ASTMatchers/Dynamic/Parser.cpp

//===- Parser.cpp - Matcher expression parser -----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Recursive parser implementation for the matcher expression grammar.
///
//===----------------------------------------------------------------------===//

#include "clang/ASTMatchers/Dynamic/Parser.h"
#include "clang/ASTMatchers/ASTMatchersInternal.h"
#include "clang/ASTMatchers/Dynamic/Diagnostics.h"
#include "clang/ASTMatchers/Dynamic/Registry.h"
#include "clang/Basic/CharInfo.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ManagedStatic.h"
#include <algorithm>
#include <cassert>
#include <cerrno>
#include <cstddef>
#include <cstdlib>
#include <optional>
#include <string>
#include <utility>
#include <vector>

namespace clang {
namespace ast_matchers {
namespace dynamic {

/// Simple structure to hold information for one token from the parser.
struct Parser::TokenInfo {
  /// Different possible tokens.
  enum TokenKind {
    TK_Eof,
    TK_NewLine,
    TK_OpenParen,
    TK_CloseParen,
    TK_Comma,
    TK_Period,
    TK_Literal,
    TK_Ident,
    TK_InvalidChar,
    TK_Error,
    TK_CodeCompletion
  };

  /// Some known identifiers.
  static const char* const ID_Bind;
  static const char *const ID_With;

  TokenInfo() = default;

  StringRef Text;
  TokenKind Kind = TK_Eof;
  SourceRange Range;
  VariantValue Value;
};

const char* const Parser::TokenInfo::ID_Bind = "bind";
const char *const Parser::TokenInfo::ID_With = "with";

/// Simple tokenizer for the parser.
class Parser::CodeTokenizer {
public:
  explicit CodeTokenizer(StringRef &MatcherCode, Diagnostics *Error)
      : Code(MatcherCode), StartOfLine(MatcherCode), Error(Error) {
    NextToken = getNextToken();
  }

  CodeTokenizer(StringRef &MatcherCode, Diagnostics *Error,
                unsigned CodeCompletionOffset)
      : Code(MatcherCode), StartOfLine(MatcherCode), Error(Error),
        CodeCompletionLocation(MatcherCode.data() + CodeCompletionOffset) {
    NextToken = getNextToken();
  }

  /// Returns but doesn't consume the next token.
  const TokenInfo &peekNextToken() const { return NextToken; }

  /// Consumes and returns the next token.
  TokenInfo consumeNextToken() {
    TokenInfo ThisToken = NextToken;
    NextToken = getNextToken();
    return ThisToken;
  }

  TokenInfo SkipNewlines() {
    while (NextToken.Kind == TokenInfo::TK_NewLine)
      NextToken = getNextToken();
    return NextToken;
  }

  TokenInfo consumeNextTokenIgnoreNewlines() {
    SkipNewlines();
    if (NextToken.Kind == TokenInfo::TK_Eof)
      return NextToken;
    return consumeNextToken();
  }

  TokenInfo::TokenKind nextTokenKind() const { return NextToken.Kind; }

private:
  TokenInfo getNextToken() {
    consumeWhitespace();
    TokenInfo Result;
    Result.Range.Start = currentLocation();

    if (CodeCompletionLocation && CodeCompletionLocation <= Code.data()) {
      Result.Kind = TokenInfo::TK_CodeCompletion;
      Result.Text = StringRef(CodeCompletionLocation, 0);
      CodeCompletionLocation = nullptr;
      return Result;
    }

    if (Code.empty()) {
      Result.Kind = TokenInfo::TK_Eof;
      Result.Text = "";
      return Result;
    }

    switch (Code[0]) {
    case '#':
      Code = Code.drop_until([](char c) { return c == '\n'; });
      return getNextToken();
    case ',':
      Result.Kind = TokenInfo::TK_Comma;
      Result.Text = Code.substr(0, 1);
      Code = Code.drop_front();
      break;
    case '.':
      Result.Kind = TokenInfo::TK_Period;
      Result.Text = Code.substr(0, 1);
      Code = Code.drop_front();
      break;
    case '\n':
      ++Line;
      StartOfLine = Code.drop_front();
      Result.Kind = TokenInfo::TK_NewLine;
      Result.Text = Code.substr(0, 1);
      Code = Code.drop_front();
      break;
    case '(':
      Result.Kind = TokenInfo::TK_OpenParen;
      Result.Text = Code.substr(0, 1);
      Code = Code.drop_front();
      break;
    case ')':
      Result.Kind = TokenInfo::TK_CloseParen;
      Result.Text = Code.substr(0, 1);
      Code = Code.drop_front();
      break;

