xref: /freebsd/contrib/llvm-project/clang/lib/Parse/ParseTemplate.cpp (revision 9f23cbd6cae82fd77edfad7173432fa8dccd0a95)
1 //===--- ParseTemplate.cpp - Template Parsing -----------------------------===//
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 //
9 //  This file implements parsing of C++ templates.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "clang/AST/ASTContext.h"
14 #include "clang/AST/DeclTemplate.h"
15 #include "clang/AST/ExprCXX.h"
16 #include "clang/Parse/ParseDiagnostic.h"
17 #include "clang/Parse/Parser.h"
18 #include "clang/Parse/RAIIObjectsForParser.h"
19 #include "clang/Sema/DeclSpec.h"
20 #include "clang/Sema/ParsedTemplate.h"
21 #include "clang/Sema/Scope.h"
22 #include "clang/Sema/SemaDiagnostic.h"
23 #include "llvm/Support/TimeProfiler.h"
24 using namespace clang;
25 
26 /// Re-enter a possible template scope, creating as many template parameter
27 /// scopes as necessary.
28 /// \return The number of template parameter scopes entered.
29 unsigned Parser::ReenterTemplateScopes(MultiParseScope &S, Decl *D) {
30   return Actions.ActOnReenterTemplateScope(D, [&] {
31     S.Enter(Scope::TemplateParamScope);
32     return Actions.getCurScope();
33   });
34 }
35 
36 /// Parse a template declaration, explicit instantiation, or
37 /// explicit specialization.
38 Decl *Parser::ParseDeclarationStartingWithTemplate(
39     DeclaratorContext Context, SourceLocation &DeclEnd,
40     ParsedAttributes &AccessAttrs, AccessSpecifier AS) {
41   ObjCDeclContextSwitch ObjCDC(*this);
42 
43   if (Tok.is(tok::kw_template) && NextToken().isNot(tok::less)) {
44     return ParseExplicitInstantiation(Context, SourceLocation(), ConsumeToken(),
45                                       DeclEnd, AccessAttrs, AS);
46   }
47   return ParseTemplateDeclarationOrSpecialization(Context, DeclEnd, AccessAttrs,
48                                                   AS);
49 }
50 
51 /// Parse a template declaration or an explicit specialization.
52 ///
53 /// Template declarations include one or more template parameter lists
54 /// and either the function or class template declaration. Explicit
55 /// specializations contain one or more 'template < >' prefixes
56 /// followed by a (possibly templated) declaration. Since the
57 /// syntactic form of both features is nearly identical, we parse all
58 /// of the template headers together and let semantic analysis sort
59 /// the declarations from the explicit specializations.
60 ///
61 ///       template-declaration: [C++ temp]
62 ///         'export'[opt] 'template' '<' template-parameter-list '>' declaration
63 ///
64 ///       template-declaration: [C++2a]
65 ///         template-head declaration
66 ///         template-head concept-definition
67 ///
68 ///       TODO: requires-clause
69 ///       template-head: [C++2a]
70 ///         'template' '<' template-parameter-list '>'
71 ///             requires-clause[opt]
72 ///
73 ///       explicit-specialization: [ C++ temp.expl.spec]
74 ///         'template' '<' '>' declaration
75 Decl *Parser::ParseTemplateDeclarationOrSpecialization(
76     DeclaratorContext Context, SourceLocation &DeclEnd,
77     ParsedAttributes &AccessAttrs, AccessSpecifier AS) {
78   assert(Tok.isOneOf(tok::kw_export, tok::kw_template) &&
79          "Token does not start a template declaration.");
80 
81   MultiParseScope TemplateParamScopes(*this);
82 
83   // Tell the action that names should be checked in the context of
84   // the declaration to come.
85   ParsingDeclRAIIObject
86     ParsingTemplateParams(*this, ParsingDeclRAIIObject::NoParent);
87 
88   // Parse multiple levels of template headers within this template
89   // parameter scope, e.g.,
90   //
91   //   template<typename T>
92   //     template<typename U>
93   //       class A<T>::B { ... };
94   //
95   // We parse multiple levels non-recursively so that we can build a
96   // single data structure containing all of the template parameter
97   // lists to easily differentiate between the case above and:
98   //
99   //   template<typename T>
100   //   class A {
101   //     template<typename U> class B;
102   //   };
103   //
104   // In the first case, the action for declaring A<T>::B receives
105   // both template parameter lists. In the second case, the action for
106   // defining A<T>::B receives just the inner template parameter list
107   // (and retrieves the outer template parameter list from its
108   // context).
109   bool isSpecialization = true;
110   bool LastParamListWasEmpty = false;
111   TemplateParameterLists ParamLists;
112   TemplateParameterDepthRAII CurTemplateDepthTracker(TemplateParameterDepth);
113 
114   do {
115     // Consume the 'export', if any.
116     SourceLocation ExportLoc;
117     TryConsumeToken(tok::kw_export, ExportLoc);
118 
119     // Consume the 'template', which should be here.
120     SourceLocation TemplateLoc;
121     if (!TryConsumeToken(tok::kw_template, TemplateLoc)) {
122       Diag(Tok.getLocation(), diag::err_expected_template);
123       return nullptr;
124     }
125 
126     // Parse the '<' template-parameter-list '>'
127     SourceLocation LAngleLoc, RAngleLoc;
128     SmallVector<NamedDecl*, 4> TemplateParams;
129     if (ParseTemplateParameters(TemplateParamScopes,
130                                 CurTemplateDepthTracker.getDepth(),
131                                 TemplateParams, LAngleLoc, RAngleLoc)) {
132       // Skip until the semi-colon or a '}'.
133       SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
134       TryConsumeToken(tok::semi);
135       return nullptr;
136     }
137 
138     ExprResult OptionalRequiresClauseConstraintER;
139     if (!TemplateParams.empty()) {
140       isSpecialization = false;
141       ++CurTemplateDepthTracker;
142 
143       if (TryConsumeToken(tok::kw_requires)) {
144         OptionalRequiresClauseConstraintER =
145             Actions.ActOnRequiresClause(ParseConstraintLogicalOrExpression(
146                 /*IsTrailingRequiresClause=*/false));
147         if (!OptionalRequiresClauseConstraintER.isUsable()) {
148           // Skip until the semi-colon or a '}'.
149           SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
150           TryConsumeToken(tok::semi);
151           return nullptr;
152         }
153       }
154     } else {
155       LastParamListWasEmpty = true;
156     }
157 
158     ParamLists.push_back(Actions.ActOnTemplateParameterList(
159         CurTemplateDepthTracker.getDepth(), ExportLoc, TemplateLoc, LAngleLoc,
160         TemplateParams, RAngleLoc, OptionalRequiresClauseConstraintER.get()));
161   } while (Tok.isOneOf(tok::kw_export, tok::kw_template));
162 
163   // Parse the actual template declaration.
164   if (Tok.is(tok::kw_concept))
165     return ParseConceptDefinition(
166         ParsedTemplateInfo(&ParamLists, isSpecialization,
167                            LastParamListWasEmpty),
168         DeclEnd);
169 
170   return ParseSingleDeclarationAfterTemplate(
171       Context,
172       ParsedTemplateInfo(&ParamLists, isSpecialization, LastParamListWasEmpty),
173       ParsingTemplateParams, DeclEnd, AccessAttrs, AS);
174 }
175 
176 /// Parse a single declaration that declares a template,
177 /// template specialization, or explicit instantiation of a template.
178 ///
179 /// \param DeclEnd will receive the source location of the last token
180 /// within this declaration.
181 ///
182 /// \param AS the access specifier associated with this
183 /// declaration. Will be AS_none for namespace-scope declarations.
184 ///
185 /// \returns the new declaration.
186 Decl *Parser::ParseSingleDeclarationAfterTemplate(
187     DeclaratorContext Context, const ParsedTemplateInfo &TemplateInfo,
188     ParsingDeclRAIIObject &DiagsFromTParams, SourceLocation &DeclEnd,
189     ParsedAttributes &AccessAttrs, AccessSpecifier AS) {
190   assert(TemplateInfo.Kind != ParsedTemplateInfo::NonTemplate &&
191          "Template information required");
192 
193   if (Tok.is(tok::kw_static_assert)) {
194     // A static_assert declaration may not be templated.
195     Diag(Tok.getLocation(), diag::err_templated_invalid_declaration)
196       << TemplateInfo.getSourceRange();
197     // Parse the static_assert declaration to improve error recovery.
198     return ParseStaticAssertDeclaration(DeclEnd);
199   }
200 
201   if (Context == DeclaratorContext::Member) {
202     // We are parsing a member template.
203     DeclGroupPtrTy D = ParseCXXClassMemberDeclaration(
204         AS, AccessAttrs, TemplateInfo, &DiagsFromTParams);
205 
206     if (!D || !D.get().isSingleDecl())
207       return nullptr;
208     return D.get().getSingleDecl();
209   }
210 
211   ParsedAttributes prefixAttrs(AttrFactory);
212   MaybeParseCXX11Attributes(prefixAttrs);
213 
214   if (Tok.is(tok::kw_using)) {
215     auto usingDeclPtr = ParseUsingDirectiveOrDeclaration(Context, TemplateInfo, DeclEnd,
216                                                          prefixAttrs);
217     if (!usingDeclPtr || !usingDeclPtr.get().isSingleDecl())
218       return nullptr;
219     return usingDeclPtr.get().getSingleDecl();
220   }
221 
222   // Parse the declaration specifiers, stealing any diagnostics from
223   // the template parameters.
224   ParsingDeclSpec DS(*this, &DiagsFromTParams);
225 
226   ParseDeclarationSpecifiers(DS, TemplateInfo, AS,
227                              getDeclSpecContextFromDeclaratorContext(Context));
228 
229   if (Tok.is(tok::semi)) {
230     ProhibitAttributes(prefixAttrs);
231     DeclEnd = ConsumeToken();
232     RecordDecl *AnonRecord = nullptr;
233     Decl *Decl = Actions.ParsedFreeStandingDeclSpec(
234         getCurScope(), AS, DS, ParsedAttributesView::none(),
235         TemplateInfo.TemplateParams ? *TemplateInfo.TemplateParams
236                                     : MultiTemplateParamsArg(),
237         TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation,
238         AnonRecord);
239     assert(!AnonRecord &&
240            "Anonymous unions/structs should not be valid with template");
241     DS.complete(Decl);
242     return Decl;
243   }
244 
245   // Move the attributes from the prefix into the DS.
246   if (TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation)
247     ProhibitAttributes(prefixAttrs);
248 
249   // Parse the declarator.
