// Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:_fe_analyzer_shared/src/messages/codes.dart'
    show
        LocatedMessage,
        Message,
        MessageCode,
        codeBuiltInIdentifierInDeclaration,
        messageAbstractClassMember,
        messageAbstractLateField,
        messageAbstractStaticField,
        messageConstConstructorWithBody,
        messageConstFactory,
        messageConstructorWithTypeParameters,
        messageDirectiveAfterDeclaration,
        messageExpectedStatement,
        messageExternalField,
        messageExternalLateField,
        messageFieldInitializerOutsideConstructor,
        messageIllegalAssignmentToNonAssignable,
        messageInterpolationInUri,
        messageInvalidInitializer,
        messageInvalidSuperInInitializer,
        messageInvalidThisInInitializer,
        messageMissingAssignableSelector,
        messageNativeClauseShouldBeAnnotation,
        messageOperatorWithTypeParameters,
        messagePositionalAfterNamedArgument,
        templateDuplicateLabelInSwitchStatement,
        templateExpectedIdentifier,
        templateExperimentNotEnabled,
        templateExtraneousModifier,
        templateInternalProblemUnhandled;
import 'package:_fe_analyzer_shared/src/parser/parser.dart'
    show
        Assert,
        BlockKind,
        ConstructorReferenceContext,
        DeclarationKind,
        FormalParameterKind,
        IdentifierContext,
        MemberKind,
        optional,
        Parser;
import 'package:_fe_analyzer_shared/src/parser/quote.dart';
import 'package:_fe_analyzer_shared/src/parser/stack_listener.dart'
    show NullValues, StackListener;
import 'package:_fe_analyzer_shared/src/scanner/errors.dart'
    show translateErrorToken;
import 'package:_fe_analyzer_shared/src/scanner/scanner.dart';
import 'package:_fe_analyzer_shared/src/scanner/token.dart'
    show KeywordToken, StringToken, SyntheticToken;
import 'package:_fe_analyzer_shared/src/scanner/token_constants.dart';
import 'package:analyzer/dart/analysis/features.dart';
import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
import 'package:analyzer/error/error.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/source/line_info.dart';
import 'package:analyzer/src/dart/analysis/experiments.dart';
import 'package:analyzer/src/dart/ast/ast.dart';
import 'package:analyzer/src/dart/ast/ast_factory.dart';
import 'package:analyzer/src/dart/error/syntactic_errors.dart';
import 'package:analyzer/src/fasta/error_converter.dart';
import 'package:analyzer/src/generated/utilities_dart.dart';
import 'package:analyzer/src/summary2/ast_binary_tokens.dart';
import 'package:collection/collection.dart';
import 'package:pub_semver/pub_semver.dart';

/// A parser listener that builds the analyzer's AST structure.
class AstBuilder extends StackListener {
  final AstFactoryImpl ast = astFactory;

  final FastaErrorReporter errorReporter;
  final Uri fileUri;
  ScriptTagImpl? scriptTag;
  final List<DirectiveImpl> directives = [];
  final List<CompilationUnitMemberImpl> declarations = [];

  @override
  final Uri uri;

  /// The parser that uses this listener, used to parse optional parts, e.g.
  /// `native` support.
  late Parser parser;

  /// The class like declaration being parsed.
  _ClassLikeDeclarationBuilder? _classLikeBuilder;

  /// If true, this is building a full AST. Otherwise, only create method
  /// bodies.
  final bool isFullAst;

  /// `true` if the `native` clause is allowed
  /// in class, method, and function declarations.
  ///
  /// This is being replaced by the @native(...) annotation.
  //
  // TODO(danrubel) Move this flag to a better location
  // and should only be true if either:
  // * The current library is a platform library
  // * The current library has an import that uses the scheme "dart-ext".
  bool allowNativeClause = false;

  StringLiteralImpl? nativeName;

  bool parseFunctionBodies = true;

  /// `true` if non-nullable behavior is enabled.
  final bool enableNonNullable;

  /// `true` if triple-shift behavior is enabled
  final bool enableTripleShift;

  /// `true` if nonfunction-type-aliases behavior is enabled
  final bool enableNonFunctionTypeAliases;

  /// `true` if variance behavior is enabled
  final bool enableVariance;

  /// `true` if constructor tearoffs are enabled
  final bool enableConstructorTearoffs;

  /// `true` if extension types are enabled
  final bool enableExtensionTypes;

  /// `true` if named arguments anywhere are enabled
  final bool enableNamedArgumentsAnywhere;

  /// `true` if super parameters are enabled
  final bool enableSuperParameters;

  /// `true` if enhanced enums are enabled
  final bool enableEnhancedEnums;

  /// `true` if macros are enabled
  final bool enableMacros;

  /// `true` if records are enabled
  final bool enableRecords;

  /// `true` if unnamed-library behavior is enabled
  final bool enableUnnamedLibraries;

  /// `true` if inline-class is enabled
  final bool enableInlineClass;

  /// `true` if sealed-class is enabled
  final bool enableSealedClass;

  /// `true` if class-modifiers is enabled
  final bool enableClassModifiers;

  final FeatureSet _featureSet;

  final LineInfo _lineInfo;

  AstBuilder(ErrorReporter? errorReporter, this.fileUri, this.isFullAst,
      this._featureSet, this._lineInfo,
      [Uri? uri])
      : errorReporter = FastaErrorReporter(errorReporter),
        enableNonNullable = _featureSet.isEnabled(Feature.non_nullable),
        enableTripleShift = _featureSet.isEnabled(Feature.triple_shift),
        enableNonFunctionTypeAliases =
            _featureSet.isEnabled(Feature.nonfunction_type_aliases),
        enableVariance = _featureSet.isEnabled(Feature.variance),
        enableConstructorTearoffs =
            _featureSet.isEnabled(Feature.constructor_tearoffs),
        enableExtensionTypes = _featureSet.isEnabled(Feature.extension_types),
        enableNamedArgumentsAnywhere =
            _featureSet.isEnabled(Feature.named_arguments_anywhere),
        enableSuperParameters = _featureSet.isEnabled(Feature.super_parameters),
        enableEnhancedEnums = _featureSet.isEnabled(Feature.enhanced_enums),
        enableMacros = _featureSet.isEnabled(Feature.macros),
        enableRecords = _featureSet.isEnabled(Feature.records),
        enableUnnamedLibraries =
            _featureSet.isEnabled(Feature.unnamedLibraries),
        enableInlineClass = _featureSet.isEnabled(Feature.inline_class),
        enableSealedClass = _featureSet.isEnabled(Feature.sealed_class),
        enableClassModifiers = _featureSet.isEnabled(Feature.class_modifiers),
        uri = uri ?? fileUri;

  @override
  Uri get importUri => uri;

  @override
  void addProblem(Message message, int charOffset, int length,
      {bool wasHandled = false, List<LocatedMessage>? context}) {
    if (directives.isEmpty &&
        (message.code.analyzerCodes
                ?.contains('NON_PART_OF_DIRECTIVE_IN_PART') ??
            false)) {
      message = messageDirectiveAfterDeclaration;
    }
    errorReporter.reportMessage(message, charOffset, length);
  }

  @override
  void beginAsOperatorType(Token asOperator) {}

  @override
  void beginCascade(Token token) {
    assert(optional('..', token) || optional('?..', token));
    debugEvent("beginCascade");

    var expression = pop() as ExpressionImpl;
    push(token);
    if (expression is CascadeExpressionImpl) {
      push(expression);
    } else {
      push(
        CascadeExpressionImpl(
          target: expression,
          cascadeSections: <ExpressionImpl>[],
        ),
      );
    }
    push(NullValues.CascadeReceiver);
  }

  @override
  void beginClassDeclaration(
      Token begin,
      Token? abstractToken,
      Token? macroToken,
      Token? inlineToken,
      Token? sealedToken,
      Token? baseToken,
      Token? interfaceToken,
      Token? finalToken,
      Token? augmentToken,
      Token? mixinToken,
      Token name) {
    assert(_classLikeBuilder == null);
    push(_Modifiers()..abstractKeyword = abstractToken);
    if (!enableMacros) {
      if (macroToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.macros,
          startToken: macroToken,
        );
        // Pretend that 'macro' didn't occur while this feature is incomplete.
        macroToken = null;
      }
    }
    if (!enableInlineClass) {
      if (inlineToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.inline_class,
          startToken: inlineToken,
        );
        // Pretend that 'inline' didn't occur while this feature is incomplete.
        inlineToken = null;
      }
    }
    if (!enableSealedClass) {
      if (sealedToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.sealed_class,
          startToken: sealedToken,
        );
        // Pretend that 'sealed' didn't occur while this feature is incomplete.
        sealedToken = null;
      }
    }
    if (!enableClassModifiers) {
      if (baseToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: baseToken,
        );
        // Pretend that 'base' didn't occur while this feature is incomplete.
        baseToken = null;
      }
      if (interfaceToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: interfaceToken,
        );
        // Pretend that 'interface' didn't occur while this feature is
        // incomplete.
        interfaceToken = null;
      }
      if (finalToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: finalToken,
        );
        // Pretend that 'final' didn't occur while this feature is
        // incomplete.
        finalToken = null;
      }
      if (mixinToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: mixinToken,
        );
        // Pretend that 'mixin' didn't occur while this feature is incomplete.
        mixinToken = null;
      }
    }
    push(macroToken ?? NullValues.Token);
    push(inlineToken ?? NullValues.Token);
    push(sealedToken ?? NullValues.Token);
    push(baseToken ?? NullValues.Token);
    push(interfaceToken ?? NullValues.Token);
    push(finalToken ?? NullValues.Token);
    push(augmentToken ?? NullValues.Token);
    push(mixinToken ?? NullValues.Token);
  }

  @override
  void beginCompilationUnit(Token token) {
    push(token);
  }

  @override
  void beginConstantPattern(Token? constKeyword) {}

  @override
  void beginEnum(Token enumKeyword) {}

  @override
  void beginExtensionDeclaration(Token extensionKeyword, Token? nameToken) {
    assert(optional('extension', extensionKeyword));
    assert(_classLikeBuilder == null);
    debugEvent("ExtensionHeader");

    var typeParameters = pop() as TypeParameterListImpl?;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, extensionKeyword);

    SimpleIdentifierImpl? name;
    if (nameToken != null) {
      name = ast.simpleIdentifier(nameToken, isDeclaration: true);
    }

    _classLikeBuilder = _ExtensionDeclarationBuilder(
      comment: comment,
      metadata: metadata,
      extensionKeyword: extensionKeyword,
      name: name?.token,
      typeParameters: typeParameters,
      leftBracket: Tokens.openCurlyBracket(),
      rightBracket: Tokens.closeCurlyBracket(),
    );
  }

  @override
  void beginFactoryMethod(DeclarationKind declarationKind, Token lastConsumed,
      Token? externalToken, Token? constToken) {
    push(_Modifiers()
      ..externalKeyword = externalToken
      ..finalConstOrVarKeyword = constToken);
  }

  @override
  void beginFormalParameter(Token token, MemberKind kind, Token? requiredToken,
      Token? covariantToken, Token? varFinalOrConst) {
    push(_Modifiers()
      ..covariantKeyword = covariantToken
      ..finalConstOrVarKeyword = varFinalOrConst
      ..requiredToken = requiredToken);
  }

  @override
  void beginFormalParameterDefaultValueExpression() {}

  @override
  void beginIfControlFlow(Token ifToken) {
    push(ifToken);
  }

  @override
  void beginIsOperatorType(Token asOperator) {}

  @override
  void beginLibraryAugmentation(Token libraryKeyword, Token augmentKeyword) {}

  @override
  void beginLiteralString(Token literalString) {
    assert(identical(literalString.kind, STRING_TOKEN));
    debugEvent("beginLiteralString");

    push(literalString);
  }

  @override
  void beginMetadataStar(Token token) {
    debugEvent("beginMetadataStar");
  }