    case '"':
    case '\'':
      // Parse a string literal.
      consumeStringLiteral(&Result);
      break;

    case '0': case '1': case '2': case '3': case '4':
    case '5': case '6': case '7': case '8': case '9':
      // Parse an unsigned and float literal.
      consumeNumberLiteral(&Result);
      break;

    default:
      if (isAlphanumeric(Code[0])) {
        // Parse an identifier
        size_t TokenLength = 1;
        while (true) {
          // A code completion location in/immediately after an identifier will
          // cause the portion of the identifier before the code completion
          // location to become a code completion token.
          if (CodeCompletionLocation == Code.data() + TokenLength) {
            CodeCompletionLocation = nullptr;
            Result.Kind = TokenInfo::TK_CodeCompletion;
            Result.Text = Code.substr(0, TokenLength);
            Code = Code.drop_front(TokenLength);
            return Result;
          }
          if (TokenLength == Code.size() || !isAlphanumeric(Code[TokenLength]))
            break;
          ++TokenLength;
        }
        if (TokenLength == 4 && Code.startswith("true")) {
          Result.Kind = TokenInfo::TK_Literal;
          Result.Value = true;
        } else if (TokenLength == 5 && Code.startswith("false")) {
          Result.Kind = TokenInfo::TK_Literal;
          Result.Value = false;
        } else {
          Result.Kind = TokenInfo::TK_Ident;
          Result.Text = Code.substr(0, TokenLength);
        }
        Code = Code.drop_front(TokenLength);
      } else {
        Result.Kind = TokenInfo::TK_InvalidChar;
        Result.Text = Code.substr(0, 1);
        Code = Code.drop_front(1);
      }
      break;
    }

    Result.Range.End = currentLocation();
    return Result;
  }

  /// Consume an unsigned and float literal.
  void consumeNumberLiteral(TokenInfo *Result) {
    bool isFloatingLiteral = false;
    unsigned Length = 1;
    if (Code.size() > 1) {
      // Consume the 'x' or 'b' radix modifier, if present.
      switch (toLowercase(Code[1])) {
      case 'x': case 'b': Length = 2;
      }
    }
    while (Length < Code.size() && isHexDigit(Code[Length]))
      ++Length;

    // Try to recognize a floating point literal.
    while (Length < Code.size()) {
      char c = Code[Length];
      if (c == '-' || c == '+' || c == '.' || isHexDigit(c)) {
        isFloatingLiteral = true;
        Length++;
      } else {
        break;
      }
    }

    Result->Text = Code.substr(0, Length);
    Code = Code.drop_front(Length);

    if (isFloatingLiteral) {
      char *end;
      errno = 0;
      std::string Text = Result->Text.str();
      double doubleValue = strtod(Text.c_str(), &end);
      if (*end == 0 && errno == 0) {
        Result->Kind = TokenInfo::TK_Literal;
        Result->Value = doubleValue;
        return;
      }
    } else {
      unsigned Value;
      if (!Result->Text.getAsInteger(0, Value)) {
        Result->Kind = TokenInfo::TK_Literal;
        Result->Value = Value;
        return;
      }
    }

    SourceRange Range;
    Range.Start = Result->Range.Start;
    Range.End = currentLocation();
    Error->addError(Range, Error->ET_ParserNumberError) << Result->Text;
    Result->Kind = TokenInfo::TK_Error;
  }