250   ParsingDeclarator DeclaratorInfo(*this, DS, prefixAttrs,
251                                    (DeclaratorContext)Context);
252   if (TemplateInfo.TemplateParams)
253     DeclaratorInfo.setTemplateParameterLists(*TemplateInfo.TemplateParams);
254 
255   // Turn off usual access checking for template specializations and
256   // instantiations.
257   // C++20 [temp.spec] 13.9/6.
258   // This disables the access checking rules for function template explicit
259   // instantiation and explicit specialization:
260   // - parameter-list;
261   // - template-argument-list;
262   // - noexcept-specifier;
263   // - dynamic-exception-specifications (deprecated in C++11, removed since
264   //   C++17).
265   bool IsTemplateSpecOrInst =
266       (TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation ||
267        TemplateInfo.Kind == ParsedTemplateInfo::ExplicitSpecialization);
268   SuppressAccessChecks SAC(*this, IsTemplateSpecOrInst);
269 
270   ParseDeclarator(DeclaratorInfo);
271 
272   if (IsTemplateSpecOrInst)
273     SAC.done();
274 
275   // Error parsing the declarator?
276   if (!DeclaratorInfo.hasName()) {
277     // If so, skip until the semi-colon or a }.
278     SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
279     if (Tok.is(tok::semi))
280       ConsumeToken();
281     return nullptr;
282   }
283 
284   llvm::TimeTraceScope TimeScope("ParseTemplate", [&]() {
285     return std::string(DeclaratorInfo.getIdentifier() != nullptr
286                            ? DeclaratorInfo.getIdentifier()->getName()
287                            : "<unknown>");
288   });
289 
290   LateParsedAttrList LateParsedAttrs(true);
291   if (DeclaratorInfo.isFunctionDeclarator()) {
292     if (Tok.is(tok::kw_requires)) {
293       CXXScopeSpec &ScopeSpec = DeclaratorInfo.getCXXScopeSpec();
294       DeclaratorScopeObj DeclScopeObj(*this, ScopeSpec);
295       if (ScopeSpec.isValid() &&
296           Actions.ShouldEnterDeclaratorScope(getCurScope(), ScopeSpec))
297         DeclScopeObj.EnterDeclaratorScope();
298       ParseTrailingRequiresClause(DeclaratorInfo);
299     }
300 
301     MaybeParseGNUAttributes(DeclaratorInfo, &LateParsedAttrs);
302   }
303 
304   if (DeclaratorInfo.isFunctionDeclarator() &&
305       isStartOfFunctionDefinition(DeclaratorInfo)) {
306 
307     // Function definitions are only allowed at file scope and in C++ classes.
308     // The C++ inline method definition case is handled elsewhere, so we only
309     // need to handle the file scope definition case.
310     if (Context != DeclaratorContext::File) {
311       Diag(Tok, diag::err_function_definition_not_allowed);
312       SkipMalformedDecl();
313       return nullptr;
314     }
315 
316     if (DS.getStorageClassSpec() == DeclSpec::SCS_typedef) {
317       // Recover by ignoring the 'typedef'. This was probably supposed to be
318       // the 'typename' keyword, which we should have already suggested adding
319       // if it's appropriate.
320       Diag(DS.getStorageClassSpecLoc(), diag::err_function_declared_typedef)
321         << FixItHint::CreateRemoval(DS.getStorageClassSpecLoc());
322       DS.ClearStorageClassSpecs();
323     }
324 
325     if (TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation) {
326       if (DeclaratorInfo.getName().getKind() !=
327           UnqualifiedIdKind::IK_TemplateId) {
328         // If the declarator-id is not a template-id, issue a diagnostic and
329         // recover by ignoring the 'template' keyword.
330         Diag(Tok, diag::err_template_defn_explicit_instantiation) << 0;
331         return ParseFunctionDefinition(DeclaratorInfo, ParsedTemplateInfo(),
332                                        &LateParsedAttrs);
333       } else {
334         SourceLocation LAngleLoc
335           = PP.getLocForEndOfToken(TemplateInfo.TemplateLoc);
336         Diag(DeclaratorInfo.getIdentifierLoc(),
337              diag::err_explicit_instantiation_with_definition)
338             << SourceRange(TemplateInfo.TemplateLoc)
339             << FixItHint::CreateInsertion(LAngleLoc, "<>");
340 
341         // Recover as if it were an explicit specialization.
342         TemplateParameterLists FakedParamLists;
343         FakedParamLists.push_back(Actions.ActOnTemplateParameterList(
344             0, SourceLocation(), TemplateInfo.TemplateLoc, LAngleLoc,
345             std::nullopt, LAngleLoc, nullptr));
346 
347         return ParseFunctionDefinition(
348             DeclaratorInfo, ParsedTemplateInfo(&FakedParamLists,
349                                                /*isSpecialization=*/true,
350                                                /*lastParameterListWasEmpty=*/true),
351             &LateParsedAttrs);
352       }
353     }
354     return ParseFunctionDefinition(DeclaratorInfo, TemplateInfo,
355                                    &LateParsedAttrs);
356   }
357 
358   // Parse this declaration.
359   Decl *ThisDecl = ParseDeclarationAfterDeclarator(DeclaratorInfo,
360                                                    TemplateInfo);
361 
362   if (Tok.is(tok::comma)) {
363     Diag(Tok, diag::err_multiple_template_declarators)
364       << (int)TemplateInfo.Kind;
365     SkipUntil(tok::semi);
366     return ThisDecl;
367   }
368 
369   // Eat the semi colon after the declaration.
370   ExpectAndConsumeSemi(diag::err_expected_semi_declaration);
371   if (LateParsedAttrs.size() > 0)
372     ParseLexedAttributeList(LateParsedAttrs, ThisDecl, true, false);
373   DeclaratorInfo.complete(ThisDecl);
374   return ThisDecl;
375 }
376 
377 /// \brief Parse a single declaration that declares a concept.
378 ///
379 /// \param DeclEnd will receive the source location of the last token
380 /// within this declaration.
381 ///
382 /// \returns the new declaration.
383 Decl *
384 Parser::ParseConceptDefinition(const ParsedTemplateInfo &TemplateInfo,
385                                SourceLocation &DeclEnd) {
386   assert(TemplateInfo.Kind != ParsedTemplateInfo::NonTemplate &&
387          "Template information required");
388   assert(Tok.is(tok::kw_concept) &&
389          "ParseConceptDefinition must be called when at a 'concept' keyword");
390 
391   ConsumeToken(); // Consume 'concept'
392 
393   SourceLocation BoolKWLoc;
394   if (TryConsumeToken(tok::kw_bool, BoolKWLoc))
395     Diag(Tok.getLocation(), diag::err_concept_legacy_bool_keyword) <<
396         FixItHint::CreateRemoval(SourceLocation(BoolKWLoc));
397 
398   DiagnoseAndSkipCXX11Attributes();
399 
400   CXXScopeSpec SS;
401   if (ParseOptionalCXXScopeSpecifier(
402           SS, /*ObjectType=*/nullptr,
403           /*ObjectHasErrors=*/false, /*EnteringContext=*/false,
404           /*MayBePseudoDestructor=*/nullptr,
405           /*IsTypename=*/false, /*LastII=*/nullptr, /*OnlyNamespace=*/true) ||
406       SS.isInvalid()) {
407     SkipUntil(tok::semi);
408     return nullptr;
409   }
410 
411   if (SS.isNotEmpty())
412     Diag(SS.getBeginLoc(),
413          diag::err_concept_definition_not_identifier);
414 
415   UnqualifiedId Result;
416   if (ParseUnqualifiedId(SS, /*ObjectType=*/nullptr,
417                          /*ObjectHadErrors=*/false, /*EnteringContext=*/false,
418                          /*AllowDestructorName=*/false,
419                          /*AllowConstructorName=*/false,
420                          /*AllowDeductionGuide=*/false,
421                          /*TemplateKWLoc=*/nullptr, Result)) {
422     SkipUntil(tok::semi);
423     return nullptr;
424   }
425 
426   if (Result.getKind() != UnqualifiedIdKind::IK_Identifier) {
427     Diag(Result.getBeginLoc(), diag::err_concept_definition_not_identifier);
428     SkipUntil(tok::semi);
429     return nullptr;
430   }
431 
432   IdentifierInfo *Id = Result.Identifier;
433   SourceLocation IdLoc = Result.getBeginLoc();
434 
435   DiagnoseAndSkipCXX11Attributes();
436 
437   if (!TryConsumeToken(tok::equal)) {
438     Diag(Tok.getLocation(), diag::err_expected) << tok::equal;
439     SkipUntil(tok::semi);
440     return nullptr;
441   }
442 
443   ExprResult ConstraintExprResult =
444       Actions.CorrectDelayedTyposInExpr(ParseConstraintExpression());
445   if (ConstraintExprResult.isInvalid()) {
446     SkipUntil(tok::semi);
447     return nullptr;
448   }
449 
450   DeclEnd = Tok.getLocation();
451   ExpectAndConsumeSemi(diag::err_expected_semi_declaration);
452   Expr *ConstraintExpr = ConstraintExprResult.get();
453   return Actions.ActOnConceptDefinition(getCurScope(),
454                                         *TemplateInfo.TemplateParams,
455                                         Id, IdLoc, ConstraintExpr);
456 }
457 
458 /// ParseTemplateParameters - Parses a template-parameter-list enclosed in
459 /// angle brackets. Depth is the depth of this template-parameter-list, which
460 /// is the number of template headers directly enclosing this template header.
461 /// TemplateParams is the current list of template parameters we're building.
462 /// The template parameter we parse will be added to this list. LAngleLoc and
463 /// RAngleLoc will receive the positions of the '<' and '>', respectively,
464 /// that enclose this template parameter list.
465 ///
466 /// \returns true if an error occurred, false otherwise.
467 bool Parser::ParseTemplateParameters(
468     MultiParseScope &TemplateScopes, unsigned Depth,
469     SmallVectorImpl<NamedDecl *> &TemplateParams, SourceLocation &LAngleLoc,
470     SourceLocation &RAngleLoc) {
471   // Get the template parameter list.
472   if (!TryConsumeToken(tok::less, LAngleLoc)) {
473     Diag(Tok.getLocation(), diag::err_expected_less_after) << "template";
474     return true;
475   }
476 
477   // Try to parse the template parameter list.
478   bool Failed = false;
479   // FIXME: Missing greatergreatergreater support.
480   if (!Tok.is(tok::greater) && !Tok.is(tok::greatergreater)) {
481     TemplateScopes.Enter(Scope::TemplateParamScope);
482     Failed = ParseTemplateParameterList(Depth, TemplateParams);
483   }
484 
485   if (Tok.is(tok::greatergreater)) {
486     // No diagnostic required here: a template-parameter-list can only be
487     // followed by a declaration or, for a template template parameter, the
488     // 'class' keyword. Therefore, the second '>' will be diagnosed later.
