331 Sema::BuildExpressionFromDeclTemplateArgument(const TemplateArgument &Arg,
7332                                               QualType ParamType,
7333                                               SourceLocation Loc) {
7334   // C++ [temp.param]p8:
7335   //
7336   //   A non-type template-parameter of type "array of T" or
7337   //   "function returning T" is adjusted to be of type "pointer to
7338   //   T" or "pointer to function returning T", respectively.
7339   if (ParamType->isArrayType())
7340     ParamType = Context.getArrayDecayedType(ParamType);
7341   else if (ParamType->isFunctionType())
7342     ParamType = Context.getPointerType(ParamType);
7343 
7344   // For a NULL non-type template argument, return nullptr casted to the
7345   // parameter's type.
7346   if (Arg.getKind() == TemplateArgument::NullPtr) {
7347     return ImpCastExprToType(
7348              new (Context) CXXNullPtrLiteralExpr(Context.NullPtrTy, Loc),
7349                              ParamType,
7350                              ParamType->getAs<MemberPointerType>()
7351                                ? CK_NullToMemberPointer
7352                                : CK_NullToPointer);
7353   }
7354   assert(Arg.getKind() == TemplateArgument::Declaration &&
7355          "Only declaration template arguments permitted here");
7356 
7357   ValueDecl *VD = Arg.getAsDecl();
7358 
7359   CXXScopeSpec SS;
7360   if (ParamType->isMemberPointerType()) {
7361     // If this is a pointer to member, we need to use a qualified name to
7362     // form a suitable pointer-to-member constant.
7363     assert(VD->getDeclContext()->isRecord() &&
7364            (isa<CXXMethodDecl>(VD) || isa<FieldDecl>(VD) ||
7365             isa<IndirectFieldDecl>(VD)));
7366     QualType ClassType
7367       = Context.getTypeDeclType(cast<RecordDecl>(VD->getDeclContext()));
7368     NestedNameSpecifier *Qualifier
7369       = NestedNameSpecifier::Create(Context, nullptr, false,
7370                                     ClassType.getTypePtr());
7371     SS.MakeTrivial(Context, Qualifier, Loc);
7372   }
7373 
7374   ExprResult RefExpr = BuildDeclarationNameExpr(
7375       SS, DeclarationNameInfo(VD->getDeclName(), Loc), VD);
7376   if (RefExpr.isInvalid())
7377     return ExprError();
7378 
7379   // For a pointer, the argument declaration is the pointee. Take its address.
7380   QualType ElemT(RefExpr.get()->getType()->getArrayElementTypeNoTypeQual(), 0);
7381   if (ParamType->isPointerType() && !ElemT.isNull() &&
7382       Context.hasSimilarType(ElemT, ParamType->getPointeeType())) {
7383     // Decay an array argument if we want a pointer to its first element.
7384     RefExpr = DefaultFunctionArrayConversion(RefExpr.get());
7385     if (RefExpr.isInvalid())
7386       return ExprError();
7387   } else if (ParamType->isPointerType() || ParamType->isMemberPointerType()) {
7388     // For any other pointer, take the address (or form a pointer-to-member).
7389     RefExpr = CreateBuiltinUnaryOp(Loc, UO_AddrOf, RefExpr.get());
7390     if (RefExpr.isInvalid())
7391       return ExprError();
7392   } else {
7393     assert(ParamType->isReferenceType() &&
7394            "unexpected type for decl template argument");
7395   }
7396 
7397   // At this point we should have the right value category.
7398   assert(ParamType->isReferenceType() == RefExpr.get()->isLValue() &&
7399          "value kind mismatch for non-type template argument");
7400 
7401   // The type of the template parameter can differ from the type of the
7402   // argument in various ways; convert it now if necessary.
7403   QualType DestExprType = ParamType.getNonLValueExprType(Context);
7404   if (!Context.hasSameType(RefExpr.get()->getType(), DestExprType)) {
7405     CastKind CK;
7406     QualType Ignored;
7407     if (Context.hasSimilarType(RefExpr.get()->getType(), DestExprType) ||
7408         IsFunctionConversion(RefExpr.get()->getType(), DestExprType, Ignored)) {
7409       CK = CK_NoOp;
7410     } else if (ParamType->isVoidPointerType() &&
7411                RefExpr.get()->getType()->isPointerType()) {
7412       CK = CK_BitCast;
7413     } else {
7414       // FIXME: Pointers to members can need conversion derived-to-base or
7415       // base-to-derived conversions. We currently don't retain enough
7416       // information to convert properly (we need to track a cast path or
7417       // subobject number in the template argument).
7418       llvm_unreachable(
7419           "unexpected conversion required for non-type template argument");
7420     }
7421     RefExpr = ImpCastExprToType(RefExpr.get(), DestExprType, CK,
7422                                 RefExpr.get()->getValueKind());
7423   }
7424 
7425   return RefExpr;
7426 }
7427 
7428 /// Construct a new expression that refers to the given
7429 /// integral template argument with the given source-location
7430 /// information.
7431 ///
7432 /// This routine takes care of the mapping from an integral template
7433 /// argument (which may have any integral type) to the appropriate
7434 /// literal value.
7435 ExprResult
7436 Sema::BuildExpressionFromIntegralTemplateArgument(const TemplateArgument &Arg,
7437                                                   SourceLocation Loc) {
7438   assert(Arg.getKind() == TemplateArgument::Integral &&
7439          "Operation is only valid for integral template arguments");
7440   QualType OrigT = Arg.getIntegralType();
7441 
7442   // If this is an enum type that we're instantiating, we need to use an integer
7443   // type the same size as the enumerator.  We don't want to build an
7444   // IntegerLiteral with enum type.  The integer type of an enum type can be of
7445   // any integral type with C++11 enum classes, make sure we create the right
7446   // type of literal for it.
7447   QualType T = OrigT;
7448   if (const EnumType *ET = OrigT->getAs<EnumType>())
7449     T = ET->getDecl()->getIntegerType();
7450 
7451   Expr *E;
7452   if (T->isAnyCharacterType()) {
7453     CharacterLiteral::CharacterKind Kind;
7454     if (T->isWideCharType())
7455       Kind = CharacterLiteral::Wide;
7456     else if (T->isChar8Type() && getLangOpts().Char8)
7457       Kind = CharacterLiteral::UTF8;
7458     else if (T->isChar16Type())
7459       Kind = CharacterLiteral::UTF16;
7460     else if (T->isChar32Type())
7461       Kind = CharacterLiteral::UTF32;
7462     else
7463       Kind = CharacterLiteral::Ascii;
7464 
7465     E = new (Context) CharacterLiteral(Arg.getAsIntegral().getZExtValue(),
7466                                        Kind, T, Loc);
7467   } else if (T->isBooleanType()) {
7468     E = new (Context) CXXBoolLiteralExpr(Arg.getAsIntegral().getBoolValue(),
7469                                          T, Loc);
7470   } else if (T->isNullPtrType()) {
7471     E = new (Context) CXXNullPtrLiteralExpr(Context.NullPtrTy, Loc);
7472   } else {
7473     E = IntegerLiteral::Create(Context, Arg.getAsIntegral(), T, Loc);
7474   }
7475 
7476   if (OrigT->isEnumeralType()) {
7477     // FIXME: This is a hack. We need a better way to handle substituted
7478     // non-type template parameters.
7479     E = CStyleCastExpr::Create(Context, OrigT, VK_RValue, CK_IntegralCast, E,
7480                                nullptr,
7481                                Context.getTrivialTypeSourceInfo(OrigT, Loc),
7482                                Loc, Loc);
7483   }
7484 
7485   return E;
7486 }
7487 
7488 /// Match two template parameters within template parameter lists.
7489 static bool MatchTemplateParameterKind(Sema &S, NamedDecl *New, NamedDecl *Old,
7490                                        bool Complain,
7491                                      Sema::TemplateParameterListEqualKind Kind,
7492                                        SourceLocation TemplateArgLoc) {
7493   // Check the actual kind (type, non-type, template).
7494   if (Old->getKind() != New->getKind()) {
7495     if (Complain) {
7496       unsigned NextDiag = diag::err_template_param_different_kind;
7497       if (TemplateArgLoc.isValid()) {
7498         S.Diag(TemplateArgLoc, diag::err_template_arg_template_params_mismatch);
7499         NextDiag = diag::note_template_param_different_kind;
7500       }
7501       S.Diag(New->getLocation(), NextDiag)
7502         << (Kind != Sema::TPL_TemplateMatch);
7503       S.Diag(Old->getLocation(), diag::note_template_prev_declaration)
7504         << (Kind != Sema::TPL_TemplateMatch);
7505     }
7506 
7507     return false;
7508   }
7509 
7510   // Check that both are parameter packs or neither are parameter packs.
7511   // However, if we are matching a template template argument to a
7512   // template template parameter, the template template parameter can have
7513   // a parameter pack where the template template argument does not.
7514   if (Old->isTemplateParameterPack() != New->isTemplateParameterPack() &&
7515       !(Kind == Sema::TPL_TemplateTemplateArgumentMatch &&
7516         Old->isTemplateParameterPack())) {
7517     if (Complain) {
7518       unsigned NextDiag = diag::err_template_parameter_pack_non_pack;
7519       if (TemplateArgLoc.isValid()) {
7520         S.Diag(TemplateArgLoc,
7521              diag::err_template_arg_template_params_mismatch);
7522         NextDiag = diag::note_template_parameter_pack_non_pack;
7523       }
7524 
7525       unsigned ParamKind = isa<TemplateTypeParmDecl>(New)? 0
7526                       : isa<NonTypeTemplateParmDecl>(New)? 1
7527                       : 2;
7528       S.Diag(New->getLocation(), NextDiag)
7529         << ParamKind << New->isParameterPack();
7530       S.Diag(Old->getLocation(), diag::note_template_parameter_pack_here)
7531         << ParamKind << Old->isParameterPack();
7532     }
7533 
7534     return false;
7535   }
7536 
7537   // For non-type template parameters, check the type of the parameter.
7538   if (NonTypeTemplateParmDecl *OldNTTP
7539                                     = dyn_cast<NonTypeTemplateParmDecl>(Old)) {
7540     NonTypeTemplateParmDecl *NewNTTP = cast<NonTypeTemplateParmDecl>(New);
7541 
7542     // If we are matching a template template argument to a template
7543     // template parameter and one of the non-type template parameter types
7544     // is dependent, then we must wait until template instantiation time
7545     // to actually compare the arguments.
7546     if (Kind != Sema::TPL_TemplateTemplateArgumentMatch ||
7547         (!OldNTTP->getType()->isDependentType() &&
7548          !NewNTTP->getType()->isDependentType()))
7549       if (!S.Context.hasSameType(OldNTTP->getType(), NewNTTP->getType())) {
7550         if (Complain) {
7551           unsigned NextDiag = diag::err_template_nontype_parm_different_type;
7552           if (TemplateArgLoc.isValid()) {
7553             S.Diag(TemplateArgLoc,
7554                    diag::err_template_arg_template_params_mismatch);
7555             NextDiag = diag::note_template_nontype_parm_different_type;
7556           }
7557           S.Diag(NewNTTP->getLocation(), NextDiag)
7558             << NewNTTP->getType()
7559             << (Kind != Sema::TPL_TemplateMatch);
7560           S.Diag(OldNTTP->getLocation(),
7561                  diag::note_template_nontype_parm_prev_declaration)
7562             << OldNTTP->getType();
7563         }
7564 
7565         return false;
7566       }
7567   }
7568   // For template template parameters, check the template parameter types.
7569   // The template parameter lists of template template
7570   // parameters must agree.
7571   else if (TemplateTemplateParmDecl *OldTTP
7572                                     = dyn_cast<TemplateTemplateParmDecl>(Old)) {
7573     TemplateTemplateParmDecl *NewTTP = cast<TemplateTemplateParmDecl>(New);
7574     if (!S.TemplateParameterListsAreEqual(NewTTP->getTemplateParameters(),
7575                                           OldTTP->getTemplateParameters(),
7576                                           Complain,
7577                                         (Kind == Sema::TPL_TemplateMatch
7578                                            ? Sema::TPL_TemplateTemplateParmMatch
7579                                            : Kind),
7580                                           TemplateArgLoc))
7581       return false;
7582   } else if (Kind != Sema::TPL_TemplateTemplateArgumentMatch) {
7583     const Expr *NewC = nullptr, *OldC = nullptr;
7584     if (const auto *TC = cast<TemplateTypeParmDecl>(New)->getTypeConstraint())
7585       NewC = TC->getImmediatelyDeclaredConstraint();
7586     if (const auto *TC = cast<TemplateTypeParmDecl>(Old)->getTypeConstraint())
7587       OldC = TC->getImmediatelyDeclaredConstraint();
7588 
7589     auto Diagnose = [&] {
7590       S.Diag(NewC ? NewC->getBeginLoc() : New->getBeginLoc(),
7591            diag::err_template_different_type_constraint);
7592       S.Diag(OldC ? OldC->getBeginLoc() : Old->getBeginLoc(),
7593            diag::note_template_prev_declaration) << /*declaration*/0;
7594     };
7595 
7596     if (!NewC != !OldC) {
7597       if (Complain)
7598         Diagnose();
7599       return false;
7600     }
7601 
7602     if (NewC) {
7603       llvm::FoldingSetNodeID OldCID, NewCID;
7604       OldC->Profile(OldCID, S.Context, /*Canonical=*/true);
7605       NewC->Profile(NewCID, S.Context, /*Canonical=*/true);
7606       if (OldCID != NewCID) {
7607         if (Complain)
7608           Diagnose();
7609         return false;
7610       }
7611     }
7612   }
7613 
7614   return true;
7615 }
7616 
7617 /// Diagnose a known arity mismatch when comparing template argument
7618 /// lists.
7619 static
7620 void DiagnoseTemplateParameterListArityMismatch(Sema &S,
7621                                                 TemplateParameterList *New,
7622                                                 TemplateParameterList *Old,
7623                                       Sema::TemplateParameterListEqualKind Kind,
7624                                                 SourceLocation TemplateArgLoc) {
7625   unsigned NextDiag = diag::err_template_param_list_different_arity;
7626   if (TemplateArgLoc.isValid()) {
7627     S.Diag(TemplateArgLoc, diag::err_template_arg_template_params_mismatch);
7628     NextDiag = diag::note_template_param_list_different_arity;
7629   }
7630   S.Diag(New->getTemplateLoc(), NextDiag)
7631     << (New->size() > Old->size())
7632     << (Kind != Sema::TPL_TemplateMatch)
7633     << SourceRange(New->getTemplateLoc(), New->getRAngleLoc());
7634   S.Diag(Old->getTemplateLoc(), diag::note_template_prev_declaration)
7635     << (Kind != Sema::TPL_TemplateMatch)
7636     << SourceRange(Old->getTemplateLoc(), Old->getRAngleLoc());
7637 }
7638 
7639 /// Determine whether the given template parameter lists are
7640 /// equivalent.
7641 ///
7642 /// \param New  The new template parameter list, typically written in the
7643 /// source code as part of a new template declaration.
7644 ///
7645 /// \param Old  The old template parameter list, typically found via
7646 /// name lookup of the template declared with this template parameter
7647 /// list.
7648 ///
7649 /// \param Complain  If true, this routine will produce a diagnostic if
7650 /// the template parameter lists are not equivalent.
7651 ///
7652 /// \param Kind describes how we are to match the template parameter lists.
7653 ///
7654 /// \param TemplateArgLoc If this source location is valid, then we
7655 /// are actually checking the template parameter list of a template
7656 /// argument (New) against the template parameter list of its
7657 /// corresponding template template parameter (Old). We produce
7658 /// slightly different diagnostics in this scenario.
7659 ///
7660 /// \returns True if the template parameter lists are equal, false
7661 /// otherwise.
7662 bool
7663 Sema::TemplateParameterListsAreEqual(TemplateParameterList *New,
7664                                      TemplateParameterList *Old,
7665                                      bool Complain,
7666                                      TemplateParameterListEqualKind Kind,
7667                                      SourceLocation TemplateArgLoc) {
7668   if (Old->size() != New->size() && Kind != TPL_TemplateTemplateArgumentMatch) {
7669     if (Complain)
7670       DiagnoseTemplateParameterListArityMismatch(*this, New, Old, Kind,
7671                                                  TemplateArgLoc);
7672 
7673     return false;
7674   }
7675 
7676   // C++0x [temp.arg.template]p3:
7677   //   A template-argument matches a template template-parameter (call it P)
7678   //   when each of the template parameters in the template-parameter-list of
7679   //   the template-argument's corresponding class template or alias template
7680   //   (call it A) matches the corresponding template parameter in the
7681   //   template-parameter-list of P. [...]
7682   TemplateParameterList::iterator NewParm = New->begin();
7683   TemplateParameterList::iterator NewParmEnd = New->end();
7684   for (TemplateParameterList::iterator OldParm = Old->begin(),
7685                                     OldParmEnd = Old->end();
7686        OldParm != OldParmEnd; ++OldParm) {
7687     if (Kind != TPL_TemplateTemplateArgumentMatch ||
7688         !(*OldParm)->isTemplateParameterPack()) {
7689       if (NewParm == NewParmEnd) {
7690         if (Complain)
7691           DiagnoseTemplateParameterListArityMismatch(*this, New, Old, Kind,
7692                                                      TemplateArgLoc);
7693 
7694         return false;
7695       }
7696 
7697       if (!MatchTemplateParameterKind(*this, *NewParm, *OldParm, Complain,
7698                                       Kind, TemplateArgLoc))
7699         return false;
7700 
7701       ++NewParm;
7702       continue;
7703     }
7704 
7705     // C++0x [temp.arg.template]p3:
7706     //   [...] When P's template- parameter-list contains a template parameter
7707     //   pack (14.5.3), the template parameter pack will match zero or more
7708     //   template parameters or template parameter packs in the
7709     //   template-parameter-list of A with the same type and form as the
7710     //   template parameter pack in P (ignoring whether those template
7711     //   parameters are template parameter packs).
7712     for (; NewParm != NewParmEnd; ++NewParm) {
7713       if (!MatchTemplateParameterKind(*this, *NewParm, *OldParm, Complain,
7714                                       Kind, TemplateArgLoc))
7715         return false;
7716     }
7717   }
7718 
7719   // Make sure we exhausted all of the arguments.
7720   if (NewParm != NewParmEnd) {
7721     if (Complain)
7722       DiagnoseTemplateParameterListArityMismatch(*this, New, Old, Kind,
7723                                                  TemplateArgLoc);
7724 
7725     return false;
7726   }
7727 
7728   if (Kind != TPL_TemplateTemplateArgumentMatch) {
7729     const Expr *NewRC = New->getRequiresClause();
7730     const Expr *OldRC = Old->getRequiresClause();
7731 
7732     auto Diagnose = [&] {
7733       Diag(NewRC ? NewRC->getBeginLoc() : New->getTemplateLoc(),
7734            diag::err_template_different_requires_clause);
7735       Diag(OldRC ? OldRC->getBeginLoc() : Old->getTemplateLoc(),
7736            diag::note_template_prev_declaration) << /*declaration*/0;
7737     };
7738 
7739     if (!NewRC != !OldRC) {
7740       if (Complain)
7741         Diagnose();
7742       return false;
7743     }
7744 
7745     if (NewRC) {
7746       llvm::FoldingSetNodeID OldRCID, NewRCID;
7747       OldRC->Profile(OldRCID, Context, /*Canonical=*/true);
7748       NewRC->Profile(NewRCID, Context, /*Canonical=*/true);
7749       if (OldRCID != NewRCID) {
7750         if (Complain)
7751           Diagnose();
7752         return false;
7753       }
7754     }
7755   }
7756 
7757   return true;
7758 }
7759 
7760 /// Check whether a template can be declared within this scope.
7761 ///
7762 /// If the template declaration is valid in this scope, returns
7763 /// false. Otherwise, issues a diagnostic and returns true.
7764 bool
7765 Sema::CheckTemplateDeclScope(Scope *S, TemplateParameterList *TemplateParams) {
7766   if (!S)
7767     return false;
7768 
7769   // Find the nearest enclosing declaration scope.
7770   while ((S->getFlags() & Scope::DeclScope) == 0 ||
7771          (S->getFlags() & Scope::TemplateParamScope) != 0)
7772     S = S->getParent();
7773 
7774   // C++ [temp]p4:
7775   //   A template [...] shall not have C linkage.
7776   DeclContext *Ctx = S->getEntity();
7777   assert(Ctx && "Unknown context");
7778   if (Ctx->isExternCContext()) {
7779     Diag(TemplateParams->getTemplateLoc(), diag::err_template_linkage)
7780         << TemplateParams->getSourceRange();
7781     if (const LinkageSpecDecl *LSD = Ctx->getExternCContext())
7782       Diag(LSD->getExternLoc(), diag::note_extern_c_begins_here);
7783     return true;
7784   }
7785   Ctx = Ctx->getRedeclContext();
7786 
7787   // C++ [temp]p2:
7788   //   A template-declaration can appear only as a namespace scope or
7789   //   class scope declaration.