  /// Consume a string literal.
  ///
  /// \c Code must be positioned at the start of the literal (the opening
  /// quote). Consumed until it finds the same closing quote character.
  void consumeStringLiteral(TokenInfo *Result) {
    bool InEscape = false;
    const char Marker = Code[0];
    for (size_t Length = 1, Size = Code.size(); Length != Size; ++Length) {
      if (InEscape) {
        InEscape = false;
        continue;
      }
      if (Code[Length] == '\\') {
        InEscape = true;
        continue;
      }
      if (Code[Length] == Marker) {
        Result->Kind = TokenInfo::TK_Literal;
        Result->Text = Code.substr(0, Length + 1);
        Result->Value = Code.substr(1, Length - 1);
        Code = Code.drop_front(Length + 1);
        return;
      }
    }

    StringRef ErrorText = Code;
    Code = Code.drop_front(Code.size());
    SourceRange Range;
    Range.Start = Result->Range.Start;
    Range.End = currentLocation();
    Error->addError(Range, Error->ET_ParserStringError) << ErrorText;
    Result->Kind = TokenInfo::TK_Error;
  }

  /// Consume all leading whitespace from \c Code.
  void consumeWhitespace() {
    Code = Code.drop_while([](char c) {
      // Don't trim newlines.
      return StringRef(" \t\v\f\r").contains(c);
    });
  }

  SourceLocation currentLocation() {
    SourceLocation Location;
    Location.Line = Line;
    Location.Column = Code.data() - StartOfLine.data() + 1;
    return Location;
  }

  StringRef &Code;
  StringRef StartOfLine;
  unsigned Line = 1;
  Diagnostics *Error;
  TokenInfo NextToken;
  const char *CodeCompletionLocation = nullptr;
};

Parser::Sema::~Sema() = default;

std::vector<ArgKind> Parser::Sema::getAcceptedCompletionTypes(
    llvm::ArrayRef<std::pair<MatcherCtor, unsigned>> Context) {
  return {};
}

std::vector<MatcherCompletion>
Parser::Sema::getMatcherCompletions(llvm::ArrayRef<ArgKind> AcceptedTypes) {
  return {};
}

struct Parser::ScopedContextEntry {
  Parser *P;

  ScopedContextEntry(Parser *P, MatcherCtor C) : P(P) {
    P->ContextStack.push_back(std::make_pair(C, 0u));
  }

  ~ScopedContextEntry() {
    P->ContextStack.pop_back();
  }

  void nextArg() {
    ++P->ContextStack.back().second;
  }
};

/// Parse expressions that start with an identifier.
///
/// This function can parse named values and matchers.
/// In case of failure it will try to determine the user's intent to give
/// an appropriate error message.
bool Parser::parseIdentifierPrefixImpl(VariantValue *Value) {
  const TokenInfo NameToken = Tokenizer->consumeNextToken();

  if (Tokenizer->nextTokenKind() != TokenInfo::TK_OpenParen) {
    // Parse as a named value.
    if (const VariantValue NamedValue =
            NamedValues ? NamedValues->lookup(NameToken.Text)
                        : VariantValue()) {

      if (Tokenizer->nextTokenKind() != TokenInfo::TK_Period) {
        *Value = NamedValue;
        return true;
      }

      std::string BindID;
      Tokenizer->consumeNextToken();
      TokenInfo ChainCallToken = Tokenizer->consumeNextToken();
      if (ChainCallToken.Kind == TokenInfo::TK_CodeCompletion) {
        addCompletion(ChainCallToken, MatcherCompletion("bind(\"", "bind", 1));
        return false;
      }

      if (ChainCallToken.Kind != TokenInfo::TK_Ident ||
          (ChainCallToken.Text != TokenInfo::ID_Bind &&
           ChainCallToken.Text != TokenInfo::ID_With)) {
        Error->addError(ChainCallToken.Range,
                        Error->ET_ParserMalformedChainedExpr);
        return false;
      }
      if (ChainCallToken.Text == TokenInfo::ID_With) {

        Diagnostics::Context Ctx(Diagnostics::Context::ConstructMatcher, Error,
                                 NameToken.Text, NameToken.Range);