489     // This matters for elegant diagnosis of:
490     //   template<template<typename>> struct S;
491     Tok.setKind(tok::greater);
492     RAngleLoc = Tok.getLocation();
493     Tok.setLocation(Tok.getLocation().getLocWithOffset(1));
494   } else if (!TryConsumeToken(tok::greater, RAngleLoc) && Failed) {
495     Diag(Tok.getLocation(), diag::err_expected) << tok::greater;
496     return true;
497   }
498   return false;
499 }
500 
501 /// ParseTemplateParameterList - Parse a template parameter list. If
502 /// the parsing fails badly (i.e., closing bracket was left out), this
503 /// will try to put the token stream in a reasonable position (closing
504 /// a statement, etc.) and return false.
505 ///
506 ///       template-parameter-list:    [C++ temp]
507 ///         template-parameter
508 ///         template-parameter-list ',' template-parameter
509 bool
510 Parser::ParseTemplateParameterList(const unsigned Depth,
511                              SmallVectorImpl<NamedDecl*> &TemplateParams) {
512   while (true) {
513 
514     if (NamedDecl *TmpParam
515           = ParseTemplateParameter(Depth, TemplateParams.size())) {
516       TemplateParams.push_back(TmpParam);
517     } else {
518       // If we failed to parse a template parameter, skip until we find
519       // a comma or closing brace.
520       SkipUntil(tok::comma, tok::greater, tok::greatergreater,
521                 StopAtSemi | StopBeforeMatch);
522     }
523 
524     // Did we find a comma or the end of the template parameter list?
525     if (Tok.is(tok::comma)) {
526       ConsumeToken();
527     } else if (Tok.isOneOf(tok::greater, tok::greatergreater)) {
528       // Don't consume this... that's done by template parser.
529       break;
530     } else {
531       // Somebody probably forgot to close the template. Skip ahead and
532       // try to get out of the expression. This error is currently
533       // subsumed by whatever goes on in ParseTemplateParameter.
534       Diag(Tok.getLocation(), diag::err_expected_comma_greater);
535       SkipUntil(tok::comma, tok::greater, tok::greatergreater,
536                 StopAtSemi | StopBeforeMatch);
537       return false;
538     }
539   }
540   return true;
541 }
542 
543 /// Determine whether the parser is at the start of a template
544 /// type parameter.
545 Parser::TPResult Parser::isStartOfTemplateTypeParameter() {
546   if (Tok.is(tok::kw_class)) {
547     // "class" may be the start of an elaborated-type-specifier or a
548     // type-parameter. Per C++ [temp.param]p3, we prefer the type-parameter.
549     switch (NextToken().getKind()) {
550     case tok::equal:
551     case tok::comma:
552     case tok::greater:
553     case tok::greatergreater:
554     case tok::ellipsis:
555       return TPResult::True;
556 
557     case tok::identifier:
558       // This may be either a type-parameter or an elaborated-type-specifier.
559       // We have to look further.
560       break;
561 
562     default:
563       return TPResult::False;
564     }
565 
566     switch (GetLookAheadToken(2).getKind()) {
567     case tok::equal:
568     case tok::comma:
569     case tok::greater:
570     case tok::greatergreater:
571       return TPResult::True;
572 
573     default:
574       return TPResult::False;
575     }
576   }
577 
578   if (TryAnnotateTypeConstraint())
579     return TPResult::Error;
580 
581   if (isTypeConstraintAnnotation() &&
582       // Next token might be 'auto' or 'decltype', indicating that this
583       // type-constraint is in fact part of a placeholder-type-specifier of a
584       // non-type template parameter.
585       !GetLookAheadToken(Tok.is(tok::annot_cxxscope) ? 2 : 1)
586            .isOneOf(tok::kw_auto, tok::kw_decltype))
587     return TPResult::True;
588 
589   // 'typedef' is a reasonably-common typo/thinko for 'typename', and is
590   // ill-formed otherwise.
591   if (Tok.isNot(tok::kw_typename) && Tok.isNot(tok::kw_typedef))
592     return TPResult::False;
593 
594   // C++ [temp.param]p2:
595   //   There is no semantic difference between class and typename in a
596   //   template-parameter. typename followed by an unqualified-id
597   //   names a template type parameter. typename followed by a
598   //   qualified-id denotes the type in a non-type
599   //   parameter-declaration.
600   Token Next = NextToken();
601 
602   // If we have an identifier, skip over it.
603   if (Next.getKind() == tok::identifier)
604     Next = GetLookAheadToken(2);
605 
606   switch (Next.getKind()) {
607   case tok::equal:
608   case tok::comma:
609   case tok::greater:
610   case tok::greatergreater:
611   case tok::ellipsis:
612     return TPResult::True;
613 
614   case tok::kw_typename:
615   case tok::kw_typedef:
616   case tok::kw_class:
617     // These indicate that a comma was missed after a type parameter, not that
618     // we have found a non-type parameter.
619     return TPResult::True;
620 
621   default:
622     return TPResult::False;
623   }
624 }
625 
626 /// ParseTemplateParameter - Parse a template-parameter (C++ [temp.param]).
627 ///
628 ///       template-parameter: [C++ temp.param]
629 ///         type-parameter
630 ///         parameter-declaration
631 ///
632 ///       type-parameter: (See below)
633 ///         type-parameter-key ...[opt] identifier[opt]
634 ///         type-parameter-key identifier[opt] = type-id
635 /// (C++2a) type-constraint ...[opt] identifier[opt]
636 /// (C++2a) type-constraint identifier[opt] = type-id
637 ///         'template' '<' template-parameter-list '>' type-parameter-key
638 ///               ...[opt] identifier[opt]
639 ///         'template' '<' template-parameter-list '>' type-parameter-key
640 ///               identifier[opt] '=' id-expression
641 ///
642 ///       type-parameter-key:
643 ///         class
644 ///         typename
645 ///
646 NamedDecl *Parser::ParseTemplateParameter(unsigned Depth, unsigned Position) {
647 
648   switch (isStartOfTemplateTypeParameter()) {
649   case TPResult::True:
650     // Is there just a typo in the input code? ('typedef' instead of
651     // 'typename')
652     if (Tok.is(tok::kw_typedef)) {
653       Diag(Tok.getLocation(), diag::err_expected_template_parameter);
654 
655       Diag(Tok.getLocation(), diag::note_meant_to_use_typename)
656           << FixItHint::CreateReplacement(CharSourceRange::getCharRange(
657                                               Tok.getLocation(),
658                                               Tok.getEndLoc()),
659                                           "typename");
660 
661       Tok.setKind(tok::kw_typename);
662     }
663 
664     return ParseTypeParameter(Depth, Position);
665   case TPResult::False:
666     break;
667 
668   case TPResult::Error: {
669     // We return an invalid parameter as opposed to null to avoid having bogus
670     // diagnostics about an empty template parameter list.
671     // FIXME: Fix ParseTemplateParameterList to better handle nullptr results
672     //  from here.
673     // Return a NTTP as if there was an error in a scope specifier, the user
674     // probably meant to write the type of a NTTP.
675     DeclSpec DS(getAttrFactory());
676     DS.SetTypeSpecError();
677     Declarator D(DS, ParsedAttributesView::none(),
678                  DeclaratorContext::TemplateParam);
679     D.SetIdentifier(nullptr, Tok.getLocation());
680     D.setInvalidType(true);
681     NamedDecl *ErrorParam = Actions.ActOnNonTypeTemplateParameter(
682         getCurScope(), D, Depth, Position, /*EqualLoc=*/SourceLocation(),
683         /*DefaultArg=*/nullptr);
684     ErrorParam->setInvalidDecl(true);
685     SkipUntil(tok::comma, tok::greater, tok::greatergreater,
686               StopAtSemi | StopBeforeMatch);
687     return ErrorParam;
688   }
689 
690   case TPResult::Ambiguous:
691     llvm_unreachable("template param classification can't be ambiguous");
692   }
693 
694   if (Tok.is(tok::kw_template))
695     return ParseTemplateTemplateParameter(Depth, Position);
696 
697   // If it's none of the above, then it must be a parameter declaration.
698   // NOTE: This will pick up errors in the closure of the template parameter
699   // list (e.g., template < ; Check here to implement >> style closures.
700   return ParseNonTypeTemplateParameter(Depth, Position);
701 }
702 
703 /// Check whether the current token is a template-id annotation denoting a
704 /// type-constraint.
705 bool Parser::isTypeConstraintAnnotation() {
706   const Token &T = Tok.is(tok::annot_cxxscope) ? NextToken() : Tok;
707   if (T.isNot(tok::annot_template_id))
708     return false;
709   const auto *ExistingAnnot =
710       static_cast<TemplateIdAnnotation *>(T.getAnnotationValue());
711   return ExistingAnnot->Kind == TNK_Concept_template;
712 }
713 
714 /// Try parsing a type-constraint at the current location.
715 ///
716 ///     type-constraint:
717 ///       nested-name-specifier[opt] concept-name
718 ///       nested-name-specifier[opt] concept-name
719 ///           '<' template-argument-list[opt] '>'[opt]
720 ///
721 /// \returns true if an error occurred, and false otherwise.
722 bool Parser::TryAnnotateTypeConstraint() {
723   if (!getLangOpts().CPlusPlus20)
724     return false;
725   CXXScopeSpec SS;
726   bool WasScopeAnnotation = Tok.is(tok::annot_cxxscope);
727   if (ParseOptionalCXXScopeSpecifier(SS, /*ObjectType=*/nullptr,
728                                      /*ObjectHasErrors=*/false,
729                                      /*EnteringContext=*/false,
730                                      /*MayBePseudoDestructor=*/nullptr,
731                                      // If this is not a type-constraint, then
732                                      // this scope-spec is part of the typename
733                                      // of a non-type template parameter
734                                      /*IsTypename=*/true, /*LastII=*/nullptr,
735                                      // We won't find concepts in
736                                      // non-namespaces anyway, so might as well
737                                      // parse this correctly for possible type
738                                      // names.
739                                      /*OnlyNamespace=*/false))
740     return true;
741 
742   if (Tok.is(tok::identifier)) {
743     UnqualifiedId PossibleConceptName;
744     PossibleConceptName.setIdentifier(Tok.getIdentifierInfo(),
745                                       Tok.getLocation());
746 
747     TemplateTy PossibleConcept;
748     bool MemberOfUnknownSpecialization = false;
749     auto TNK = Actions.isTemplateName(getCurScope(), SS,
750                                       /*hasTemplateKeyword=*/false,
751                                       PossibleConceptName,
752                                       /*ObjectType=*/ParsedType(),
753                                       /*EnteringContext=*/false,
754                                       PossibleConcept,
755                                       MemberOfUnknownSpecialization,
756                                       /*Disambiguation=*/true);
757     if (MemberOfUnknownSpecialization || !PossibleConcept ||
758         TNK != TNK_Concept_template) {
759       if (SS.isNotEmpty())
760         AnnotateScopeToken(SS, !WasScopeAnnotation);
761       return false;
762     }
763 
764     // At this point we're sure we're dealing with a constrained parameter. It
765     // may or may not have a template parameter list following the concept
766     // name.