7790   if (Ctx) {
7791     if (Ctx->isFileContext())
7792       return false;
7793     if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Ctx)) {
7794       // C++ [temp.mem]p2:
7795       //   A local class shall not have member templates.
7796       if (RD->isLocalClass())
7797         return Diag(TemplateParams->getTemplateLoc(),
7798                     diag::err_template_inside_local_class)
7799           << TemplateParams->getSourceRange();
7800       else
7801         return false;
7802     }
7803   }
7804 
7805   return Diag(TemplateParams->getTemplateLoc(),
7806               diag::err_template_outside_namespace_or_class_scope)
7807     << TemplateParams->getSourceRange();
7808 }
7809 
7810 /// Determine what kind of template specialization the given declaration
7811 /// is.
7812 static TemplateSpecializationKind getTemplateSpecializationKind(Decl *D) {
7813   if (!D)
7814     return TSK_Undeclared;
7815 
7816   if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D))
7817     return Record->getTemplateSpecializationKind();
7818   if (FunctionDecl *Function = dyn_cast<FunctionDecl>(D))
7819     return Function->getTemplateSpecializationKind();
7820   if (VarDecl *Var = dyn_cast<VarDecl>(D))
7821     return Var->getTemplateSpecializationKind();
7822 
7823   return TSK_Undeclared;
7824 }
7825 
7826 /// Check whether a specialization is well-formed in the current
7827 /// context.
7828 ///
7829 /// This routine determines whether a template specialization can be declared
7830 /// in the current context (C++ [temp.expl.spec]p2).
7831 ///
7832 /// \param S the semantic analysis object for which this check is being
7833 /// performed.
7834 ///
7835 /// \param Specialized the entity being specialized or instantiated, which
7836 /// may be a kind of template (class template, function template, etc.) or
7837 /// a member of a class template (member function, static data member,
7838 /// member class).
7839 ///
7840 /// \param PrevDecl the previous declaration of this entity, if any.
7841 ///
7842 /// \param Loc the location of the explicit specialization or instantiation of
7843 /// this entity.
7844 ///
7845 /// \param IsPartialSpecialization whether this is a partial specialization of
7846 /// a class template.
7847 ///
7848 /// \returns true if there was an error that we cannot recover from, false
7849 /// otherwise.
7850 static bool CheckTemplateSpecializationScope(Sema &S,
7851                                              NamedDecl *Specialized,
7852                                              NamedDecl *PrevDecl,
7853                                              SourceLocation Loc,
7854                                              bool IsPartialSpecialization) {
7855   // Keep these "kind" numbers in sync with the %select statements in the
7856   // various diagnostics emitted by this routine.
7857   int EntityKind = 0;
7858   if (isa<ClassTemplateDecl>(Specialized))
7859     EntityKind = IsPartialSpecialization? 1 : 0;
7860   else if (isa<VarTemplateDecl>(Specialized))
7861     EntityKind = IsPartialSpecialization ? 3 : 2;
7862   else if (isa<FunctionTemplateDecl>(Specialized))
7863     EntityKind = 4;
7864   else if (isa<CXXMethodDecl>(Specialized))
7865     EntityKind = 5;
7866   else if (isa<VarDecl>(Specialized))
7867     EntityKind = 6;
7868   else if (isa<RecordDecl>(Specialized))
7869     EntityKind = 7;
7870   else if (isa<EnumDecl>(Specialized) && S.getLangOpts().CPlusPlus11)
7871     EntityKind = 8;
7872   else {
7873     S.Diag(Loc, diag::err_template_spec_unknown_kind)
7874       << S.getLangOpts().CPlusPlus11;
7875     S.Diag(Specialized->getLocation(), diag::note_specialized_entity);
7876     return true;
7877   }
7878 
7879   // C++ [temp.expl.spec]p2:
7880   //   An explicit specialization may be declared in any scope in which
7881   //   the corresponding primary template may be defined.
7882   if (S.CurContext->getRedeclContext()->isFunctionOrMethod()) {
7883     S.Diag(Loc, diag::err_template_spec_decl_function_scope)
7884       << Specialized;
7885     return true;
7886   }
7887 
7888   // C++ [temp.class.spec]p6:
7889   //   A class template partial specialization may be declared in any
7890   //   scope in which the primary template may be defined.
7891   DeclContext *SpecializedContext =
7892       Specialized->getDeclContext()->getRedeclContext();
7893   DeclContext *DC = S.CurContext->getRedeclContext();
7894 
7895   // Make sure that this redeclaration (or definition) occurs in the same
7896   // scope or an enclosing namespace.
7897   if (!(DC->isFileContext() ? DC->Encloses(SpecializedContext)
7898                             : DC->Equals(SpecializedContext))) {
7899     if (isa<TranslationUnitDecl>(SpecializedContext))
7900       S.Diag(Loc, diag::err_template_spec_redecl_global_scope)
7901         << EntityKind << Specialized;
7902     else {
7903       auto *ND = cast<NamedDecl>(SpecializedContext);
7904       int Diag = diag::err_template_spec_redecl_out_of_scope;
7905       if (S.getLangOpts().MicrosoftExt && !DC->isRecord())
7906         Diag = diag::ext_ms_template_spec_redecl_out_of_scope;
7907       S.Diag(Loc, Diag) << EntityKind << Specialized
7908                         << ND << isa<CXXRecordDecl>(ND);
7909     }
7910 
7911     S.Diag(Specialized->getLocation(), diag::note_specialized_entity);
7912 
7913     // Don't allow specializing in the wrong class during error recovery.
7914     // Otherwise, things can go horribly wrong.
7915     if (DC->isRecord())
7916       return true;
7917   }
7918 
7919   return false;
7920 }
7921 
7922 static SourceRange findTemplateParameterInType(unsigned Depth, Expr *E) {
7923   if (!E->isTypeDependent())
7924     return SourceLocation();
7925   DependencyChecker Checker(Depth, /*IgnoreNonTypeDependent*/true);
7926   Checker.TraverseStmt(E);
7927   if (Checker.MatchLoc.isInvalid())
7928     return E->getSourceRange();
7929   return Checker.MatchLoc;
7930 }
7931 
7932 static SourceRange findTemplateParameter(unsigned Depth, TypeLoc TL) {
7933   if (!TL.getType()->isDependentType())
7934     return SourceLocation();
7935   DependencyChecker Checker(Depth, /*IgnoreNonTypeDependent*/true);
7936   Checker.TraverseTypeLoc(TL);
7937   if (Checker.MatchLoc.isInvalid())
7938     return TL.getSourceRange();
7939   return Checker.MatchLoc;
7940 }
7941 
7942 /// Subroutine of Sema::CheckTemplatePartialSpecializationArgs
7943 /// that checks non-type template partial specialization arguments.
7944 static bool CheckNonTypeTemplatePartialSpecializationArgs(
7945     Sema &S, SourceLocation TemplateNameLoc, NonTypeTemplateParmDecl *Param,
7946     const TemplateArgument *Args, unsigned NumArgs, bool IsDefaultArgument) {
7947   for (unsigned I = 0; I != NumArgs; ++I) {
7948     if (Args[I].getKind() == TemplateArgument::Pack) {
7949       if (CheckNonTypeTemplatePartialSpecializationArgs(
7950               S, TemplateNameLoc, Param, Args[I].pack_begin(),
7951               Args[I].pack_size(), IsDefaultArgument))
7952         return true;
7953 
7954       continue;
7955     }
7956 
7957     if (Args[I].getKind() != TemplateArgument::Expression)
7958       continue;
7959 
7960     Expr *ArgExpr = Args[I].getAsExpr();
7961 
7962     // We can have a pack expansion of any of the bullets below.
7963     if (PackExpansionExpr *Expansion = dyn_cast<PackExpansionExpr>(ArgExpr))
7964       ArgExpr = Expansion->getPattern();
7965 
7966     // Strip off any implicit casts we added as part of type checking.
7967     while (ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(ArgExpr))
7968       ArgExpr = ICE->getSubExpr();
7969 
7970     // C++ [temp.class.spec]p8:
7971     //   A non-type argument is non-specialized if it is the name of a
7972     //   non-type parameter. All other non-type arguments are
7973     //   specialized.
7974     //
7975     // Below, we check the two conditions that only apply to
7976     // specialized non-type arguments, so skip any non-specialized
7977     // arguments.
7978     if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(ArgExpr))
7979       if (isa<NonTypeTemplateParmDecl>(DRE->getDecl()))
7980         continue;
7981 
7982     // C++ [temp.class.spec]p9:
7983     //   Within the argument list of a class template partial
7984     //   specialization, the following restrictions apply:
7985     //     -- A partially specialized non-type argument expression
7986     //        shall not involve a template parameter of the partial
7987     //        specialization except when the argument expression is a
7988     //        simple identifier.
7989     //     -- The type of a template parameter corresponding to a
7990     //        specialized non-type argument shall not be dependent on a
7991     //        parameter of the specialization.
7992     // DR1315 removes the first bullet, leaving an incoherent set of rules.
7993     // We implement a compromise between the original rules and DR1315:
7994     //     --  A specialized non-type template argument shall not be
7995     //         type-dependent and the corresponding template parameter
7996     //         shall have a non-dependent type.
7997     SourceRange ParamUseRange =
7998         findTemplateParameterInType(Param->getDepth(), ArgExpr);
7999     if (ParamUseRange.isValid()) {
8000       if (IsDefaultArgument) {
8001         S.Diag(TemplateNameLoc,
8002                diag::err_dependent_non_type_arg_in_partial_spec);
8003         S.Diag(ParamUseRange.getBegin(),
8004                diag::note_dependent_non_type_default_arg_in_partial_spec)
8005           << ParamUseRange;
8006       } else {
8007         S.Diag(ParamUseRange.getBegin(),
8008                diag::err_dependent_non_type_arg_in_partial_spec)
8009           << ParamUseRange;
8010       }
8011       return true;
8012     }
8013 
8014     ParamUseRange = findTemplateParameter(
8015         Param->getDepth(), Param->getTypeSourceInfo()->getTypeLoc());
8016     if (ParamUseRange.isValid()) {
8017       S.Diag(IsDefaultArgument ? TemplateNameLoc : ArgExpr->getBeginLoc(),
8018              diag::err_dependent_typed_non_type_arg_in_partial_spec)
8019           << Param->getType();
8020       S.Diag(Param->getLocation(), diag::note_template_param_here)
8021         << (IsDefaultArgument ? ParamUseRange : SourceRange())
8022         << ParamUseRange;
8023       return true;
8024     }
8025   }
8026 
8027   return false;
8028 }
8029 
8030 /// Check the non-type template arguments of a class template
8031 /// partial specialization according to C++ [temp.class.spec]p9.
8032 ///
8033 /// \param TemplateNameLoc the location of the template name.
8034 /// \param PrimaryTemplate the template parameters of the primary class
8035 ///        template.
8036 /// \param NumExplicit the number of explicitly-specified template arguments.
8037 /// \param TemplateArgs the template arguments of the class template
8038 ///        partial specialization.
8039 ///
8040 /// \returns \c true if there was an error, \c false otherwise.
8041 bool Sema::CheckTemplatePartialSpecializationArgs(
8042     SourceLocation TemplateNameLoc, TemplateDecl *PrimaryTemplate,
8043     unsigned NumExplicit, ArrayRef<TemplateArgument> TemplateArgs) {
8044   // We have to be conservative when checking a template in a dependent
8045   // context.
8046   if (PrimaryTemplate->getDeclContext()->isDependentContext())
8047     return false;
8048 
8049   TemplateParameterList *TemplateParams =
8050       PrimaryTemplate->getTemplateParameters();
8051   for (unsigned I = 0, N = TemplateParams->size(); I != N; ++I) {
8052     NonTypeTemplateParmDecl *Param
8053       = dyn_cast<NonTypeTemplateParmDecl>(TemplateParams->getParam(I));
8054     if (!Param)
8055       continue;
8056 
8057     if (CheckNonTypeTemplatePartialSpecializationArgs(*this, TemplateNameLoc,
8058                                                       Param, &TemplateArgs[I],
8059                                                       1, I >= NumExplicit))
8060       return true;
8061   }
8062 
8063   return false;
8064 }
8065 
8066 DeclResult Sema::ActOnClassTemplateSpecialization(
8067     Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
8068     SourceLocation ModulePrivateLoc, CXXScopeSpec &SS,
8069     TemplateIdAnnotation &TemplateId, const ParsedAttributesView &Attr,
8070     MultiTemplateParamsArg TemplateParameterLists, SkipBodyInfo *SkipBody) {
8071   assert(TUK != TUK_Reference && "References are not specializations");
8072 
8073   // NOTE: KWLoc is the location of the tag keyword. This will instead
8074   // store the location of the outermost template keyword in the declaration.
8075   SourceLocation TemplateKWLoc = TemplateParameterLists.size() > 0
8076     ? TemplateParameterLists[0]->getTemplateLoc() : KWLoc;
8077   SourceLocation TemplateNameLoc = TemplateId.TemplateNameLoc;
8078   SourceLocation LAngleLoc = TemplateId.LAngleLoc;
8079   SourceLocation RAngleLoc = TemplateId.RAngleLoc;
8080 
8081   // Find the class template we're specializing
8082   TemplateName Name = TemplateId.Template.get();
8083   ClassTemplateDecl *ClassTemplate
8084     = dyn_cast_or_null<ClassTemplateDecl>(Name.getAsTemplateDecl());
8085 
8086   if (!ClassTemplate) {
8087     Diag(TemplateNameLoc, diag::err_not_class_template_specialization)
8088       << (Name.getAsTemplateDecl() &&
8089           isa<TemplateTemplateParmDecl>(Name.getAsTemplateDecl()));
8090     return true;
8091   }
8092 
8093   bool isMemberSpecialization = false;
8094   bool isPartialSpecialization = false;
8095 
8096   // Check the validity of the template headers that introduce this
8097   // template.
8098   // FIXME: We probably shouldn't complain about these headers for
8099   // friend declarations.
8100   bool Invalid = false;
8101   TemplateParameterList *TemplateParams =
8102       MatchTemplateParametersToScopeSpecifier(
8103           KWLoc, TemplateNameLoc, SS, &TemplateId,
8104           TemplateParameterLists, TUK == TUK_Friend, isMemberSpecialization,
8105           Invalid);
8106   if (Invalid)
8107     return true;
8108 
8109   if (TemplateParams && TemplateParams->size() > 0) {
8110     isPartialSpecialization = true;
8111 
8112     if (TUK == TUK_Friend) {
8113       Diag(KWLoc, diag::err_partial_specialization_friend)
8114         << SourceRange(LAngleLoc, RAngleLoc);
8115       return true;
8116     }
8117 
8118     // C++ [temp.class.spec]p10:
8119     //   The template parameter list of a specialization shall not
8120     //   contain default template argument values.
8121     for (unsigned I = 0, N = TemplateParams->size(); I != N; ++I) {
8122       Decl *Param = TemplateParams->getParam(I);
8123       if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(Param)) {
8124         if (TTP->hasDefaultArgument()) {
8125           Diag(TTP->getDefaultArgumentLoc(),
8126                diag::err_default_arg_in_partial_spec);
8127           TTP->removeDefaultArgument();
8128         }
8129       } else if (NonTypeTemplateParmDecl *NTTP
8130                    = dyn_cast<NonTypeTemplateParmDecl>(Param)) {
8131         if (Expr *DefArg = NTTP->getDefaultArgument()) {
8132           Diag(NTTP->getDefaultArgumentLoc(),
8133                diag::err_default_arg_in_partial_spec)
8134             << DefArg->getSourceRange();
8135           NTTP->removeDefaultArgument();
8136         }
8137       } else {
8138         TemplateTemplateParmDecl *TTP = cast<TemplateTemplateParmDecl>(Param);
8139         if (TTP->hasDefaultArgument()) {
8140           Diag(TTP->getDefaultArgument().getLocation(),
8141                diag::err_default_arg_in_partial_spec)
8142             << TTP->getDefaultArgument().getSourceRange();
8143           TTP->removeDefaultArgument();
8144         }
8145       }
8146     }
8147   } else if (TemplateParams) {
8148     if (TUK == TUK_Friend)
8149       Diag(KWLoc, diag::err_template_spec_friend)
8150         << FixItHint::CreateRemoval(
8151                                 SourceRange(TemplateParams->getTemplateLoc(),
8152                                             TemplateParams->getRAngleLoc()))
8153         << SourceRange(LAngleLoc, RAngleLoc);
8154   } else {
8155     assert(TUK == TUK_Friend && "should have a 'template<>' for this decl");
8156   }
8157 
8158   // Check that the specialization uses the same tag kind as the
8159   // original template.
8160   TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForTypeSpec(TagSpec);
8161   assert(Kind != TTK_Enum && "Invalid enum tag in class template spec!");
8162   if (!isAcceptableTagRedeclaration(ClassTemplate->getTemplatedDecl(),
8163                                     Kind, TUK == TUK_Definition, KWLoc,
8164                                     ClassTemplate->getIdentifier())) {
8165     Diag(KWLoc, diag::err_use_with_wrong_tag)
8166       << ClassTemplate
8167       << FixItHint::CreateReplacement(KWLoc,
8168                             ClassTemplate->getTemplatedDecl()->getKindName());
8169     Diag(ClassTemplate->getTemplatedDecl()->getLocation(),
8170          diag::note_previous_use);
8171     Kind = ClassTemplate->getTemplatedDecl()->getTagKind();
8172   }
8173 
8174   // Translate the parser's template argument list in our AST format.
8175   TemplateArgumentListInfo TemplateArgs =
8176       makeTemplateArgumentListInfo(*this, TemplateId);
8177 
8178   // Check for unexpanded parameter packs in any of the template arguments.
8179   for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
8180     if (DiagnoseUnexpandedParameterPack(TemplateArgs[I],
8181                                         UPPC_PartialSpecialization))
8182       return true;
8183 
8184   // Check that the template argument list is well-formed for this
8185   // template.
8186   SmallVector<TemplateArgument, 4> Converted;
8187   if (CheckTemplateArgumentList(ClassTemplate, TemplateNameLoc,
8188                                 TemplateArgs, false, Converted,
8189                                 /*UpdateArgsWithConversion=*/true))
8190     return true;
8191 
8192   // Find the class template (partial) specialization declaration that
8193   // corresponds to these arguments.
8194   if (isPartialSpecialization) {
8195     if (CheckTemplatePartialSpecializationArgs(TemplateNameLoc, ClassTemplate,
8196                                                TemplateArgs.size(), Converted))
8197       return true;
8198 
8199     // FIXME: Move this to CheckTemplatePartialSpecializationArgs so we
8200     // also do it during instantiation.
8201     bool InstantiationDependent;
8202     if (!Name.isDependent() &&
8203         !TemplateSpecializationType::anyDependentTemplateArguments(
8204             TemplateArgs.arguments(), InstantiationDependent)) {
8205       Diag(TemplateNameLoc, diag::err_partial_spec_fully_specialized)
8206         << ClassTemplate->getDeclName();
8207       isPartialSpecialization = false;
8208     }
8209   }
8210 
8211   void *InsertPos = nullptr;
8212   ClassTemplateSpecializationDecl *PrevDecl = nullptr;
8213 
8214   if (isPartialSpecialization)
8215     PrevDecl = ClassTemplate->findPartialSpecialization(Converted,
8216                                                         TemplateParams,
8217                                                         InsertPos);
8218   else
8219     PrevDecl = ClassTemplate->findSpecialization(Converted, InsertPos);
8220 
8221   ClassTemplateSpecializationDecl *Specialization = nullptr;
8222 
8223   // Check whether we can declare a class template specialization in
8224   // the current scope.
8225   if (TUK != TUK_Friend &&
8226       CheckTemplateSpecializationScope(*this, ClassTemplate, PrevDecl,
8227                                        TemplateNameLoc,
8228                                        isPartialSpecialization))
8229     return true;
8230 
8231   // The canonical type
8232   QualType CanonType;
8233   if (isPartialSpecialization) {
8234     // Build the canonical type that describes the converted template
8235     // arguments of the class template partial specialization.
8236     TemplateName CanonTemplate = Context.getCanonicalTemplateName(Name);
8237     CanonType = Context.getTemplateSpecializationType(CanonTemplate,
8238                                                       Converted);
8239 
8240     if (Context.hasSameType(CanonType,
8241                         ClassTemplate->getInjectedClassNameSpecialization()) &&
8242         (!Context.getLangOpts().CPlusPlus20 ||
8243          !TemplateParams->hasAssociatedConstraints())) {
8244       // C++ [temp.class.spec]p9b3:
8245       //
8246       //   -- The argument list of the specialization shall not be identical
8247       //      to the implicit argument list of the primary template.