  @override
  void beginMethod(
      DeclarationKind declarationKind,
      Token? augmentToken,
      Token? externalToken,
      Token? staticToken,
      Token? covariantToken,
      Token? varFinalOrConst,
      Token? getOrSet,
      Token name) {
    _Modifiers modifiers = _Modifiers();
    if (augmentToken != null) {
      assert(augmentToken.isModifier);
      modifiers.augmentKeyword = augmentToken;
    }
    if (externalToken != null) {
      assert(externalToken.isModifier);
      modifiers.externalKeyword = externalToken;
    }
    if (staticToken != null) {
      assert(staticToken.isModifier);
      final builder = _classLikeBuilder;
      if (builder is! _ClassDeclarationBuilder ||
          builder.name.lexeme != name.lexeme ||
          getOrSet != null) {
        modifiers.staticKeyword = staticToken;
      }
    }
    if (covariantToken != null) {
      assert(covariantToken.isModifier);
      modifiers.covariantKeyword = covariantToken;
    }
    if (varFinalOrConst != null) {
      assert(varFinalOrConst.isModifier);
      modifiers.finalConstOrVarKeyword = varFinalOrConst;
    }
    push(modifiers);
  }

  @override
  void beginMixinDeclaration(
      Token? augmentToken,
      Token? sealedToken,
      Token? baseToken,
      Token? interfaceToken,
      Token? finalToken,
      Token mixinKeyword,
      Token name) {
    assert(_classLikeBuilder == null);
    if (!enableSealedClass) {
      if (sealedToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.sealed_class,
          startToken: sealedToken,
        );
        // Pretend that 'sealed' didn't occur while this feature is incomplete.
        sealedToken = null;
      }
    }
    if (!enableClassModifiers) {
      if (baseToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: baseToken,
        );
        // Pretend that 'base' didn't occur while this feature is incomplete.
        baseToken = null;
      }
      if (interfaceToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: interfaceToken,
        );
        // Pretend that 'interface' didn't occur while this feature is incomplete.
        interfaceToken = null;
      }
      if (finalToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: finalToken,
        );
        // Pretend that 'final' didn't occur while this feature is incomplete.
        finalToken = null;
      }
    }
    push(augmentToken ?? NullValues.Token);
    push(sealedToken ?? NullValues.Token);
    push(baseToken ?? NullValues.Token);
    push(interfaceToken ?? NullValues.Token);
    push(finalToken ?? NullValues.Token);
  }

  @override
  void beginNamedMixinApplication(
      Token begin,
      Token? abstractToken,
      Token? macroToken,
      Token? inlineToken,
      Token? sealedToken,
      Token? baseToken,
      Token? interfaceToken,
      Token? finalToken,
      Token? augmentToken,
      Token? mixinToken,
      Token name) {
    push(_Modifiers()..abstractKeyword = abstractToken);
    if (!enableMacros) {
      if (macroToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.macros,
          startToken: macroToken,
        );
        // Pretend that 'macro' didn't occur while this feature is incomplete.
        macroToken = null;
      }
    }
    if (!enableInlineClass) {
      if (inlineToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.inline_class,
          startToken: inlineToken,
        );
        // Pretend that 'inline' didn't occur while this feature is incomplete.
        inlineToken = null;
      }
    }
    if (!enableSealedClass) {
      if (sealedToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.sealed_class,
          startToken: sealedToken,
        );
        // Pretend that 'sealed' didn't occur while this feature is incomplete.
        sealedToken = null;
      }
    }
    if (!enableClassModifiers) {
      if (baseToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: baseToken,
        );
        // Pretend that 'base' didn't occur while this feature is incomplete.
        baseToken = null;
      }
      if (interfaceToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: interfaceToken,
        );
        // Pretend that 'interface' didn't occur while this feature is
        // incomplete.
        interfaceToken = null;
      }
      if (finalToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: finalToken,
        );
        // Pretend that 'final' didn't occur while this feature is incomplete.
        finalToken = null;
      }
      if (mixinToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.class_modifiers,
          startToken: mixinToken,
        );
        // Pretend that 'mixin' didn't occur while this feature is incomplete.
        mixinToken = null;
      }
    }
    push(macroToken ?? NullValues.Token);
    push(inlineToken ?? NullValues.Token);
    push(sealedToken ?? NullValues.Token);
    push(baseToken ?? NullValues.Token);
    push(interfaceToken ?? NullValues.Token);
    push(finalToken ?? NullValues.Token);
    push(augmentToken ?? NullValues.Token);
    push(mixinToken ?? NullValues.Token);
  }

  @override
  void beginPatternGuard(Token when) {
    debugEvent("PatternGuard");
  }

  @override
  void beginSwitchCaseWhenClause(Token when) {
    debugEvent("PatternSwitchCaseGuard");
  }

  @override
  void beginTopLevelMethod(
      Token lastConsumed, Token? augmentToken, Token? externalToken) {
    push(_Modifiers()
      ..augmentKeyword = augmentToken
      ..externalKeyword = externalToken);
  }

  @override
  void beginTypeVariable(Token token) {
    debugEvent("beginTypeVariable");
    var name = pop() as SimpleIdentifierImpl;
    var metadata = pop() as List<AnnotationImpl>?;

    var comment = _findComment(metadata, name.beginToken);
    var typeParameter = TypeParameterImpl(
      comment: comment,
      metadata: metadata,
      name: name.token,
      extendsKeyword: null,
      bound: null,
    );
    push(typeParameter);
  }

  @override
  void beginVariablesDeclaration(
      Token token, Token? lateToken, Token? varFinalOrConst) {
    debugEvent("beginVariablesDeclaration");
    if (varFinalOrConst != null || lateToken != null) {
      push(_Modifiers()
        ..finalConstOrVarKeyword = varFinalOrConst
        ..lateToken = lateToken);
    } else {
      push(NullValues.Modifiers);
    }
  }

  ConstructorInitializerImpl? buildInitializer(Object initializerObject) {
    if (initializerObject is FunctionExpressionInvocationImpl) {
      var function = initializerObject.function;
      if (function is SuperExpressionImpl) {
        return SuperConstructorInvocationImpl(
          superKeyword: function.superKeyword,
          period: null,
          constructorName: null,
          argumentList: initializerObject.argumentList,
        );
      }
      if (function is ThisExpressionImpl) {
        return RedirectingConstructorInvocationImpl(
          thisKeyword: function.thisKeyword,
          period: null,
          constructorName: null,
          argumentList: initializerObject.argumentList,
        );
      }
      return null;
    }

    if (initializerObject is MethodInvocationImpl) {
      var target = initializerObject.target;
      if (target is SuperExpressionImpl) {
        return SuperConstructorInvocationImpl(
          superKeyword: target.superKeyword,
          period: initializerObject.operator,
          constructorName: initializerObject.methodName,
          argumentList: initializerObject.argumentList,
        );
      }
      if (target is ThisExpressionImpl) {
        return RedirectingConstructorInvocationImpl(
          thisKeyword: target.thisKeyword,
          period: initializerObject.operator,
          constructorName: initializerObject.methodName,
          argumentList: initializerObject.argumentList,
        );
      }
      return buildInitializerTargetExpressionRecovery(
          target, initializerObject);
    }

    if (initializerObject is PropertyAccessImpl) {
      return buildInitializerTargetExpressionRecovery(
          initializerObject.target, initializerObject);
    }

    if (initializerObject is AssignmentExpressionImpl) {
      Token? thisKeyword;
      Token? period;
      SimpleIdentifierImpl fieldName;
      var left = initializerObject.leftHandSide;
      if (left is PropertyAccessImpl) {
        var target = left.target;
        if (target is ThisExpressionImpl) {
          thisKeyword = target.thisKeyword;
          period = left.operator;
        } else {
          assert(target is SuperExpressionImpl);
          // Recovery:
          // Parser has reported FieldInitializedOutsideDeclaringClass.
        }
        fieldName = left.propertyName;
      } else if (left is SimpleIdentifierImpl) {
        fieldName = left;
      } else {
        // Recovery:
        // Parser has reported invalid assignment.
        var superExpression = left as SuperExpressionImpl;
        fieldName = ast.simpleIdentifier(superExpression.superKeyword);
      }
      return ConstructorFieldInitializerImpl(
        thisKeyword: thisKeyword,
        period: period,
        fieldName: fieldName,
        equals: initializerObject.operator,
        expression: initializerObject.rightHandSide,
      );
    }

    if (initializerObject is AssertInitializerImpl) {
      return initializerObject;
    }

    if (initializerObject is IndexExpressionImpl) {
      return buildInitializerTargetExpressionRecovery(
          initializerObject.target, initializerObject);
    }

    if (initializerObject is CascadeExpressionImpl) {
      return buildInitializerTargetExpressionRecovery(
          initializerObject.target, initializerObject);
    }

    return null;
  }

  ConstructorInitializerImpl? buildInitializerTargetExpressionRecovery(
      ExpressionImpl? target, Object initializerObject) {
    ArgumentListImpl? argumentList;
    while (true) {
      if (target is FunctionExpressionInvocationImpl) {
        argumentList = target.argumentList;
        target = target.function;
      } else if (target is MethodInvocationImpl) {
        argumentList = target.argumentList;
        target = target.target;
      } else if (target is PropertyAccessImpl) {
        argumentList = null;
        target = target.target;
      } else {
        break;
      }
    }
    if (target is SuperExpressionImpl) {
      // TODO(danrubel): Consider generating this error in the parser
      // This error is also reported in the body builder
      handleRecoverableError(messageInvalidSuperInInitializer,
          target.superKeyword, target.superKeyword);
      return SuperConstructorInvocationImpl(
        superKeyword: target.superKeyword,
        period: null,
        constructorName: null,
        argumentList:
            argumentList ?? _syntheticArgumentList(target.superKeyword),
      );
    } else if (target is ThisExpressionImpl) {
      // TODO(danrubel): Consider generating this error in the parser
      // This error is also reported in the body builder
      handleRecoverableError(messageInvalidThisInInitializer,
          target.thisKeyword, target.thisKeyword);
      return RedirectingConstructorInvocationImpl(
        thisKeyword: target.thisKeyword,
        period: null,
        constructorName: null,
        argumentList:
            argumentList ?? _syntheticArgumentList(target.thisKeyword),
      );
    }
    return null;
  }

  void checkFieldFormalParameters(FormalParameterListImpl? parameterList) {
    var parameters = parameterList?.parameters;
    if (parameters != null) {
      for (var parameter in parameters) {
        if (parameter is FieldFormalParameterImpl) {
          // This error is reported in the BodyBuilder.endFormalParameter.
          handleRecoverableError(messageFieldInitializerOutsideConstructor,
              parameter.thisKeyword, parameter.thisKeyword);
        }
      }
    }
  }

  /// TODO(scheglov) We should not do this.
  /// Ideally, we should not test parsing pieces of class, and instead parse
  /// the whole unit, and extract pieces that we need to validate.
  _ClassDeclarationBuilder createFakeClassDeclarationBuilder(String className) {
    return _classLikeBuilder = _ClassDeclarationBuilder(
      comment: null,
      metadata: null,
      abstractKeyword: null,
      macroKeyword: null,
      inlineKeyword: null,
      sealedKeyword: null,
      baseKeyword: null,
      interfaceKeyword: null,
      finalKeyword: null,
      augmentKeyword: null,
      mixinKeyword: null,
      classKeyword: Token(Keyword.CLASS, 0),
      name: StringToken(TokenType.STRING, className, -1),
      typeParameters: null,
      extendsClause: null,
      withClause: null,
      implementsClause: null,
      nativeClause: null,
      leftBracket: Tokens.openCurlyBracket(),
      rightBracket: Tokens.closeCurlyBracket(),
    );
  }