        Error->addError(ChainCallToken.Range,
                        Error->ET_RegistryMatcherNoWithSupport);
        return false;
      }
      if (!parseBindID(BindID))
        return false;

      assert(NamedValue.isMatcher());
      std::optional<DynTypedMatcher> Result =
          NamedValue.getMatcher().getSingleMatcher();
      if (Result) {
        std::optional<DynTypedMatcher> Bound = Result->tryBind(BindID);
        if (Bound) {
          *Value = VariantMatcher::SingleMatcher(*Bound);
          return true;
        }
      }
      return false;
    }

    if (Tokenizer->nextTokenKind() == TokenInfo::TK_NewLine) {
      Error->addError(Tokenizer->peekNextToken().Range,
                      Error->ET_ParserNoOpenParen)
          << "NewLine";
      return false;
    }

    // If the syntax is correct and the name is not a matcher either, report
    // unknown named value.
    if ((Tokenizer->nextTokenKind() == TokenInfo::TK_Comma ||
         Tokenizer->nextTokenKind() == TokenInfo::TK_CloseParen ||
         Tokenizer->nextTokenKind() == TokenInfo::TK_NewLine ||
         Tokenizer->nextTokenKind() == TokenInfo::TK_Eof) &&
        !S->lookupMatcherCtor(NameToken.Text)) {
      Error->addError(NameToken.Range, Error->ET_RegistryValueNotFound)
          << NameToken.Text;
      return false;
    }
    // Otherwise, fallback to the matcher parser.
  }

  Tokenizer->SkipNewlines();

  assert(NameToken.Kind == TokenInfo::TK_Ident);
  TokenInfo OpenToken = Tokenizer->consumeNextToken();
  if (OpenToken.Kind != TokenInfo::TK_OpenParen) {
    Error->addError(OpenToken.Range, Error->ET_ParserNoOpenParen)
        << OpenToken.Text;
    return false;
  }

  std::optional<MatcherCtor> Ctor = S->lookupMatcherCtor(NameToken.Text);

  // Parse as a matcher expression.
  return parseMatcherExpressionImpl(NameToken, OpenToken, Ctor, Value);
}

bool Parser::parseBindID(std::string &BindID) {
  // Parse the parenthesized argument to .bind("foo")
  const TokenInfo OpenToken = Tokenizer->consumeNextToken();
  const TokenInfo IDToken = Tokenizer->consumeNextTokenIgnoreNewlines();
  const TokenInfo CloseToken = Tokenizer->consumeNextTokenIgnoreNewlines();

  // TODO: We could use different error codes for each/some to be more
  //       explicit about the syntax error.
  if (OpenToken.Kind != TokenInfo::TK_OpenParen) {
    Error->addError(OpenToken.Range, Error->ET_ParserMalformedBindExpr);
    return false;
  }
  if (IDToken.Kind != TokenInfo::TK_Literal || !IDToken.Value.isString()) {
    Error->addError(IDToken.Range, Error->ET_ParserMalformedBindExpr);
    return false;
  }
  if (CloseToken.Kind != TokenInfo::TK_CloseParen) {
    Error->addError(CloseToken.Range, Error->ET_ParserMalformedBindExpr);
    return false;
  }
  BindID = IDToken.Value.getString();
  return true;
}

bool Parser::parseMatcherBuilder(MatcherCtor Ctor, const TokenInfo &NameToken,
                                 const TokenInfo &OpenToken,
                                 VariantValue *Value) {
  std::vector<ParserValue> Args;
  TokenInfo EndToken;

  Tokenizer->SkipNewlines();

  {
    ScopedContextEntry SCE(this, Ctor);

    while (Tokenizer->nextTokenKind() != TokenInfo::TK_Eof) {
      if (Tokenizer->nextTokenKind() == TokenInfo::TK_CloseParen) {
        // End of args.
        EndToken = Tokenizer->consumeNextToken();
        break;
      }
      if (!Args.empty()) {
        // We must find a , token to continue.
        TokenInfo CommaToken = Tokenizer->consumeNextToken();
        if (CommaToken.Kind != TokenInfo::TK_Comma) {
          Error->addError(CommaToken.Range, Error->ET_ParserNoComma)
              << CommaToken.Text;
          return false;
        }
      }