8248       //
8249       // This rule has since been removed, because it's redundant given DR1495,
8250       // but we keep it because it produces better diagnostics and recovery.
8251       Diag(TemplateNameLoc, diag::err_partial_spec_args_match_primary_template)
8252         << /*class template*/0 << (TUK == TUK_Definition)
8253         << FixItHint::CreateRemoval(SourceRange(LAngleLoc, RAngleLoc));
8254       return CheckClassTemplate(S, TagSpec, TUK, KWLoc, SS,
8255                                 ClassTemplate->getIdentifier(),
8256                                 TemplateNameLoc,
8257                                 Attr,
8258                                 TemplateParams,
8259                                 AS_none, /*ModulePrivateLoc=*/SourceLocation(),
8260                                 /*FriendLoc*/SourceLocation(),
8261                                 TemplateParameterLists.size() - 1,
8262                                 TemplateParameterLists.data());
8263     }
8264 
8265     // Create a new class template partial specialization declaration node.
8266     ClassTemplatePartialSpecializationDecl *PrevPartial
8267       = cast_or_null<ClassTemplatePartialSpecializationDecl>(PrevDecl);
8268     ClassTemplatePartialSpecializationDecl *Partial
8269       = ClassTemplatePartialSpecializationDecl::Create(Context, Kind,
8270                                              ClassTemplate->getDeclContext(),
8271                                                        KWLoc, TemplateNameLoc,
8272                                                        TemplateParams,
8273                                                        ClassTemplate,
8274                                                        Converted,
8275                                                        TemplateArgs,
8276                                                        CanonType,
8277                                                        PrevPartial);
8278     SetNestedNameSpecifier(*this, Partial, SS);
8279     if (TemplateParameterLists.size() > 1 && SS.isSet()) {
8280       Partial->setTemplateParameterListsInfo(
8281           Context, TemplateParameterLists.drop_back(1));
8282     }
8283 
8284     if (!PrevPartial)
8285       ClassTemplate->AddPartialSpecialization(Partial, InsertPos);
8286     Specialization = Partial;
8287 
8288     // If we are providing an explicit specialization of a member class
8289     // template specialization, make a note of that.
8290     if (PrevPartial && PrevPartial->getInstantiatedFromMember())
8291       PrevPartial->setMemberSpecialization();
8292 
8293     CheckTemplatePartialSpecialization(Partial);
8294   } else {
8295     // Create a new class template specialization declaration node for
8296     // this explicit specialization or friend declaration.
8297     Specialization
8298       = ClassTemplateSpecializationDecl::Create(Context, Kind,
8299                                              ClassTemplate->getDeclContext(),
8300                                                 KWLoc, TemplateNameLoc,
8301                                                 ClassTemplate,
8302                                                 Converted,
8303                                                 PrevDecl);
8304     SetNestedNameSpecifier(*this, Specialization, SS);
8305     if (TemplateParameterLists.size() > 0) {
8306       Specialization->setTemplateParameterListsInfo(Context,
8307                                                     TemplateParameterLists);
8308     }
8309 
8310     if (!PrevDecl)
8311       ClassTemplate->AddSpecialization(Specialization, InsertPos);
8312 
8313     if (CurContext->isDependentContext()) {
8314       TemplateName CanonTemplate = Context.getCanonicalTemplateName(Name);
8315       CanonType = Context.getTemplateSpecializationType(
8316           CanonTemplate, Converted);
8317     } else {
8318       CanonType = Context.getTypeDeclType(Specialization);
8319     }
8320   }
8321 
8322   // C++ [temp.expl.spec]p6:
8323   //   If a template, a member template or the member of a class template is
8324   //   explicitly specialized then that specialization shall be declared
8325   //   before the first use of that specialization that would cause an implicit
8326   //   instantiation to take place, in every translation unit in which such a
8327   //   use occurs; no diagnostic is required.
8328   if (PrevDecl && PrevDecl->getPointOfInstantiation().isValid()) {
8329     bool Okay = false;
8330     for (Decl *Prev = PrevDecl; Prev; Prev = Prev->getPreviousDecl()) {
8331       // Is there any previous explicit specialization declaration?
8332       if (getTemplateSpecializationKind(Prev) == TSK_ExplicitSpecialization) {
8333         Okay = true;
8334         break;
8335       }
8336     }
8337 
8338     if (!Okay) {
8339       SourceRange Range(TemplateNameLoc, RAngleLoc);
8340       Diag(TemplateNameLoc, diag::err_specialization_after_instantiation)
8341         << Context.getTypeDeclType(Specialization) << Range;
8342 
8343       Diag(PrevDecl->getPointOfInstantiation(),
8344            diag::note_instantiation_required_here)
8345         << (PrevDecl->getTemplateSpecializationKind()
8346                                                 != TSK_ImplicitInstantiation);
8347       return true;
8348     }
8349   }
8350 
8351   // If this is not a friend, note that this is an explicit specialization.
8352   if (TUK != TUK_Friend)
8353     Specialization->setSpecializationKind(TSK_ExplicitSpecialization);
8354 
8355   // Check that this isn't a redefinition of this specialization.
8356   if (TUK == TUK_Definition) {
8357     RecordDecl *Def = Specialization->getDefinition();
8358     NamedDecl *Hidden = nullptr;
8359     if (Def && SkipBody && !hasVisibleDefinition(Def, &Hidden)) {
8360       SkipBody->ShouldSkip = true;
8361       SkipBody->Previous = Def;
8362       makeMergedDefinitionVisible(Hidden);
8363     } else if (Def) {
8364       SourceRange Range(TemplateNameLoc, RAngleLoc);
8365       Diag(TemplateNameLoc, diag::err_redefinition) << Specialization << Range;
8366       Diag(Def->getLocation(), diag::note_previous_definition);
8367       Specialization->setInvalidDecl();
8368       return true;
8369     }
8370   }
8371 
8372   ProcessDeclAttributeList(S, Specialization, Attr);
8373 
8374   // Add alignment attributes if necessary; these attributes are checked when
8375   // the ASTContext lays out the structure.
8376   if (TUK == TUK_Definition && (!SkipBody || !SkipBody->ShouldSkip)) {
8377     AddAlignmentAttributesForRecord(Specialization);
8378     AddMsStructLayoutForRecord(Specialization);
8379   }
8380 
8381   if (ModulePrivateLoc.isValid())
8382     Diag(Specialization->getLocation(), diag::err_module_private_specialization)
8383       << (isPartialSpecialization? 1 : 0)
8384       << FixItHint::CreateRemoval(ModulePrivateLoc);
8385 
8386   // Build the fully-sugared type for this class template
8387   // specialization as the user wrote in the specialization
8388   // itself. This means that we'll pretty-print the type retrieved
8389   // from the specialization's declaration the way that the user
8390   // actually wrote the specialization, rather than formatting the
8391   // name based on the "canonical" representation used to store the
8392   // template arguments in the specialization.
8393   TypeSourceInfo *WrittenTy
8394     = Context.getTemplateSpecializationTypeInfo(Name, TemplateNameLoc,
8395                                                 TemplateArgs, CanonType);
8396   if (TUK != TUK_Friend) {
8397     Specialization->setTypeAsWritten(WrittenTy);
8398     Specialization->setTemplateKeywordLoc(TemplateKWLoc);
8399   }
8400 
8401   // C++ [temp.expl.spec]p9:
8402   //   A template explicit specialization is in the scope of the
8403   //   namespace in which the template was defined.
8404   //
8405   // We actually implement this paragraph where we set the semantic
8406   // context (in the creation of the ClassTemplateSpecializationDecl),
8407   // but we also maintain the lexical context where the actual
8408   // definition occurs.
8409   Specialization->setLexicalDeclContext(CurContext);
8410 
8411   // We may be starting the definition of this specialization.
8412   if (TUK == TUK_Definition && (!SkipBody || !SkipBody->ShouldSkip))
8413     Specialization->startDefinition();
8414 
8415   if (TUK == TUK_Friend) {
8416     FriendDecl *Friend = FriendDecl::Create(Context, CurContext,
8417                                             TemplateNameLoc,
8418                                             WrittenTy,
8419                                             /*FIXME:*/KWLoc);
8420     Friend->setAccess(AS_public);
8421     CurContext->addDecl(Friend);
8422   } else {
8423     // Add the specialization into its lexical context, so that it can
8424     // be seen when iterating through the list of declarations in that
8425     // context. However, specializations are not found by name lookup.
8426     CurContext->addDecl(Specialization);
8427   }
8428 
8429   if (SkipBody && SkipBody->ShouldSkip)
8430     return SkipBody->Previous;
8431 
8432   return Specialization;
8433 }
8434 
8435 Decl *Sema::ActOnTemplateDeclarator(Scope *S,
8436                               MultiTemplateParamsArg TemplateParameterLists,
8437                                     Declarator &D) {
8438   Decl *NewDecl = HandleDeclarator(S, D, TemplateParameterLists);
8439   ActOnDocumentableDecl(NewDecl);
8440   return NewDecl;
8441 }
8442 
8443 Decl *Sema::ActOnConceptDefinition(Scope *S,
8444                               MultiTemplateParamsArg TemplateParameterLists,
8445                                    IdentifierInfo *Name, SourceLocation NameLoc,
8446                                    Expr *ConstraintExpr) {
8447   DeclContext *DC = CurContext;
8448 
8449   if (!DC->getRedeclContext()->isFileContext()) {
8450     Diag(NameLoc,
8451       diag::err_concept_decls_may_only_appear_in_global_namespace_scope);
8452     return nullptr;
8453   }
8454 
8455   if (TemplateParameterLists.size() > 1) {
8456     Diag(NameLoc, diag::err_concept_extra_headers);
8457     return nullptr;
8458   }
8459 
8460   if (TemplateParameterLists.front()->size() == 0) {
8461     Diag(NameLoc, diag::err_concept_no_parameters);
8462     return nullptr;
8463   }
8464 
8465   ConceptDecl *NewDecl = ConceptDecl::Create(Context, DC, NameLoc, Name,
8466                                              TemplateParameterLists.front(),
8467                                              ConstraintExpr);
8468 
8469   if (NewDecl->hasAssociatedConstraints()) {
8470     // C++2a [temp.concept]p4:
8471     // A concept shall not have associated constraints.
8472     Diag(NameLoc, diag::err_concept_no_associated_constraints);
8473     NewDecl->setInvalidDecl();
8474   }
8475 
8476   // Check for conflicting previous declaration.
8477   DeclarationNameInfo NameInfo(NewDecl->getDeclName(), NameLoc);
8478   LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
8479                         ForVisibleRedeclaration);
8480   LookupName(Previous, S);
8481 
8482   FilterLookupForScope(Previous, DC, S, /*ConsiderLinkage=*/false,
8483                        /*AllowInlineNamespace*/false);
8484   if (!Previous.empty()) {
8485     auto *Old = Previous.getRepresentativeDecl();
8486     Diag(NameLoc, isa<ConceptDecl>(Old) ? diag::err_redefinition :
8487          diag::err_redefinition_different_kind) << NewDecl->getDeclName();
8488     Diag(Old->getLocation(), diag::note_previous_definition);
8489   }
8490 
8491   ActOnDocumentableDecl(NewDecl);
8492   PushOnScopeChains(NewDecl, S);
8493   return NewDecl;
8494 }
8495 
8496 /// \brief Strips various properties off an implicit instantiation
8497 /// that has just been explicitly specialized.
8498 static void StripImplicitInstantiation(NamedDecl *D) {
8499   D->dropAttr<DLLImportAttr>();
8500   D->dropAttr<DLLExportAttr>();
8501 
8502   if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
8503     FD->setInlineSpecified(false);
8504 }
8505 
8506 /// Compute the diagnostic location for an explicit instantiation
8507 //  declaration or definition.
8508 static SourceLocation DiagLocForExplicitInstantiation(
8509     NamedDecl* D, SourceLocation PointOfInstantiation) {
8510   // Explicit instantiations following a specialization have no effect and
8511   // hence no PointOfInstantiation. In that case, walk decl backwards
8512   // until a valid name loc is found.
8513   SourceLocation PrevDiagLoc = PointOfInstantiation;
8514   for (Decl *Prev = D; Prev && !PrevDiagLoc.isValid();
8515        Prev = Prev->getPreviousDecl()) {
8516     PrevDiagLoc = Prev->getLocation();
8517   }
8518   assert(PrevDiagLoc.isValid() &&
8519          "Explicit instantiation without point of instantiation?");
8520   return PrevDiagLoc;
8521 }
8522 
8523 /// Diagnose cases where we have an explicit template specialization
8524 /// before/after an explicit template instantiation, producing diagnostics
8525 /// for those cases where they are required and determining whether the
8526 /// new specialization/instantiation will have any effect.
8527 ///
8528 /// \param NewLoc the location of the new explicit specialization or
8529 /// instantiation.
8530 ///
8531 /// \param NewTSK the kind of the new explicit specialization or instantiation.
8532 ///
8533 /// \param PrevDecl the previous declaration of the entity.
8534 ///
8535 /// \param PrevTSK the kind of the old explicit specialization or instantiatin.
8536 ///
8537 /// \param PrevPointOfInstantiation if valid, indicates where the previus
8538 /// declaration was instantiated (either implicitly or explicitly).
8539 ///
8540 /// \param HasNoEffect will be set to true to indicate that the new
8541 /// specialization or instantiation has no effect and should be ignored.
8542 ///
8543 /// \returns true if there was an error that should prevent the introduction of
8544 /// the new declaration into the AST, false otherwise.
8545 bool
8546 Sema::CheckSpecializationInstantiationRedecl(SourceLocation NewLoc,
8547                                              TemplateSpecializationKind NewTSK,
8548                                              NamedDecl *PrevDecl,
8549                                              TemplateSpecializationKind PrevTSK,
8550                                         SourceLocation PrevPointOfInstantiation,
8551                                              bool &HasNoEffect) {
8552   HasNoEffect = false;
8553 
8554   switch (NewTSK) {
8555   case TSK_Undeclared:
8556   case TSK_ImplicitInstantiation:
8557     assert(
8558         (PrevTSK == TSK_Undeclared || PrevTSK == TSK_ImplicitInstantiation) &&
8559         "previous declaration must be implicit!");
8560     return false;
8561 
8562   case TSK_ExplicitSpecialization:
8563     switch (PrevTSK) {
8564     case TSK_Undeclared:
8565     case TSK_ExplicitSpecialization:
8566       // Okay, we're just specializing something that is either already
8567       // explicitly specialized or has merely been mentioned without any
8568       // instantiation.
8569       return false;
8570 
8571     case TSK_ImplicitInstantiation:
8572       if (PrevPointOfInstantiation.isInvalid()) {
8573         // The declaration itself has not actually been instantiated, so it is
8574         // still okay to specialize it.
8575         StripImplicitInstantiation(PrevDecl);
8576         return false;
8577       }
8578       // Fall through
8579       LLVM_FALLTHROUGH;
8580 
8581     case TSK_ExplicitInstantiationDeclaration:
8582     case TSK_ExplicitInstantiationDefinition:
8583       assert((PrevTSK == TSK_ImplicitInstantiation ||
8584               PrevPointOfInstantiation.isValid()) &&
8585              "Explicit instantiation without point of instantiation?");
8586 
8587       // C++ [temp.expl.spec]p6:
8588       //   If a template, a member template or the member of a class template
8589       //   is explicitly specialized then that specialization shall be declared
8590       //   before the first use of that specialization that would cause an
8591       //   implicit instantiation to take place, in every translation unit in
8592       //   which such a use occurs; no diagnostic is required.
8593       for (Decl *Prev = PrevDecl; Prev; Prev = Prev->getPreviousDecl()) {
8594         // Is there any previous explicit specialization declaration?
8595         if (getTemplateSpecializationKind(Prev) == TSK_ExplicitSpecialization)
8596           return false;
8597       }
8598 
8599       Diag(NewLoc, diag::err_specialization_after_instantiation)
8600         << PrevDecl;
8601       Diag(PrevPointOfInstantiation, diag::note_instantiation_required_here)
8602         << (PrevTSK != TSK_ImplicitInstantiation);
8603 
8604       return true;
8605     }
8606     llvm_unreachable("The switch over PrevTSK must be exhaustive.");
8607 
8608   case TSK_ExplicitInstantiationDeclaration:
8609     switch (PrevTSK) {
8610     case TSK_ExplicitInstantiationDeclaration:
8611       // This explicit instantiation declaration is redundant (that's okay).
8612       HasNoEffect = true;
8613       return false;
8614 
8615     case TSK_Undeclared:
8616     case TSK_ImplicitInstantiation:
8617       // We're explicitly instantiating something that may have already been
8618       // implicitly instantiated; that's fine.
8619       return false;
8620 
8621     case TSK_ExplicitSpecialization:
8622       // C++0x [temp.explicit]p4:
8623       //   For a given set of template parameters, if an explicit instantiation
8624       //   of a template appears after a declaration of an explicit
8625       //   specialization for that template, the explicit instantiation has no
8626       //   effect.
8627       HasNoEffect = true;
8628       return false;
8629 
8630     case TSK_ExplicitInstantiationDefinition:
8631       // C++0x [temp.explicit]p10:
8632       //   If an entity is the subject of both an explicit instantiation
8633       //   declaration and an explicit instantiation definition in the same
8634       //   translation unit, the definition shall follow the declaration.
8635       Diag(NewLoc,
8636            diag::err_explicit_instantiation_declaration_after_definition);
8637 
8638       // Explicit instantiations following a specialization have no effect and
8639       // hence no PrevPointOfInstantiation. In that case, walk decl backwards
8640       // until a valid name loc is found.
8641       Diag(DiagLocForExplicitInstantiation(PrevDecl, PrevPointOfInstantiation),
8642            diag::note_explicit_instantiation_definition_here);
8643       HasNoEffect = true;
8644       return false;
8645     }
8646     llvm_unreachable("Unexpected TemplateSpecializationKind!");
8647 
8648   case TSK_ExplicitInstantiationDefinition:
8649     switch (PrevTSK) {
8650     case TSK_Undeclared:
8651     case TSK_ImplicitInstantiation:
8652       // We're explicitly instantiating something that may have already been
8653       // implicitly instantiated; that's fine.
8654       return false;
8655 
8656     case TSK_ExplicitSpecialization:
8657       // C++ DR 259, C++0x [temp.explicit]p4:
8658       //   For a given set of template parameters, if an explicit
8659       //   instantiation of a template appears after a declaration of
8660       //   an explicit specialization for that template, the explicit
8661       //   instantiation has no effect.
8662       Diag(NewLoc, diag::warn_explicit_instantiation_after_specialization)
8663         << PrevDecl;
8664       Diag(PrevDecl->getLocation(),
8665            diag::note_previous_template_specialization);
8666       HasNoEffect = true;
8667       return false;
8668 
8669     case TSK_ExplicitInstantiationDeclaration:
8670       // We're explicitly instantiating a definition for something for which we
8671       // were previously asked to suppress instantiations. That's fine.
8672 
8673       // C++0x [temp.explicit]p4:
8674       //   For a given set of template parameters, if an explicit instantiation
8675       //   of a template appears after a declaration of an explicit
8676       //   specialization for that template, the explicit instantiation has no
8677       //   effect.
8678       for (Decl *Prev = PrevDecl; Prev; Prev = Prev->getPreviousDecl()) {
8679         // Is there any previous explicit specialization declaration?
8680         if (getTemplateSpecializationKind(Prev) == TSK_ExplicitSpecialization) {
8681           HasNoEffect = true;
8682           break;
8683         }
8684       }
8685 
8686       return false;
8687 
8688     case TSK_ExplicitInstantiationDefinition:
8689       // C++0x [temp.spec]p5:
8690       //   For a given template and a given set of template-arguments,
8691       //     - an explicit instantiation definition shall appear at most once
8692       //       in a program,
8693 
8694       // MSVCCompat: MSVC silently ignores duplicate explicit instantiations.
8695       Diag(NewLoc, (getLangOpts().MSVCCompat)
8696                        ? diag::ext_explicit_instantiation_duplicate
8697                        : diag::err_explicit_instantiation_duplicate)
8698           << PrevDecl;
8699       Diag(DiagLocForExplicitInstantiation(PrevDecl, PrevPointOfInstantiation),
8700            diag::note_previous_explicit_instantiation);
8701       HasNoEffect = true;
8702       return false;
8703     }
8704   }
8705 
8706   llvm_unreachable("Missing specialization/instantiation case?");
8707 }
8708 
8709 /// Perform semantic analysis for the given dependent function
8710 /// template specialization.