  @override
  void debugEvent(String name) {
    // printEvent('AstBuilder: $name');
  }

  void doDotExpression(Token dot) {
    var identifierOrInvoke = pop() as ExpressionImpl;
    var receiver = pop() as ExpressionImpl?;
    if (identifierOrInvoke is SimpleIdentifierImpl) {
      if (receiver is SimpleIdentifierImpl && identical('.', dot.stringValue)) {
        push(
          PrefixedIdentifierImpl(
            prefix: receiver,
            period: dot,
            identifier: identifierOrInvoke,
          ),
        );
      } else {
        push(
          PropertyAccessImpl(
            target: receiver,
            operator: dot,
            propertyName: identifierOrInvoke,
          ),
        );
      }
    } else if (identifierOrInvoke is MethodInvocationImpl) {
      assert(identifierOrInvoke.target == null);
      identifierOrInvoke
        ..target = receiver
        ..operator = dot;
      push(identifierOrInvoke);
    } else {
      // This same error is reported in BodyBuilder.doDotOrCascadeExpression
      Token token = identifierOrInvoke.beginToken;
      // TODO(danrubel): Consider specializing the error message based
      // upon the type of expression. e.g. "x.this" -> templateThisAsIdentifier
      handleRecoverableError(
          templateExpectedIdentifier.withArguments(token), token, token);
      SimpleIdentifierImpl identifier =
          ast.simpleIdentifier(token, isDeclaration: false);
      push(
        PropertyAccessImpl(
          target: receiver,
          operator: dot,
          propertyName: identifier,
        ),
      );
    }
  }

  void doInvocation(
      TypeArgumentListImpl? typeArguments, MethodInvocationImpl arguments) {
    var receiver = pop() as ExpressionImpl;
    if (receiver is SimpleIdentifierImpl) {
      arguments.methodName = receiver;
      if (typeArguments != null) {
        arguments.typeArguments = typeArguments;
      }
      push(arguments);
    } else {
      push(
        FunctionExpressionInvocationImpl(
          function: receiver,
          typeArguments: typeArguments,
          argumentList: arguments.argumentList,
        ),
      );
    }
  }

  void doPropertyGet() {}

  @override
  void endArguments(int count, Token leftParenthesis, Token rightParenthesis) {
    assert(optional('(', leftParenthesis));
    assert(optional(')', rightParenthesis));
    debugEvent("Arguments");

    var expressions = popTypedList2<ExpressionImpl>(count);
    final arguments = ArgumentListImpl(
      leftParenthesis: leftParenthesis,
      arguments: expressions,
      rightParenthesis: rightParenthesis,
    );

    if (!enableNamedArgumentsAnywhere) {
      bool hasSeenNamedArgument = false;
      for (var expression in expressions) {
        if (expression is NamedExpressionImpl) {
          hasSeenNamedArgument = true;
        } else if (hasSeenNamedArgument) {
          // Positional argument after named argument.
          handleRecoverableError(messagePositionalAfterNamedArgument,
              expression.beginToken, expression.endToken);
        }
      }
    }

    push(
      MethodInvocationImpl(
        target: null,
        operator: null,
        methodName: _tmpSimpleIdentifier(),
        typeArguments: null,
        argumentList: arguments,
      ),
    );
  }

  @override
  void endAsOperatorType(Token asOperator) {
    debugEvent("AsOperatorType");
  }

  @override
  void endAssert(Token assertKeyword, Assert kind, Token leftParenthesis,
      Token? comma, Token semicolon) {
    assert(optional('assert', assertKeyword));
    assert(optional('(', leftParenthesis));
    assert(optionalOrNull(',', comma));
    assert(kind != Assert.Statement || optionalOrNull(';', semicolon));
    debugEvent("Assert");

    var message = popIfNotNull(comma) as ExpressionImpl?;
    var condition = pop() as ExpressionImpl;
    switch (kind) {
      case Assert.Expression:
        // The parser has already reported an error indicating that assert
        // cannot be used in an expression. Insert a placeholder.
        final arguments = <ExpressionImpl>[condition];
        if (message != null) {
          arguments.add(message);
        }
        push(
          FunctionExpressionInvocationImpl(
            function: ast.simpleIdentifier(assertKeyword),
            typeArguments: null,
            argumentList: ArgumentListImpl(
              leftParenthesis: leftParenthesis,
              arguments: arguments,
              rightParenthesis: leftParenthesis.endGroup!,
            ),
          ),
        );
        break;
      case Assert.Initializer:
        push(
          AssertInitializerImpl(
            assertKeyword: assertKeyword,
            leftParenthesis: leftParenthesis,
            condition: condition,
            comma: comma,
            message: message,
            rightParenthesis: leftParenthesis.endGroup!,
          ),
        );
        break;
      case Assert.Statement:
        push(
          AssertStatementImpl(
            assertKeyword: assertKeyword,
            leftParenthesis: leftParenthesis,
            condition: condition,
            comma: comma,
            message: message,
            rightParenthesis: leftParenthesis.endGroup!,
            semicolon: semicolon,
          ),
        );
        break;
    }
  }

  @override
  void endAwaitExpression(Token awaitKeyword, Token endToken) {
    assert(optional('await', awaitKeyword));
    debugEvent("AwaitExpression");

    var expression = pop() as ExpressionImpl;
    push(
      AwaitExpressionImpl(
        awaitKeyword: awaitKeyword,
        expression: expression,
      ),
    );
  }

  @override
  void endBinaryExpression(Token operatorToken) {
    assert(operatorToken.isOperator ||
        optional('.', operatorToken) ||
        optional('?.', operatorToken) ||
        optional('..', operatorToken) ||
        optional('?..', operatorToken) ||
        optional('===', operatorToken) ||
        optional('!==', operatorToken));
    debugEvent("BinaryExpression");

    if (identical(".", operatorToken.stringValue) ||
        identical("?.", operatorToken.stringValue) ||
        identical("..", operatorToken.stringValue) ||
        identical("?..", operatorToken.stringValue)) {
      doDotExpression(operatorToken);
    } else {
      var right = pop() as ExpressionImpl;
      var left = pop() as ExpressionImpl;
      reportErrorIfSuper(right);
      push(
        BinaryExpressionImpl(
          leftOperand: left,
          operator: operatorToken,
          rightOperand: right,
        ),
      );
      if (!enableTripleShift && operatorToken.type == TokenType.GT_GT_GT) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.triple_shift,
          startToken: operatorToken,
        );
      }
    }
  }

  @override
  void endBinaryPattern(Token operatorToken) {
    assert(operatorToken.isOperator);
    debugEvent("BinaryPattern");

    var right = pop() as DartPatternImpl;
    var left = pop() as DartPatternImpl;
    if (operatorToken.lexeme == '&&') {
      push(
        LogicalAndPatternImpl(
          leftOperand: left,
          operator: operatorToken,
          rightOperand: right,
        ),
      );
    } else if (operatorToken.lexeme == '||') {
      push(
        LogicalOrPatternImpl(
          leftOperand: left,
          operator: operatorToken,
          rightOperand: right,
        ),
      );
    } else {
      throw UnimplementedError('operatorToken: $operatorToken');
    }
  }

  @override
  void endBlock(
      int count, Token leftBracket, Token rightBracket, BlockKind blockKind) {
    assert(optional('{', leftBracket));
    assert(optional('}', rightBracket));
    debugEvent("Block");

    var statements = popTypedList2<StatementImpl>(count);
    push(
      BlockImpl(
        leftBracket: leftBracket,
        statements: statements,
        rightBracket: rightBracket,
      ),
    );
  }

  @override
  void endBlockFunctionBody(int count, Token leftBracket, Token rightBracket) {
    assert(optional('{', leftBracket));
    assert(optional('}', rightBracket));
    debugEvent("BlockFunctionBody");

    var statements = popTypedList2<StatementImpl>(count);
    final block = BlockImpl(
      leftBracket: leftBracket,
      statements: statements,
      rightBracket: rightBracket,
    );
    var star = pop() as Token?;
    var asyncKeyword = pop() as Token?;
    if (parseFunctionBodies) {
      push(
        BlockFunctionBodyImpl(
          keyword: asyncKeyword,
          star: star,
          block: block,
        ),
      );
    } else {
      // TODO(danrubel): Skip the block rather than parsing it.
      push(
        EmptyFunctionBodyImpl(
          semicolon: SyntheticToken(
            TokenType.SEMICOLON,
            leftBracket.charOffset,
          ),
        ),
      );
    }
  }

  @override
  void endCascade() {
    debugEvent("Cascade");

    var expression = pop() as ExpressionImpl;
    var cascade = pop() as CascadeExpressionImpl;
    pop(); // Token.
    push(
      CascadeExpressionImpl(
        target: cascade.target,
        cascadeSections: <ExpressionImpl>[
          ...cascade.cascadeSections,
          expression,
        ],
      ),
    );
  }

  @override
  void endCaseExpression(Token caseKeyword, Token? when, Token colon) {
    assert(optional('case', caseKeyword));
    assert(optional(':', colon));
    debugEvent("CaseMatch");

    WhenClauseImpl? whenClause;
    if (when != null) {
      var expression = pop() as ExpressionImpl;
      whenClause = WhenClauseImpl(
        whenKeyword: when,
        expression: expression,
      );
    }

    if (_featureSet.isEnabled(Feature.patterns)) {
      var pattern = pop() as DartPatternImpl;
      push(
        SwitchPatternCaseImpl(
          labels: <LabelImpl>[],
          keyword: caseKeyword,
          guardedPattern: GuardedPatternImpl(
            pattern: pattern,
            whenClause: whenClause,
          ),
          colon: colon,
          statements: <StatementImpl>[],
        ),
      );
    } else {
      var expression = pop() as ExpressionImpl;
      push(
        SwitchCaseImpl(
          labels: <LabelImpl>[],
          keyword: caseKeyword,
          expression: expression,
          colon: colon,
          statements: <StatementImpl>[],
        ),
      );
    }
  }

  @override
  void endClassConstructor(Token? getOrSet, Token beginToken, Token beginParam,
      Token? beginInitializers, Token endToken) {
    assert(getOrSet == null ||
        optional('get', getOrSet) ||
        optional('set', getOrSet));
    debugEvent("ClassConstructor");

    var bodyObject = pop();
    var initializers = (pop() as List<ConstructorInitializerImpl>?) ?? const [];
    var separator = pop() as Token?;
    var parameters = pop() as FormalParameterListImpl;
    var typeParameters = pop() as TypeParameterListImpl?;
    var name = pop();
    pop(); // return type
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, beginToken);

    ConstructorNameImpl? redirectedConstructor;
    FunctionBodyImpl body;
    if (bodyObject is FunctionBodyImpl) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      separator = bodyObject.equalToken;
      redirectedConstructor = bodyObject.constructorName;
      body = EmptyFunctionBodyImpl(
        semicolon: endToken,
      );
    } else {
      internalProblem(
          templateInternalProblemUnhandled.withArguments(
              "${bodyObject.runtimeType}", "bodyObject"),
          beginToken.charOffset,
          uri);
    }

    SimpleIdentifierImpl prefixOrName;
    Token? period;
    SimpleIdentifierImpl? nameOrNull;
    if (name is SimpleIdentifierImpl) {
      prefixOrName = name;
    } else if (name is PrefixedIdentifierImpl) {
      prefixOrName = name.prefix;
      period = name.period;
      nameOrNull = name.identifier;
    } else if (name is _OperatorName) {
      prefixOrName = name.name;
    } else {
      throw UnimplementedError(
          'name is an instance of ${name.runtimeType} in endClassConstructor');
    }

    if (typeParameters != null) {
      // Outline builder also reports this error message.
      handleRecoverableError(messageConstructorWithTypeParameters,
          typeParameters.beginToken, typeParameters.endToken);
    }
    if (modifiers?.constKeyword != null &&
        (body.length > 1 || body.beginToken.lexeme != ';')) {
      // This error is also reported in BodyBuilder.finishFunction
      Token bodyToken = body.beginToken;
      // Token bodyToken = body.beginToken ?? modifiers.constKeyword;
      handleRecoverableError(
          messageConstConstructorWithBody, bodyToken, bodyToken);
    }
    var constructor = ConstructorDeclarationImpl(
      comment: comment,
      metadata: metadata,
      externalKeyword: modifiers?.externalKeyword,
      constKeyword: modifiers?.finalConstOrVarKeyword,
      factoryKeyword: null,
      returnType: ast.simpleIdentifier(prefixOrName.token),
      period: period,
      name: nameOrNull?.token,
      parameters: parameters,
      separator: separator,
      initializers: initializers,
      redirectedConstructor: redirectedConstructor,
      body: body,
    );