767     if (AnnotateTemplateIdToken(PossibleConcept, TNK, SS,
768                                    /*TemplateKWLoc=*/SourceLocation(),
769                                    PossibleConceptName,
770                                    /*AllowTypeAnnotation=*/false,
771                                    /*TypeConstraint=*/true))
772       return true;
773   }
774 
775   if (SS.isNotEmpty())
776     AnnotateScopeToken(SS, !WasScopeAnnotation);
777   return false;
778 }
779 
780 /// ParseTypeParameter - Parse a template type parameter (C++ [temp.param]).
781 /// Other kinds of template parameters are parsed in
782 /// ParseTemplateTemplateParameter and ParseNonTypeTemplateParameter.
783 ///
784 ///       type-parameter:     [C++ temp.param]
785 ///         'class' ...[opt][C++0x] identifier[opt]
786 ///         'class' identifier[opt] '=' type-id
787 ///         'typename' ...[opt][C++0x] identifier[opt]
788 ///         'typename' identifier[opt] '=' type-id
789 NamedDecl *Parser::ParseTypeParameter(unsigned Depth, unsigned Position) {
790   assert((Tok.isOneOf(tok::kw_class, tok::kw_typename) ||
791           isTypeConstraintAnnotation()) &&
792          "A type-parameter starts with 'class', 'typename' or a "
793          "type-constraint");
794 
795   CXXScopeSpec TypeConstraintSS;
796   TemplateIdAnnotation *TypeConstraint = nullptr;
797   bool TypenameKeyword = false;
798   SourceLocation KeyLoc;
799   ParseOptionalCXXScopeSpecifier(TypeConstraintSS, /*ObjectType=*/nullptr,
800                                  /*ObjectHasErrors=*/false,
801                                  /*EnteringContext*/ false);
802   if (Tok.is(tok::annot_template_id)) {
803     // Consume the 'type-constraint'.
804     TypeConstraint =
805         static_cast<TemplateIdAnnotation *>(Tok.getAnnotationValue());
806     assert(TypeConstraint->Kind == TNK_Concept_template &&
807            "stray non-concept template-id annotation");
808     KeyLoc = ConsumeAnnotationToken();
809   } else {
810     assert(TypeConstraintSS.isEmpty() &&
811            "expected type constraint after scope specifier");
812 
813     // Consume the 'class' or 'typename' keyword.
814     TypenameKeyword = Tok.is(tok::kw_typename);
815     KeyLoc = ConsumeToken();
816   }
817 
818   // Grab the ellipsis (if given).
819   SourceLocation EllipsisLoc;
820   if (TryConsumeToken(tok::ellipsis, EllipsisLoc)) {
821     Diag(EllipsisLoc,
822          getLangOpts().CPlusPlus11
823            ? diag::warn_cxx98_compat_variadic_templates
824            : diag::ext_variadic_templates);
825   }
826 
827   // Grab the template parameter name (if given)
828   SourceLocation NameLoc = Tok.getLocation();
829   IdentifierInfo *ParamName = nullptr;
830   if (Tok.is(tok::identifier)) {
831     ParamName = Tok.getIdentifierInfo();
832     ConsumeToken();
833   } else if (Tok.isOneOf(tok::equal, tok::comma, tok::greater,
834                          tok::greatergreater)) {
835     // Unnamed template parameter. Don't have to do anything here, just
836     // don't consume this token.
837   } else {
838     Diag(Tok.getLocation(), diag::err_expected) << tok::identifier;
839     return nullptr;
840   }
841 
842   // Recover from misplaced ellipsis.
843   bool AlreadyHasEllipsis = EllipsisLoc.isValid();
844   if (TryConsumeToken(tok::ellipsis, EllipsisLoc))
845     DiagnoseMisplacedEllipsis(EllipsisLoc, NameLoc, AlreadyHasEllipsis, true);
846 
847   // Grab a default argument (if available).
848   // Per C++0x [basic.scope.pdecl]p9, we parse the default argument before
849   // we introduce the type parameter into the local scope.
850   SourceLocation EqualLoc;
851   ParsedType DefaultArg;
852   if (TryConsumeToken(tok::equal, EqualLoc))
853     DefaultArg =
854         ParseTypeName(/*Range=*/nullptr, DeclaratorContext::TemplateTypeArg)
855             .get();
856 
857   NamedDecl *NewDecl = Actions.ActOnTypeParameter(getCurScope(),
858                                                   TypenameKeyword, EllipsisLoc,
859                                                   KeyLoc, ParamName, NameLoc,
860                                                   Depth, Position, EqualLoc,
861                                                   DefaultArg,
862                                                   TypeConstraint != nullptr);
863 
864   if (TypeConstraint) {
865     Actions.ActOnTypeConstraint(TypeConstraintSS, TypeConstraint,
866                                 cast<TemplateTypeParmDecl>(NewDecl),
867                                 EllipsisLoc);
868   }
869 
870   return NewDecl;
871 }
872 
873 /// ParseTemplateTemplateParameter - Handle the parsing of template
874 /// template parameters.
875 ///
876 ///       type-parameter:    [C++ temp.param]
877 ///         template-head type-parameter-key ...[opt] identifier[opt]
878 ///         template-head type-parameter-key identifier[opt] = id-expression
879 ///       type-parameter-key:
880 ///         'class'
881 ///         'typename'       [C++1z]
882 ///       template-head:     [C++2a]
883 ///         'template' '<' template-parameter-list '>'
884 ///             requires-clause[opt]
885 NamedDecl *Parser::ParseTemplateTemplateParameter(unsigned Depth,
886                                                   unsigned Position) {
887   assert(Tok.is(tok::kw_template) && "Expected 'template' keyword");
888 
889   // Handle the template <...> part.
890   SourceLocation TemplateLoc = ConsumeToken();
891   SmallVector<NamedDecl*,8> TemplateParams;
892   SourceLocation LAngleLoc, RAngleLoc;
893   ExprResult OptionalRequiresClauseConstraintER;
894   {
895     MultiParseScope TemplateParmScope(*this);
896     if (ParseTemplateParameters(TemplateParmScope, Depth + 1, TemplateParams,
897                                 LAngleLoc, RAngleLoc)) {
898       return nullptr;
899     }
900     if (TryConsumeToken(tok::kw_requires)) {
901       OptionalRequiresClauseConstraintER =
902           Actions.ActOnRequiresClause(ParseConstraintLogicalOrExpression(
903               /*IsTrailingRequiresClause=*/false));
904       if (!OptionalRequiresClauseConstraintER.isUsable()) {
905         SkipUntil(tok::comma, tok::greater, tok::greatergreater,
906                   StopAtSemi | StopBeforeMatch);
907         return nullptr;
908       }
909     }
910   }
911 
912   // Provide an ExtWarn if the C++1z feature of using 'typename' here is used.
913   // Generate a meaningful error if the user forgot to put class before the
914   // identifier, comma, or greater. Provide a fixit if the identifier, comma,
915   // or greater appear immediately or after 'struct'. In the latter case,
916   // replace the keyword with 'class'.
917   if (!TryConsumeToken(tok::kw_class)) {
918     bool Replace = Tok.isOneOf(tok::kw_typename, tok::kw_struct);
919     const Token &Next = Tok.is(tok::kw_struct) ? NextToken() : Tok;
920     if (Tok.is(tok::kw_typename)) {
921       Diag(Tok.getLocation(),
922            getLangOpts().CPlusPlus17
923                ? diag::warn_cxx14_compat_template_template_param_typename
924                : diag::ext_template_template_param_typename)
925         << (!getLangOpts().CPlusPlus17
926                 ? FixItHint::CreateReplacement(Tok.getLocation(), "class")
927                 : FixItHint());
928     } else if (Next.isOneOf(tok::identifier, tok::comma, tok::greater,
929                             tok::greatergreater, tok::ellipsis)) {
930       Diag(Tok.getLocation(), diag::err_class_on_template_template_param)
931           << getLangOpts().CPlusPlus17
932           << (Replace
933                   ? FixItHint::CreateReplacement(Tok.getLocation(), "class")
934                   : FixItHint::CreateInsertion(Tok.getLocation(), "class "));
935     } else
936       Diag(Tok.getLocation(), diag::err_class_on_template_template_param)
937           << getLangOpts().CPlusPlus17;
938 
939     if (Replace)
940       ConsumeToken();
941   }
942 
943   // Parse the ellipsis, if given.
944   SourceLocation EllipsisLoc;
945   if (TryConsumeToken(tok::ellipsis, EllipsisLoc))
946     Diag(EllipsisLoc,
947          getLangOpts().CPlusPlus11
948            ? diag::warn_cxx98_compat_variadic_templates
949            : diag::ext_variadic_templates);
950 
951   // Get the identifier, if given.
952   SourceLocation NameLoc = Tok.getLocation();
953   IdentifierInfo *ParamName = nullptr;
954   if (Tok.is(tok::identifier)) {
955     ParamName = Tok.getIdentifierInfo();
956     ConsumeToken();
957   } else if (Tok.isOneOf(tok::equal, tok::comma, tok::greater,
958                          tok::greatergreater)) {
959     // Unnamed template parameter. Don't have to do anything here, just
960     // don't consume this token.
961   } else {
962     Diag(Tok.getLocation(), diag::err_expected) << tok::identifier;
963     return nullptr;
964   }
965 
966   // Recover from misplaced ellipsis.
967   bool AlreadyHasEllipsis = EllipsisLoc.isValid();
968   if (TryConsumeToken(tok::ellipsis, EllipsisLoc))
969     DiagnoseMisplacedEllipsis(EllipsisLoc, NameLoc, AlreadyHasEllipsis, true);
970 
971   TemplateParameterList *ParamList = Actions.ActOnTemplateParameterList(
972       Depth, SourceLocation(), TemplateLoc, LAngleLoc, TemplateParams,
973       RAngleLoc, OptionalRequiresClauseConstraintER.get());
974 
975   // Grab a default argument (if available).
976   // Per C++0x [basic.scope.pdecl]p9, we parse the default argument before
977   // we introduce the template parameter into the local scope.