8711 ///
8712 /// The only possible way to get a dependent function template specialization
8713 /// is with a friend declaration, like so:
8714 ///
8715 /// \code
8716 ///   template \<class T> void foo(T);
8717 ///   template \<class T> class A {
8718 ///     friend void foo<>(T);
8719 ///   };
8720 /// \endcode
8721 ///
8722 /// There really isn't any useful analysis we can do here, so we
8723 /// just store the information.
8724 bool
8725 Sema::CheckDependentFunctionTemplateSpecialization(FunctionDecl *FD,
8726                    const TemplateArgumentListInfo &ExplicitTemplateArgs,
8727                                                    LookupResult &Previous) {
8728   // Remove anything from Previous that isn't a function template in
8729   // the correct context.
8730   DeclContext *FDLookupContext = FD->getDeclContext()->getRedeclContext();
8731   LookupResult::Filter F = Previous.makeFilter();
8732   enum DiscardReason { NotAFunctionTemplate, NotAMemberOfEnclosing };
8733   SmallVector<std::pair<DiscardReason, Decl *>, 8> DiscardedCandidates;
8734   while (F.hasNext()) {
8735     NamedDecl *D = F.next()->getUnderlyingDecl();
8736     if (!isa<FunctionTemplateDecl>(D)) {
8737       F.erase();
8738       DiscardedCandidates.push_back(std::make_pair(NotAFunctionTemplate, D));
8739       continue;
8740     }
8741 
8742     if (!FDLookupContext->InEnclosingNamespaceSetOf(
8743             D->getDeclContext()->getRedeclContext())) {
8744       F.erase();
8745       DiscardedCandidates.push_back(std::make_pair(NotAMemberOfEnclosing, D));
8746       continue;
8747     }
8748   }
8749   F.done();
8750 
8751   if (Previous.empty()) {
8752     Diag(FD->getLocation(),
8753          diag::err_dependent_function_template_spec_no_match);
8754     for (auto &P : DiscardedCandidates)
8755       Diag(P.second->getLocation(),
8756            diag::note_dependent_function_template_spec_discard_reason)
8757           << P.first;
8758     return true;
8759   }
8760 
8761   FD->setDependentTemplateSpecialization(Context, Previous.asUnresolvedSet(),
8762                                          ExplicitTemplateArgs);
8763   return false;
8764 }
8765 
8766 /// Perform semantic analysis for the given function template
8767 /// specialization.
8768 ///
8769 /// This routine performs all of the semantic analysis required for an
8770 /// explicit function template specialization. On successful completion,
8771 /// the function declaration \p FD will become a function template
8772 /// specialization.
8773 ///
8774 /// \param FD the function declaration, which will be updated to become a
8775 /// function template specialization.
8776 ///
8777 /// \param ExplicitTemplateArgs the explicitly-provided template arguments,
8778 /// if any. Note that this may be valid info even when 0 arguments are
8779 /// explicitly provided as in, e.g., \c void sort<>(char*, char*);
8780 /// as it anyway contains info on the angle brackets locations.
8781 ///
8782 /// \param Previous the set of declarations that may be specialized by
8783 /// this function specialization.
8784 ///
8785 /// \param QualifiedFriend whether this is a lookup for a qualified friend
8786 /// declaration with no explicit template argument list that might be
8787 /// befriending a function template specialization.
8788 bool Sema::CheckFunctionTemplateSpecialization(
8789     FunctionDecl *FD, TemplateArgumentListInfo *ExplicitTemplateArgs,
8790     LookupResult &Previous, bool QualifiedFriend) {
8791   // The set of function template specializations that could match this
8792   // explicit function template specialization.
8793   UnresolvedSet<8> Candidates;
8794   TemplateSpecCandidateSet FailedCandidates(FD->getLocation(),
8795                                             /*ForTakingAddress=*/false);
8796 
8797   llvm::SmallDenseMap<FunctionDecl *, TemplateArgumentListInfo, 8>
8798       ConvertedTemplateArgs;
8799 
8800   DeclContext *FDLookupContext = FD->getDeclContext()->getRedeclContext();
8801   for (LookupResult::iterator I = Previous.begin(), E = Previous.end();
8802          I != E; ++I) {
8803     NamedDecl *Ovl = (*I)->getUnderlyingDecl();
8804     if (FunctionTemplateDecl *FunTmpl = dyn_cast<FunctionTemplateDecl>(Ovl)) {
8805       // Only consider templates found within the same semantic lookup scope as
8806       // FD.
8807       if (!FDLookupContext->InEnclosingNamespaceSetOf(
8808                                 Ovl->getDeclContext()->getRedeclContext()))
8809         continue;
8810 
8811       // When matching a constexpr member function template specialization
8812       // against the primary template, we don't yet know whether the
8813       // specialization has an implicit 'const' (because we don't know whether
8814       // it will be a static member function until we know which template it
8815       // specializes), so adjust it now assuming it specializes this template.
8816       QualType FT = FD->getType();
8817       if (FD->isConstexpr()) {
8818         CXXMethodDecl *OldMD =
8819           dyn_cast<CXXMethodDecl>(FunTmpl->getTemplatedDecl());
8820         if (OldMD && OldMD->isConst()) {
8821           const FunctionProtoType *FPT = FT->castAs<FunctionProtoType>();
8822           FunctionProtoType::ExtProtoInfo EPI = FPT->getExtProtoInfo();
8823           EPI.TypeQuals.addConst();
8824           FT = Context.getFunctionType(FPT->getReturnType(),
8825                                        FPT->getParamTypes(), EPI);
8826         }
8827       }
8828 
8829       TemplateArgumentListInfo Args;
8830       if (ExplicitTemplateArgs)
8831         Args = *ExplicitTemplateArgs;
8832 
8833       // C++ [temp.expl.spec]p11:
8834       //   A trailing template-argument can be left unspecified in the
8835       //   template-id naming an explicit function template specialization
8836       //   provided it can be deduced from the function argument type.
8837       // Perform template argument deduction to determine whether we may be
8838       // specializing this template.
8839       // FIXME: It is somewhat wasteful to build
8840       TemplateDeductionInfo Info(FailedCandidates.getLocation());
8841       FunctionDecl *Specialization = nullptr;
8842       if (TemplateDeductionResult TDK = DeduceTemplateArguments(
8843               cast<FunctionTemplateDecl>(FunTmpl->getFirstDecl()),
8844               ExplicitTemplateArgs ? &Args : nullptr, FT, Specialization,
8845               Info)) {
8846         // Template argument deduction failed; record why it failed, so
8847         // that we can provide nifty diagnostics.
8848         FailedCandidates.addCandidate().set(
8849             I.getPair(), FunTmpl->getTemplatedDecl(),
8850             MakeDeductionFailureInfo(Context, TDK, Info));
8851         (void)TDK;
8852         continue;
8853       }
8854 
8855       // Target attributes are part of the cuda function signature, so
8856       // the deduced template's cuda target must match that of the
8857       // specialization.  Given that C++ template deduction does not
8858       // take target attributes into account, we reject candidates
8859       // here that have a different target.
8860       if (LangOpts.CUDA &&
8861           IdentifyCUDATarget(Specialization,
8862                              /* IgnoreImplicitHDAttr = */ true) !=
8863               IdentifyCUDATarget(FD, /* IgnoreImplicitHDAttr = */ true)) {
8864         FailedCandidates.addCandidate().set(
8865             I.getPair(), FunTmpl->getTemplatedDecl(),
8866             MakeDeductionFailureInfo(Context, TDK_CUDATargetMismatch, Info));
8867         continue;
8868       }
8869 
8870       // Record this candidate.
8871       if (ExplicitTemplateArgs)
8872         ConvertedTemplateArgs[Specialization] = std::move(Args);
8873       Candidates.addDecl(Specialization, I.getAccess());
8874     }
8875   }
8876 
8877   // For a qualified friend declaration (with no explicit marker to indicate
8878   // that a template specialization was intended), note all (template and
8879   // non-template) candidates.
8880   if (QualifiedFriend && Candidates.empty()) {
8881     Diag(FD->getLocation(), diag::err_qualified_friend_no_match)
8882         << FD->getDeclName() << FDLookupContext;
8883     // FIXME: We should form a single candidate list and diagnose all
8884     // candidates at once, to get proper sorting and limiting.
8885     for (auto *OldND : Previous) {
8886       if (auto *OldFD = dyn_cast<FunctionDecl>(OldND->getUnderlyingDecl()))
8887         NoteOverloadCandidate(OldND, OldFD, CRK_None, FD->getType(), false);
8888     }
8889     FailedCandidates.NoteCandidates(*this, FD->getLocation());
8890     return true;
8891   }
8892 
8893   // Find the most specialized function template.
8894   UnresolvedSetIterator Result = getMostSpecialized(
8895       Candidates.begin(), Candidates.end(), FailedCandidates, FD->getLocation(),
8896       PDiag(diag::err_function_template_spec_no_match) << FD->getDeclName(),
8897       PDiag(diag::err_function_template_spec_ambiguous)
8898           << FD->getDeclName() << (ExplicitTemplateArgs != nullptr),
8899       PDiag(diag::note_function_template_spec_matched));
8900 
8901   if (Result == Candidates.end())
8902     return true;
8903 
8904   // Ignore access information;  it doesn't figure into redeclaration checking.
8905   FunctionDecl *Specialization = cast<FunctionDecl>(*Result);
8906 
8907   FunctionTemplateSpecializationInfo *SpecInfo
8908     = Specialization->getTemplateSpecializationInfo();
8909   assert(SpecInfo && "Function template specialization info missing?");
8910 
8911   // Note: do not overwrite location info if previous template
8912   // specialization kind was explicit.
8913   TemplateSpecializationKind TSK = SpecInfo->getTemplateSpecializationKind();
8914   if (TSK == TSK_Undeclared || TSK == TSK_ImplicitInstantiation) {
8915     Specialization->setLocation(FD->getLocation());
8916     Specialization->setLexicalDeclContext(FD->getLexicalDeclContext());
8917     // C++11 [dcl.constexpr]p1: An explicit specialization of a constexpr
8918     // function can differ from the template declaration with respect to
8919     // the constexpr specifier.
8920     // FIXME: We need an update record for this AST mutation.
8921     // FIXME: What if there are multiple such prior declarations (for instance,
8922     // from different modules)?
8923     Specialization->setConstexprKind(FD->getConstexprKind());
8924   }
8925 
8926   // FIXME: Check if the prior specialization has a point of instantiation.
8927   // If so, we have run afoul of .
8928 
8929   // If this is a friend declaration, then we're not really declaring
8930   // an explicit specialization.
8931   bool isFriend = (FD->getFriendObjectKind() != Decl::FOK_None);
8932 
8933   // Check the scope of this explicit specialization.
8934   if (!isFriend &&
8935       CheckTemplateSpecializationScope(*this,
8936                                        Specialization->getPrimaryTemplate(),
8937                                        Specialization, FD->getLocation(),
8938                                        false))
8939     return true;
8940 
8941   // C++ [temp.expl.spec]p6:
8942   //   If a template, a member template or the member of a class template is
8943   //   explicitly specialized then that specialization shall be declared
8944   //   before the first use of that specialization that would cause an implicit
8945   //   instantiation to take place, in every translation unit in which such a
8946   //   use occurs; no diagnostic is required.
8947   bool HasNoEffect = false;
8948   if (!isFriend &&
8949       CheckSpecializationInstantiationRedecl(FD->getLocation(),
8950                                              TSK_ExplicitSpecialization,
8951                                              Specialization,
8952                                    SpecInfo->getTemplateSpecializationKind(),
8953                                          SpecInfo->getPointOfInstantiation(),
8954                                              HasNoEffect))
8955     return true;
8956 
8957   // Mark the prior declaration as an explicit specialization, so that later
8958   // clients know that this is an explicit specialization.
8959   if (!isFriend) {
8960     // Since explicit specializations do not inherit '=delete' from their
8961     // primary function template - check if the 'specialization' that was
8962     // implicitly generated (during template argument deduction for partial
8963     // ordering) from the most specialized of all the function templates that
8964     // 'FD' could have been specializing, has a 'deleted' definition.  If so,
8965     // first check that it was implicitly generated during template argument
8966     // deduction by making sure it wasn't referenced, and then reset the deleted
8967     // flag to not-deleted, so that we can inherit that information from 'FD'.
8968     if (Specialization->isDeleted() && !SpecInfo->isExplicitSpecialization() &&
8969         !Specialization->getCanonicalDecl()->isReferenced()) {
8970       // FIXME: This assert will not hold in the presence of modules.
8971       assert(
8972           Specialization->getCanonicalDecl() == Specialization &&
8973           "This must be the only existing declaration of this specialization");
8974       // FIXME: We need an update record for this AST mutation.
8975       Specialization->setDeletedAsWritten(false);
8976     }
8977     // FIXME: We need an update record for this AST mutation.
8978     SpecInfo->setTemplateSpecializationKind(TSK_ExplicitSpecialization);
8979     MarkUnusedFileScopedDecl(Specialization);
8980   }
8981 
8982   // Turn the given function declaration into a function template
8983   // specialization, with the template arguments from the previous
8984   // specialization.
8985   // Take copies of (semantic and syntactic) template argument lists.
8986   const TemplateArgumentList* TemplArgs = new (Context)
8987     TemplateArgumentList(Specialization->getTemplateSpecializationArgs());
8988   FD->setFunctionTemplateSpecialization(
8989       Specialization->getPrimaryTemplate(), TemplArgs, /*InsertPos=*/nullptr,
8990       SpecInfo->getTemplateSpecializationKind(),
8991       ExplicitTemplateArgs ? &ConvertedTemplateArgs[Specialization] : nullptr);
8992 
8993   // A function template specialization inherits the target attributes
8994   // of its template.  (We require the attributes explicitly in the
8995   // code to match, but a template may have implicit attributes by
8996   // virtue e.g. of being constexpr, and it passes these implicit
8997   // attributes on to its specializations.)
8998   if (LangOpts.CUDA)
8999     inheritCUDATargetAttrs(FD, *Specialization->getPrimaryTemplate());
9000 
9001   // The "previous declaration" for this function template specialization is
9002   // the prior function template specialization.
9003   Previous.clear();
9004   Previous.addDecl(Specialization);
9005   return false;
9006 }
9007 
9008 /// Perform semantic analysis for the given non-template member
9009 /// specialization.
9010 ///
9011 /// This routine performs all of the semantic analysis required for an
9012 /// explicit member function specialization. On successful completion,
9013 /// the function declaration \p FD will become a member function
9014 /// specialization.
9015 ///
9016 /// \param Member the member declaration, which will be updated to become a
9017 /// specialization.
9018 ///
9019 /// \param Previous the set of declarations, one of which may be specialized
9020 /// by this function specialization;  the set will be modified to contain the
9021 /// redeclared member.
9022 bool
9023 Sema::CheckMemberSpecialization(NamedDecl *Member, LookupResult &Previous) {
9024   assert(!isa<TemplateDecl>(Member) && "Only for non-template members");
9025 
9026   // Try to find the member we are instantiating.
9027   NamedDecl *FoundInstantiation = nullptr;
9028   NamedDecl *Instantiation = nullptr;
9029   NamedDecl *InstantiatedFrom = nullptr;
9030   MemberSpecializationInfo *MSInfo = nullptr;
9031 
9032   if (Previous.empty()) {
9033     // Nowhere to look anyway.
9034   } else if (FunctionDecl *Function = dyn_cast<FunctionDecl>(Member)) {
9035     for (LookupResult::iterator I = Previous.begin(), E = Previous.end();
9036            I != E; ++I) {
9037       NamedDecl *D = (*I)->getUnderlyingDecl();
9038       if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D)) {
9039         QualType Adjusted = Function->getType();
9040         if (!hasExplicitCallingConv(Adjusted))
9041           Adjusted = adjustCCAndNoReturn(Adjusted, Method->getType());
9042         // This doesn't handle deduced return types, but both function
9043         // declarations should be undeduced at this point.
9044         if (Context.hasSameType(Adjusted, Method->getType())) {
9045           FoundInstantiation = *I;
9046           Instantiation = Method;
9047           InstantiatedFrom = Method->getInstantiatedFromMemberFunction();
9048           MSInfo = Method->getMemberSpecializationInfo();
9049           break;
9050         }
9051       }
9052     }
9053   } else if (isa<VarDecl>(Member)) {
9054     VarDecl *PrevVar;
9055     if (Previous.isSingleResult() &&
9056         (PrevVar = dyn_cast<VarDecl>(Previous.getFoundDecl())))
9057       if (PrevVar->isStaticDataMember()) {
9058         FoundInstantiation = Previous.getRepresentativeDecl();
9059         Instantiation = PrevVar;
9060         InstantiatedFrom = PrevVar->getInstantiatedFromStaticDataMember();
9061         MSInfo = PrevVar->getMemberSpecializationInfo();
9062       }
9063   } else if (isa<RecordDecl>(Member)) {
9064     CXXRecordDecl *PrevRecord;
9065     if (Previous.isSingleResult() &&
9066         (PrevRecord = dyn_cast<CXXRecordDecl>(Previous.getFoundDecl()))) {
9067       FoundInstantiation = Previous.getRepresentativeDecl();
9068       Instantiation = PrevRecord;
9069       InstantiatedFrom = PrevRecord->getInstantiatedFromMemberClass();
9070       MSInfo = PrevRecord->getMemberSpecializationInfo();
9071     }
9072   } else if (isa<EnumDecl>(Member)) {
9073     EnumDecl *PrevEnum;
9074     if (Previous.isSingleResult() &&
9075         (PrevEnum = dyn_cast<EnumDecl>(Previous.getFoundDecl()))) {
9076       FoundInstantiation = Previous.getRepresentativeDecl();
9077       Instantiation = PrevEnum;
9078       InstantiatedFrom = PrevEnum->getInstantiatedFromMemberEnum();
9079       MSInfo = PrevEnum->getMemberSpecializationInfo();
9080     }
9081   }
9082 
9083   if (!Instantiation) {
9084     // There is no previous declaration that matches. Since member
9085     // specializations are always out-of-line, the caller will complain about
9086     // this mismatch later.
9087     return false;
9088   }
9089 
9090   // A member specialization in a friend declaration isn't really declaring
9091   // an explicit specialization, just identifying a specific (possibly implicit)
9092   // specialization. Don't change the template specialization kind.
9093   //
9094   // FIXME: Is this really valid? Other compilers reject.
9095   if (Member->getFriendObjectKind() != Decl::FOK_None) {
9096     // Preserve instantiation information.
9097     if (InstantiatedFrom && isa<CXXMethodDecl>(Member)) {
9098       cast<CXXMethodDecl>(Member)->setInstantiationOfMemberFunction(
9099                                       cast<CXXMethodDecl>(InstantiatedFrom),
9100         cast<CXXMethodDecl>(Instantiation)->getTemplateSpecializationKind());
9101     } else if (InstantiatedFrom && isa<CXXRecordDecl>(Member)) {
9102       cast<CXXRecordDecl>(Member)->setInstantiationOfMemberClass(
9103                                       cast<CXXRecordDecl>(InstantiatedFrom),
9104         cast<CXXRecordDecl>(Instantiation)->getTemplateSpecializationKind());
9105     }
9106 
9107     Previous.clear();
9108     Previous.addDecl(FoundInstantiation);
9109     return false;
9110   }
9111 
9112   // Make sure that this is a specialization of a member.
9113   if (!InstantiatedFrom) {
9114     Diag(Member->getLocation(), diag::err_spec_member_not_instantiated)
9115       << Member;
9116     Diag(Instantiation->getLocation(), diag::note_specialized_decl);
9117     return true;
9118   }
9119 
9120   // C++ [temp.expl.spec]p6:
9121   //   If a template, a member template or the member of a class template is
9122   //   explicitly specialized then that specialization shall be declared
9123   //   before the first use of that specialization that would cause an implicit
9124   //   instantiation to take place, in every translation unit in which such a
9125   //   use occurs; no diagnostic is required.
9126   assert(MSInfo && "Member specialization info missing?");
9127 
9128   bool HasNoEffect = false;
9129   if (CheckSpecializationInstantiationRedecl(Member->getLocation(),
9130                                              TSK_ExplicitSpecialization,
9131                                              Instantiation,
9132                                      MSInfo->getTemplateSpecializationKind(),
9133                                            MSInfo->getPointOfInstantiation(),
9134                                              HasNoEffect))
9135     return true;
9136 
9137   // Check the scope of this explicit specialization.
9138   if (CheckTemplateSpecializationScope(*this,
9139                                        InstantiatedFrom,
9140                                        Instantiation, Member->getLocation(),
9141                                        false))
9142     return true;
9143 
9144   // Note that this member specialization is an "instantiation of" the
9145   // corresponding member of the original template.