    _classLikeBuilder?.members.add(constructor);
    if (_classLikeBuilder is MixinDeclarationImpl) {
      // TODO (danrubel): Report an error if this is a mixin declaration.
    }
  }

  @override
  void endClassDeclaration(Token beginToken, Token endToken) {
    debugEvent("ClassDeclaration");

    final builder = _classLikeBuilder as _ClassDeclarationBuilder;
    declarations.add(
      builder.build(),
    );
    _classLikeBuilder = null;
  }

  @override
  void endClassFactoryMethod(
      Token beginToken, Token factoryKeyword, Token endToken) {
    assert(optional('factory', factoryKeyword));
    assert(optional(';', endToken) || optional('}', endToken));
    debugEvent("ClassFactoryMethod");

    FunctionBodyImpl body;
    Token? separator;
    ConstructorNameImpl? redirectedConstructor;
    var bodyObject = pop();
    if (bodyObject is FunctionBodyImpl) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      separator = bodyObject.equalToken;
      redirectedConstructor = bodyObject.constructorName;
      body = EmptyFunctionBodyImpl(
        semicolon: endToken,
      );
    } else {
      internalProblem(
          templateInternalProblemUnhandled.withArguments(
              "${bodyObject.runtimeType}", "bodyObject"),
          beginToken.charOffset,
          uri);
    }

    var parameters = pop() as FormalParameterListImpl;
    var typeParameters = pop() as TypeParameterListImpl?;
    var constructorName = pop() as IdentifierImpl;
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, beginToken);

    if (typeParameters != null) {
      // TODO(danrubel): Update OutlineBuilder to report this error message.
      handleRecoverableError(messageConstructorWithTypeParameters,
          typeParameters.beginToken, typeParameters.endToken);
    }

    // Decompose the preliminary ConstructorName into the type name and
    // the actual constructor name.
    SimpleIdentifierImpl returnType;
    Token? period;
    SimpleIdentifierImpl? name;
    IdentifierImpl typeName = constructorName;
    if (typeName is SimpleIdentifierImpl) {
      returnType = typeName;
    } else if (typeName is PrefixedIdentifierImpl) {
      returnType = typeName.prefix;
      period = typeName.period;
      name =
          ast.simpleIdentifier(typeName.identifier.token, isDeclaration: true);
    } else {
      throw UnimplementedError();
    }

    _classLikeBuilder?.members.add(
      ConstructorDeclarationImpl(
        comment: comment,
        metadata: metadata,
        externalKeyword: modifiers?.externalKeyword,
        constKeyword: modifiers?.finalConstOrVarKeyword,
        factoryKeyword: factoryKeyword,
        returnType: ast.simpleIdentifier(returnType.token),
        period: period,
        name: name?.token,
        parameters: parameters,
        separator: separator,
        initializers: null,
        redirectedConstructor: redirectedConstructor,
        body: body,
      ),
    );
  }

  @override
  void endClassFields(
      Token? abstractToken,
      Token? augmentToken,
      Token? externalToken,
      Token? staticToken,
      Token? covariantToken,
      Token? lateToken,
      Token? varFinalOrConst,
      int count,
      Token beginToken,
      Token semicolon) {
    assert(optional(';', semicolon));
    debugEvent("Fields");

    if (abstractToken != null) {
      if (!enableNonNullable) {
        handleRecoverableError(
            messageAbstractClassMember, abstractToken, abstractToken);
      } else {
        if (staticToken != null) {
          handleRecoverableError(
              messageAbstractStaticField, abstractToken, abstractToken);
        }
        if (lateToken != null) {
          handleRecoverableError(
              messageAbstractLateField, abstractToken, abstractToken);
        }
      }
    }
    if (externalToken != null) {
      if (!enableNonNullable) {
        handleRecoverableError(
            messageExternalField, externalToken, externalToken);
      } else if (lateToken != null) {
        handleRecoverableError(
            messageExternalLateField, externalToken, externalToken);
      }
    }

    var variables = popTypedList2<VariableDeclarationImpl>(count);
    var type = pop() as TypeAnnotationImpl?;
    var variableList = VariableDeclarationListImpl(
      comment: null,
      metadata: null,
      lateKeyword: lateToken,
      keyword: varFinalOrConst,
      type: type,
      variables: variables,
    );
    var covariantKeyword = covariantToken;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, beginToken);
    _classLikeBuilder?.members.add(
      FieldDeclarationImpl(
        comment: comment,
        metadata: metadata,
        abstractKeyword: abstractToken,
        augmentKeyword: augmentToken,
        covariantKeyword: covariantKeyword,
        externalKeyword: externalToken,
        staticKeyword: staticToken,
        fieldList: variableList,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endClassMethod(Token? getOrSet, Token beginToken, Token beginParam,
      Token? beginInitializers, Token endToken) {
    assert(getOrSet == null ||
        optional('get', getOrSet) ||
        optional('set', getOrSet));
    debugEvent("ClassMethod");

    var bodyObject = pop();
    pop(); // initializers
    pop(); // separator
    var parameters = pop() as FormalParameterListImpl?;
    var typeParameters = pop() as TypeParameterListImpl?;
    var name = pop();
    var returnType = pop() as TypeAnnotationImpl?;
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, beginToken);

    assert(parameters != null || optional('get', getOrSet!));

    FunctionBodyImpl body;
    if (bodyObject is FunctionBodyImpl) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      body = EmptyFunctionBodyImpl(
        semicolon: endToken,
      );
    } else {
      internalProblem(
          templateInternalProblemUnhandled.withArguments(
              "${bodyObject.runtimeType}", "bodyObject"),
          beginToken.charOffset,
          uri);
    }

    Token? operatorKeyword;
    SimpleIdentifierImpl nameId;
    if (name is SimpleIdentifierImpl) {
      nameId = name;
    } else if (name is _OperatorName) {
      operatorKeyword = name.operatorKeyword;
      nameId = name.name;
      if (typeParameters != null) {
        handleRecoverableError(messageOperatorWithTypeParameters,
            typeParameters.beginToken, typeParameters.endToken);
      }
    } else {
      throw UnimplementedError(
          'name is an instance of ${name.runtimeType} in endClassMethod');
    }

    checkFieldFormalParameters(parameters);
    _classLikeBuilder?.members.add(
      MethodDeclarationImpl(
        comment: comment,
        metadata: metadata,
        externalKeyword: modifiers?.externalKeyword,
        modifierKeyword: modifiers?.abstractKeyword ?? modifiers?.staticKeyword,
        returnType: returnType,
        propertyKeyword: getOrSet,
        operatorKeyword: operatorKeyword,
        name: nameId.token,
        typeParameters: typeParameters,
        parameters: parameters,
        body: body,
      ),
    );
  }

  @override
  void endClassOrMixinOrExtensionBody(DeclarationKind kind, int memberCount,
      Token leftBracket, Token rightBracket) {
    // TODO(danrubel): consider renaming endClassOrMixinBody
    // to endClassOrMixinOrExtensionBody
    assert(optional('{', leftBracket));
    assert(optional('}', rightBracket));
    debugEvent("ClassOrMixinBody");

    final builder = _classLikeBuilder;
    if (builder != null) {
      builder
        ..leftBracket = leftBracket
        ..rightBracket = rightBracket;
    }
  }

  @override
  void endCombinators(int count) {
    debugEvent("Combinators");
    push(popTypedList<CombinatorImpl>(count) ?? NullValues.Combinators);
  }

  @override
  void endCompilationUnit(int count, Token endToken) {
    debugEvent("CompilationUnit");

    var beginToken = pop() as Token;
    checkEmpty(endToken.charOffset);

    CompilationUnitImpl unit = CompilationUnitImpl(
      beginToken: beginToken,
      scriptTag: scriptTag,
      directives: directives,
      declarations: declarations,
      endToken: endToken,
      featureSet: _featureSet,
      lineInfo: _lineInfo,
    );
    push(unit);
  }

  @override
  void endConditionalExpression(Token question, Token colon) {
    assert(optional('?', question));
    assert(optional(':', colon));
    debugEvent("ConditionalExpression");

    var elseExpression = pop() as ExpressionImpl;
    var thenExpression = pop() as ExpressionImpl;
    var condition = pop() as ExpressionImpl;
    reportErrorIfSuper(elseExpression);
    reportErrorIfSuper(thenExpression);
    push(
      ConditionalExpressionImpl(
        condition: condition,
        question: question,
        thenExpression: thenExpression,
        colon: colon,
        elseExpression: elseExpression,
      ),
    );
  }

  @override
  void endConditionalUri(Token ifKeyword, Token leftParen, Token? equalSign) {
    assert(optional('if', ifKeyword));
    assert(optionalOrNull('(', leftParen));
    assert(optionalOrNull('==', equalSign));
    debugEvent("ConditionalUri");

    var libraryUri = pop() as StringLiteralImpl;
    var value = popIfNotNull(equalSign) as StringLiteralImpl?;
    if (value is StringInterpolationImpl) {
      for (var child in value.childEntities) {
        if (child is InterpolationExpressionImpl) {
          // This error is reported in OutlineBuilder.endLiteralString
          handleRecoverableError(
              messageInterpolationInUri, child.beginToken, child.endToken);
          break;
        }
      }
    }
    var name = pop() as DottedNameImpl;
    push(
      ConfigurationImpl(
        ifKeyword: ifKeyword,
        leftParenthesis: leftParen,
        name: name,
        equalToken: equalSign,
        value: value,
        rightParenthesis: leftParen.endGroup!,
        uri: libraryUri,
      ),
    );
  }

  @override
  void endConditionalUris(int count) {
    debugEvent("ConditionalUris");

    push(popTypedList<ConfigurationImpl>(count) ?? NullValues.ConditionalUris);
  }

  @override
  void endConstantPattern(Token? constKeyword) {
    push(ConstantPatternImpl(
        constKeyword: constKeyword, expression: pop() as ExpressionImpl));
  }

  @override
  void endConstExpression(Token constKeyword) {
    assert(optional('const', constKeyword));
    debugEvent("ConstExpression");

    _handleInstanceCreation(constKeyword);
  }

  @override
  void endConstLiteral(Token token) {
    debugEvent("endConstLiteral");
  }

  @override
  void endConstructorReference(Token start, Token? periodBeforeName,
      Token endToken, ConstructorReferenceContext constructorReferenceContext) {
    assert(optionalOrNull('.', periodBeforeName));
    debugEvent("ConstructorReference");

    var constructorName = pop() as SimpleIdentifierImpl?;
    var typeArguments = pop() as TypeArgumentListImpl?;
    var typeNameIdentifier = pop() as IdentifierImpl;
    push(
      ConstructorNameImpl(
        type: NamedTypeImpl(
          name: typeNameIdentifier,
          typeArguments: typeArguments,
          question: null,
        ),
        period: periodBeforeName,
        name: constructorName,
      ),
    );
  }