      Diagnostics::Context Ctx(Diagnostics::Context::MatcherArg, Error,
                               NameToken.Text, NameToken.Range,
                               Args.size() + 1);
      ParserValue ArgValue;
      Tokenizer->SkipNewlines();

      if (Tokenizer->peekNextToken().Kind == TokenInfo::TK_CodeCompletion) {
        addExpressionCompletions();
        return false;
      }

      TokenInfo NodeMatcherToken = Tokenizer->consumeNextToken();

      if (NodeMatcherToken.Kind != TokenInfo::TK_Ident) {
        Error->addError(NameToken.Range, Error->ET_ParserFailedToBuildMatcher)
            << NameToken.Text;
        return false;
      }

      ArgValue.Text = NodeMatcherToken.Text;
      ArgValue.Range = NodeMatcherToken.Range;

      std::optional<MatcherCtor> MappedMatcher =
          S->lookupMatcherCtor(ArgValue.Text);

      if (!MappedMatcher) {
        Error->addError(NodeMatcherToken.Range,
                        Error->ET_RegistryMatcherNotFound)
            << NodeMatcherToken.Text;
        return false;
      }

      ASTNodeKind NK = S->nodeMatcherType(*MappedMatcher);

      if (NK.isNone()) {
        Error->addError(NodeMatcherToken.Range,
                        Error->ET_RegistryNonNodeMatcher)
            << NodeMatcherToken.Text;
        return false;
      }

      ArgValue.Value = NK;

      Tokenizer->SkipNewlines();
      Args.push_back(ArgValue);

      SCE.nextArg();
    }
  }

  if (EndToken.Kind == TokenInfo::TK_Eof) {
    Error->addError(OpenToken.Range, Error->ET_ParserNoCloseParen);
    return false;
  }

  internal::MatcherDescriptorPtr BuiltCtor =
      S->buildMatcherCtor(Ctor, NameToken.Range, Args, Error);

  if (!BuiltCtor.get()) {
    Error->addError(NameToken.Range, Error->ET_ParserFailedToBuildMatcher)
        << NameToken.Text;
    return false;
  }

  std::string BindID;
  if (Tokenizer->peekNextToken().Kind == TokenInfo::TK_Period) {
    Tokenizer->consumeNextToken();
    TokenInfo ChainCallToken = Tokenizer->consumeNextToken();
    if (ChainCallToken.Kind == TokenInfo::TK_CodeCompletion) {
      addCompletion(ChainCallToken, MatcherCompletion("bind(\"", "bind", 1));
      addCompletion(ChainCallToken, MatcherCompletion("with(", "with", 1));
      return false;
    }
    if (ChainCallToken.Kind != TokenInfo::TK_Ident ||
        (ChainCallToken.Text != TokenInfo::ID_Bind &&
         ChainCallToken.Text != TokenInfo::ID_With)) {
      Error->addError(ChainCallToken.Range,
                      Error->ET_ParserMalformedChainedExpr);
      return false;
    }
    if (ChainCallToken.Text == TokenInfo::ID_Bind) {
      if (!parseBindID(BindID))
        return false;
      Diagnostics::Context Ctx(Diagnostics::Context::ConstructMatcher, Error,
                               NameToken.Text, NameToken.Range);
      SourceRange MatcherRange = NameToken.Range;
      MatcherRange.End = ChainCallToken.Range.End;
      VariantMatcher Result = S->actOnMatcherExpression(
          BuiltCtor.get(), MatcherRange, BindID, {}, Error);
      if (Result.isNull())
        return false;

      *Value = Result;
      return true;
    } else if (ChainCallToken.Text == TokenInfo::ID_With) {
      Tokenizer->SkipNewlines();

      if (Tokenizer->nextTokenKind() != TokenInfo::TK_OpenParen) {
        StringRef ErrTxt = Tokenizer->nextTokenKind() == TokenInfo::TK_Eof
                               ? StringRef("EOF")
                               : Tokenizer->peekNextToken().Text;
        Error->addError(Tokenizer->peekNextToken().Range,
                        Error->ET_ParserNoOpenParen)
            << ErrTxt;
        return false;
      }

      TokenInfo WithOpenToken = Tokenizer->consumeNextToken();

      return parseMatcherExpressionImpl(NameToken, WithOpenToken,
                                        BuiltCtor.get(), Value);
    }
  }