9146   if (auto *MemberFunction = dyn_cast<FunctionDecl>(Member)) {
9147     FunctionDecl *InstantiationFunction = cast<FunctionDecl>(Instantiation);
9148     if (InstantiationFunction->getTemplateSpecializationKind() ==
9149           TSK_ImplicitInstantiation) {
9150       // Explicit specializations of member functions of class templates do not
9151       // inherit '=delete' from the member function they are specializing.
9152       if (InstantiationFunction->isDeleted()) {
9153         // FIXME: This assert will not hold in the presence of modules.
9154         assert(InstantiationFunction->getCanonicalDecl() ==
9155                InstantiationFunction);
9156         // FIXME: We need an update record for this AST mutation.
9157         InstantiationFunction->setDeletedAsWritten(false);
9158       }
9159     }
9160 
9161     MemberFunction->setInstantiationOfMemberFunction(
9162         cast<CXXMethodDecl>(InstantiatedFrom), TSK_ExplicitSpecialization);
9163   } else if (auto *MemberVar = dyn_cast<VarDecl>(Member)) {
9164     MemberVar->setInstantiationOfStaticDataMember(
9165         cast<VarDecl>(InstantiatedFrom), TSK_ExplicitSpecialization);
9166   } else if (auto *MemberClass = dyn_cast<CXXRecordDecl>(Member)) {
9167     MemberClass->setInstantiationOfMemberClass(
9168         cast<CXXRecordDecl>(InstantiatedFrom), TSK_ExplicitSpecialization);
9169   } else if (auto *MemberEnum = dyn_cast<EnumDecl>(Member)) {
9170     MemberEnum->setInstantiationOfMemberEnum(
9171         cast<EnumDecl>(InstantiatedFrom), TSK_ExplicitSpecialization);
9172   } else {
9173     llvm_unreachable("unknown member specialization kind");
9174   }
9175 
9176   // Save the caller the trouble of having to figure out which declaration
9177   // this specialization matches.
9178   Previous.clear();
9179   Previous.addDecl(FoundInstantiation);
9180   return false;
9181 }
9182 
9183 /// Complete the explicit specialization of a member of a class template by
9184 /// updating the instantiated member to be marked as an explicit specialization.
9185 ///
9186 /// \param OrigD The member declaration instantiated from the template.
9187 /// \param Loc The location of the explicit specialization of the member.
9188 template<typename DeclT>
9189 static void completeMemberSpecializationImpl(Sema &S, DeclT *OrigD,
9190                                              SourceLocation Loc) {
9191   if (OrigD->getTemplateSpecializationKind() != TSK_ImplicitInstantiation)
9192     return;
9193 
9194   // FIXME: Inform AST mutation listeners of this AST mutation.
9195   // FIXME: If there are multiple in-class declarations of the member (from
9196   // multiple modules, or a declaration and later definition of a member type),
9197   // should we update all of them?
9198   OrigD->setTemplateSpecializationKind(TSK_ExplicitSpecialization);
9199   OrigD->setLocation(Loc);
9200 }
9201 
9202 void Sema::CompleteMemberSpecialization(NamedDecl *Member,
9203                                         LookupResult &Previous) {
9204   NamedDecl *Instantiation = cast<NamedDecl>(Member->getCanonicalDecl());
9205   if (Instantiation == Member)
9206     return;
9207 
9208   if (auto *Function = dyn_cast<CXXMethodDecl>(Instantiation))
9209     completeMemberSpecializationImpl(*this, Function, Member->getLocation());
9210   else if (auto *Var = dyn_cast<VarDecl>(Instantiation))
9211     completeMemberSpecializationImpl(*this, Var, Member->getLocation());
9212   else if (auto *Record = dyn_cast<CXXRecordDecl>(Instantiation))
9213     completeMemberSpecializationImpl(*this, Record, Member->getLocation());
9214   else if (auto *Enum = dyn_cast<EnumDecl>(Instantiation))
9215     completeMemberSpecializationImpl(*this, Enum, Member->getLocation());
9216   else
9217     llvm_unreachable("unknown member specialization kind");
9218 }
9219 
9220 /// Check the scope of an explicit instantiation.
9221 ///
9222 /// \returns true if a serious error occurs, false otherwise.
9223 static bool CheckExplicitInstantiationScope(Sema &S, NamedDecl *D,
9224                                             SourceLocation InstLoc,
9225                                             bool WasQualifiedName) {
9226   DeclContext *OrigContext= D->getDeclContext()->getEnclosingNamespaceContext();
9227   DeclContext *CurContext = S.CurContext->getRedeclContext();
9228 
9229   if (CurContext->isRecord()) {
9230     S.Diag(InstLoc, diag::err_explicit_instantiation_in_class)
9231       << D;
9232     return true;
9233   }
9234 
9235   // C++11 [temp.explicit]p3:
9236   //   An explicit instantiation shall appear in an enclosing namespace of its
9237   //   template. If the name declared in the explicit instantiation is an
9238   //   unqualified name, the explicit instantiation shall appear in the
9239   //   namespace where its template is declared or, if that namespace is inline
9240   //   (7.3.1), any namespace from its enclosing namespace set.
9241   //
9242   // This is DR275, which we do not retroactively apply to C++98/03.
9243   if (WasQualifiedName) {
9244     if (CurContext->Encloses(OrigContext))
9245       return false;
9246   } else {
9247     if (CurContext->InEnclosingNamespaceSetOf(OrigContext))
9248       return false;
9249   }
9250 
9251   if (NamespaceDecl *NS = dyn_cast<NamespaceDecl>(OrigContext)) {
9252     if (WasQualifiedName)
9253       S.Diag(InstLoc,
9254              S.getLangOpts().CPlusPlus11?
9255                diag::err_explicit_instantiation_out_of_scope :
9256                diag::warn_explicit_instantiation_out_of_scope_0x)
9257         << D << NS;
9258     else
9259       S.Diag(InstLoc,
9260              S.getLangOpts().CPlusPlus11?
9261                diag::err_explicit_instantiation_unqualified_wrong_namespace :
9262                diag::warn_explicit_instantiation_unqualified_wrong_namespace_0x)
9263         << D << NS;
9264   } else
9265     S.Diag(InstLoc,
9266            S.getLangOpts().CPlusPlus11?
9267              diag::err_explicit_instantiation_must_be_global :
9268              diag::warn_explicit_instantiation_must_be_global_0x)
9269       << D;
9270   S.Diag(D->getLocation(), diag::note_explicit_instantiation_here);
9271   return false;
9272 }
9273 
9274 /// Common checks for whether an explicit instantiation of \p D is valid.
9275 static bool CheckExplicitInstantiation(Sema &S, NamedDecl *D,
9276                                        SourceLocation InstLoc,
9277                                        bool WasQualifiedName,
9278                                        TemplateSpecializationKind TSK) {
9279   // C++ [temp.explicit]p13:
9280   //   An explicit instantiation declaration shall not name a specialization of
9281   //   a template with internal linkage.
9282   if (TSK == TSK_ExplicitInstantiationDeclaration &&
9283       D->getFormalLinkage() == InternalLinkage) {
9284     S.Diag(InstLoc, diag::err_explicit_instantiation_internal_linkage) << D;
9285     return true;
9286   }
9287 
9288   // C++11 [temp.explicit]p3: [DR 275]
9289   //   An explicit instantiation shall appear in an enclosing namespace of its
9290   //   template.
9291   if (CheckExplicitInstantiationScope(S, D, InstLoc, WasQualifiedName))
9292     return true;
9293 
9294   return false;
9295 }
9296 
9297 /// Determine whether the given scope specifier has a template-id in it.
9298 static bool ScopeSpecifierHasTemplateId(const CXXScopeSpec &SS) {
9299   if (!SS.isSet())
9300     return false;
9301 
9302   // C++11 [temp.explicit]p3:
9303   //   If the explicit instantiation is for a member function, a member class
9304   //   or a static data member of a class template specialization, the name of
9305   //   the class template specialization in the qualified-id for the member
9306   //   name shall be a simple-template-id.
9307   //
9308   // C++98 has the same restriction, just worded differently.
9309   for (NestedNameSpecifier *NNS = SS.getScopeRep(); NNS;
9310        NNS = NNS->getPrefix())
9311     if (const Type *T = NNS->getAsType())
9312       if (isa<TemplateSpecializationType>(T))
9313         return true;
9314 
9315   return false;
9316 }
9317 
9318 /// Make a dllexport or dllimport attr on a class template specialization take
9319 /// effect.
9320 static void dllExportImportClassTemplateSpecialization(
9321     Sema &S, ClassTemplateSpecializationDecl *Def) {
9322   auto *A = cast_or_null<InheritableAttr>(getDLLAttr(Def));
9323   assert(A && "dllExportImportClassTemplateSpecialization called "
9324               "on Def without dllexport or dllimport");
9325 
9326   // We reject explicit instantiations in class scope, so there should
9327   // never be any delayed exported classes to worry about.
9328   assert(S.DelayedDllExportClasses.empty() &&
9329          "delayed exports present at explicit instantiation");
9330   S.checkClassLevelDLLAttribute(Def);
9331 
9332   // Propagate attribute to base class templates.
9333   for (auto &B : Def->bases()) {
9334     if (auto *BT = dyn_cast_or_null<ClassTemplateSpecializationDecl>(
9335             B.getType()->getAsCXXRecordDecl()))
9336       S.propagateDLLAttrToBaseClassTemplate(Def, A, BT, B.getBeginLoc());
9337   }
9338 
9339   S.referenceDLLExportedClassMethods();
9340 }
9341 
9342 // Explicit instantiation of a class template specialization
9343 DeclResult Sema::ActOnExplicitInstantiation(
9344     Scope *S, SourceLocation ExternLoc, SourceLocation TemplateLoc,
9345     unsigned TagSpec, SourceLocation KWLoc, const CXXScopeSpec &SS,
9346     TemplateTy TemplateD, SourceLocation TemplateNameLoc,
9347     SourceLocation LAngleLoc, ASTTemplateArgsPtr TemplateArgsIn,
9348     SourceLocation RAngleLoc, const ParsedAttributesView &Attr) {
9349   // Find the class template we're specializing
9350   TemplateName Name = TemplateD.get();
9351   TemplateDecl *TD = Name.getAsTemplateDecl();
9352   // Check that the specialization uses the same tag kind as the
9353   // original template.
9354   TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForTypeSpec(TagSpec);
9355   assert(Kind != TTK_Enum &&
9356          "Invalid enum tag in class template explicit instantiation!");
9357 
9358   ClassTemplateDecl *ClassTemplate = dyn_cast<ClassTemplateDecl>(TD);
9359 
9360   if (!ClassTemplate) {
9361     NonTagKind NTK = getNonTagTypeDeclKind(TD, Kind);
9362     Diag(TemplateNameLoc, diag::err_tag_reference_non_tag) << TD << NTK << Kind;
9363     Diag(TD->getLocation(), diag::note_previous_use);
9364     return true;
9365   }
9366 
9367   if (!isAcceptableTagRedeclaration(ClassTemplate->getTemplatedDecl(),
9368                                     Kind, /*isDefinition*/false, KWLoc,
9369                                     ClassTemplate->getIdentifier())) {
9370     Diag(KWLoc, diag::err_use_with_wrong_tag)
9371       << ClassTemplate
9372       << FixItHint::CreateReplacement(KWLoc,
9373                             ClassTemplate->getTemplatedDecl()->getKindName());
9374     Diag(ClassTemplate->getTemplatedDecl()->getLocation(),
9375          diag::note_previous_use);
9376     Kind = ClassTemplate->getTemplatedDecl()->getTagKind();
9377   }
9378 
9379   // C++0x [temp.explicit]p2:
9380   //   There are two forms of explicit instantiation: an explicit instantiation
9381   //   definition and an explicit instantiation declaration. An explicit
9382   //   instantiation declaration begins with the extern keyword. [...]
9383   TemplateSpecializationKind TSK = ExternLoc.isInvalid()
9384                                        ? TSK_ExplicitInstantiationDefinition
9385                                        : TSK_ExplicitInstantiationDeclaration;
9386 
9387   if (TSK == TSK_ExplicitInstantiationDeclaration &&
9388       !Context.getTargetInfo().getTriple().isWindowsGNUEnvironment()) {
9389     // Check for dllexport class template instantiation declarations,
9390     // except for MinGW mode.
9391     for (const ParsedAttr &AL : Attr) {
9392       if (AL.getKind() == ParsedAttr::AT_DLLExport) {
9393         Diag(ExternLoc,
9394              diag::warn_attribute_dllexport_explicit_instantiation_decl);
9395         Diag(AL.getLoc(), diag::note_attribute);
9396         break;
9397       }
9398     }
9399 
9400     if (auto *A = ClassTemplate->getTemplatedDecl()->getAttr<DLLExportAttr>()) {
9401       Diag(ExternLoc,
9402            diag::warn_attribute_dllexport_explicit_instantiation_decl);
9403       Diag(A->getLocation(), diag::note_attribute);
9404     }
9405   }
9406 
9407   // In MSVC mode, dllimported explicit instantiation definitions are treated as
9408   // instantiation declarations for most purposes.
9409   bool DLLImportExplicitInstantiationDef = false;
9410   if (TSK == TSK_ExplicitInstantiationDefinition &&
9411       Context.getTargetInfo().getCXXABI().isMicrosoft()) {
9412     // Check for dllimport class template instantiation definitions.
9413     bool DLLImport =
9414         ClassTemplate->getTemplatedDecl()->getAttr<DLLImportAttr>();
9415     for (const ParsedAttr &AL : Attr) {
9416       if (AL.getKind() == ParsedAttr::AT_DLLImport)
9417         DLLImport = true;
9418       if (AL.getKind() == ParsedAttr::AT_DLLExport) {
9419         // dllexport trumps dllimport here.
9420         DLLImport = false;
9421         break;
9422       }
9423     }
9424     if (DLLImport) {
9425       TSK = TSK_ExplicitInstantiationDeclaration;
9426       DLLImportExplicitInstantiationDef = true;
9427     }
9428   }
9429 
9430   // Translate the parser's template argument list in our AST format.
9431   TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
9432   translateTemplateArguments(TemplateArgsIn, TemplateArgs);
9433 
9434   // Check that the template argument list is well-formed for this
9435   // template.
9436   SmallVector<TemplateArgument, 4> Converted;
9437   if (CheckTemplateArgumentList(ClassTemplate, TemplateNameLoc,
9438                                 TemplateArgs, false, Converted,
9439                                 /*UpdateArgsWithConversion=*/true))
9440     return true;
9441 
9442   // Find the class template specialization declaration that
9443   // corresponds to these arguments.
9444   void *InsertPos = nullptr;
9445   ClassTemplateSpecializationDecl *PrevDecl
9446     = ClassTemplate->findSpecialization(Converted, InsertPos);
9447 
9448   TemplateSpecializationKind PrevDecl_TSK
9449     = PrevDecl ? PrevDecl->getTemplateSpecializationKind() : TSK_Undeclared;
9450 
9451   if (TSK == TSK_ExplicitInstantiationDefinition && PrevDecl != nullptr &&
9452       Context.getTargetInfo().getTriple().isWindowsGNUEnvironment()) {
9453     // Check for dllexport class template instantiation definitions in MinGW
9454     // mode, if a previous declaration of the instantiation was seen.
9455     for (const ParsedAttr &AL : Attr) {
9456       if (AL.getKind() == ParsedAttr::AT_DLLExport) {
9457         Diag(AL.getLoc(),
9458              diag::warn_attribute_dllexport_explicit_instantiation_def);
9459         break;
9460       }
9461     }
9462   }
9463 
9464   if (CheckExplicitInstantiation(*this, ClassTemplate, TemplateNameLoc,
9465                                  SS.isSet(), TSK))
9466     return true;
9467 
9468   ClassTemplateSpecializationDecl *Specialization = nullptr;
9469 
9470   bool HasNoEffect = false;
9471   if (PrevDecl) {
9472     if (CheckSpecializationInstantiationRedecl(TemplateNameLoc, TSK,
9473                                                PrevDecl, PrevDecl_TSK,
9474                                             PrevDecl->getPointOfInstantiation(),
9475                                                HasNoEffect))
9476       return PrevDecl;
9477 
9478     // Even though HasNoEffect == true means that this explicit instantiation
9479     // has no effect on semantics, we go on to put its syntax in the AST.
9480 
9481     if (PrevDecl_TSK == TSK_ImplicitInstantiation ||
9482         PrevDecl_TSK == TSK_Undeclared) {
9483       // Since the only prior class template specialization with these
9484       // arguments was referenced but not declared, reuse that
9485       // declaration node as our own, updating the source location
9486       // for the template name to reflect our new declaration.
9487       // (Other source locations will be updated later.)
9488       Specialization = PrevDecl;
9489       Specialization->setLocation(TemplateNameLoc);
9490       PrevDecl = nullptr;
9491     }
9492 
9493     if (PrevDecl_TSK == TSK_ExplicitInstantiationDeclaration &&
9494         DLLImportExplicitInstantiationDef) {
9495       // The new specialization might add a dllimport attribute.
9496       HasNoEffect = false;
9497     }
9498   }
9499 
9500   if (!Specialization) {
9501     // Create a new class template specialization declaration node for
9502     // this explicit specialization.
9503     Specialization
9504       = ClassTemplateSpecializationDecl::Create(Context, Kind,
9505                                              ClassTemplate->getDeclContext(),
9506                                                 KWLoc, TemplateNameLoc,
9507                                                 ClassTemplate,
9508                                                 Converted,
9509                                                 PrevDecl);
9510     SetNestedNameSpecifier(*this, Specialization, SS);
9511 
9512     if (!HasNoEffect && !PrevDecl) {
9513       // Insert the new specialization.
9514       ClassTemplate->AddSpecialization(Specialization, InsertPos);
9515     }
9516   }
9517 
9518   // Build the fully-sugared type for this explicit instantiation as
9519   // the user wrote in the explicit instantiation itself. This means
9520   // that we'll pretty-print the type retrieved from the
9521   // specialization's declaration the way that the user actually wrote
9522   // the explicit instantiation, rather than formatting the name based
9523   // on the "canonical" representation used to store the template
9524   // arguments in the specialization.
9525   TypeSourceInfo *WrittenTy
9526     = Context.getTemplateSpecializationTypeInfo(Name, TemplateNameLoc,
9527                                                 TemplateArgs,
9528                                   Context.getTypeDeclType(Specialization));
9529   Specialization->setTypeAsWritten(WrittenTy);
9530 
9531   // Set source locations for keywords.
9532   Specialization->setExternLoc(ExternLoc);
9533   Specialization->setTemplateKeywordLoc(TemplateLoc);
9534   Specialization->setBraceRange(SourceRange());
9535 
9536   bool PreviouslyDLLExported = Specialization->hasAttr<DLLExportAttr>();
9537   ProcessDeclAttributeList(S, Specialization, Attr);
9538 
9539   // Add the explicit instantiation into its lexical context. However,
9540   // since explicit instantiations are never found by name lookup, we
9541   // just put it into the declaration context directly.
9542   Specialization->setLexicalDeclContext(CurContext);
9543   CurContext->addDecl(Specialization);
9544 
9545   // Syntax is now OK, so return if it has no other effect on semantics.
9546   if (HasNoEffect) {
9547     // Set the template specialization kind.
9548     Specialization->setTemplateSpecializationKind(TSK);
9549     return Specialization;
9550   }
9551 
9552   // C++ [temp.explicit]p3:
9553   //   A definition of a class template or class member template
9554   //   shall be in scope at the point of the explicit instantiation of
9555   //   the class template or class member template.
9556   //
9557   // This check comes when we actually try to perform the
9558   // instantiation.
9559   ClassTemplateSpecializationDecl *Def
9560     = cast_or_null<ClassTemplateSpecializationDecl>(
9561                                               Specialization->getDefinition());
9562   if (!Def)
9563     InstantiateClassTemplateSpecialization(TemplateNameLoc, Specialization, TSK);
9564   else if (TSK == TSK_ExplicitInstantiationDefinition) {
9565     MarkVTableUsed(TemplateNameLoc, Specialization, true);
9566     Specialization->setPointOfInstantiation(Def->getPointOfInstantiation());
9567   }
9568 
9569   // Instantiate the members of this class template specialization.
9570   Def = cast_or_null<ClassTemplateSpecializationDecl>(
9571                                        Specialization->getDefinition());
9572   if (Def) {
9573     TemplateSpecializationKind Old_TSK = Def->getTemplateSpecializationKind();
9574     // Fix a TSK_ExplicitInstantiationDeclaration followed by a
9575     // TSK_ExplicitInstantiationDefinition
9576     if (Old_TSK == TSK_ExplicitInstantiationDeclaration &&
9577         (TSK == TSK_ExplicitInstantiationDefinition ||
9578          DLLImportExplicitInstantiationDef)) {
9579       // FIXME: Need to notify the ASTMutationListener that we did this.