978   SourceLocation EqualLoc;
979   ParsedTemplateArgument DefaultArg;
980   if (TryConsumeToken(tok::equal, EqualLoc)) {
981     DefaultArg = ParseTemplateTemplateArgument();
982     if (DefaultArg.isInvalid()) {
983       Diag(Tok.getLocation(),
984            diag::err_default_template_template_parameter_not_template);
985       SkipUntil(tok::comma, tok::greater, tok::greatergreater,
986                 StopAtSemi | StopBeforeMatch);
987     }
988   }
989 
990   return Actions.ActOnTemplateTemplateParameter(getCurScope(), TemplateLoc,
991                                                 ParamList, EllipsisLoc,
992                                                 ParamName, NameLoc, Depth,
993                                                 Position, EqualLoc, DefaultArg);
994 }
995 
996 /// ParseNonTypeTemplateParameter - Handle the parsing of non-type
997 /// template parameters (e.g., in "template<int Size> class array;").
998 ///
999 ///       template-parameter:
1000 ///         ...
1001 ///         parameter-declaration
1002 NamedDecl *
1003 Parser::ParseNonTypeTemplateParameter(unsigned Depth, unsigned Position) {
1004   // Parse the declaration-specifiers (i.e., the type).
1005   // FIXME: The type should probably be restricted in some way... Not all
1006   // declarators (parts of declarators?) are accepted for parameters.
1007   DeclSpec DS(AttrFactory);
1008   ParseDeclarationSpecifiers(DS, ParsedTemplateInfo(), AS_none,
1009                              DeclSpecContext::DSC_template_param);
1010 
1011   // Parse this as a typename.
1012   Declarator ParamDecl(DS, ParsedAttributesView::none(),
1013                        DeclaratorContext::TemplateParam);
1014   ParseDeclarator(ParamDecl);
1015   if (DS.getTypeSpecType() == DeclSpec::TST_unspecified) {
1016     Diag(Tok.getLocation(), diag::err_expected_template_parameter);
1017     return nullptr;
1018   }
1019 
1020   // Recover from misplaced ellipsis.
1021   SourceLocation EllipsisLoc;
1022   if (TryConsumeToken(tok::ellipsis, EllipsisLoc))
1023     DiagnoseMisplacedEllipsisInDeclarator(EllipsisLoc, ParamDecl);
1024 
1025   // If there is a default value, parse it.
1026   // Per C++0x [basic.scope.pdecl]p9, we parse the default argument before
1027   // we introduce the template parameter into the local scope.
1028   SourceLocation EqualLoc;
1029   ExprResult DefaultArg;
1030   if (TryConsumeToken(tok::equal, EqualLoc)) {
1031     if (Tok.is(tok::l_paren) && NextToken().is(tok::l_brace)) {
1032       Diag(Tok.getLocation(), diag::err_stmt_expr_in_default_arg) << 1;
1033       SkipUntil(tok::comma, tok::greater, StopAtSemi | StopBeforeMatch);
1034     } else {
1035       // C++ [temp.param]p15:
1036       //   When parsing a default template-argument for a non-type
1037       //   template-parameter, the first non-nested > is taken as the
1038       //   end of the template-parameter-list rather than a greater-than
1039       //   operator.
1040       GreaterThanIsOperatorScope G(GreaterThanIsOperator, false);
1041       EnterExpressionEvaluationContext ConstantEvaluated(
1042           Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated);
1043       DefaultArg =
1044           Actions.CorrectDelayedTyposInExpr(ParseAssignmentExpression());
1045       if (DefaultArg.isInvalid())
1046         SkipUntil(tok::comma, tok::greater, StopAtSemi | StopBeforeMatch);
1047     }
1048   }
1049 
1050   // Create the parameter.
1051   return Actions.ActOnNonTypeTemplateParameter(getCurScope(), ParamDecl,
1052                                                Depth, Position, EqualLoc,
1053                                                DefaultArg.get());
1054 }
1055 
1056 void Parser::DiagnoseMisplacedEllipsis(SourceLocation EllipsisLoc,
1057                                        SourceLocation CorrectLoc,
1058                                        bool AlreadyHasEllipsis,
1059                                        bool IdentifierHasName) {
1060   FixItHint Insertion;
1061   if (!AlreadyHasEllipsis)
1062     Insertion = FixItHint::CreateInsertion(CorrectLoc, "...");
1063   Diag(EllipsisLoc, diag::err_misplaced_ellipsis_in_declaration)
1064       << FixItHint::CreateRemoval(EllipsisLoc) << Insertion
1065       << !IdentifierHasName;
1066 }
1067 
1068 void Parser::DiagnoseMisplacedEllipsisInDeclarator(SourceLocation EllipsisLoc,
1069                                                    Declarator &D) {
1070   assert(EllipsisLoc.isValid());
1071   bool AlreadyHasEllipsis = D.getEllipsisLoc().isValid();
1072   if (!AlreadyHasEllipsis)
1073     D.setEllipsisLoc(EllipsisLoc);
1074   DiagnoseMisplacedEllipsis(EllipsisLoc, D.getIdentifierLoc(),
1075                             AlreadyHasEllipsis, D.hasName());
1076 }
1077 
1078 /// Parses a '>' at the end of a template list.
1079 ///
1080 /// If this function encounters '>>', '>>>', '>=', or '>>=', it tries
1081 /// to determine if these tokens were supposed to be a '>' followed by
1082 /// '>', '>>', '>=', or '>='. It emits an appropriate diagnostic if necessary.
1083 ///
1084 /// \param RAngleLoc the location of the consumed '>'.
1085 ///
1086 /// \param ConsumeLastToken if true, the '>' is consumed.
1087 ///
1088 /// \param ObjCGenericList if true, this is the '>' closing an Objective-C
1089 /// type parameter or type argument list, rather than a C++ template parameter
1090 /// or argument list.
1091 ///
1092 /// \returns true, if current token does not start with '>', false otherwise.
1093 bool Parser::ParseGreaterThanInTemplateList(SourceLocation LAngleLoc,
1094                                             SourceLocation &RAngleLoc,
1095                                             bool ConsumeLastToken,
1096                                             bool ObjCGenericList) {
1097   // What will be left once we've consumed the '>'.
1098   tok::TokenKind RemainingToken;
1099   const char *ReplacementStr = "> >";
1100   bool MergeWithNextToken = false;
1101 
1102   switch (Tok.getKind()) {
1103   default:
1104     Diag(getEndOfPreviousToken(), diag::err_expected) << tok::greater;
1105     Diag(LAngleLoc, diag::note_matching) << tok::less;
1106     return true;
1107 
1108   case tok::greater:
1109     // Determine the location of the '>' token. Only consume this token
1110     // if the caller asked us to.
1111     RAngleLoc = Tok.getLocation();
1112     if (ConsumeLastToken)
1113       ConsumeToken();
1114     return false;
1115 
1116   case tok::greatergreater:
1117     RemainingToken = tok::greater;
1118     break;
1119 
1120   case tok::greatergreatergreater:
1121     RemainingToken = tok::greatergreater;
1122     break;
1123 
1124   case tok::greaterequal:
1125     RemainingToken = tok::equal;
1126     ReplacementStr = "> =";
1127 
1128     // Join two adjacent '=' tokens into one, for cases like:
1129     //   void (*p)() = f<int>;
1130     //   return f<int>==p;
1131     if (NextToken().is(tok::equal) &&
1132         areTokensAdjacent(Tok, NextToken())) {
1133       RemainingToken = tok::equalequal;
1134       MergeWithNextToken = true;
1135     }
1136     break;
1137 
1138   case tok::greatergreaterequal:
1139     RemainingToken = tok::greaterequal;
1140     break;
1141   }
1142 
1143   // This template-id is terminated by a token that starts with a '>'.
1144   // Outside C++11 and Objective-C, this is now error recovery.
1145   //
1146   // C++11 allows this when the token is '>>', and in CUDA + C++11 mode, we
1147   // extend that treatment to also apply to the '>>>' token.
1148   //
1149   // Objective-C allows this in its type parameter / argument lists.
1150 
1151   SourceLocation TokBeforeGreaterLoc = PrevTokLocation;
1152   SourceLocation TokLoc = Tok.getLocation();
1153   Token Next = NextToken();
1154 
1155   // Whether splitting the current token after the '>' would undesirably result
1156   // in the remaining token pasting with the token after it. This excludes the
1157   // MergeWithNextToken cases, which we've already handled.
1158   bool PreventMergeWithNextToken =
1159       (RemainingToken == tok::greater ||
1160        RemainingToken == tok::greatergreater) &&
1161       (Next.isOneOf(tok::greater, tok::greatergreater,
1162                     tok::greatergreatergreater, tok::equal, tok::greaterequal,
1163                     tok::greatergreaterequal, tok::equalequal)) &&
1164       areTokensAdjacent(Tok, Next);
1165 
1166   // Diagnose this situation as appropriate.
1167   if (!ObjCGenericList) {
1168     // The source range of the replaced token(s).
1169     CharSourceRange ReplacementRange = CharSourceRange::getCharRange(
1170         TokLoc, Lexer::AdvanceToTokenCharacter(TokLoc, 2, PP.getSourceManager(),
1171                                                getLangOpts()));
1172 
1173     // A hint to put a space between the '>>'s. In order to make the hint as
1174     // clear as possible, we include the characters either side of the space in
1175     // the replacement, rather than just inserting a space at SecondCharLoc.
1176     FixItHint Hint1 = FixItHint::CreateReplacement(ReplacementRange,
1177                                                    ReplacementStr);
1178 
1179     // A hint to put another space after the token, if it would otherwise be
1180     // lexed differently.
1181     FixItHint Hint2;
1182     if (PreventMergeWithNextToken)
1183       Hint2 = FixItHint::CreateInsertion(Next.getLocation(), " ");
1184 
1185     unsigned DiagId = diag::err_two_right_angle_brackets_need_space;
1186     if (getLangOpts().CPlusPlus11 &&
1187         (Tok.is(tok::greatergreater) || Tok.is(tok::greatergreatergreater)))
1188       DiagId = diag::warn_cxx98_compat_two_right_angle_brackets;
1189     else if (Tok.is(tok::greaterequal))
1190       DiagId = diag::err_right_angle_bracket_equal_needs_space;
1191     Diag(TokLoc, DiagId) << Hint1 << Hint2;
1192   }
1193 
1194   // Find the "length" of the resulting '>' token. This is not always 1, as it
1195   // can contain escaped newlines.
1196   unsigned GreaterLength = Lexer::getTokenPrefixLength(
1197       TokLoc, 1, PP.getSourceManager(), getLangOpts());
1198 
1199   // Annotate the source buffer to indicate that we split the token after the
1200   // '>'. This allows us to properly find the end of, and extract the spelling
1201   // of, the '>' token later.
1202   RAngleLoc = PP.SplitToken(TokLoc, GreaterLength);
1203 
1204   // Strip the initial '>' from the token.