  Diagnostics::Context Ctx(Diagnostics::Context::ConstructMatcher, Error,
                           NameToken.Text, NameToken.Range);
  SourceRange MatcherRange = NameToken.Range;
  MatcherRange.End = EndToken.Range.End;
  VariantMatcher Result = S->actOnMatcherExpression(
      BuiltCtor.get(), MatcherRange, BindID, {}, Error);
  if (Result.isNull())
    return false;

  *Value = Result;
  return true;
}

/// Parse and validate a matcher expression.
/// \return \c true on success, in which case \c Value has the matcher parsed.
///   If the input is malformed, or some argument has an error, it
///   returns \c false.
bool Parser::parseMatcherExpressionImpl(const TokenInfo &NameToken,
                                        const TokenInfo &OpenToken,
                                        std::optional<MatcherCtor> Ctor,
                                        VariantValue *Value) {
  if (!Ctor) {
    Error->addError(NameToken.Range, Error->ET_RegistryMatcherNotFound)
        << NameToken.Text;
    // Do not return here. We need to continue to give completion suggestions.
  }

  if (Ctor && *Ctor && S->isBuilderMatcher(*Ctor))
    return parseMatcherBuilder(*Ctor, NameToken, OpenToken, Value);

  std::vector<ParserValue> Args;
  TokenInfo EndToken;

  Tokenizer->SkipNewlines();

  {
    ScopedContextEntry SCE(this, Ctor.value_or(nullptr));

    while (Tokenizer->nextTokenKind() != TokenInfo::TK_Eof) {
      if (Tokenizer->nextTokenKind() == TokenInfo::TK_CloseParen) {
        // End of args.
        EndToken = Tokenizer->consumeNextToken();
        break;
      }
      if (!Args.empty()) {
        // We must find a , token to continue.
        const TokenInfo CommaToken = Tokenizer->consumeNextToken();
        if (CommaToken.Kind != TokenInfo::TK_Comma) {
          Error->addError(CommaToken.Range, Error->ET_ParserNoComma)
              << CommaToken.Text;
          return false;
        }
      }

      Diagnostics::Context Ctx(Diagnostics::Context::MatcherArg, Error,
                               NameToken.Text, NameToken.Range,
                               Args.size() + 1);
      ParserValue ArgValue;
      Tokenizer->SkipNewlines();
      ArgValue.Text = Tokenizer->peekNextToken().Text;
      ArgValue.Range = Tokenizer->peekNextToken().Range;
      if (!parseExpressionImpl(&ArgValue.Value)) {
        return false;
      }

      Tokenizer->SkipNewlines();
      Args.push_back(ArgValue);
      SCE.nextArg();
    }
  }

  if (EndToken.Kind == TokenInfo::TK_Eof) {
    Error->addError(OpenToken.Range, Error->ET_ParserNoCloseParen);
    return false;
  }

  std::string BindID;
  if (Tokenizer->peekNextToken().Kind == TokenInfo::TK_Period) {
    Tokenizer->consumeNextToken();
    TokenInfo ChainCallToken = Tokenizer->consumeNextToken();
    if (ChainCallToken.Kind == TokenInfo::TK_CodeCompletion) {
      addCompletion(ChainCallToken, MatcherCompletion("bind(\"", "bind", 1));
      return false;
    }

    if (ChainCallToken.Kind != TokenInfo::TK_Ident) {
      Error->addError(ChainCallToken.Range,
                      Error->ET_ParserMalformedChainedExpr);
      return false;
    }
    if (ChainCallToken.Text == TokenInfo::ID_With) {

      Diagnostics::Context Ctx(Diagnostics::Context::ConstructMatcher, Error,
                               NameToken.Text, NameToken.Range);

      Error->addError(ChainCallToken.Range,
                      Error->ET_RegistryMatcherNoWithSupport);
      return false;
    }
    if (ChainCallToken.Text != TokenInfo::ID_Bind) {
      Error->addError(ChainCallToken.Range,
                      Error->ET_ParserMalformedChainedExpr);
      return false;
    }
    if (!parseBindID(BindID))
      return false;
  }

  if (!Ctor)
    return false;