9580       Def->setTemplateSpecializationKind(TSK);
9581 
9582       if (!getDLLAttr(Def) && getDLLAttr(Specialization) &&
9583           (Context.getTargetInfo().getCXXABI().isMicrosoft() ||
9584            Context.getTargetInfo().getTriple().isWindowsItaniumEnvironment())) {
9585         // In the MS ABI, an explicit instantiation definition can add a dll
9586         // attribute to a template with a previous instantiation declaration.
9587         // MinGW doesn't allow this.
9588         auto *A = cast<InheritableAttr>(
9589             getDLLAttr(Specialization)->clone(getASTContext()));
9590         A->setInherited(true);
9591         Def->addAttr(A);
9592         dllExportImportClassTemplateSpecialization(*this, Def);
9593       }
9594     }
9595 
9596     // Fix a TSK_ImplicitInstantiation followed by a
9597     // TSK_ExplicitInstantiationDefinition
9598     bool NewlyDLLExported =
9599         !PreviouslyDLLExported && Specialization->hasAttr<DLLExportAttr>();
9600     if (Old_TSK == TSK_ImplicitInstantiation && NewlyDLLExported &&
9601         (Context.getTargetInfo().getCXXABI().isMicrosoft() ||
9602          Context.getTargetInfo().getTriple().isWindowsItaniumEnvironment())) {
9603       // In the MS ABI, an explicit instantiation definition can add a dll
9604       // attribute to a template with a previous implicit instantiation.
9605       // MinGW doesn't allow this. We limit clang to only adding dllexport, to
9606       // avoid potentially strange codegen behavior.  For example, if we extend
9607       // this conditional to dllimport, and we have a source file calling a
9608       // method on an implicitly instantiated template class instance and then
9609       // declaring a dllimport explicit instantiation definition for the same
9610       // template class, the codegen for the method call will not respect the
9611       // dllimport, while it will with cl. The Def will already have the DLL
9612       // attribute, since the Def and Specialization will be the same in the
9613       // case of Old_TSK == TSK_ImplicitInstantiation, and we already added the
9614       // attribute to the Specialization; we just need to make it take effect.
9615       assert(Def == Specialization &&
9616              "Def and Specialization should match for implicit instantiation");
9617       dllExportImportClassTemplateSpecialization(*this, Def);
9618     }
9619 
9620     // In MinGW mode, export the template instantiation if the declaration
9621     // was marked dllexport.
9622     if (PrevDecl_TSK == TSK_ExplicitInstantiationDeclaration &&
9623         Context.getTargetInfo().getTriple().isWindowsGNUEnvironment() &&
9624         PrevDecl->hasAttr<DLLExportAttr>()) {
9625       dllExportImportClassTemplateSpecialization(*this, Def);
9626     }
9627 
9628     // Set the template specialization kind. Make sure it is set before
9629     // instantiating the members which will trigger ASTConsumer callbacks.
9630     Specialization->setTemplateSpecializationKind(TSK);
9631     InstantiateClassTemplateSpecializationMembers(TemplateNameLoc, Def, TSK);
9632   } else {
9633 
9634     // Set the template specialization kind.
9635     Specialization->setTemplateSpecializationKind(TSK);
9636   }
9637 
9638   return Specialization;
9639 }
9640 
9641 // Explicit instantiation of a member class of a class template.
9642 DeclResult
9643 Sema::ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
9644                                  SourceLocation TemplateLoc, unsigned TagSpec,
9645                                  SourceLocation KWLoc, CXXScopeSpec &SS,
9646                                  IdentifierInfo *Name, SourceLocation NameLoc,
9647                                  const ParsedAttributesView &Attr) {
9648 
9649   bool Owned = false;
9650   bool IsDependent = false;
9651   Decl *TagD = ActOnTag(S, TagSpec, Sema::TUK_Reference,
9652                         KWLoc, SS, Name, NameLoc, Attr, AS_none,
9653                         /*ModulePrivateLoc=*/SourceLocation(),
9654                         MultiTemplateParamsArg(), Owned, IsDependent,
9655                         SourceLocation(), false, TypeResult(),
9656                         /*IsTypeSpecifier*/false,
9657                         /*IsTemplateParamOrArg*/false);
9658   assert(!IsDependent && "explicit instantiation of dependent name not yet handled");
9659 
9660   if (!TagD)
9661     return true;
9662 
9663   TagDecl *Tag = cast<TagDecl>(TagD);
9664   assert(!Tag->isEnum() && "shouldn't see enumerations here");
9665 
9666   if (Tag->isInvalidDecl())
9667     return true;
9668 
9669   CXXRecordDecl *Record = cast<CXXRecordDecl>(Tag);
9670   CXXRecordDecl *Pattern = Record->getInstantiatedFromMemberClass();
9671   if (!Pattern) {
9672     Diag(TemplateLoc, diag::err_explicit_instantiation_nontemplate_type)
9673       << Context.getTypeDeclType(Record);
9674     Diag(Record->getLocation(), diag::note_nontemplate_decl_here);
9675     return true;
9676   }
9677 
9678   // C++0x [temp.explicit]p2:
9679   //   If the explicit instantiation is for a class or member class, the
9680   //   elaborated-type-specifier in the declaration shall include a
9681   //   simple-template-id.
9682   //
9683   // C++98 has the same restriction, just worded differently.
9684   if (!ScopeSpecifierHasTemplateId(SS))
9685     Diag(TemplateLoc, diag::ext_explicit_instantiation_without_qualified_id)
9686       << Record << SS.getRange();
9687 
9688   // C++0x [temp.explicit]p2:
9689   //   There are two forms of explicit instantiation: an explicit instantiation
9690   //   definition and an explicit instantiation declaration. An explicit
9691   //   instantiation declaration begins with the extern keyword. [...]
9692   TemplateSpecializationKind TSK
9693     = ExternLoc.isInvalid()? TSK_ExplicitInstantiationDefinition
9694                            : TSK_ExplicitInstantiationDeclaration;
9695 
9696   CheckExplicitInstantiation(*this, Record, NameLoc, true, TSK);
9697 
9698   // Verify that it is okay to explicitly instantiate here.
9699   CXXRecordDecl *PrevDecl
9700     = cast_or_null<CXXRecordDecl>(Record->getPreviousDecl());
9701   if (!PrevDecl && Record->getDefinition())
9702     PrevDecl = Record;
9703   if (PrevDecl) {
9704     MemberSpecializationInfo *MSInfo = PrevDecl->getMemberSpecializationInfo();
9705     bool HasNoEffect = false;
9706     assert(MSInfo && "No member specialization information?");
9707     if (CheckSpecializationInstantiationRedecl(TemplateLoc, TSK,
9708                                                PrevDecl,
9709                                         MSInfo->getTemplateSpecializationKind(),
9710                                              MSInfo->getPointOfInstantiation(),
9711                                                HasNoEffect))
9712       return true;
9713     if (HasNoEffect)
9714       return TagD;
9715   }
9716 
9717   CXXRecordDecl *RecordDef
9718     = cast_or_null<CXXRecordDecl>(Record->getDefinition());
9719   if (!RecordDef) {
9720     // C++ [temp.explicit]p3:
9721     //   A definition of a member class of a class template shall be in scope
9722     //   at the point of an explicit instantiation of the member class.
9723     CXXRecordDecl *Def
9724       = cast_or_null<CXXRecordDecl>(Pattern->getDefinition());
9725     if (!Def) {
9726       Diag(TemplateLoc, diag::err_explicit_instantiation_undefined_member)
9727         << 0 << Record->getDeclName() << Record->getDeclContext();
9728       Diag(Pattern->getLocation(), diag::note_forward_declaration)
9729         << Pattern;
9730       return true;
9731     } else {
9732       if (InstantiateClass(NameLoc, Record, Def,
9733                            getTemplateInstantiationArgs(Record),
9734                            TSK))
9735         return true;
9736 
9737       RecordDef = cast_or_null<CXXRecordDecl>(Record->getDefinition());
9738       if (!RecordDef)
9739         return true;
9740     }
9741   }
9742 
9743   // Instantiate all of the members of the class.
9744   InstantiateClassMembers(NameLoc, RecordDef,
9745                           getTemplateInstantiationArgs(Record), TSK);
9746 
9747   if (TSK == TSK_ExplicitInstantiationDefinition)
9748     MarkVTableUsed(NameLoc, RecordDef, true);
9749 
9750   // FIXME: We don't have any representation for explicit instantiations of
9751   // member classes. Such a representation is not needed for compilation, but it
9752   // should be available for clients that want to see all of the declarations in
9753   // the source code.
9754   return TagD;
9755 }
9756 
9757 DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
9758                                             SourceLocation ExternLoc,
9759                                             SourceLocation TemplateLoc,
9760                                             Declarator &D) {
9761   // Explicit instantiations always require a name.
9762   // TODO: check if/when DNInfo should replace Name.
9763   DeclarationNameInfo NameInfo = GetNameForDeclarator(D);
9764   DeclarationName Name = NameInfo.getName();
9765   if (!Name) {
9766     if (!D.isInvalidType())
9767       Diag(D.getDeclSpec().getBeginLoc(),
9768            diag::err_explicit_instantiation_requires_name)
9769           << D.getDeclSpec().getSourceRange() << D.getSourceRange();
9770 
9771     return true;
9772   }
9773 
9774   // The scope passed in may not be a decl scope.  Zip up the scope tree until
9775   // we find one that is.
9776   while ((S->getFlags() & Scope::DeclScope) == 0 ||
9777          (S->getFlags() & Scope::TemplateParamScope) != 0)
9778     S = S->getParent();
9779 
9780   // Determine the type of the declaration.
9781   TypeSourceInfo *T = GetTypeForDeclarator(D, S);
9782   QualType R = T->getType();
9783   if (R.isNull())
9784     return true;
9785 
9786   // C++ [dcl.stc]p1:
9787   //   A storage-class-specifier shall not be specified in [...] an explicit
9788   //   instantiation (14.7.2) directive.
9789   if (D.getDeclSpec().getStorageClassSpec() == DeclSpec::SCS_typedef) {
9790     Diag(D.getIdentifierLoc(), diag::err_explicit_instantiation_of_typedef)
9791       << Name;
9792     return true;
9793   } else if (D.getDeclSpec().getStorageClassSpec()
9794                                                 != DeclSpec::SCS_unspecified) {
9795     // Complain about then remove the storage class specifier.
9796     Diag(D.getIdentifierLoc(), diag::err_explicit_instantiation_storage_class)
9797       << FixItHint::CreateRemoval(D.getDeclSpec().getStorageClassSpecLoc());
9798 
9799     D.getMutableDeclSpec().ClearStorageClassSpecs();
9800   }
9801 
9802   // C++0x [temp.explicit]p1:
9803   //   [...] An explicit instantiation of a function template shall not use the
9804   //   inline or constexpr specifiers.
9805   // Presumably, this also applies to member functions of class templates as
9806   // well.
9807   if (D.getDeclSpec().isInlineSpecified())
9808     Diag(D.getDeclSpec().getInlineSpecLoc(),
9809          getLangOpts().CPlusPlus11 ?
9810            diag::err_explicit_instantiation_inline :
9811            diag::warn_explicit_instantiation_inline_0x)
9812       << FixItHint::CreateRemoval(D.getDeclSpec().getInlineSpecLoc());
9813   if (D.getDeclSpec().hasConstexprSpecifier() && R->isFunctionType())
9814     // FIXME: Add a fix-it to remove the 'constexpr' and add a 'const' if one is
9815     // not already specified.
9816     Diag(D.getDeclSpec().getConstexprSpecLoc(),
9817          diag::err_explicit_instantiation_constexpr);
9818 
9819   // A deduction guide is not on the list of entities that can be explicitly
9820   // instantiated.
9821   if (Name.getNameKind() == DeclarationName::CXXDeductionGuideName) {
9822     Diag(D.getDeclSpec().getBeginLoc(), diag::err_deduction_guide_specialized)
9823         << /*explicit instantiation*/ 0;
9824     return true;
9825   }
9826 
9827   // C++0x [temp.explicit]p2:
9828   //   There are two forms of explicit instantiation: an explicit instantiation
9829   //   definition and an explicit instantiation declaration. An explicit
9830   //   instantiation declaration begins with the extern keyword. [...]
9831   TemplateSpecializationKind TSK
9832     = ExternLoc.isInvalid()? TSK_ExplicitInstantiationDefinition
9833                            : TSK_ExplicitInstantiationDeclaration;
9834 
9835   LookupResult Previous(*this, NameInfo, LookupOrdinaryName);
9836   LookupParsedName(Previous, S, &D.getCXXScopeSpec());
9837 
9838   if (!R->isFunctionType()) {
9839     // C++ [temp.explicit]p1:
9840     //   A [...] static data member of a class template can be explicitly
9841     //   instantiated from the member definition associated with its class
9842     //   template.
9843     // C++1y [temp.explicit]p1:
9844     //   A [...] variable [...] template specialization can be explicitly
9845     //   instantiated from its template.
9846     if (Previous.isAmbiguous())
9847       return true;
9848 
9849     VarDecl *Prev = Previous.getAsSingle<VarDecl>();
9850     VarTemplateDecl *PrevTemplate = Previous.getAsSingle<VarTemplateDecl>();
9851 
9852     if (!PrevTemplate) {
9853       if (!Prev || !Prev->isStaticDataMember()) {
9854         // We expect to see a static data member here.
9855         Diag(D.getIdentifierLoc(), diag::err_explicit_instantiation_not_known)
9856             << Name;
9857         for (LookupResult::iterator P = Previous.begin(), PEnd = Previous.end();
9858              P != PEnd; ++P)
9859           Diag((*P)->getLocation(), diag::note_explicit_instantiation_here);
9860         return true;
9861       }
9862 
9863       if (!Prev->getInstantiatedFromStaticDataMember()) {
9864         // FIXME: Check for explicit specialization?
9865         Diag(D.getIdentifierLoc(),
9866              diag::err_explicit_instantiation_data_member_not_instantiated)
9867             << Prev;
9868         Diag(Prev->getLocation(), diag::note_explicit_instantiation_here);
9869         // FIXME: Can we provide a note showing where this was declared?
9870         return true;
9871       }
9872     } else {
9873       // Explicitly instantiate a variable template.
9874 
9875       // C++1y [dcl.spec.auto]p6:
9876       //   ... A program that uses auto or decltype(auto) in a context not
9877       //   explicitly allowed in this section is ill-formed.
9878       //
9879       // This includes auto-typed variable template instantiations.
9880       if (R->isUndeducedType()) {
9881         Diag(T->getTypeLoc().getBeginLoc(),
9882              diag::err_auto_not_allowed_var_inst);
9883         return true;
9884       }
9885 
9886       if (D.getName().getKind() != UnqualifiedIdKind::IK_TemplateId) {
9887         // C++1y [temp.explicit]p3:
9888         //   If the explicit instantiation is for a variable, the unqualified-id
9889         //   in the declaration shall be a template-id.
9890         Diag(D.getIdentifierLoc(),
9891              diag::err_explicit_instantiation_without_template_id)
9892           << PrevTemplate;
9893         Diag(PrevTemplate->getLocation(),
9894              diag::note_explicit_instantiation_here);
9895         return true;
9896       }
9897 
9898       // Translate the parser's template argument list into our AST format.
9899       TemplateArgumentListInfo TemplateArgs =
9900           makeTemplateArgumentListInfo(*this, *D.getName().TemplateId);
9901 
9902       DeclResult Res = CheckVarTemplateId(PrevTemplate, TemplateLoc,
9903                                           D.getIdentifierLoc(), TemplateArgs);
9904       if (Res.isInvalid())
9905         return true;
9906 
9907       // Ignore access control bits, we don't need them for redeclaration
9908       // checking.
9909       Prev = cast<VarDecl>(Res.get());
9910     }
9911 
9912     // C++0x [temp.explicit]p2:
9913     //   If the explicit instantiation is for a member function, a member class
9914     //   or a static data member of a class template specialization, the name of
9915     //   the class template specialization in the qualified-id for the member
9916     //   name shall be a simple-template-id.
9917     //
9918     // C++98 has the same restriction, just worded differently.
9919     //
9920     // This does not apply to variable template specializations, where the
9921     // template-id is in the unqualified-id instead.
9922     if (!ScopeSpecifierHasTemplateId(D.getCXXScopeSpec()) && !PrevTemplate)
9923       Diag(D.getIdentifierLoc(),
9924            diag::ext_explicit_instantiation_without_qualified_id)
9925         << Prev << D.getCXXScopeSpec().getRange();
9926 
9927     CheckExplicitInstantiation(*this, Prev, D.getIdentifierLoc(), true, TSK);
9928 
9929     // Verify that it is okay to explicitly instantiate here.
9930     TemplateSpecializationKind PrevTSK = Prev->getTemplateSpecializationKind();
9931     SourceLocation POI = Prev->getPointOfInstantiation();
9932     bool HasNoEffect = false;
9933     if (CheckSpecializationInstantiationRedecl(D.getIdentifierLoc(), TSK, Prev,
9934                                                PrevTSK, POI, HasNoEffect))
9935       return true;
9936 
9937     if (!HasNoEffect) {
9938       // Instantiate static data member or variable template.
9939       Prev->setTemplateSpecializationKind(TSK, D.getIdentifierLoc());
9940       // Merge attributes.
9941       ProcessDeclAttributeList(S, Prev, D.getDeclSpec().getAttributes());
9942       if (TSK == TSK_ExplicitInstantiationDefinition)
9943         InstantiateVariableDefinition(D.getIdentifierLoc(), Prev);
9944     }
9945 
9946     // Check the new variable specialization against the parsed input.
9947     if (PrevTemplate && Prev && !Context.hasSameType(Prev->getType(), R)) {
9948       Diag(T->getTypeLoc().getBeginLoc(),
9949            diag::err_invalid_var_template_spec_type)
9950           << 0 << PrevTemplate << R << Prev->getType();
9951       Diag(PrevTemplate->getLocation(), diag::note_template_declared_here)
9952           << 2 << PrevTemplate->getDeclName();
9953       return true;
9954     }
9955 
9956     // FIXME: Create an ExplicitInstantiation node?
9957     return (Decl*) nullptr;
9958   }
9959 
9960   // If the declarator is a template-id, translate the parser's template
9961   // argument list into our AST format.
9962   bool HasExplicitTemplateArgs = false;
9963   TemplateArgumentListInfo TemplateArgs;
9964   if (D.getName().getKind() == UnqualifiedIdKind::IK_TemplateId) {
9965     TemplateArgs = makeTemplateArgumentListInfo(*this, *D.getName().TemplateId);
9966     HasExplicitTemplateArgs = true;
9967   }
9968 
9969   // C++ [temp.explicit]p1:
9970   //   A [...] function [...] can be explicitly instantiated from its template.
9971   //   A member function [...] of a class template can be explicitly
9972   //  instantiated from the member definition associated with its class
9973   //  template.
9974   UnresolvedSet<8> TemplateMatches;
9975   FunctionDecl *NonTemplateMatch = nullptr;
9976   TemplateSpecCandidateSet FailedCandidates(D.getIdentifierLoc());
9977   for (LookupResult::iterator P = Previous.begin(), PEnd = Previous.end();
9978        P != PEnd; ++P) {
9979     NamedDecl *Prev = *P;
9980     if (!HasExplicitTemplateArgs) {
9981       if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Prev)) {
9982         QualType Adjusted = adjustCCAndNoReturn(R, Method->getType(),
9983                                                 /*AdjustExceptionSpec*/true);
9984         if (Context.hasSameUnqualifiedType(Method->getType(), Adjusted)) {
9985           if (Method->getPrimaryTemplate()) {
9986             TemplateMatches.addDecl(Method, P.getAccess());
9987           } else {
9988             // FIXME: Can this assert ever happen?  Needs a test.
9989             assert(!NonTemplateMatch && "Multiple NonTemplateMatches");
9990             NonTemplateMatch = Method;
9991           }
9992         }
9993       }
9994     }
9995 
9996     FunctionTemplateDecl *FunTmpl = dyn_cast<FunctionTemplateDecl>(Prev);
9997     if (!FunTmpl)
9998       continue;
9999 
10000     TemplateDeductionInfo Info(FailedCandidates.getLocation());
10001     FunctionDecl *Specialization = nullptr;
10002     if (TemplateDeductionResult TDK
10003           = DeduceTemplateArguments(FunTmpl,
10004                                (HasExplicitTemplateArgs ? &TemplateArgs
10005                                                         : nullptr),
10006                                     R, Specialization, Info)) {
10007       // Keep track of almost-matches.