1205   bool CachingTokens = PP.IsPreviousCachedToken(Tok);
1206 
1207   Token Greater = Tok;
1208   Greater.setLocation(RAngleLoc);
1209   Greater.setKind(tok::greater);
1210   Greater.setLength(GreaterLength);
1211 
1212   unsigned OldLength = Tok.getLength();
1213   if (MergeWithNextToken) {
1214     ConsumeToken();
1215     OldLength += Tok.getLength();
1216   }
1217 
1218   Tok.setKind(RemainingToken);
1219   Tok.setLength(OldLength - GreaterLength);
1220 
1221   // Split the second token if lexing it normally would lex a different token
1222   // (eg, the fifth token in 'A<B>>>' should re-lex as '>', not '>>').
1223   SourceLocation AfterGreaterLoc = TokLoc.getLocWithOffset(GreaterLength);
1224   if (PreventMergeWithNextToken)
1225     AfterGreaterLoc = PP.SplitToken(AfterGreaterLoc, Tok.getLength());
1226   Tok.setLocation(AfterGreaterLoc);
1227 
1228   // Update the token cache to match what we just did if necessary.
1229   if (CachingTokens) {
1230     // If the previous cached token is being merged, delete it.
1231     if (MergeWithNextToken)
1232       PP.ReplacePreviousCachedToken({});
1233 
1234     if (ConsumeLastToken)
1235       PP.ReplacePreviousCachedToken({Greater, Tok});
1236     else
1237       PP.ReplacePreviousCachedToken({Greater});
1238   }
1239 
1240   if (ConsumeLastToken) {
1241     PrevTokLocation = RAngleLoc;
1242   } else {
1243     PrevTokLocation = TokBeforeGreaterLoc;
1244     PP.EnterToken(Tok, /*IsReinject=*/true);
1245     Tok = Greater;
1246   }
1247 
1248   return false;
1249 }
1250 
1251 /// Parses a template-id that after the template name has
1252 /// already been parsed.
1253 ///
1254 /// This routine takes care of parsing the enclosed template argument
1255 /// list ('<' template-parameter-list [opt] '>') and placing the
1256 /// results into a form that can be transferred to semantic analysis.
1257 ///
1258 /// \param ConsumeLastToken if true, then we will consume the last
1259 /// token that forms the template-id. Otherwise, we will leave the
1260 /// last token in the stream (e.g., so that it can be replaced with an
1261 /// annotation token).
1262 bool Parser::ParseTemplateIdAfterTemplateName(bool ConsumeLastToken,
1263                                               SourceLocation &LAngleLoc,
1264                                               TemplateArgList &TemplateArgs,
1265                                               SourceLocation &RAngleLoc,
1266                                               TemplateTy Template) {
1267   assert(Tok.is(tok::less) && "Must have already parsed the template-name");
1268 
1269   // Consume the '<'.
1270   LAngleLoc = ConsumeToken();
1271 
1272   // Parse the optional template-argument-list.
1273   bool Invalid = false;
1274   {
1275     GreaterThanIsOperatorScope G(GreaterThanIsOperator, false);
1276     if (!Tok.isOneOf(tok::greater, tok::greatergreater,
1277                      tok::greatergreatergreater, tok::greaterequal,
1278                      tok::greatergreaterequal))
1279       Invalid = ParseTemplateArgumentList(TemplateArgs, Template, LAngleLoc);
1280 
1281     if (Invalid) {
1282       // Try to find the closing '>'.
1283       if (getLangOpts().CPlusPlus11)
1284         SkipUntil(tok::greater, tok::greatergreater,
1285                   tok::greatergreatergreater, StopAtSemi | StopBeforeMatch);
1286       else
1287         SkipUntil(tok::greater, StopAtSemi | StopBeforeMatch);
1288     }
1289   }
1290 
1291   return ParseGreaterThanInTemplateList(LAngleLoc, RAngleLoc, ConsumeLastToken,
1292                                         /*ObjCGenericList=*/false) ||
1293          Invalid;
1294 }
1295 
1296 /// Replace the tokens that form a simple-template-id with an
1297 /// annotation token containing the complete template-id.
1298 ///
1299 /// The first token in the stream must be the name of a template that
1300 /// is followed by a '<'. This routine will parse the complete
1301 /// simple-template-id and replace the tokens with a single annotation
1302 /// token with one of two different kinds: if the template-id names a
1303 /// type (and \p AllowTypeAnnotation is true), the annotation token is
1304 /// a type annotation that includes the optional nested-name-specifier
1305 /// (\p SS). Otherwise, the annotation token is a template-id
1306 /// annotation that does not include the optional
1307 /// nested-name-specifier.
1308 ///
1309 /// \param Template  the declaration of the template named by the first
1310 /// token (an identifier), as returned from \c Action::isTemplateName().
1311 ///
1312 /// \param TNK the kind of template that \p Template
1313 /// refers to, as returned from \c Action::isTemplateName().
1314 ///
1315 /// \param SS if non-NULL, the nested-name-specifier that precedes
1316 /// this template name.
1317 ///
1318 /// \param TemplateKWLoc if valid, specifies that this template-id
1319 /// annotation was preceded by the 'template' keyword and gives the
1320 /// location of that keyword. If invalid (the default), then this
1321 /// template-id was not preceded by a 'template' keyword.
1322 ///
1323 /// \param AllowTypeAnnotation if true (the default), then a
1324 /// simple-template-id that refers to a class template, template
1325 /// template parameter, or other template that produces a type will be
1326 /// replaced with a type annotation token. Otherwise, the
1327 /// simple-template-id is always replaced with a template-id
1328 /// annotation token.
1329 ///
1330 /// \param TypeConstraint if true, then this is actually a type-constraint,
1331 /// meaning that the template argument list can be omitted (and the template in
1332 /// question must be a concept).
1333 ///
1334 /// If an unrecoverable parse error occurs and no annotation token can be
1335 /// formed, this function returns true.
1336 ///
1337 bool Parser::AnnotateTemplateIdToken(TemplateTy Template, TemplateNameKind TNK,
1338                                      CXXScopeSpec &SS,
1339                                      SourceLocation TemplateKWLoc,
1340                                      UnqualifiedId &TemplateName,
1341                                      bool AllowTypeAnnotation,
1342                                      bool TypeConstraint) {
1343   assert(getLangOpts().CPlusPlus && "Can only annotate template-ids in C++");
1344   assert((Tok.is(tok::less) || TypeConstraint) &&
1345          "Parser isn't at the beginning of a template-id");
1346   assert(!(TypeConstraint && AllowTypeAnnotation) && "type-constraint can't be "
1347                                                      "a type annotation");
1348   assert((!TypeConstraint || TNK == TNK_Concept_template) && "type-constraint "
1349          "must accompany a concept name");
1350   assert((Template || TNK == TNK_Non_template) && "missing template name");
1351 
1352   // Consume the template-name.
1353   SourceLocation TemplateNameLoc = TemplateName.getSourceRange().getBegin();
1354 
1355   // Parse the enclosed template argument list.
1356   SourceLocation LAngleLoc, RAngleLoc;
1357   TemplateArgList TemplateArgs;
1358   bool ArgsInvalid = false;
1359   if (!TypeConstraint || Tok.is(tok::less)) {
1360     ArgsInvalid = ParseTemplateIdAfterTemplateName(
1361         false, LAngleLoc, TemplateArgs, RAngleLoc, Template);
1362     // If we couldn't recover from invalid arguments, don't form an annotation
1363     // token -- we don't know how much to annotate.
1364     // FIXME: This can lead to duplicate diagnostics if we retry parsing this
1365     // template-id in another context. Try to annotate anyway?
1366     if (RAngleLoc.isInvalid())
1367       return true;
1368   }
1369 
1370   ASTTemplateArgsPtr TemplateArgsPtr(TemplateArgs);
1371 
1372   // Build the annotation token.
1373   if (TNK == TNK_Type_template && AllowTypeAnnotation) {
1374     TypeResult Type = ArgsInvalid
1375                           ? TypeError()
1376                           : Actions.ActOnTemplateIdType(
1377                                 getCurScope(), SS, TemplateKWLoc, Template,
1378                                 TemplateName.Identifier, TemplateNameLoc,
1379                                 LAngleLoc, TemplateArgsPtr, RAngleLoc);
1380 
1381     Tok.setKind(tok::annot_typename);
1382     setTypeAnnotation(Tok, Type);
1383     if (SS.isNotEmpty())
1384       Tok.setLocation(SS.getBeginLoc());
1385     else if (TemplateKWLoc.isValid())
1386       Tok.setLocation(TemplateKWLoc);
1387     else
1388       Tok.setLocation(TemplateNameLoc);
1389   } else {
1390     // Build a template-id annotation token that can be processed
1391     // later.
1392     Tok.setKind(tok::annot_template_id);
1393 
1394     IdentifierInfo *TemplateII =
1395         TemplateName.getKind() == UnqualifiedIdKind::IK_Identifier
1396             ? TemplateName.Identifier
1397             : nullptr;
1398 
1399     OverloadedOperatorKind OpKind =
1400         TemplateName.getKind() == UnqualifiedIdKind::IK_Identifier
1401             ? OO_None
1402             : TemplateName.OperatorFunctionId.Operator;
1403 
1404     TemplateIdAnnotation *TemplateId = TemplateIdAnnotation::Create(
1405         TemplateKWLoc, TemplateNameLoc, TemplateII, OpKind, Template, TNK,
1406         LAngleLoc, RAngleLoc, TemplateArgs, ArgsInvalid, TemplateIds);
1407 
1408     Tok.setAnnotationValue(TemplateId);
1409     if (TemplateKWLoc.isValid())
1410       Tok.setLocation(TemplateKWLoc);
1411     else
1412       Tok.setLocation(TemplateNameLoc);
1413   }
1414 
1415   // Common fields for the annotation token
1416   Tok.setAnnotationEndLoc(RAngleLoc);
1417 
1418   // In case the tokens were cached, have Preprocessor replace them with the
1419   // annotation token.
1420   PP.AnnotateCachedTokens(Tok);
1421   return false;
1422 }
1423 
1424 /// Replaces a template-id annotation token with a type
1425 /// annotation token.
1426 ///
1427 /// If there was a failure when forming the type from the template-id,
1428 /// a type annotation token will still be created, but will have a
1429 /// NULL type pointer to signify an error.
1430 ///
1431 /// \param SS The scope specifier appearing before the template-id, if any.
1432 ///
1433 /// \param AllowImplicitTypename whether this is a context where T::type
1434 /// denotes a dependent type.