  @override
  void endDoWhileStatement(
      Token doKeyword, Token whileKeyword, Token semicolon) {
    assert(optional('do', doKeyword));
    assert(optional('while', whileKeyword));
    assert(optional(';', semicolon));
    debugEvent("DoWhileStatement");

    var condition = pop() as _ParenthesizedCondition;
    var body = pop() as StatementImpl;
    push(
      DoStatementImpl(
        doKeyword: doKeyword,
        body: body,
        whileKeyword: whileKeyword,
        leftParenthesis: condition.leftParenthesis,
        condition: condition.expression,
        rightParenthesis: condition.rightParenthesis,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endDoWhileStatementBody(Token token) {
    debugEvent("endDoWhileStatementBody");
  }

  @override
  void endElseStatement(Token token) {
    debugEvent("endElseStatement");
  }

  @override
  void endEnum(Token enumKeyword, Token leftBrace, int memberCount) {
    assert(optional('enum', enumKeyword));
    assert(optional('{', leftBrace));
    debugEvent("Enum");

    final builder = _classLikeBuilder as _EnumDeclarationBuilder;
    declarations.add(
      builder.build(),
    );
    _classLikeBuilder = null;
  }

  @override
  void endEnumConstructor(Token? getOrSet, Token beginToken, Token beginParam,
      Token? beginInitializers, Token endToken) {
    debugEvent("endEnumConstructor");
    endClassConstructor(
        getOrSet, beginToken, beginParam, beginInitializers, endToken);
  }

  @override
  void endExport(Token exportKeyword, Token semicolon) {
    assert(optional('export', exportKeyword));
    assert(optional(';', semicolon));
    debugEvent("Export");

    var combinators = pop() as List<CombinatorImpl>?;
    var configurations = pop() as List<ConfigurationImpl>?;
    var uri = pop() as StringLiteralImpl;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, exportKeyword);
    directives.add(
      ExportDirectiveImpl(
        comment: comment,
        metadata: metadata,
        exportKeyword: exportKeyword,
        uri: uri,
        configurations: configurations,
        combinators: combinators,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endExtensionConstructor(Token? getOrSet, Token beginToken,
      Token beginParam, Token? beginInitializers, Token endToken) {
    debugEvent("ExtensionConstructor");
    // TODO(danrubel) Decide how to handle constructor declarations within
    // extensions. They are invalid and the parser has already reported an
    // error at this point. In the future, we should include them in order
    // to get navigation, search, etc.
    pop(); // body
    pop(); // initializers
    pop(); // separator
    pop(); // parameters
    pop(); // typeParameters
    pop(); // name
    pop(); // returnType
    pop(); // modifiers
    pop(); // metadata
  }

  @override
  void endExtensionDeclaration(Token extensionKeyword, Token? typeKeyword,
      Token onKeyword, Token? showKeyword, Token? hideKeyword, Token token) {
    final builder = _classLikeBuilder as _ExtensionDeclarationBuilder;

    if (typeKeyword != null && !enableExtensionTypes) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.extension_types,
        startToken: typeKeyword,
      );
    }

    final showOrHideKeyword = showKeyword ?? hideKeyword;
    if (showOrHideKeyword != null && !enableExtensionTypes) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.extension_types,
        startToken: showOrHideKeyword,
      );
    }

    final type = pop() as TypeAnnotationImpl;

    declarations.add(
      builder.build(
        extendedType: type,
        onKeyword: onKeyword,
        typeKeyword: typeKeyword,
      ),
    );

    _classLikeBuilder = null;
  }

  @override
  void endExtensionFactoryMethod(
      Token beginToken, Token factoryKeyword, Token endToken) {
    assert(optional('factory', factoryKeyword));
    assert(optional(';', endToken) || optional('}', endToken));
    debugEvent("ExtensionFactoryMethod");

    var bodyObject = pop();
    var parameters = pop() as FormalParameterListImpl;
    var typeParameters = pop() as TypeParameterListImpl?;
    var constructorName = pop();
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<AnnotationImpl>?;

    FunctionBodyImpl body;
    if (bodyObject is FunctionBodyImpl) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      body = EmptyFunctionBodyImpl(
        semicolon: endToken,
      );
    } else {
      // Unhandled situation which should never happen.
      // Since this event handler is just a recovery attempt,
      // don't bother adding this declaration to the AST.
      return;
    }
    var comment = _findComment(metadata, beginToken);

    // Constructor declarations within extensions are invalid and the parser
    // has already reported an error at this point, but we include them in as
    // a method declaration in order to get navigation, search, etc.

    SimpleIdentifierImpl methodName;
    if (constructorName is SimpleIdentifierImpl) {
      methodName = constructorName;
    } else if (constructorName is PrefixedIdentifierImpl) {
      methodName = constructorName.identifier;
    } else {
      // Unsure what the method name should be in this situation.
      // Since this event handler is just a recovery attempt,
      // don't bother adding this declaration to the AST.
      return;
    }
    _classLikeBuilder?.members.add(
      MethodDeclarationImpl(
        comment: comment,
        metadata: metadata,
        externalKeyword: modifiers?.externalKeyword,
        modifierKeyword: modifiers?.abstractKeyword ?? modifiers?.staticKeyword,
        returnType: null,
        propertyKeyword: null,
        operatorKeyword: null,
        name: methodName.token,
        typeParameters: typeParameters,
        parameters: parameters,
        body: body,
      ),
    );
  }

  @override
  void endExtensionFields(
      Token? abstractToken,
      Token? augmentToken,
      Token? externalToken,
      Token? staticToken,
      Token? covariantToken,
      Token? lateToken,
      Token? varFinalOrConst,
      int count,
      Token beginToken,
      Token endToken) {
    if (staticToken == null) {
      // TODO(danrubel) Decide how to handle instance field declarations
      // within extensions. They are invalid and the parser has already reported
      // an error at this point, but we include them in order to get navigation,
      // search, etc.
    }
    endClassFields(
        abstractToken,
        augmentToken,
        externalToken,
        staticToken,
        covariantToken,
        lateToken,
        varFinalOrConst,
        count,
        beginToken,
        endToken);
  }

  @override
  void endExtensionMethod(Token? getOrSet, Token beginToken, Token beginParam,
      Token? beginInitializers, Token endToken) {
    debugEvent("ExtensionMethod");
    endClassMethod(
        getOrSet, beginToken, beginParam, beginInitializers, endToken);
  }

  @override
  void endFieldInitializer(Token equals, Token token) {
    assert(optional('=', equals));
    debugEvent("FieldInitializer");

    var initializer = pop() as ExpressionImpl;
    var name = pop() as SimpleIdentifierImpl;
    push(
      VariableDeclarationImpl(
        name: name.token,
        equals: equals,
        initializer: initializer,
      ),
    );
  }

  @override
  void endForControlFlow(Token token) {
    debugEvent("endForControlFlow");
    var body = pop() as CollectionElementImpl;
    var forLoopParts = pop() as ForPartsImpl;
    var leftParenthesis = pop() as Token;
    var forToken = pop() as Token;

    push(
      ForElementImpl(
        awaitKeyword: null,
        forKeyword: forToken,
        leftParenthesis: leftParenthesis,
        forLoopParts: forLoopParts,
        rightParenthesis: leftParenthesis.endGroup!,
        body: body,
      ),
    );
  }

  @override
  void endForIn(Token endToken) {
    debugEvent("ForInExpression");

    var body = pop() as StatementImpl;
    var forLoopParts = pop() as ForEachPartsImpl;
    var leftParenthesis = pop() as Token;
    var forToken = pop() as Token;
    var awaitToken = pop(NullValues.AwaitToken) as Token?;

    push(
      ForStatementImpl(
        awaitKeyword: awaitToken,
        forKeyword: forToken,
        leftParenthesis: leftParenthesis,
        forLoopParts: forLoopParts,
        rightParenthesis: leftParenthesis.endGroup!,
        body: body,
      ),
    );
  }

  @override
  void endForInBody(Token token) {
    debugEvent("endForInBody");
  }

  @override
  void endForInControlFlow(Token token) {
    debugEvent("endForInControlFlow");

    var body = pop() as CollectionElementImpl;
    var forLoopParts = pop() as ForEachPartsImpl;
    var leftParenthesis = pop() as Token;
    var forToken = pop() as Token;
    var awaitToken = pop(NullValues.AwaitToken) as Token?;

    push(
      ForElementImpl(
        awaitKeyword: awaitToken,
        forKeyword: forToken,
        leftParenthesis: leftParenthesis,
        forLoopParts: forLoopParts,
        rightParenthesis: leftParenthesis.endGroup!,
        body: body,
      ),
    );
  }

  @override
  void endForInExpression(Token token) {
    debugEvent("ForInExpression");
  }

  @override
  void endFormalParameter(
      Token? thisKeyword,
      Token? superKeyword,
      Token? periodAfterThisOrSuper,
      Token nameToken,
      Token? initializerStart,
      Token? initializerEnd,
      FormalParameterKind kind,
      MemberKind memberKind) {
    assert(optionalOrNull('this', thisKeyword));
    assert(optionalOrNull('super', superKeyword));
    assert(thisKeyword == null && superKeyword == null
        ? periodAfterThisOrSuper == null
        : optional('.', periodAfterThisOrSuper!));
    debugEvent("FormalParameter");

    if (superKeyword != null && !enableSuperParameters) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.super_parameters,
        startToken: superKeyword,
      );
    }

    var defaultValue = pop() as _ParameterDefaultValue?;
    var name = pop() as SimpleIdentifierImpl?;
    var typeOrFunctionTypedParameter = pop() as AstNodeImpl?;
    var modifiers = pop() as _Modifiers?;
    var keyword = modifiers?.finalConstOrVarKeyword;
    var covariantKeyword = modifiers?.covariantKeyword;
    var requiredKeyword = modifiers?.requiredToken;
    if (!enableNonNullable && requiredKeyword != null) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.non_nullable,
        startToken: requiredKeyword,
      );
    }
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata,
        thisKeyword ?? typeOrFunctionTypedParameter?.beginToken ?? nameToken);

    NormalFormalParameterImpl node;
    if (typeOrFunctionTypedParameter is FunctionTypedFormalParameterImpl) {
      // This is a temporary AST node that was constructed in
      // [endFunctionTypedFormalParameter]. We now deconstruct it and create
      // the final AST node.
      if (superKeyword != null) {
        assert(thisKeyword == null,
            "Can't have both 'this' and 'super' in a parameter.");
        node = SuperFormalParameterImpl(
          name: name!.token,
          comment: comment,
          metadata: metadata,
          covariantKeyword: covariantKeyword,
          keyword: keyword,
          requiredKeyword: requiredKeyword,
          type: typeOrFunctionTypedParameter.returnType,
          superKeyword: superKeyword,
          period: periodAfterThisOrSuper!,
          typeParameters: typeOrFunctionTypedParameter.typeParameters,
          parameters: typeOrFunctionTypedParameter.parameters,
          question: typeOrFunctionTypedParameter.question,
        );
      } else if (thisKeyword != null) {
        assert(superKeyword == null,
            "Can't have both 'this' and 'super' in a parameter.");
        node = FieldFormalParameterImpl(
          name: name!.token,
          comment: comment,
          metadata: metadata,
          covariantKeyword: covariantKeyword,
          keyword: keyword,
          requiredKeyword: requiredKeyword,
          type: typeOrFunctionTypedParameter.returnType,
          thisKeyword: thisKeyword,
          period: periodAfterThisOrSuper!,
          typeParameters: typeOrFunctionTypedParameter.typeParameters,
          parameters: typeOrFunctionTypedParameter.parameters,
          question: typeOrFunctionTypedParameter.question,
        );
      } else {
        node = FunctionTypedFormalParameterImpl(
          name: name!.token,
          comment: comment,
          metadata: metadata,
          covariantKeyword: covariantKeyword,
          requiredKeyword: requiredKeyword,
          returnType: typeOrFunctionTypedParameter.returnType,
          typeParameters: typeOrFunctionTypedParameter.typeParameters,
          parameters: typeOrFunctionTypedParameter.parameters,
          question: typeOrFunctionTypedParameter.question,
        );
      }
    } else {
      var type = typeOrFunctionTypedParameter as TypeAnnotationImpl?;
      if (superKeyword != null) {
        assert(thisKeyword == null,
            "Can't have both 'this' and 'super' in a parameter.");
        if (keyword is KeywordToken && keyword.keyword == Keyword.VAR) {
          handleRecoverableError(
            templateExtraneousModifier.withArguments(keyword),
            keyword,
            keyword,
          );
        }
        node = SuperFormalParameterImpl(
          comment: comment,
          metadata: metadata,
          covariantKeyword: covariantKeyword,
          requiredKeyword: requiredKeyword,
          keyword: keyword,
          type: type,
          superKeyword: superKeyword,
          period: periodAfterThisOrSuper!,
          name: name!.token,
          typeParameters: null,
          parameters: null,
          question: null,
        );
      } else if (thisKeyword != null) {
        assert(superKeyword == null,
            "Can't have both 'this' and 'super' in a parameter.");
        node = FieldFormalParameterImpl(
          comment: comment,
          metadata: metadata,
          covariantKeyword: covariantKeyword,
          requiredKeyword: requiredKeyword,
          keyword: keyword,
          type: type,
          thisKeyword: thisKeyword,
          period: thisKeyword.next!,
          name: name!.token,
          typeParameters: null,
          parameters: null,
          question: null,
        );
      } else {
        node = SimpleFormalParameterImpl(
          comment: comment,
          metadata: metadata,
          covariantKeyword: covariantKeyword,
          requiredKeyword: requiredKeyword,
          keyword: keyword,
          type: type,
          name: name?.token,
        );
      }
    }