  // Merge the start and end infos.
  Diagnostics::Context Ctx(Diagnostics::Context::ConstructMatcher, Error,
                           NameToken.Text, NameToken.Range);
  SourceRange MatcherRange = NameToken.Range;
  MatcherRange.End = EndToken.Range.End;
  VariantMatcher Result = S->actOnMatcherExpression(
      *Ctor, MatcherRange, BindID, Args, Error);
  if (Result.isNull()) return false;

  *Value = Result;
  return true;
}

// If the prefix of this completion matches the completion token, add it to
// Completions minus the prefix.
void Parser::addCompletion(const TokenInfo &CompToken,
                           const MatcherCompletion& Completion) {
  if (StringRef(Completion.TypedText).startswith(CompToken.Text) &&
      Completion.Specificity > 0) {
    Completions.emplace_back(Completion.TypedText.substr(CompToken.Text.size()),
                             Completion.MatcherDecl, Completion.Specificity);
  }
}

std::vector<MatcherCompletion> Parser::getNamedValueCompletions(
    ArrayRef<ArgKind> AcceptedTypes) {
  if (!NamedValues) return std::vector<MatcherCompletion>();
  std::vector<MatcherCompletion> Result;
  for (const auto &Entry : *NamedValues) {
    unsigned Specificity;
    if (Entry.getValue().isConvertibleTo(AcceptedTypes, &Specificity)) {
      std::string Decl =
          (Entry.getValue().getTypeAsString() + " " + Entry.getKey()).str();
      Result.emplace_back(Entry.getKey(), Decl, Specificity);
    }
  }
  return Result;
}

void Parser::addExpressionCompletions() {
  const TokenInfo CompToken = Tokenizer->consumeNextTokenIgnoreNewlines();
  assert(CompToken.Kind == TokenInfo::TK_CodeCompletion);

  // We cannot complete code if there is an invalid element on the context
  // stack.
  for (ContextStackTy::iterator I = ContextStack.begin(),
                                E = ContextStack.end();
       I != E; ++I) {
    if (!I->first)
      return;
  }

  auto AcceptedTypes = S->getAcceptedCompletionTypes(ContextStack);
  for (const auto &Completion : S->getMatcherCompletions(AcceptedTypes)) {
    addCompletion(CompToken, Completion);
  }

  for (const auto &Completion : getNamedValueCompletions(AcceptedTypes)) {
    addCompletion(CompToken, Completion);
  }
}

/// Parse an <Expression>
bool Parser::parseExpressionImpl(VariantValue *Value) {
  switch (Tokenizer->nextTokenKind()) {
  case TokenInfo::TK_Literal:
    *Value = Tokenizer->consumeNextToken().Value;
    return true;

  case TokenInfo::TK_Ident:
    return parseIdentifierPrefixImpl(Value);

  case TokenInfo::TK_CodeCompletion:
    addExpressionCompletions();
    return false;

  case TokenInfo::TK_Eof:
    Error->addError(Tokenizer->consumeNextToken().Range,
                    Error->ET_ParserNoCode);
    return false;

  case TokenInfo::TK_Error:
    // This error was already reported by the tokenizer.
    return false;
  case TokenInfo::TK_NewLine:
  case TokenInfo::TK_OpenParen:
  case TokenInfo::TK_CloseParen:
  case TokenInfo::TK_Comma:
  case TokenInfo::TK_Period:
  case TokenInfo::TK_InvalidChar:
    const TokenInfo Token = Tokenizer->consumeNextToken();
    Error->addError(Token.Range, Error->ET_ParserInvalidToken)
        << (Token.Kind == TokenInfo::TK_NewLine ? "NewLine" : Token.Text);
    return false;
  }

  llvm_unreachable("Unknown token kind.");
}

static llvm::ManagedStatic<Parser::RegistrySema> DefaultRegistrySema;

Parser::Parser(CodeTokenizer *Tokenizer, Sema *S,
               const NamedValueMap *NamedValues, Diagnostics *Error)
    : Tokenizer(Tokenizer), S(S ? S : &*DefaultRegistrySema),
      NamedValues(NamedValues), Error(Error) {}