1435 /// \param IsClassName Is this template-id appearing in a context where we
1436 /// know it names a class, such as in an elaborated-type-specifier or
1437 /// base-specifier? ('typename' and 'template' are unneeded and disallowed
1438 /// in those contexts.)
1439 void Parser::AnnotateTemplateIdTokenAsType(
1440     CXXScopeSpec &SS, ImplicitTypenameContext AllowImplicitTypename,
1441     bool IsClassName) {
1442   assert(Tok.is(tok::annot_template_id) && "Requires template-id tokens");
1443 
1444   TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
1445   assert(TemplateId->mightBeType() &&
1446          "Only works for type and dependent templates");
1447 
1448   ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
1449                                      TemplateId->NumArgs);
1450 
1451   TypeResult Type =
1452       TemplateId->isInvalid()
1453           ? TypeError()
1454           : Actions.ActOnTemplateIdType(
1455                 getCurScope(), SS, TemplateId->TemplateKWLoc,
1456                 TemplateId->Template, TemplateId->Name,
1457                 TemplateId->TemplateNameLoc, TemplateId->LAngleLoc,
1458                 TemplateArgsPtr, TemplateId->RAngleLoc,
1459                 /*IsCtorOrDtorName=*/false, IsClassName, AllowImplicitTypename);
1460   // Create the new "type" annotation token.
1461   Tok.setKind(tok::annot_typename);
1462   setTypeAnnotation(Tok, Type);
1463   if (SS.isNotEmpty()) // it was a C++ qualified type name.
1464     Tok.setLocation(SS.getBeginLoc());
1465   // End location stays the same
1466 
1467   // Replace the template-id annotation token, and possible the scope-specifier
1468   // that precedes it, with the typename annotation token.
1469   PP.AnnotateCachedTokens(Tok);
1470 }
1471 
1472 /// Determine whether the given token can end a template argument.
1473 static bool isEndOfTemplateArgument(Token Tok) {
1474   // FIXME: Handle '>>>'.
1475   return Tok.isOneOf(tok::comma, tok::greater, tok::greatergreater,
1476                      tok::greatergreatergreater);
1477 }
1478 
1479 /// Parse a C++ template template argument.
1480 ParsedTemplateArgument Parser::ParseTemplateTemplateArgument() {
1481   if (!Tok.is(tok::identifier) && !Tok.is(tok::coloncolon) &&
1482       !Tok.is(tok::annot_cxxscope))
1483     return ParsedTemplateArgument();
1484 
1485   // C++0x [temp.arg.template]p1:
1486   //   A template-argument for a template template-parameter shall be the name
1487   //   of a class template or an alias template, expressed as id-expression.
1488   //
1489   // We parse an id-expression that refers to a class template or alias
1490   // template. The grammar we parse is:
1491   //
1492   //   nested-name-specifier[opt] template[opt] identifier ...[opt]
1493   //
1494   // followed by a token that terminates a template argument, such as ',',
1495   // '>', or (in some cases) '>>'.
1496   CXXScopeSpec SS; // nested-name-specifier, if present
1497   ParseOptionalCXXScopeSpecifier(SS, /*ObjectType=*/nullptr,
1498                                  /*ObjectHasErrors=*/false,
1499                                  /*EnteringContext=*/false);
1500 
1501   ParsedTemplateArgument Result;
1502   SourceLocation EllipsisLoc;
1503   if (SS.isSet() && Tok.is(tok::kw_template)) {
1504     // Parse the optional 'template' keyword following the
1505     // nested-name-specifier.
1506     SourceLocation TemplateKWLoc = ConsumeToken();
1507 
1508     if (Tok.is(tok::identifier)) {
1509       // We appear to have a dependent template name.
1510       UnqualifiedId Name;
1511       Name.setIdentifier(Tok.getIdentifierInfo(), Tok.getLocation());
1512       ConsumeToken(); // the identifier
1513 
1514       TryConsumeToken(tok::ellipsis, EllipsisLoc);
1515 
1516       // If the next token signals the end of a template argument, then we have
1517       // a (possibly-dependent) template name that could be a template template
1518       // argument.
1519       TemplateTy Template;
1520       if (isEndOfTemplateArgument(Tok) &&
1521           Actions.ActOnTemplateName(getCurScope(), SS, TemplateKWLoc, Name,
1522                                     /*ObjectType=*/nullptr,
1523                                     /*EnteringContext=*/false, Template))
1524         Result = ParsedTemplateArgument(SS, Template, Name.StartLocation);
1525     }
1526   } else if (Tok.is(tok::identifier)) {
1527     // We may have a (non-dependent) template name.
1528     TemplateTy Template;
1529     UnqualifiedId Name;
1530     Name.setIdentifier(Tok.getIdentifierInfo(), Tok.getLocation());
1531     ConsumeToken(); // the identifier
1532 
1533     TryConsumeToken(tok::ellipsis, EllipsisLoc);
1534 
1535     if (isEndOfTemplateArgument(Tok)) {
1536       bool MemberOfUnknownSpecialization;
1537       TemplateNameKind TNK = Actions.isTemplateName(
1538           getCurScope(), SS,
1539           /*hasTemplateKeyword=*/false, Name,
1540           /*ObjectType=*/nullptr,
1541           /*EnteringContext=*/false, Template, MemberOfUnknownSpecialization);
1542       if (TNK == TNK_Dependent_template_name || TNK == TNK_Type_template) {
1543         // We have an id-expression that refers to a class template or
1544         // (C++0x) alias template.
1545         Result = ParsedTemplateArgument(SS, Template, Name.StartLocation);
1546       }
1547     }
1548   }
1549 
1550   // If this is a pack expansion, build it as such.
1551   if (EllipsisLoc.isValid() && !Result.isInvalid())
1552     Result = Actions.ActOnPackExpansion(Result, EllipsisLoc);
1553 
1554   return Result;
1555 }
1556 
1557 /// ParseTemplateArgument - Parse a C++ template argument (C++ [temp.names]).
1558 ///
1559 ///       template-argument: [C++ 14.2]
1560 ///         constant-expression
1561 ///         type-id
1562 ///         id-expression
1563 ParsedTemplateArgument Parser::ParseTemplateArgument() {
1564   // C++ [temp.arg]p2:
1565   //   In a template-argument, an ambiguity between a type-id and an
1566   //   expression is resolved to a type-id, regardless of the form of
1567   //   the corresponding template-parameter.
1568   //
1569   // Therefore, we initially try to parse a type-id - and isCXXTypeId might look
1570   // up and annotate an identifier as an id-expression during disambiguation,
1571   // so enter the appropriate context for a constant expression template
1572   // argument before trying to disambiguate.
1573 
1574   EnterExpressionEvaluationContext EnterConstantEvaluated(
1575     Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated,
1576     /*LambdaContextDecl=*/nullptr,
1577     /*ExprContext=*/Sema::ExpressionEvaluationContextRecord::EK_TemplateArgument);
1578   if (isCXXTypeId(TypeIdAsTemplateArgument)) {
1579     TypeResult TypeArg = ParseTypeName(
1580         /*Range=*/nullptr, DeclaratorContext::TemplateArg);
1581     return Actions.ActOnTemplateTypeArgument(TypeArg);
1582   }
1583 
1584   // Try to parse a template template argument.
1585   {
1586     TentativeParsingAction TPA(*this);
1587 
1588     ParsedTemplateArgument TemplateTemplateArgument
1589       = ParseTemplateTemplateArgument();
1590     if (!TemplateTemplateArgument.isInvalid()) {
1591       TPA.Commit();
1592       return TemplateTemplateArgument;
1593     }
1594 
1595     // Revert this tentative parse to parse a non-type template argument.
1596     TPA.Revert();
1597   }
1598 
1599   // Parse a non-type template argument.
1600   SourceLocation Loc = Tok.getLocation();
1601   ExprResult ExprArg = ParseConstantExpressionInExprEvalContext(MaybeTypeCast);
1602   if (ExprArg.isInvalid() || !ExprArg.get()) {
1603     return ParsedTemplateArgument();
1604   }
1605 
1606   return ParsedTemplateArgument(ParsedTemplateArgument::NonType,
1607                                 ExprArg.get(), Loc);
1608 }
1609 
1610 /// ParseTemplateArgumentList - Parse a C++ template-argument-list
1611 /// (C++ [temp.names]). Returns true if there was an error.
1612 ///
1613 ///       template-argument-list: [C++ 14.2]
1614 ///         template-argument
1615 ///         template-argument-list ',' template-argument
1616 ///
1617 /// \param Template is only used for code completion, and may be null.
1618 bool Parser::ParseTemplateArgumentList(TemplateArgList &TemplateArgs,
1619                                        TemplateTy Template,
1620                                        SourceLocation OpenLoc) {
1621 
1622   ColonProtectionRAIIObject ColonProtection(*this, false);
1623 
1624   auto RunSignatureHelp = [&] {
1625     if (!Template)
1626       return QualType();
1627     CalledSignatureHelp = true;
1628     return Actions.ProduceTemplateArgumentSignatureHelp(Template, TemplateArgs,
1629                                                         OpenLoc);
1630   };
1631 
1632   do {
1633     PreferredType.enterFunctionArgument(Tok.getLocation(), RunSignatureHelp);
1634     ParsedTemplateArgument Arg = ParseTemplateArgument();
1635     SourceLocation EllipsisLoc;
1636     if (TryConsumeToken(tok::ellipsis, EllipsisLoc))
1637       Arg = Actions.ActOnPackExpansion(Arg, EllipsisLoc);
1638 
1639     if (Arg.isInvalid()) {
1640       if (PP.isCodeCompletionReached() && !CalledSignatureHelp)
1641         RunSignatureHelp();
1642       return true;
1643     }
1644 
1645     // Save this template argument.
1646     TemplateArgs.push_back(Arg);
1647 
1648     // If the next token is a comma, consume it and keep reading
1649     // arguments.
1650   } while (TryConsumeToken(tok::comma));
1651 
1652   return false;
1653 }
1654 
1655 /// Parse a C++ explicit template instantiation
1656 /// (C++ [temp.explicit]).
1657 ///
1658 ///       explicit-instantiation:
1659 ///         'extern' [opt] 'template' declaration
1660 ///
1661 /// Note that the 'extern' is a GNU extension and C++11 feature.
1662 Decl *Parser::ParseExplicitInstantiation(DeclaratorContext Context,
1663                                          SourceLocation ExternLoc,
1664                                          SourceLocation TemplateLoc,
1665                                          SourceLocation &DeclEnd,
1666                                          ParsedAttributes &AccessAttrs,
1667                                          AccessSpecifier AS) {
1668   // This isn't really required here.