    ParameterKind analyzerKind = _toAnalyzerParameterKind(kind);
    FormalParameterImpl parameter = node;
    if (analyzerKind != ParameterKind.REQUIRED) {
      parameter = DefaultFormalParameterImpl(
        parameter: node,
        kind: analyzerKind,
        separator: defaultValue?.separator,
        defaultValue: defaultValue?.value,
      );
    } else if (defaultValue != null) {
      // An error is reported if a required parameter has a default value.
      // Record it as named parameter for recovery.
      parameter = DefaultFormalParameterImpl(
        parameter: node,
        kind: ParameterKind.NAMED,
        separator: defaultValue.separator,
        defaultValue: defaultValue.value,
      );
    }
    push(parameter);
  }

  @override
  void endFormalParameterDefaultValueExpression() {
    debugEvent("FormalParameterDefaultValueExpression");
  }

  @override
  void endFormalParameters(int count, Token leftParenthesis,
      Token rightParenthesis, MemberKind kind) {
    assert(optional('(', leftParenthesis));
    assert(optional(')', rightParenthesis));
    debugEvent("FormalParameters");

    var rawParameters = popTypedList(count) ?? const <Object>[];
    var parameters = <FormalParameterImpl>[];
    Token? leftDelimiter;
    Token? rightDelimiter;
    for (Object raw in rawParameters) {
      if (raw is _OptionalFormalParameters) {
        parameters.addAll(raw.parameters ?? const []);
        leftDelimiter = raw.leftDelimiter;
        rightDelimiter = raw.rightDelimiter;
      } else {
        parameters.add(raw as FormalParameterImpl);
      }
    }
    push(
      FormalParameterListImpl(
        leftParenthesis: leftParenthesis,
        parameters: parameters,
        leftDelimiter: leftDelimiter,
        rightDelimiter: rightDelimiter,
        rightParenthesis: rightParenthesis,
      ),
    );
  }

  @override
  void endForStatement(Token endToken) {
    debugEvent("ForStatement");
    var body = pop() as StatementImpl;
    var forLoopParts = pop() as ForPartsImpl;
    var leftParen = pop() as Token;
    var forToken = pop() as Token;

    push(
      ForStatementImpl(
        awaitKeyword: null,
        forKeyword: forToken,
        leftParenthesis: leftParen,
        forLoopParts: forLoopParts,
        rightParenthesis: leftParen.endGroup!,
        body: body,
      ),
    );
  }

  @override
  void endForStatementBody(Token token) {
    debugEvent("endForStatementBody");
  }

  @override
  void endFunctionExpression(Token beginToken, Token token) {
    // TODO(paulberry): set up scopes properly to resolve parameters and type
    // variables.  Note that this is tricky due to the handling of initializers
    // in constructors, so the logic should be shared with BodyBuilder as much
    // as possible.
    debugEvent("FunctionExpression");

    var body = pop() as FunctionBodyImpl;
    var parameters = pop() as FormalParameterListImpl?;
    var typeParameters = pop() as TypeParameterListImpl?;
    push(
      FunctionExpressionImpl(
        typeParameters: typeParameters,
        parameters: parameters,
        body: body,
      ),
    );
  }

  @override
  void endFunctionName(Token beginToken, Token token) {
    debugEvent("FunctionName");
  }

  @override
  void endFunctionType(Token functionToken, Token? questionMark) {
    assert(optional('Function', functionToken));
    debugEvent("FunctionType");
    if (!enableNonNullable) {
      reportErrorIfNullableType(questionMark);
    }

    var parameters = pop() as FormalParameterListImpl;
    var returnType = pop() as TypeAnnotationImpl?;
    var typeParameters = pop() as TypeParameterListImpl?;
    push(
      GenericFunctionTypeImpl(
        returnType: returnType,
        functionKeyword: functionToken,
        typeParameters: typeParameters,
        parameters: parameters,
        question: questionMark,
      ),
    );
  }

  @override
  void endFunctionTypedFormalParameter(Token nameToken, Token? question) {
    debugEvent("FunctionTypedFormalParameter");
    if (!enableNonNullable) {
      reportErrorIfNullableType(question);
    }

    var formalParameters = pop() as FormalParameterListImpl;
    var returnType = pop() as TypeAnnotationImpl?;
    var typeParameters = pop() as TypeParameterListImpl?;

    // Create a temporary formal parameter that will be dissected later in
    // [endFormalParameter].
    push(
      FunctionTypedFormalParameterImpl(
        comment: null,
        metadata: null,
        covariantKeyword: null,
        requiredKeyword: null,
        name: StringToken(TokenType.IDENTIFIER, '', 0),
        returnType: returnType,
        typeParameters: typeParameters,
        parameters: formalParameters,
        question: question,
      ),
    );
  }

  @override
  void endHide(Token hideKeyword) {
    assert(optional('hide', hideKeyword));
    debugEvent("Hide");

    var hiddenNames = pop() as List<SimpleIdentifierImpl>;
    push(
      HideCombinatorImpl(
        keyword: hideKeyword,
        hiddenNames: hiddenNames,
      ),
    );
  }

  @override
  void endIfControlFlow(Token token) {
    var thenElement = pop() as CollectionElementImpl;
    var condition = pop() as _ParenthesizedCondition;
    var ifToken = pop() as Token;
    push(
      IfElementImpl(
        ifKeyword: ifToken,
        leftParenthesis: condition.leftParenthesis,
        condition: condition.expression,
        caseClause: condition.caseClause,
        rightParenthesis: condition.rightParenthesis,
        thenElement: thenElement,
        elseKeyword: null,
        elseElement: null,
      ),
    );
  }

  @override
  void endIfElseControlFlow(Token token) {
    var elseElement = pop() as CollectionElementImpl;
    var elseToken = pop() as Token;
    var thenElement = pop() as CollectionElementImpl;
    var condition = pop() as _ParenthesizedCondition;
    var ifToken = pop() as Token;
    push(
      IfElementImpl(
        ifKeyword: ifToken,
        leftParenthesis: condition.leftParenthesis,
        condition: condition.expression,
        caseClause: condition.caseClause,
        rightParenthesis: condition.rightParenthesis,
        thenElement: thenElement,
        elseKeyword: elseToken,
        elseElement: elseElement,
      ),
    );
  }

  @override
  void endIfStatement(Token ifToken, Token? elseToken) {
    assert(optional('if', ifToken));
    assert(optionalOrNull('else', elseToken));

    var elsePart = popIfNotNull(elseToken) as StatementImpl?;
    var thenPart = pop() as StatementImpl;
    var condition = pop() as _ParenthesizedCondition;
    push(
      IfStatementImpl(
        ifKeyword: ifToken,
        leftParenthesis: condition.leftParenthesis,
        condition: condition.expression,
        caseClause: condition.caseClause,
        rightParenthesis: condition.rightParenthesis,
        thenStatement: thenPart,
        elseKeyword: elseToken,
        elseStatement: elsePart,
      ),
    );
  }

  @override
  void endImplicitCreationExpression(Token token, Token openAngleBracket) {
    debugEvent("ImplicitCreationExpression");

    _handleInstanceCreation(null);
  }

  @override
  void endImport(Token importKeyword, Token? augmentToken, Token? semicolon) {
    assert(optional('import', importKeyword));
    assert(optionalOrNull(';', semicolon));
    debugEvent("Import");

    var combinators = pop() as List<CombinatorImpl>?;
    var deferredKeyword = pop(NullValues.Deferred) as Token?;
    var asKeyword = pop(NullValues.As) as Token?;
    var prefix = pop(NullValues.Prefix) as SimpleIdentifierImpl?;
    var configurations = pop() as List<ConfigurationImpl>?;
    var uri = pop() as StringLiteralImpl;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, importKeyword);

    if (!enableMacros) {
      if (augmentToken != null) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.macros,
          startToken: augmentToken,
        );
        // Pretend that 'augment' didn't occur while this feature is incomplete.
        augmentToken = null;
      }
    }

    if (augmentToken != null) {
      directives.add(
        AugmentationImportDirectiveImpl(
          comment: comment,
          uri: uri,
          importKeyword: importKeyword,
          augmentKeyword: augmentToken,
          metadata: metadata,
          semicolon: semicolon ?? Tokens.semicolon(),
        ),
      );
    } else {
      directives.add(
        ImportDirectiveImpl(
          comment: comment,
          metadata: metadata,
          importKeyword: importKeyword,
          uri: uri,
          configurations: configurations,
          deferredKeyword: deferredKeyword,
          asKeyword: asKeyword,
          prefix: prefix,
          combinators: combinators,
          semicolon: semicolon ?? Tokens.semicolon(),
        ),
      );
    }
  }

  @override
  void endInitializedIdentifier(Token nameToken) {
    debugEvent("InitializedIdentifier");

    var node = pop() as AstNodeImpl?;
    VariableDeclarationImpl variable;
    // TODO(paulberry): This seems kludgy.  It would be preferable if we
    // could respond to a "handleNoVariableInitializer" event by converting a
    // SimpleIdentifier into a VariableDeclaration, and then when this code was
    // reached, node would always be a VariableDeclaration.
    if (node is VariableDeclarationImpl) {
      variable = node;
    } else if (node is SimpleIdentifierImpl) {
      variable = VariableDeclarationImpl(
        name: node.token,
        equals: null,
        initializer: null,
      );
    } else {
      internalProblem(
          templateInternalProblemUnhandled.withArguments(
              "${node.runtimeType}", "identifier"),
          nameToken.charOffset,
          uri);
    }
    push(variable);
  }

  @override
  void endInitializers(int count, Token colon, Token endToken) {
    assert(optional(':', colon));
    debugEvent("Initializers");

    var initializerObjects = popTypedList(count) ?? const [];
    if (!isFullAst) return;

    push(colon);

    var initializers = <ConstructorInitializerImpl>[];
    for (Object initializerObject in initializerObjects) {
      var initializer = buildInitializer(initializerObject);
      if (initializer != null) {
        initializers.add(initializer);
      } else {
        handleRecoverableError(
            messageInvalidInitializer,
            initializerObject is AstNodeImpl
                ? initializerObject.beginToken
                : colon,
            initializerObject is AstNodeImpl
                ? initializerObject.endToken
                : colon);
      }
    }

    push(initializers);
  }

  @override
  void endInvalidAwaitExpression(
      Token awaitKeyword, Token endToken, MessageCode errorCode) {
    debugEvent("InvalidAwaitExpression");
    endAwaitExpression(awaitKeyword, endToken);
  }