10008       FailedCandidates.addCandidate()
10009           .set(P.getPair(), FunTmpl->getTemplatedDecl(),
10010                MakeDeductionFailureInfo(Context, TDK, Info));
10011       (void)TDK;
10012       continue;
10013     }
10014 
10015     // Target attributes are part of the cuda function signature, so
10016     // the cuda target of the instantiated function must match that of its
10017     // template.  Given that C++ template deduction does not take
10018     // target attributes into account, we reject candidates here that
10019     // have a different target.
10020     if (LangOpts.CUDA &&
10021         IdentifyCUDATarget(Specialization,
10022                            /* IgnoreImplicitHDAttr = */ true) !=
10023             IdentifyCUDATarget(D.getDeclSpec().getAttributes())) {
10024       FailedCandidates.addCandidate().set(
10025           P.getPair(), FunTmpl->getTemplatedDecl(),
10026           MakeDeductionFailureInfo(Context, TDK_CUDATargetMismatch, Info));
10027       continue;
10028     }
10029 
10030     TemplateMatches.addDecl(Specialization, P.getAccess());
10031   }
10032 
10033   FunctionDecl *Specialization = NonTemplateMatch;
10034   if (!Specialization) {
10035     // Find the most specialized function template specialization.
10036     UnresolvedSetIterator Result = getMostSpecialized(
10037         TemplateMatches.begin(), TemplateMatches.end(), FailedCandidates,
10038         D.getIdentifierLoc(),
10039         PDiag(diag::err_explicit_instantiation_not_known) << Name,
10040         PDiag(diag::err_explicit_instantiation_ambiguous) << Name,
10041         PDiag(diag::note_explicit_instantiation_candidate));
10042 
10043     if (Result == TemplateMatches.end())
10044       return true;
10045 
10046     // Ignore access control bits, we don't need them for redeclaration checking.
10047     Specialization = cast<FunctionDecl>(*Result);
10048   }
10049 
10050   // C++11 [except.spec]p4
10051   // In an explicit instantiation an exception-specification may be specified,
10052   // but is not required.
10053   // If an exception-specification is specified in an explicit instantiation
10054   // directive, it shall be compatible with the exception-specifications of
10055   // other declarations of that function.
10056   if (auto *FPT = R->getAs<FunctionProtoType>())
10057     if (FPT->hasExceptionSpec()) {
10058       unsigned DiagID =
10059           diag::err_mismatched_exception_spec_explicit_instantiation;
10060       if (getLangOpts().MicrosoftExt)
10061         DiagID = diag::ext_mismatched_exception_spec_explicit_instantiation;
10062       bool Result = CheckEquivalentExceptionSpec(
10063           PDiag(DiagID) << Specialization->getType(),
10064           PDiag(diag::note_explicit_instantiation_here),
10065           Specialization->getType()->getAs<FunctionProtoType>(),
10066           Specialization->getLocation(), FPT, D.getBeginLoc());
10067       // In Microsoft mode, mismatching exception specifications just cause a
10068       // warning.
10069       if (!getLangOpts().MicrosoftExt && Result)
10070         return true;
10071     }
10072 
10073   if (Specialization->getTemplateSpecializationKind() == TSK_Undeclared) {
10074     Diag(D.getIdentifierLoc(),
10075          diag::err_explicit_instantiation_member_function_not_instantiated)
10076       << Specialization
10077       << (Specialization->getTemplateSpecializationKind() ==
10078           TSK_ExplicitSpecialization);
10079     Diag(Specialization->getLocation(), diag::note_explicit_instantiation_here);
10080     return true;
10081   }
10082 
10083   FunctionDecl *PrevDecl = Specialization->getPreviousDecl();
10084   if (!PrevDecl && Specialization->isThisDeclarationADefinition())
10085     PrevDecl = Specialization;
10086 
10087   if (PrevDecl) {
10088     bool HasNoEffect = false;
10089     if (CheckSpecializationInstantiationRedecl(D.getIdentifierLoc(), TSK,
10090                                                PrevDecl,
10091                                      PrevDecl->getTemplateSpecializationKind(),
10092                                           PrevDecl->getPointOfInstantiation(),
10093                                                HasNoEffect))
10094       return true;
10095 
10096     // FIXME: We may still want to build some representation of this
10097     // explicit specialization.
10098     if (HasNoEffect)
10099       return (Decl*) nullptr;
10100   }
10101 
10102   // HACK: libc++ has a bug where it attempts to explicitly instantiate the
10103   // functions
10104   //     valarray<size_t>::valarray(size_t) and
10105   //     valarray<size_t>::~valarray()
10106   // that it declared to have internal linkage with the internal_linkage
10107   // attribute. Ignore the explicit instantiation declaration in this case.
10108   if (Specialization->hasAttr<InternalLinkageAttr>() &&
10109       TSK == TSK_ExplicitInstantiationDeclaration) {
10110     if (auto *RD = dyn_cast<CXXRecordDecl>(Specialization->getDeclContext()))
10111       if (RD->getIdentifier() && RD->getIdentifier()->isStr("valarray") &&
10112           RD->isInStdNamespace())
10113         return (Decl*) nullptr;
10114   }
10115 
10116   ProcessDeclAttributeList(S, Specialization, D.getDeclSpec().getAttributes());
10117 
10118   // In MSVC mode, dllimported explicit instantiation definitions are treated as
10119   // instantiation declarations.
10120   if (TSK == TSK_ExplicitInstantiationDefinition &&
10121       Specialization->hasAttr<DLLImportAttr>() &&
10122       Context.getTargetInfo().getCXXABI().isMicrosoft())
10123     TSK = TSK_ExplicitInstantiationDeclaration;
10124 
10125   Specialization->setTemplateSpecializationKind(TSK, D.getIdentifierLoc());
10126 
10127   if (Specialization->isDefined()) {
10128     // Let the ASTConsumer know that this function has been explicitly
10129     // instantiated now, and its linkage might have changed.
10130     Consumer.HandleTopLevelDecl(DeclGroupRef(Specialization));
10131   } else if (TSK == TSK_ExplicitInstantiationDefinition)
10132     InstantiateFunctionDefinition(D.getIdentifierLoc(), Specialization);
10133 
10134   // C++0x [temp.explicit]p2:
10135   //   If the explicit instantiation is for a member function, a member class
10136   //   or a static data member of a class template specialization, the name of
10137   //   the class template specialization in the qualified-id for the member
10138   //   name shall be a simple-template-id.
10139   //
10140   // C++98 has the same restriction, just worded differently.
10141   FunctionTemplateDecl *FunTmpl = Specialization->getPrimaryTemplate();
10142   if (D.getName().getKind() != UnqualifiedIdKind::IK_TemplateId && !FunTmpl &&
10143       D.getCXXScopeSpec().isSet() &&
10144       !ScopeSpecifierHasTemplateId(D.getCXXScopeSpec()))
10145     Diag(D.getIdentifierLoc(),
10146          diag::ext_explicit_instantiation_without_qualified_id)
10147     << Specialization << D.getCXXScopeSpec().getRange();
10148 
10149   CheckExplicitInstantiation(
10150       *this,
10151       FunTmpl ? (NamedDecl *)FunTmpl
10152               : Specialization->getInstantiatedFromMemberFunction(),
10153       D.getIdentifierLoc(), D.getCXXScopeSpec().isSet(), TSK);
10154 
10155   // FIXME: Create some kind of ExplicitInstantiationDecl here.
10156   return (Decl*) nullptr;
10157 }
10158 
10159 TypeResult
10160 Sema::ActOnDependentTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
10161                         const CXXScopeSpec &SS, IdentifierInfo *Name,
10162                         SourceLocation TagLoc, SourceLocation NameLoc) {
10163   // This has to hold, because SS is expected to be defined.
10164   assert(Name && "Expected a name in a dependent tag");
10165 
10166   NestedNameSpecifier *NNS = SS.getScopeRep();
10167   if (!NNS)
10168     return true;
10169 
10170   TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForTypeSpec(TagSpec);
10171 
10172   if (TUK == TUK_Declaration || TUK == TUK_Definition) {
10173     Diag(NameLoc, diag::err_dependent_tag_decl)
10174       << (TUK == TUK_Definition) << Kind << SS.getRange();
10175     return true;
10176   }
10177 
10178   // Create the resulting type.
10179   ElaboratedTypeKeyword Kwd = TypeWithKeyword::getKeywordForTagTypeKind(Kind);
10180   QualType Result = Context.getDependentNameType(Kwd, NNS, Name);
10181 
10182   // Create type-source location information for this type.
10183   TypeLocBuilder TLB;
10184   DependentNameTypeLoc TL = TLB.push<DependentNameTypeLoc>(Result);
10185   TL.setElaboratedKeywordLoc(TagLoc);
10186   TL.setQualifierLoc(SS.getWithLocInContext(Context));
10187   TL.setNameLoc(NameLoc);
10188   return CreateParsedType(Result, TLB.getTypeSourceInfo(Context, Result));
10189 }
10190 
10191 TypeResult
10192 Sema::ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
10193                         const CXXScopeSpec &SS, const IdentifierInfo &II,
10194                         SourceLocation IdLoc) {
10195   if (SS.isInvalid())
10196     return true;
10197 
10198   if (TypenameLoc.isValid() && S && !S->getTemplateParamParent())
10199     Diag(TypenameLoc,
10200          getLangOpts().CPlusPlus11 ?
10201            diag::warn_cxx98_compat_typename_outside_of_template :
10202            diag::ext_typename_outside_of_template)
10203       << FixItHint::CreateRemoval(TypenameLoc);
10204 
10205   NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
10206   TypeSourceInfo *TSI = nullptr;
10207   QualType T = CheckTypenameType(TypenameLoc.isValid()? ETK_Typename : ETK_None,
10208                                  TypenameLoc, QualifierLoc, II, IdLoc, &TSI,
10209                                  /*DeducedTSTContext=*/true);
10210   if (T.isNull())
10211     return true;
10212   return CreateParsedType(T, TSI);
10213 }
10214 
10215 TypeResult
10216 Sema::ActOnTypenameType(Scope *S,
10217                         SourceLocation TypenameLoc,
10218                         const CXXScopeSpec &SS,
10219                         SourceLocation TemplateKWLoc,
10220                         TemplateTy TemplateIn,
10221                         IdentifierInfo *TemplateII,
10222                         SourceLocation TemplateIILoc,
10223                         SourceLocation LAngleLoc,
10224                         ASTTemplateArgsPtr TemplateArgsIn,
10225                         SourceLocation RAngleLoc) {
10226   if (TypenameLoc.isValid() && S && !S->getTemplateParamParent())
10227     Diag(TypenameLoc,
10228          getLangOpts().CPlusPlus11 ?
10229            diag::warn_cxx98_compat_typename_outside_of_template :
10230            diag::ext_typename_outside_of_template)
10231       << FixItHint::CreateRemoval(TypenameLoc);
10232 
10233   // Strangely, non-type results are not ignored by this lookup, so the
10234   // program is ill-formed if it finds an injected-class-name.
10235   if (TypenameLoc.isValid()) {
10236     auto *LookupRD =
10237         dyn_cast_or_null<CXXRecordDecl>(computeDeclContext(SS, false));
10238     if (LookupRD && LookupRD->getIdentifier() == TemplateII) {
10239       Diag(TemplateIILoc,
10240            diag::ext_out_of_line_qualified_id_type_names_constructor)
10241         << TemplateII << 0 /*injected-class-name used as template name*/
10242         << (TemplateKWLoc.isValid() ? 1 : 0 /*'template'/'typename' keyword*/);
10243     }
10244   }
10245 
10246   // Translate the parser's template argument list in our AST format.
10247   TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
10248   translateTemplateArguments(TemplateArgsIn, TemplateArgs);
10249 
10250   TemplateName Template = TemplateIn.get();
10251   if (DependentTemplateName *DTN = Template.getAsDependentTemplateName()) {
10252     // Construct a dependent template specialization type.
10253     assert(DTN && "dependent template has non-dependent name?");
10254     assert(DTN->getQualifier() == SS.getScopeRep());
10255     QualType T = Context.getDependentTemplateSpecializationType(ETK_Typename,
10256                                                           DTN->getQualifier(),
10257                                                           DTN->getIdentifier(),
10258                                                                 TemplateArgs);
10259 
10260     // Create source-location information for this type.
10261     TypeLocBuilder Builder;
10262     DependentTemplateSpecializationTypeLoc SpecTL
10263     = Builder.push<DependentTemplateSpecializationTypeLoc>(T);
10264     SpecTL.setElaboratedKeywordLoc(TypenameLoc);
10265     SpecTL.setQualifierLoc(SS.getWithLocInContext(Context));
10266     SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
10267     SpecTL.setTemplateNameLoc(TemplateIILoc);
10268     SpecTL.setLAngleLoc(LAngleLoc);
10269     SpecTL.setRAngleLoc(RAngleLoc);
10270     for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
10271       SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
10272     return CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
10273   }
10274 
10275   QualType T = CheckTemplateIdType(Template, TemplateIILoc, TemplateArgs);
10276   if (T.isNull())
10277     return true;
10278 
10279   // Provide source-location information for the template specialization type.
10280   TypeLocBuilder Builder;
10281   TemplateSpecializationTypeLoc SpecTL
10282     = Builder.push<TemplateSpecializationTypeLoc>(T);
10283   SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
10284   SpecTL.setTemplateNameLoc(TemplateIILoc);
10285   SpecTL.setLAngleLoc(LAngleLoc);
10286   SpecTL.setRAngleLoc(RAngleLoc);
10287   for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
10288     SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
10289 
10290   T = Context.getElaboratedType(ETK_Typename, SS.getScopeRep(), T);
10291   ElaboratedTypeLoc TL = Builder.push<ElaboratedTypeLoc>(T);
10292   TL.setElaboratedKeywordLoc(TypenameLoc);
10293   TL.setQualifierLoc(SS.getWithLocInContext(Context));
10294 
10295   TypeSourceInfo *TSI = Builder.getTypeSourceInfo(Context, T);
10296   return CreateParsedType(T, TSI);
10297 }
10298 
10299 
10300 /// Determine whether this failed name lookup should be treated as being
10301 /// disabled by a usage of std::enable_if.
10302 static bool isEnableIf(NestedNameSpecifierLoc NNS, const IdentifierInfo &II,
10303                        SourceRange &CondRange, Expr *&Cond) {
10304   // We must be looking for a ::type...
10305   if (!II.isStr("type"))
10306     return false;
10307 
10308   // ... within an explicitly-written template specialization...
10309   if (!NNS || !NNS.getNestedNameSpecifier()->getAsType())
10310     return false;
10311   TypeLoc EnableIfTy = NNS.getTypeLoc();
10312   TemplateSpecializationTypeLoc EnableIfTSTLoc =
10313       EnableIfTy.getAs<TemplateSpecializationTypeLoc>();
10314   if (!EnableIfTSTLoc || EnableIfTSTLoc.getNumArgs() == 0)
10315     return false;
10316   const TemplateSpecializationType *EnableIfTST = EnableIfTSTLoc.getTypePtr();
10317 
10318   // ... which names a complete class template declaration...
10319   const TemplateDecl *EnableIfDecl =
10320     EnableIfTST->getTemplateName().getAsTemplateDecl();
10321   if (!EnableIfDecl || EnableIfTST->isIncompleteType())
10322     return false;
10323 
10324   // ... called "enable_if".
10325   const IdentifierInfo *EnableIfII =
10326     EnableIfDecl->getDeclName().getAsIdentifierInfo();
10327   if (!EnableIfII || !EnableIfII->isStr("enable_if"))
10328     return false;
10329 
10330   // Assume the first template argument is the condition.
10331   CondRange = EnableIfTSTLoc.getArgLoc(0).getSourceRange();
10332 
10333   // Dig out the condition.
10334   Cond = nullptr;
10335   if (EnableIfTSTLoc.getArgLoc(0).getArgument().getKind()
10336         != TemplateArgument::Expression)
10337     return true;
10338 
10339   Cond = EnableIfTSTLoc.getArgLoc(0).getSourceExpression();
10340 
10341   // Ignore Boolean literals; they add no value.
10342   if (isa<CXXBoolLiteralExpr>(Cond->IgnoreParenCasts()))
10343     Cond = nullptr;
10344 
10345   return true;
10346 }
10347 
10348 QualType
10349 Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
10350                         SourceLocation KeywordLoc,
10351                         NestedNameSpecifierLoc QualifierLoc,
10352                         const IdentifierInfo &II,
10353                         SourceLocation IILoc,
10354                         TypeSourceInfo **TSI,
10355                         bool DeducedTSTContext) {
10356   QualType T = CheckTypenameType(Keyword, KeywordLoc, QualifierLoc, II, IILoc,
10357                                  DeducedTSTContext);
10358   if (T.isNull())
10359     return QualType();
10360 
10361   *TSI = Context.CreateTypeSourceInfo(T);
10362   if (isa<DependentNameType>(T)) {
10363     DependentNameTypeLoc TL =
10364         (*TSI)->getTypeLoc().castAs<DependentNameTypeLoc>();
10365     TL.setElaboratedKeywordLoc(KeywordLoc);
10366     TL.setQualifierLoc(QualifierLoc);
10367     TL.setNameLoc(IILoc);
10368   } else {
10369     ElaboratedTypeLoc TL = (*TSI)->getTypeLoc().castAs<ElaboratedTypeLoc>();
10370     TL.setElaboratedKeywordLoc(KeywordLoc);
10371     TL.setQualifierLoc(QualifierLoc);
10372     TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(IILoc);
10373   }
10374   return T;
10375 }
10376 
10377 /// Build the type that describes a C++ typename specifier,
10378 /// e.g., "typename T::type".
10379 QualType
10380 Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
10381                         SourceLocation KeywordLoc,
10382                         NestedNameSpecifierLoc QualifierLoc,
10383                         const IdentifierInfo &II,
10384                         SourceLocation IILoc, bool DeducedTSTContext) {
10385   CXXScopeSpec SS;
10386   SS.Adopt(QualifierLoc);
10387 
10388   DeclContext *Ctx = nullptr;
10389   if (QualifierLoc) {
10390     Ctx = computeDeclContext(SS);
10391     if (!Ctx) {
10392       // If the nested-name-specifier is dependent and couldn't be
10393       // resolved to a type, build a typename type.
10394       assert(QualifierLoc.getNestedNameSpecifier()->isDependent());
10395       return Context.getDependentNameType(Keyword,
10396                                           QualifierLoc.getNestedNameSpecifier(),
10397                                           &II);
10398     }
10399 
10400     // If the nested-name-specifier refers to the current instantiation,
10401     // the "typename" keyword itself is superfluous. In C++03, the
10402     // program is actually ill-formed. However, DR 382 (in C++0x CD1)
10403     // allows such extraneous "typename" keywords, and we retroactively
10404     // apply this DR to C++03 code with only a warning. In any case we continue.
10405 
10406     if (RequireCompleteDeclContext(SS, Ctx))
10407       return QualType();
10408   }
10409 
10410   DeclarationName Name(&II);
10411   LookupResult Result(*this, Name, IILoc, LookupOrdinaryName);
10412   if (Ctx)
10413     LookupQualifiedName(Result, Ctx, SS);
10414   else
10415     LookupName(Result, CurScope);
10416   unsigned DiagID = 0;
10417   Decl *Referenced = nullptr;
10418   switch (Result.getResultKind()) {
10419   case LookupResult::NotFound: {
10420     // If we're looking up 'type' within a template named 'enable_if', produce
10421     // a more specific diagnostic.
10422     SourceRange CondRange;
10423     Expr *Cond = nullptr;
10424     if (Ctx && isEnableIf(QualifierLoc, II, CondRange, Cond)) {
10425       // If we have a condition, narrow it down to the specific failed
10426       // condition.
10427       if (Cond) {
10428         Expr *FailedCond;
10429         std::string FailedDescription;
10430         std::tie(FailedCond, FailedDescription) =
10431           findFailedBooleanCondition(Cond);
10432 
10433         Diag(FailedCond->getExprLoc(),
10434              diag::err_typename_nested_not_found_requirement)
10435           << FailedDescription
10436           << FailedCond->getSourceRange();
10437         return QualType();
10438       }
10439 
10440       Diag(CondRange.getBegin(),
10441            diag::err_typename_nested_not_found_enable_if)
10442           << Ctx << CondRange;
10443       return QualType();
10444     }
10445 
10446     DiagID = Ctx ? diag::err_typename_nested_not_found
10447                  : diag::err_unknown_typename;
10448     break;
10449   }
10450 
10451   case LookupResult::FoundUnresolvedValue: {
10452     // We found a using declaration that is a value. Most likely, the using
10453     // declaration itself is meant to have the 'typename' keyword.