1669   ParsingDeclRAIIObject
1670     ParsingTemplateParams(*this, ParsingDeclRAIIObject::NoParent);
1671 
1672   return ParseSingleDeclarationAfterTemplate(
1673       Context, ParsedTemplateInfo(ExternLoc, TemplateLoc),
1674       ParsingTemplateParams, DeclEnd, AccessAttrs, AS);
1675 }
1676 
1677 SourceRange Parser::ParsedTemplateInfo::getSourceRange() const {
1678   if (TemplateParams)
1679     return getTemplateParamsRange(TemplateParams->data(),
1680                                   TemplateParams->size());
1681 
1682   SourceRange R(TemplateLoc);
1683   if (ExternLoc.isValid())
1684     R.setBegin(ExternLoc);
1685   return R;
1686 }
1687 
1688 void Parser::LateTemplateParserCallback(void *P, LateParsedTemplate &LPT) {
1689   ((Parser *)P)->ParseLateTemplatedFuncDef(LPT);
1690 }
1691 
1692 /// Late parse a C++ function template in Microsoft mode.
1693 void Parser::ParseLateTemplatedFuncDef(LateParsedTemplate &LPT) {
1694   if (!LPT.D)
1695      return;
1696 
1697   // Destroy TemplateIdAnnotations when we're done, if possible.
1698   DestroyTemplateIdAnnotationsRAIIObj CleanupRAII(*this);
1699 
1700   // Get the FunctionDecl.
1701   FunctionDecl *FunD = LPT.D->getAsFunction();
1702   // Track template parameter depth.
1703   TemplateParameterDepthRAII CurTemplateDepthTracker(TemplateParameterDepth);
1704 
1705   // To restore the context after late parsing.
1706   Sema::ContextRAII GlobalSavedContext(
1707       Actions, Actions.Context.getTranslationUnitDecl());
1708 
1709   MultiParseScope Scopes(*this);
1710 
1711   // Get the list of DeclContexts to reenter.
1712   SmallVector<DeclContext*, 4> DeclContextsToReenter;
1713   for (DeclContext *DC = FunD; DC && !DC->isTranslationUnit();
1714        DC = DC->getLexicalParent())
1715     DeclContextsToReenter.push_back(DC);
1716 
1717   // Reenter scopes from outermost to innermost.
1718   for (DeclContext *DC : reverse(DeclContextsToReenter)) {
1719     CurTemplateDepthTracker.addDepth(
1720         ReenterTemplateScopes(Scopes, cast<Decl>(DC)));
1721     Scopes.Enter(Scope::DeclScope);
1722     // We'll reenter the function context itself below.
1723     if (DC != FunD)
1724       Actions.PushDeclContext(Actions.getCurScope(), DC);
1725   }
1726 
1727   assert(!LPT.Toks.empty() && "Empty body!");
1728 
1729   // Append the current token at the end of the new token stream so that it
1730   // doesn't get lost.
1731   LPT.Toks.push_back(Tok);
1732   PP.EnterTokenStream(LPT.Toks, true, /*IsReinject*/true);
1733 
1734   // Consume the previously pushed token.
1735   ConsumeAnyToken(/*ConsumeCodeCompletionTok=*/true);
1736   assert(Tok.isOneOf(tok::l_brace, tok::colon, tok::kw_try) &&
1737          "Inline method not starting with '{', ':' or 'try'");
1738 
1739   // Parse the method body. Function body parsing code is similar enough
1740   // to be re-used for method bodies as well.
1741   ParseScope FnScope(this, Scope::FnScope | Scope::DeclScope |
1742                                Scope::CompoundStmtScope);
1743 
1744   // Recreate the containing function DeclContext.
1745   Sema::ContextRAII FunctionSavedContext(Actions, FunD->getLexicalParent());
1746 
1747   Actions.ActOnStartOfFunctionDef(getCurScope(), FunD);
1748 
1749   if (Tok.is(tok::kw_try)) {
1750     ParseFunctionTryBlock(LPT.D, FnScope);
1751   } else {
1752     if (Tok.is(tok::colon))
1753       ParseConstructorInitializer(LPT.D);
1754     else
1755       Actions.ActOnDefaultCtorInitializers(LPT.D);
1756 
1757     if (Tok.is(tok::l_brace)) {
1758       assert((!isa<FunctionTemplateDecl>(LPT.D) ||
1759               cast<FunctionTemplateDecl>(LPT.D)
1760                       ->getTemplateParameters()
1761                       ->getDepth() == TemplateParameterDepth - 1) &&
1762              "TemplateParameterDepth should be greater than the depth of "
1763              "current template being instantiated!");
1764       ParseFunctionStatementBody(LPT.D, FnScope);
1765       Actions.UnmarkAsLateParsedTemplate(FunD);
1766     } else
1767       Actions.ActOnFinishFunctionBody(LPT.D, nullptr);
1768   }
1769 }
1770 
1771 /// Lex a delayed template function for late parsing.
1772 void Parser::LexTemplateFunctionForLateParsing(CachedTokens &Toks) {
1773   tok::TokenKind kind = Tok.getKind();
1774   if (!ConsumeAndStoreFunctionPrologue(Toks)) {
1775     // Consume everything up to (and including) the matching right brace.
1776     ConsumeAndStoreUntil(tok::r_brace, Toks, /*StopAtSemi=*/false);
1777   }
1778 
1779   // If we're in a function-try-block, we need to store all the catch blocks.
1780   if (kind == tok::kw_try) {
1781     while (Tok.is(tok::kw_catch)) {
1782       ConsumeAndStoreUntil(tok::l_brace, Toks, /*StopAtSemi=*/false);
1783       ConsumeAndStoreUntil(tok::r_brace, Toks, /*StopAtSemi=*/false);
1784     }
1785   }
1786 }
1787 
1788 /// We've parsed something that could plausibly be intended to be a template
1789 /// name (\p LHS) followed by a '<' token, and the following code can't possibly
1790 /// be an expression. Determine if this is likely to be a template-id and if so,
1791 /// diagnose it.
1792 bool Parser::diagnoseUnknownTemplateId(ExprResult LHS, SourceLocation Less) {
1793   TentativeParsingAction TPA(*this);
1794   // FIXME: We could look at the token sequence in a lot more detail here.
1795   if (SkipUntil(tok::greater, tok::greatergreater, tok::greatergreatergreater,
1796                 StopAtSemi | StopBeforeMatch)) {
1797     TPA.Commit();
1798 
1799     SourceLocation Greater;
1800     ParseGreaterThanInTemplateList(Less, Greater, true, false);
1801     Actions.diagnoseExprIntendedAsTemplateName(getCurScope(), LHS,
1802                                                Less, Greater);
1803     return true;
1804   }
1805 
1806   // There's no matching '>' token, this probably isn't supposed to be
1807   // interpreted as a template-id. Parse it as an (ill-formed) comparison.
1808   TPA.Revert();
1809   return false;
1810 }
1811 
1812 void Parser::checkPotentialAngleBracket(ExprResult &PotentialTemplateName) {
1813   assert(Tok.is(tok::less) && "not at a potential angle bracket");
1814 
1815   bool DependentTemplateName = false;
1816   if (!Actions.mightBeIntendedToBeTemplateName(PotentialTemplateName,
1817                                                DependentTemplateName))
1818     return;
1819 
1820   // OK, this might be a name that the user intended to be parsed as a
1821   // template-name, followed by a '<' token. Check for some easy cases.
1822 
1823   // If we have potential_template<>, then it's supposed to be a template-name.
1824   if (NextToken().is(tok::greater) ||
1825       (getLangOpts().CPlusPlus11 &&
1826        NextToken().isOneOf(tok::greatergreater, tok::greatergreatergreater))) {
1827     SourceLocation Less = ConsumeToken();
1828     SourceLocation Greater;
1829     ParseGreaterThanInTemplateList(Less, Greater, true, false);
1830     Actions.diagnoseExprIntendedAsTemplateName(
1831         getCurScope(), PotentialTemplateName, Less, Greater);
1832     // FIXME: Perform error recovery.
1833     PotentialTemplateName = ExprError();
1834     return;
1835   }
1836 
1837   // If we have 'potential_template<type-id', assume it's supposed to be a
1838   // template-name if there's a matching '>' later on.
1839   {
1840     // FIXME: Avoid the tentative parse when NextToken() can't begin a type.
1841     TentativeParsingAction TPA(*this);
1842     SourceLocation Less = ConsumeToken();
1843     if (isTypeIdUnambiguously() &&
1844         diagnoseUnknownTemplateId(PotentialTemplateName, Less)) {
1845       TPA.Commit();
1846       // FIXME: Perform error recovery.
1847       PotentialTemplateName = ExprError();
1848       return;
1849     }
1850     TPA.Revert();
1851   }
1852 
1853   // Otherwise, remember that we saw this in case we see a potentially-matching
1854   // '>' token later on.
1855   AngleBracketTracker::Priority Priority =
1856       (DependentTemplateName ? AngleBracketTracker::DependentName
1857                              : AngleBracketTracker::PotentialTypo) |
1858       (Tok.hasLeadingSpace() ? AngleBracketTracker::SpaceBeforeLess
1859                              : AngleBracketTracker::NoSpaceBeforeLess);
1860   AngleBrackets.add(*this, PotentialTemplateName.get(), Tok.getLocation(),
1861                     Priority);
1862 }
1863 
1864 bool Parser::checkPotentialAngleBracketDelimiter(
1865     const AngleBracketTracker::Loc &LAngle, const Token &OpToken) {
1866   // If a comma in an expression context is followed by a type that can be a
1867   // template argument and cannot be an expression, then this is ill-formed,
1868   // but might be intended to be part of a template-id.
1869   if (OpToken.is(tok::comma) && isTypeIdUnambiguously() &&
1870       diagnoseUnknownTemplateId(LAngle.TemplateName, LAngle.LessLoc)) {
1871     AngleBrackets.clear(*this);
1872     return true;
1873   }
1874 
1875   // If a context that looks like a template-id is followed by '()', then
1876   // this is ill-formed, but might be intended to be a template-id
1877   // followed by '()'.
1878   if (OpToken.is(tok::greater) && Tok.is(tok::l_paren) &&
1879       NextToken().is(tok::r_paren)) {
1880     Actions.diagnoseExprIntendedAsTemplateName(
1881         getCurScope(), LAngle.TemplateName, LAngle.LessLoc,
1882         OpToken.getLocation());
1883     AngleBrackets.clear(*this);
1884     return true;
1885   }
1886 
1887   // After a '>' (etc), we're no longer potentially in a construct that's
1888   // intended to be treated as a template-id.
1889   if (OpToken.is(tok::greater) ||
1890       (getLangOpts().CPlusPlus11 &&
1891        OpToken.isOneOf(tok::greatergreater, tok::greatergreatergreater)))
1892     AngleBrackets.clear(*this);
1893   return false;
1894 }
1895