  @override
  void endInvalidYieldStatement(Token yieldKeyword, Token? starToken,
      Token endToken, MessageCode errorCode) {
    debugEvent("InvalidYieldStatement");
    endYieldStatement(yieldKeyword, starToken, endToken);
  }

  @override
  void endIsOperatorType(Token asOperator) {
    debugEvent("IsOperatorType");
  }

  @override
  void endLabeledStatement(int labelCount) {
    debugEvent("LabeledStatement");

    var statement = pop() as StatementImpl;
    var labels = popTypedList2<LabelImpl>(labelCount);
    push(
      LabeledStatementImpl(
        labels: labels,
        statement: statement,
      ),
    );
  }

  @override
  void endLibraryAugmentation(
      Token libraryKeyword, Token augmentKeyword, Token semicolon) {
    final uri = pop() as StringLiteralImpl;
    final metadata = pop() as List<AnnotationImpl>?;
    final comment = _findComment(metadata, libraryKeyword);
    directives.add(
      LibraryAugmentationDirectiveImpl(
        comment: comment,
        metadata: metadata,
        libraryKeyword: libraryKeyword,
        augmentKeyword: augmentKeyword,
        uri: uri,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
    assert(optional('library', libraryKeyword));
    assert(optional(';', semicolon));
    debugEvent("LibraryName");

    var libraryName = hasName ? pop() as List<SimpleIdentifierImpl>? : null;

    if (!hasName && !enableUnnamedLibraries) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.unnamed_libraries,
        startToken: libraryKeyword,
      );
    }
    var name = libraryName == null
        ? null
        : LibraryIdentifierImpl(
            components: libraryName,
          );
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, libraryKeyword);
    directives.add(
      LibraryDirectiveImpl(
        comment: comment,
        metadata: metadata,
        libraryKeyword: libraryKeyword,
        name: name,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endLiteralString(int interpolationCount, Token endToken) {
    debugEvent("endLiteralString");

    if (interpolationCount == 0) {
      var token = pop() as Token;
      String value = unescapeString(token.lexeme, token, this);
      push(
        SimpleStringLiteralImpl(
          literal: token,
          value: value,
        ),
      );
    } else {
      var parts = popTypedList(1 + interpolationCount * 2)!;
      var first = parts.first as Token;
      var last = parts.last as Token;
      Quote quote = analyzeQuote(first.lexeme);
      var elements = <InterpolationElementImpl>[];
      elements.add(
        InterpolationStringImpl(
          contents: first,
          value: unescapeFirstStringPart(first.lexeme, quote, first, this),
        ),
      );
      for (int i = 1; i < parts.length - 1; i++) {
        var part = parts[i];
        if (part is Token) {
          elements.add(
            InterpolationStringImpl(
              contents: part,
              value: unescape(part.lexeme, quote, part, this),
            ),
          );
        } else if (part is InterpolationExpressionImpl) {
          elements.add(part);
        } else {
          internalProblem(
              templateInternalProblemUnhandled.withArguments(
                  "${part.runtimeType}", "string interpolation"),
              first.charOffset,
              uri);
        }
      }
      elements.add(
        InterpolationStringImpl(
          contents: last,
          value: unescapeLastStringPart(
              last.lexeme, quote, last, last.isSynthetic, this),
        ),
      );
      push(
        StringInterpolationImpl(
          elements: elements,
        ),
      );
    }
  }

  @override
  void endLiteralSymbol(Token hashToken, int tokenCount) {
    assert(optional('#', hashToken));
    debugEvent("LiteralSymbol");

    var components = popTypedList2<Token>(tokenCount);
    push(
      SymbolLiteralImpl(
        poundSign: hashToken,
        components: components,
      ),
    );
  }

  @override
  void endLocalFunctionDeclaration(Token token) {
    debugEvent("LocalFunctionDeclaration");
    var body = pop() as FunctionBodyImpl;
    if (isFullAst) {
      pop(); // constructor initializers
      pop(); // separator before constructor initializers
    }
    var parameters = pop() as FormalParameterListImpl;
    checkFieldFormalParameters(parameters);
    var name = pop() as SimpleIdentifierImpl;
    var returnType = pop() as TypeAnnotationImpl?;
    var typeParameters = pop() as TypeParameterListImpl?;
    var metadata = pop(NullValues.Metadata) as List<AnnotationImpl>?;
    final functionExpression = FunctionExpressionImpl(
      typeParameters: typeParameters,
      parameters: parameters,
      body: body,
    );
    var functionDeclaration = FunctionDeclarationImpl(
      comment: null,
      metadata: metadata,
      augmentKeyword: null,
      externalKeyword: null,
      returnType: returnType,
      propertyKeyword: null,
      name: name.token,
      functionExpression: functionExpression,
    );
    push(
      FunctionDeclarationStatementImpl(
        functionDeclaration: functionDeclaration,
      ),
    );
  }

  @override
  void endMember() {
    debugEvent("Member");
  }

  @override
  void endMetadata(Token atSign, Token? periodBeforeName, Token endToken) {
    assert(optional('@', atSign));
    assert(optionalOrNull('.', periodBeforeName));
    debugEvent("Metadata");

    var invocation = pop() as MethodInvocationImpl?;
    var constructorName =
        periodBeforeName != null ? pop() as SimpleIdentifierImpl : null;
    var typeArguments = pop() as TypeArgumentListImpl?;
    if (typeArguments != null &&
        !_featureSet.isEnabled(Feature.generic_metadata)) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.generic_metadata,
        startToken: typeArguments.beginToken,
      );
    }
    var name = pop() as IdentifierImpl;
    push(
      AnnotationImpl(
        atSign: atSign,
        name: name,
        typeArguments: typeArguments,
        period: periodBeforeName,
        constructorName: constructorName,
        arguments: invocation?.argumentList,
      ),
    );
  }

  @override
  void endMetadataStar(int count) {
    debugEvent("MetadataStar");

    push(popTypedList<AnnotationImpl>(count) ?? NullValues.Metadata);
  }

  @override
  void endMixinConstructor(Token? getOrSet, Token beginToken, Token beginParam,
      Token? beginInitializers, Token endToken) {
    debugEvent("MixinConstructor");
    // TODO(danrubel) Decide how to handle constructor declarations within
    // mixins. They are invalid, but we include them in order to get navigation,
    // search, etc. Currently the error is reported by multiple listeners,
    // but should be moved into the parser.
    endClassConstructor(
        getOrSet, beginToken, beginParam, beginInitializers, endToken);
  }

  @override
  void endMixinDeclaration(Token mixinKeyword, Token endToken) {
    debugEvent("MixinDeclaration");

    final builder = _classLikeBuilder as _MixinDeclarationBuilder;
    declarations.add(
      builder.build(),
    );
    _classLikeBuilder = null;
  }

  @override
  void endMixinFactoryMethod(
      Token beginToken, Token factoryKeyword, Token endToken) {
    debugEvent("MixinFactoryMethod");
    endClassFactoryMethod(beginToken, factoryKeyword, endToken);
  }

  @override
  void endMixinFields(
      Token? abstractToken,
      Token? augmentToken,
      Token? externalToken,
      Token? staticToken,
      Token? covariantToken,
      Token? lateToken,
      Token? varFinalOrConst,
      int count,
      Token beginToken,
      Token endToken) {
    endClassFields(
        abstractToken,
        augmentToken,
        externalToken,
        staticToken,
        covariantToken,
        lateToken,
        varFinalOrConst,
        count,
        beginToken,
        endToken);
  }

  @override
  void endMixinMethod(Token? getOrSet, Token beginToken, Token beginParam,
      Token? beginInitializers, Token endToken) {
    debugEvent("MixinMethod");
    endClassMethod(
        getOrSet, beginToken, beginParam, beginInitializers, endToken);
  }

  @override
  void endNamedFunctionExpression(Token endToken) {
    debugEvent("NamedFunctionExpression");
    var body = pop() as FunctionBodyImpl;
    if (isFullAst) {
      pop(); // constructor initializers
      pop(); // separator before constructor initializers
    }
    var parameters = pop() as FormalParameterListImpl;
    pop(); // name
    pop(); // returnType
    var typeParameters = pop() as TypeParameterListImpl?;
    push(
      FunctionExpressionImpl(
        typeParameters: typeParameters,
        parameters: parameters,
        body: body,
      ),
    );
  }

  @override
  void endNamedMixinApplication(Token beginToken, Token classKeyword,
      Token equalsToken, Token? implementsKeyword, Token semicolon) {
    assert(optional('class', classKeyword));
    assert(optionalOrNull('=', equalsToken));
    assert(optionalOrNull('implements', implementsKeyword));
    assert(optional(';', semicolon));
    debugEvent("NamedMixinApplication");

    ImplementsClauseImpl? implementsClause;
    if (implementsKeyword != null) {
      var interfaces = _popNamedTypeList(
        errorCode: ParserErrorCode.EXPECTED_NAMED_TYPE_IMPLEMENTS,
      );
      implementsClause = ImplementsClauseImpl(
        implementsKeyword: implementsKeyword,
        interfaces: interfaces,
      );
    }
    var withClause = pop(NullValues.WithClause) as WithClauseImpl;
    var superclass = pop() as TypeAnnotationImpl;
    if (superclass is! NamedTypeImpl) {
      errorReporter.errorReporter?.reportErrorForNode(
          ParserErrorCode.EXPECTED_NAMED_TYPE_EXTENDS, superclass);
      var beginToken = superclass.beginToken;
      var endToken = superclass.endToken;
      var currentToken = beginToken;
      var count = 1;
      while (currentToken != endToken) {
        count++;
        currentToken = currentToken.next!;
      }
      var nameToken = parser.rewriter.replaceNextTokensWithSyntheticToken(
          beginToken.previous!, count, TokenType.IDENTIFIER);
      superclass = NamedTypeImpl(
          name: SimpleIdentifierImpl(nameToken),
          typeArguments: null,
          question: null);
    }
    var mixinKeyword = pop(NullValues.Token) as Token?;
    var augmentKeyword = pop(NullValues.Token) as Token?;
    var finalKeyword = pop(NullValues.Token) as Token?;
    var interfaceKeyword = pop(NullValues.Token) as Token?;
    var baseKeyword = pop(NullValues.Token) as Token?;
    var sealedKeyword = pop(NullValues.Token) as Token?;
    var inlineKeyword = pop(NullValues.Token) as Token?;
    var macroKeyword = pop(NullValues.Token) as Token?;
    var modifiers = pop() as _Modifiers?;
    var typeParameters = pop() as TypeParameterListImpl?;
    var name = pop() as SimpleIdentifierImpl;
    var abstractKeyword = modifiers?.abstractKeyword;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, beginToken);
    declarations.add(
      ClassTypeAliasImpl(
        comment: comment,
        metadata: metadata,
        typedefKeyword: classKeyword,
        name: name.token,
        typeParameters: typeParameters,
        equals: equalsToken,
        abstractKeyword: abstractKeyword,
        macroKeyword: macroKeyword,
        inlineKeyword: inlineKeyword,
        sealedKeyword: sealedKeyword,
        baseKeyword: baseKeyword,
        interfaceKeyword: interfaceKeyword,
        finalKeyword: finalKeyword,
        augmentKeyword: augmentKeyword,
        mixinKeyword: mixinKeyword,
        superclass: superclass,
        withClause: withClause,
        implementsClause: implementsClause,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endNewExpression(Token newKeyword) {
    assert(optional('new', newKeyword));
    debugEvent("NewExpression");

    _handleInstanceCreation(newKeyword);
  }

  @override
  void endOptionalFormalParameters(
      int count, Token leftDelimiter, Token rightDelimiter) {
    assert((optional('[', leftDelimiter) && optional(']', rightDelimiter)) ||
        (optional('{', leftDelimiter) && optional('}', rightDelimiter)));
    debugEvent("OptionalFormalParameters");

    push(
      _OptionalFormalParameters(
        popTypedList2<FormalParameterImpl>(count),
        leftDelimiter,
        rightDelimiter,
      ),
    );
  }