Parser::RegistrySema::~RegistrySema() = default;

std::optional<MatcherCtor>
Parser::RegistrySema::lookupMatcherCtor(StringRef MatcherName) {
  return Registry::lookupMatcherCtor(MatcherName);
}

VariantMatcher Parser::RegistrySema::actOnMatcherExpression(
    MatcherCtor Ctor, SourceRange NameRange, StringRef BindID,
    ArrayRef<ParserValue> Args, Diagnostics *Error) {
  if (BindID.empty()) {
    return Registry::constructMatcher(Ctor, NameRange, Args, Error);
  } else {
    return Registry::constructBoundMatcher(Ctor, NameRange, BindID, Args,
                                           Error);
  }
}

std::vector<ArgKind> Parser::RegistrySema::getAcceptedCompletionTypes(
    ArrayRef<std::pair<MatcherCtor, unsigned>> Context) {
  return Registry::getAcceptedCompletionTypes(Context);
}

std::vector<MatcherCompletion> Parser::RegistrySema::getMatcherCompletions(
    ArrayRef<ArgKind> AcceptedTypes) {
  return Registry::getMatcherCompletions(AcceptedTypes);
}

bool Parser::RegistrySema::isBuilderMatcher(MatcherCtor Ctor) const {
  return Registry::isBuilderMatcher(Ctor);
}

ASTNodeKind Parser::RegistrySema::nodeMatcherType(MatcherCtor Ctor) const {
  return Registry::nodeMatcherType(Ctor);
}

internal::MatcherDescriptorPtr
Parser::RegistrySema::buildMatcherCtor(MatcherCtor Ctor, SourceRange NameRange,
                                       ArrayRef<ParserValue> Args,
                                       Diagnostics *Error) const {
  return Registry::buildMatcherCtor(Ctor, NameRange, Args, Error);
}

bool Parser::parseExpression(StringRef &Code, Sema *S,
                             const NamedValueMap *NamedValues,
                             VariantValue *Value, Diagnostics *Error) {
  CodeTokenizer Tokenizer(Code, Error);
  if (!Parser(&Tokenizer, S, NamedValues, Error).parseExpressionImpl(Value))
    return false;
  auto NT = Tokenizer.peekNextToken();
  if (NT.Kind != TokenInfo::TK_Eof && NT.Kind != TokenInfo::TK_NewLine) {
    Error->addError(Tokenizer.peekNextToken().Range,
                    Error->ET_ParserTrailingCode);
    return false;
  }
  return true;
}

std::vector<MatcherCompletion>
Parser::completeExpression(StringRef &Code, unsigned CompletionOffset, Sema *S,
                           const NamedValueMap *NamedValues) {
  Diagnostics Error;
  CodeTokenizer Tokenizer(Code, &Error, CompletionOffset);
  Parser P(&Tokenizer, S, NamedValues, &Error);
  VariantValue Dummy;
  P.parseExpressionImpl(&Dummy);

  // Sort by specificity, then by name.
  llvm::sort(P.Completions,
             [](const MatcherCompletion &A, const MatcherCompletion &B) {
               if (A.Specificity != B.Specificity)
                 return A.Specificity > B.Specificity;
               return A.TypedText < B.TypedText;
             });

  return P.Completions;
}

std::optional<DynTypedMatcher>
Parser::parseMatcherExpression(StringRef &Code, Sema *S,
                               const NamedValueMap *NamedValues,
                               Diagnostics *Error) {
  VariantValue Value;
  if (!parseExpression(Code, S, NamedValues, &Value, Error))
    return std::nullopt;
  if (!Value.isMatcher()) {
    Error->addError(SourceRange(), Error->ET_ParserNotAMatcher);
    return std::nullopt;
  }
  std::optional<DynTypedMatcher> Result = Value.getMatcher().getSingleMatcher();
  if (!Result) {
    Error->addError(SourceRange(), Error->ET_ParserOverloadedType)
        << Value.getTypeAsString();
  }
  return Result;
}

} // namespace dynamic
} // namespace ast_matchers
} // namespace clang