10454     SourceRange FullRange(KeywordLoc.isValid() ? KeywordLoc : SS.getBeginLoc(),
10455                           IILoc);
10456     Diag(IILoc, diag::err_typename_refers_to_using_value_decl)
10457       << Name << Ctx << FullRange;
10458     if (UnresolvedUsingValueDecl *Using
10459           = dyn_cast<UnresolvedUsingValueDecl>(Result.getRepresentativeDecl())){
10460       SourceLocation Loc = Using->getQualifierLoc().getBeginLoc();
10461       Diag(Loc, diag::note_using_value_decl_missing_typename)
10462         << FixItHint::CreateInsertion(Loc, "typename ");
10463     }
10464   }
10465   // Fall through to create a dependent typename type, from which we can recover
10466   // better.
10467   LLVM_FALLTHROUGH;
10468 
10469   case LookupResult::NotFoundInCurrentInstantiation:
10470     // Okay, it's a member of an unknown instantiation.
10471     return Context.getDependentNameType(Keyword,
10472                                         QualifierLoc.getNestedNameSpecifier(),
10473                                         &II);
10474 
10475   case LookupResult::Found:
10476     if (TypeDecl *Type = dyn_cast<TypeDecl>(Result.getFoundDecl())) {
10477       // C++ [class.qual]p2:
10478       //   In a lookup in which function names are not ignored and the
10479       //   nested-name-specifier nominates a class C, if the name specified
10480       //   after the nested-name-specifier, when looked up in C, is the
10481       //   injected-class-name of C [...] then the name is instead considered
10482       //   to name the constructor of class C.
10483       //
10484       // Unlike in an elaborated-type-specifier, function names are not ignored
10485       // in typename-specifier lookup. However, they are ignored in all the
10486       // contexts where we form a typename type with no keyword (that is, in
10487       // mem-initializer-ids, base-specifiers, and elaborated-type-specifiers).
10488       //
10489       // FIXME: That's not strictly true: mem-initializer-id lookup does not
10490       // ignore functions, but that appears to be an oversight.
10491       auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(Ctx);
10492       auto *FoundRD = dyn_cast<CXXRecordDecl>(Type);
10493       if (Keyword == ETK_Typename && LookupRD && FoundRD &&
10494           FoundRD->isInjectedClassName() &&
10495           declaresSameEntity(LookupRD, cast<Decl>(FoundRD->getParent())))
10496         Diag(IILoc, diag::ext_out_of_line_qualified_id_type_names_constructor)
10497             << &II << 1 << 0 /*'typename' keyword used*/;
10498 
10499       // We found a type. Build an ElaboratedType, since the
10500       // typename-specifier was just sugar.
10501       MarkAnyDeclReferenced(Type->getLocation(), Type, /*OdrUse=*/false);
10502       return Context.getElaboratedType(Keyword,
10503                                        QualifierLoc.getNestedNameSpecifier(),
10504                                        Context.getTypeDeclType(Type));
10505     }
10506 
10507     // C++ [dcl.type.simple]p2:
10508     //   A type-specifier of the form
10509     //     typename[opt] nested-name-specifier[opt] template-name
10510     //   is a placeholder for a deduced class type [...].
10511     if (getLangOpts().CPlusPlus17) {
10512       if (auto *TD = getAsTypeTemplateDecl(Result.getFoundDecl())) {
10513         if (!DeducedTSTContext) {
10514           QualType T(QualifierLoc
10515                          ? QualifierLoc.getNestedNameSpecifier()->getAsType()
10516                          : nullptr, 0);
10517           if (!T.isNull())
10518             Diag(IILoc, diag::err_dependent_deduced_tst)
10519               << (int)getTemplateNameKindForDiagnostics(TemplateName(TD)) << T;
10520           else
10521             Diag(IILoc, diag::err_deduced_tst)
10522               << (int)getTemplateNameKindForDiagnostics(TemplateName(TD));
10523           Diag(TD->getLocation(), diag::note_template_decl_here);
10524           return QualType();
10525         }
10526         return Context.getElaboratedType(
10527             Keyword, QualifierLoc.getNestedNameSpecifier(),
10528             Context.getDeducedTemplateSpecializationType(TemplateName(TD),
10529                                                          QualType(), false));
10530       }
10531     }
10532 
10533     DiagID = Ctx ? diag::err_typename_nested_not_type
10534                  : diag::err_typename_not_type;
10535     Referenced = Result.getFoundDecl();
10536     break;
10537 
10538   case LookupResult::FoundOverloaded:
10539     DiagID = Ctx ? diag::err_typename_nested_not_type
10540                  : diag::err_typename_not_type;
10541     Referenced = *Result.begin();
10542     break;
10543 
10544   case LookupResult::Ambiguous:
10545     return QualType();
10546   }
10547 
10548   // If we get here, it's because name lookup did not find a
10549   // type. Emit an appropriate diagnostic and return an error.
10550   SourceRange FullRange(KeywordLoc.isValid() ? KeywordLoc : SS.getBeginLoc(),
10551                         IILoc);
10552   if (Ctx)
10553     Diag(IILoc, DiagID) << FullRange << Name << Ctx;
10554   else
10555     Diag(IILoc, DiagID) << FullRange << Name;
10556   if (Referenced)
10557     Diag(Referenced->getLocation(),
10558          Ctx ? diag::note_typename_member_refers_here
10559              : diag::note_typename_refers_here)
10560       << Name;
10561   return QualType();
10562 }
10563 
10564 namespace {
10565   // See Sema::RebuildTypeInCurrentInstantiation
10566   class CurrentInstantiationRebuilder
10567     : public TreeTransform<CurrentInstantiationRebuilder> {
10568     SourceLocation Loc;
10569     DeclarationName Entity;
10570 
10571   public:
10572     typedef TreeTransform<CurrentInstantiationRebuilder> inherited;
10573 
10574     CurrentInstantiationRebuilder(Sema &SemaRef,
10575                                   SourceLocation Loc,
10576                                   DeclarationName Entity)
10577     : TreeTransform<CurrentInstantiationRebuilder>(SemaRef),
10578       Loc(Loc), Entity(Entity) { }
10579 
10580     /// Determine whether the given type \p T has already been
10581     /// transformed.
10582     ///
10583     /// For the purposes of type reconstruction, a type has already been
10584     /// transformed if it is NULL or if it is not dependent.
10585     bool AlreadyTransformed(QualType T) {
10586       return T.isNull() || !T->isDependentType();
10587     }
10588 
10589     /// Returns the location of the entity whose type is being
10590     /// rebuilt.
10591     SourceLocation getBaseLocation() { return Loc; }
10592 
10593     /// Returns the name of the entity whose type is being rebuilt.
10594     DeclarationName getBaseEntity() { return Entity; }
10595 
10596     /// Sets the "base" location and entity when that
10597     /// information is known based on another transformation.
10598     void setBase(SourceLocation Loc, DeclarationName Entity) {
10599       this->Loc = Loc;
10600       this->Entity = Entity;
10601     }
10602 
10603     ExprResult TransformLambdaExpr(LambdaExpr *E) {
10604       // Lambdas never need to be transformed.
10605       return E;
10606     }
10607   };
10608 } // end anonymous namespace
10609 
10610 /// Rebuilds a type within the context of the current instantiation.
10611 ///
10612 /// The type \p T is part of the type of an out-of-line member definition of
10613 /// a class template (or class template partial specialization) that was parsed
10614 /// and constructed before we entered the scope of the class template (or
10615 /// partial specialization thereof). This routine will rebuild that type now
10616 /// that we have entered the declarator's scope, which may produce different
10617 /// canonical types, e.g.,
10618 ///
10619 /// \code
10620 /// template<typename T>
10621 /// struct X {
10622 ///   typedef T* pointer;
10623 ///   pointer data();
10624 /// };
10625 ///
10626 /// template<typename T>
10627 /// typename X<T>::pointer X<T>::data() { ... }
10628 /// \endcode
10629 ///
10630 /// Here, the type "typename X<T>::pointer" will be created as a DependentNameType,
10631 /// since we do not know that we can look into X<T> when we parsed the type.
10632 /// This function will rebuild the type, performing the lookup of "pointer"
10633 /// in X<T> and returning an ElaboratedType whose canonical type is the same
10634 /// as the canonical type of T*, allowing the return types of the out-of-line
10635 /// definition and the declaration to match.
10636 TypeSourceInfo *Sema::RebuildTypeInCurrentInstantiation(TypeSourceInfo *T,
10637                                                         SourceLocation Loc,
10638                                                         DeclarationName Name) {
10639   if (!T || !T->getType()->isDependentType())
10640     return T;
10641 
10642   CurrentInstantiationRebuilder Rebuilder(*this, Loc, Name);
10643   return Rebuilder.TransformType(T);
10644 }
10645 
10646 ExprResult Sema::RebuildExprInCurrentInstantiation(Expr *E) {
10647   CurrentInstantiationRebuilder Rebuilder(*this, E->getExprLoc(),
10648                                           DeclarationName());
10649   return Rebuilder.TransformExpr(E);
10650 }
10651 
10652 bool Sema::RebuildNestedNameSpecifierInCurrentInstantiation(CXXScopeSpec &SS) {
10653   if (SS.isInvalid())
10654     return true;
10655 
10656   NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
10657   CurrentInstantiationRebuilder Rebuilder(*this, SS.getRange().getBegin(),
10658                                           DeclarationName());
10659   NestedNameSpecifierLoc Rebuilt
10660     = Rebuilder.TransformNestedNameSpecifierLoc(QualifierLoc);
10661   if (!Rebuilt)
10662     return true;
10663 
10664   SS.Adopt(Rebuilt);
10665   return false;
10666 }
10667 
10668 /// Rebuild the template parameters now that we know we're in a current
10669 /// instantiation.
10670 bool Sema::RebuildTemplateParamsInCurrentInstantiation(
10671                                                TemplateParameterList *Params) {
10672   for (unsigned I = 0, N = Params->size(); I != N; ++I) {
10673     Decl *Param = Params->getParam(I);
10674 
10675     // There is nothing to rebuild in a type parameter.
10676     if (isa<TemplateTypeParmDecl>(Param))
10677       continue;
10678 
10679     // Rebuild the template parameter list of a template template parameter.
10680     if (TemplateTemplateParmDecl *TTP
10681         = dyn_cast<TemplateTemplateParmDecl>(Param)) {
10682       if (RebuildTemplateParamsInCurrentInstantiation(
10683             TTP->getTemplateParameters()))
10684         return true;
10685 
10686       continue;
10687     }
10688 
10689     // Rebuild the type of a non-type template parameter.
10690     NonTypeTemplateParmDecl *NTTP = cast<NonTypeTemplateParmDecl>(Param);
10691     TypeSourceInfo *NewTSI
10692       = RebuildTypeInCurrentInstantiation(NTTP->getTypeSourceInfo(),
10693                                           NTTP->getLocation(),
10694                                           NTTP->getDeclName());
10695     if (!NewTSI)
10696       return true;
10697 
10698     if (NewTSI->getType()->isUndeducedType()) {
10699       // C++17 [temp.dep.expr]p3:
10700       //   An id-expression is type-dependent if it contains
10701       //    - an identifier associated by name lookup with a non-type
10702       //      template-parameter declared with a type that contains a
10703       //      placeholder type (7.1.7.4),
10704       NewTSI = SubstAutoTypeSourceInfo(NewTSI, Context.DependentTy);
10705     }
10706 
10707     if (NewTSI != NTTP->getTypeSourceInfo()) {
10708       NTTP->setTypeSourceInfo(NewTSI);
10709       NTTP->setType(NewTSI->getType());
10710     }
10711   }
10712 
10713   return false;
10714 }
10715 
10716 /// Produces a formatted string that describes the binding of
10717 /// template parameters to template arguments.
10718 std::string
10719 Sema::getTemplateArgumentBindingsText(const TemplateParameterList *Params,
10720                                       const TemplateArgumentList &Args) {
10721   return getTemplateArgumentBindingsText(Params, Args.data(), Args.size());
10722 }
10723 
10724 std::string
10725 Sema::getTemplateArgumentBindingsText(const TemplateParameterList *Params,
10726                                       const TemplateArgument *Args,
10727                                       unsigned NumArgs) {
10728   SmallString<128> Str;
10729   llvm::raw_svector_ostream Out(Str);
10730 
10731   if (!Params || Params->size() == 0 || NumArgs == 0)
10732     return std::string();
10733 
10734   for (unsigned I = 0, N = Params->size(); I != N; ++I) {
10735     if (I >= NumArgs)
10736       break;
10737 
10738     if (I == 0)
10739       Out << "[with ";
10740     else
10741       Out << ", ";
10742 
10743     if (const IdentifierInfo *Id = Params->getParam(I)->getIdentifier()) {
10744       Out << Id->getName();
10745     } else {
10746       Out << '$' << I;
10747     }
10748 
10749     Out << " = ";
10750     Args[I].print(getPrintingPolicy(), Out);
10751   }
10752 
10753   Out << ']';
10754   return std::string(Out.str());
10755 }
10756 
10757 void Sema::MarkAsLateParsedTemplate(FunctionDecl *FD, Decl *FnD,
10758                                     CachedTokens &Toks) {
10759   if (!FD)
10760     return;
10761 
10762   auto LPT = std::make_unique<LateParsedTemplate>();
10763 
10764   // Take tokens to avoid allocations
10765   LPT->Toks.swap(Toks);
10766   LPT->D = FnD;
10767   LateParsedTemplateMap.insert(std::make_pair(FD, std::move(LPT)));
10768 
10769   FD->setLateTemplateParsed(true);
10770 }
10771 
10772 void Sema::UnmarkAsLateParsedTemplate(FunctionDecl *FD) {
10773   if (!FD)
10774     return;
10775   FD->setLateTemplateParsed(false);
10776 }
10777 
10778 bool Sema::IsInsideALocalClassWithinATemplateFunction() {
10779   DeclContext *DC = CurContext;
10780 
10781   while (DC) {
10782     if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(CurContext)) {
10783       const FunctionDecl *FD = RD->isLocalClass();
10784       return (FD && FD->getTemplatedKind() != FunctionDecl::TK_NonTemplate);
10785     } else if (DC->isTranslationUnit() || DC->isNamespace())
10786       return false;
10787 
10788     DC = DC->getParent();
10789   }
10790   return false;
10791 }
10792 
10793 namespace {
10794 /// Walk the path from which a declaration was instantiated, and check
10795 /// that every explicit specialization along that path is visible. This enforces
10796 /// C++ [temp.expl.spec]/6:
10797 ///
10798 ///   If a template, a member template or a member of a class template is
10799 ///   explicitly specialized then that specialization shall be declared before
10800 ///   the first use of that specialization that would cause an implicit
10801 ///   instantiation to take place, in every translation unit in which such a
10802 ///   use occurs; no diagnostic is required.
10803 ///
10804 /// and also C++ [temp.class.spec]/1:
10805 ///
10806 ///   A partial specialization shall be declared before the first use of a
10807 ///   class template specialization that would make use of the partial
10808 ///   specialization as the result of an implicit or explicit instantiation
10809 ///   in every translation unit in which such a use occurs; no diagnostic is
10810 ///   required.
10811 class ExplicitSpecializationVisibilityChecker {
10812   Sema &S;
10813   SourceLocation Loc;
10814   llvm::SmallVector<Module *, 8> Modules;
10815 
10816 public:
10817   ExplicitSpecializationVisibilityChecker(Sema &S, SourceLocation Loc)
10818       : S(S), Loc(Loc) {}
10819 
10820   void check(NamedDecl *ND) {
10821     if (auto *FD = dyn_cast<FunctionDecl>(ND))
10822       return checkImpl(FD);
10823     if (auto *RD = dyn_cast<CXXRecordDecl>(ND))
10824       return checkImpl(RD);
10825     if (auto *VD = dyn_cast<VarDecl>(ND))
10826       return checkImpl(VD);
10827     if (auto *ED = dyn_cast<EnumDecl>(ND))
10828       return checkImpl(ED);
10829   }
10830 
10831 private:
10832   void diagnose(NamedDecl *D, bool IsPartialSpec) {
10833     auto Kind = IsPartialSpec ? Sema::MissingImportKind::PartialSpecialization
10834                               : Sema::MissingImportKind::ExplicitSpecialization;
10835     const bool Recover = true;
10836 
10837     // If we got a custom set of modules (because only a subset of the
10838     // declarations are interesting), use them, otherwise let
10839     // diagnoseMissingImport intelligently pick some.
10840     if (Modules.empty())
10841       S.diagnoseMissingImport(Loc, D, Kind, Recover);
10842     else
10843       S.diagnoseMissingImport(Loc, D, D->getLocation(), Modules, Kind, Recover);
10844   }
10845 
10846   // Check a specific declaration. There are three problematic cases:
10847   //
10848   //  1) The declaration is an explicit specialization of a template
10849   //     specialization.
10850   //  2) The declaration is an explicit specialization of a member of an
10851   //     templated class.
10852   //  3) The declaration is an instantiation of a template, and that template
10853   //     is an explicit specialization of a member of a templated class.
10854   //
10855   // We don't need to go any deeper than that, as the instantiation of the
10856   // surrounding class / etc is not triggered by whatever triggered this
10857   // instantiation, and thus should be checked elsewhere.
10858   template<typename SpecDecl>
10859   void checkImpl(SpecDecl *Spec) {
10860     bool IsHiddenExplicitSpecialization = false;
10861     if (Spec->getTemplateSpecializationKind() == TSK_ExplicitSpecialization) {
10862       IsHiddenExplicitSpecialization =
10863           Spec->getMemberSpecializationInfo()
10864               ? !S.hasVisibleMemberSpecialization(Spec, &Modules)
10865               : !S.hasVisibleExplicitSpecialization(Spec, &Modules);
10866     } else {
10867       checkInstantiated(Spec);
10868     }
10869 
10870     if (IsHiddenExplicitSpecialization)
10871       diagnose(Spec->getMostRecentDecl(), false);
10872   }
10873 
10874   void checkInstantiated(FunctionDecl *FD) {
10875     if (auto *TD = FD->getPrimaryTemplate())
10876       checkTemplate(TD);
10877   }
10878 
10879   void checkInstantiated(CXXRecordDecl *RD) {
10880     auto *SD = dyn_cast<ClassTemplateSpecializationDecl>(RD);
10881     if (!SD)
10882       return;
10883 
10884     auto From = SD->getSpecializedTemplateOrPartial();
10885     if (auto *TD = From.dyn_cast<ClassTemplateDecl *>())
10886       checkTemplate(TD);
10887     else if (auto *TD =
10888                  From.dyn_cast<ClassTemplatePartialSpecializationDecl *>()) {
10889       if (!S.hasVisibleDeclaration(TD))
10890         diagnose(TD, true);
10891       checkTemplate(TD);
10892     }
10893   }
10894 
10895   void checkInstantiated(VarDecl *RD) {
10896     auto *SD = dyn_cast<VarTemplateSpecializationDecl>(RD);
10897     if (!SD)
10898       return;
10899 
10900     auto From = SD->getSpecializedTemplateOrPartial();
10901     if (auto *TD = From.dyn_cast<VarTemplateDecl *>())
10902       checkTemplate(TD);
10903     else if (auto *TD =
10904                  From.dyn_cast<VarTemplatePartialSpecializationDecl *>()) {
10905       if (!S.hasVisibleDeclaration(TD))
10906         diagnose(TD, true);
10907       checkTemplate(TD);
10908     }
10909   }
10910 
10911   void checkInstantiated(EnumDecl *FD) {}
10912 
10913   template<typename TemplDecl>
10914   void checkTemplate(TemplDecl *TD) {
10915     if (TD->isMemberSpecialization()) {
10916       if (!S.hasVisibleMemberSpecialization(TD, &Modules))
10917         diagnose(TD->getMostRecentDecl(), false);
10918     }
10919   }
10920 };
10921 } // end anonymous namespace
10922 
10923 void Sema::checkSpecializationVisibility(SourceLocation Loc, NamedDecl *Spec) {
10924   if (!getLangOpts().Modules)
10925     return;
10926 
10927   ExplicitSpecializationVisibilityChecker(*this, Loc).check(Spec);
10928 }
10929 
10930 /// Check whether a template partial specialization that we've discovered
10931 /// is hidden, and produce suitable diagnostics if so.
10932 void Sema::checkPartialSpecializationVisibility(SourceLocation Loc,
10933                                                 NamedDecl *Spec) {
10934   llvm::SmallVector<Module *, 8> Modules;
10935   if (!hasVisibleDeclaration(Spec, &Modules))
10936     diagnoseMissingImport(Loc, Spec, Spec->getLocation(), Modules,
10937                           MissingImportKind::PartialSpecialization,
10938                           /*Recover*/true);
10939 }
10940