  @override
  void endParenthesizedExpression(Token leftParenthesis) {
    assert(optional('(', leftParenthesis));
    debugEvent("ParenthesizedExpression");

    var expression = pop() as ExpressionImpl;
    push(
      ParenthesizedExpressionImpl(
        leftParenthesis: leftParenthesis,
        expression: expression,
        rightParenthesis: leftParenthesis.endGroup!,
      ),
    );
  }

  @override
  void endPart(Token partKeyword, Token semicolon) {
    assert(optional('part', partKeyword));
    assert(optional(';', semicolon));
    debugEvent("Part");

    var uri = pop() as StringLiteralImpl;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, partKeyword);
    directives.add(
      PartDirectiveImpl(
        comment: comment,
        metadata: metadata,
        partKeyword: partKeyword,
        uri: uri,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endPartOf(
      Token partKeyword, Token ofKeyword, Token semicolon, bool hasName) {
    assert(optional('part', partKeyword));
    assert(optional('of', ofKeyword));
    assert(optional(';', semicolon));
    debugEvent("PartOf");
    var libraryNameOrUri = pop();
    LibraryIdentifierImpl? name;
    StringLiteralImpl? uri;
    if (libraryNameOrUri is StringLiteralImpl) {
      uri = libraryNameOrUri;
    } else {
      name = LibraryIdentifierImpl(
        components: libraryNameOrUri as List<SimpleIdentifierImpl>,
      );
    }
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, partKeyword);
    directives.add(
      PartOfDirectiveImpl(
        comment: comment,
        metadata: metadata,
        partKeyword: partKeyword,
        ofKeyword: ofKeyword,
        uri: uri,
        libraryName: name,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endPatternGuard(Token when) {
    debugEvent("PatternGuard");
    var expression = pop() as ExpressionImpl;
    push(
      WhenClauseImpl(
        whenKeyword: when,
        expression: expression,
      ),
    );
  }

  @override
  void endRecordLiteral(Token token, int count, Token? constKeyword) {
    debugEvent("RecordLiteral");

    if (!enableRecords) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.records,
        startToken: token,
      );
    }

    var fields = popTypedList<ExpressionImpl>(count) ?? const [];

    push(RecordLiteralImpl(
      constKeyword: constKeyword,
      leftParenthesis: token,
      fields: fields,
      rightParenthesis: token.endGroup!,
    ));
  }

  @override
  void endRecordType(
      Token leftBracket, Token? questionMark, int count, bool hasNamedFields) {
    debugEvent("RecordType");

    if (!enableRecords) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.records,
        startToken: leftBracket,
      );
    }
    RecordTypeAnnotationNamedFieldsImpl? namedFields;
    var elements = popTypedList<Object>(count) ?? const [];
    var last = elements.lastOrNull;
    if (last is RecordTypeAnnotationNamedFieldsImpl) {
      elements.removeLast();
      namedFields = last;
    }
    var positionalFields = <RecordTypeAnnotationPositionalFieldImpl>[];
    for (var elem in elements) {
      positionalFields.add(elem as RecordTypeAnnotationPositionalFieldImpl);
    }
    push(RecordTypeAnnotationImpl(
      leftParenthesis: leftBracket,
      positionalFields: positionalFields,
      namedFields: namedFields,
      rightParenthesis: leftBracket.endGroup!,
      question: questionMark,
    ));
  }

  @override
  void endRecordTypeEntry() {
    debugEvent("RecordTypeEntry");

    var name = pop() as SimpleIdentifierImpl?;
    var type = pop() as TypeAnnotationImpl;
    var metadata = pop() as List<AnnotationImpl>?;

    push(RecordTypeAnnotationPositionalFieldImpl(
      metadata: metadata,
      type: type,
      name: name?.token,
    ));
  }

  @override
  void endRecordTypeNamedFields(int count, Token leftBracket) {
    debugEvent("RecordTypeNamedFields");

    var elements =
        popTypedList<RecordTypeAnnotationPositionalFieldImpl>(count) ??
            const [];
    var fields = <RecordTypeAnnotationNamedFieldImpl>[];
    for (var elem in elements) {
      fields.add(RecordTypeAnnotationNamedFieldImpl(
        metadata: elem.metadata,
        type: elem.type,
        name: elem.name!,
      ));
    }
    push(RecordTypeAnnotationNamedFieldsImpl(
      leftBracket: leftBracket,
      fields: fields,
      rightBracket: leftBracket.endGroup!,
    ));
  }

  @override
  void endRedirectingFactoryBody(Token equalToken, Token endToken) {
    assert(optional('=', equalToken));
    debugEvent("RedirectingFactoryBody");

    var constructorName = pop() as ConstructorNameImpl;
    var starToken = pop() as Token?;
    var asyncToken = pop() as Token?;
    push(_RedirectingFactoryBody(
        asyncToken, starToken, equalToken, constructorName));
  }

  @override
  void endRethrowStatement(Token rethrowToken, Token semicolon) {
    assert(optional('rethrow', rethrowToken));
    assert(optional(';', semicolon));
    debugEvent("RethrowStatement");

    final expression = RethrowExpressionImpl(
      rethrowKeyword: rethrowToken,
    );
    // TODO(scheglov) According to the specification, 'rethrow' is a statement.
    push(
      ExpressionStatementImpl(
        expression: expression,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endReturnStatement(
      bool hasExpression, Token returnKeyword, Token semicolon) {
    assert(optional('return', returnKeyword));
    assert(optional(';', semicolon));
    debugEvent("ReturnStatement");

    var expression = hasExpression ? pop() as ExpressionImpl : null;
    push(
      ReturnStatementImpl(
        returnKeyword: returnKeyword,
        expression: expression,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endShow(Token showKeyword) {
    assert(optional('show', showKeyword));
    debugEvent("Show");

    var shownNames = pop() as List<SimpleIdentifierImpl>;
    push(
      ShowCombinatorImpl(
        keyword: showKeyword,
        shownNames: shownNames,
      ),
    );
  }

  @override
  void endSwitchBlock(int caseCount, Token leftBracket, Token rightBracket) {
    assert(optional('{', leftBracket));
    assert(optional('}', rightBracket));
    debugEvent("SwitchBlock");

    var membersList = popTypedList2<List<SwitchMemberImpl>>(caseCount);
    var members = membersList.expand((members) => members).toList();

    Set<String> labels = <String>{};
    for (var member in members) {
      for (var label in member.labels) {
        if (!labels.add(label.label.name)) {
          handleRecoverableError(
              templateDuplicateLabelInSwitchStatement
                  .withArguments(label.label.name),
              label.beginToken,
              label.beginToken);
        }
      }
    }

    push(leftBracket);
    push(members);
    push(rightBracket);
  }

  @override
  void endSwitchCase(
      int labelCount,
      int expressionCount,
      Token? defaultKeyword,
      Token? colonAfterDefault,
      int statementCount,
      Token firstToken,
      Token endToken) {
    assert(optionalOrNull('default', defaultKeyword));
    assert(defaultKeyword == null
        ? colonAfterDefault == null
        : optional(':', colonAfterDefault!));
    debugEvent("SwitchCase");

    var statements = popTypedList2<StatementImpl>(statementCount);
    List<SwitchMemberImpl?> members;

    List<LabelImpl> popLabels() {
      final labels = <LabelImpl>[];
      while (peek() is LabelImpl) {
        labels.insert(0, pop() as LabelImpl);
        --labelCount;
      }
      return labels;
    }

    SwitchMemberImpl updateSwitchMember({
      required SwitchMemberImpl member,
      List<LabelImpl>? labels,
      List<StatementImpl>? statements,
    }) {
      if (member is SwitchCaseImpl) {
        return SwitchCaseImpl(
          labels: labels ?? member.labels,
          keyword: member.keyword,
          expression: member.expression,
          colon: member.colon,
          statements: statements ?? member.statements,
        );
      } else if (member is SwitchDefaultImpl) {
        return SwitchDefaultImpl(
          labels: labels ?? member.labels,
          keyword: member.keyword,
          colon: member.colon,
          statements: statements ?? member.statements,
        );
      } else if (member is SwitchPatternCaseImpl) {
        return SwitchPatternCaseImpl(
          labels: labels ?? member.labels,
          keyword: member.keyword,
          guardedPattern: member.guardedPattern,
          colon: member.colon,
          statements: statements ?? member.statements,
        );
      } else {
        throw UnimplementedError('(${member.runtimeType}) $member');
      }
    }

    if (labelCount == 0 && defaultKeyword == null) {
      // Common situation: case with no default and no labels.
      members = popTypedList2<SwitchMemberImpl>(expressionCount);
    } else {
      // Labels and case statements may be intertwined
      if (defaultKeyword != null) {
        final labels = popLabels();
        final member = SwitchDefaultImpl(
          labels: labels,
          keyword: defaultKeyword,
          colon: colonAfterDefault!,
          statements: <StatementImpl>[],
        );
        members = List.filled(expressionCount + 1, null);
        members[expressionCount] = member;
      } else {
        members = List.filled(expressionCount, null);
      }
      for (int index = expressionCount - 1; index >= 0; --index) {
        var member = pop() as SwitchMemberImpl;
        final labels = popLabels();
        members[index] = updateSwitchMember(
          member: member,
          labels: labels,
          statements: null,
        );
      }
      assert(labelCount == 0);
    }

    var members2 = members.whereNotNull().toList();
    if (members2.isNotEmpty) {
      members2.last = updateSwitchMember(
        member: members2.last,
        labels: null,
        statements: statements,
      );
    }
    push(members2);
  }

  @override
  void endSwitchCaseWhenClause(Token token) {
    debugEvent("SwitchCaseWhenClause");
  }

  @override
  void endSwitchExpression(Token switchKeyword, Token endToken) {
    assert(optional('switch', switchKeyword));
    debugEvent("SwitchExpression");

    var rightBracket = pop() as Token;
    var cases = pop() as List<SwitchExpressionCaseImpl>;
    var leftBracket = pop() as Token;
    var condition = pop() as _ParenthesizedCondition;
    push(
      SwitchExpressionImpl(
        switchKeyword: switchKeyword,
        leftParenthesis: condition.leftParenthesis,
        expression: condition.expression,
        rightParenthesis: condition.rightParenthesis,
        leftBracket: leftBracket,
        cases: cases,
        rightBracket: rightBracket,
      ),
    );
  }

  @override
  void endSwitchExpressionBlock(
      int caseCount, Token leftBracket, Token rightBracket) {
    assert(optional('{', leftBracket));
    assert(optional('}', rightBracket));
    debugEvent("SwitchExpressionBlock");

    var cases = popTypedList2<SwitchExpressionCaseImpl>(caseCount);

    push(leftBracket);
    push(cases);
    push(rightBracket);
  }

  @override
  void endSwitchExpressionCase(Token? when, Token arrow, Token endToken) {
    debugEvent("SwitchExpressionCase");
    var expression = pop() as ExpressionImpl;
    WhenClauseImpl? whenClause;
    if (when != null) {
      var expression = pop() as ExpressionImpl;
      whenClause = WhenClauseImpl(whenKeyword: when, expression: expression);
    }
    var pattern = pop() as DartPatternImpl;
    push(SwitchExpressionCaseImpl(
        guardedPattern: GuardedPatternImpl(
          pattern: pattern,
          whenClause: whenClause,
        ),
        arrow: arrow,
        expression: expression));
  }

  @override
  void endSwitchStatement(Token switchKeyword, Token endToken) {
    assert(optional('switch', switchKeyword));
    debugEvent("SwitchStatement");

    var rightBracket = pop() as Token;
    var members = pop() as List<SwitchMemberImpl>;
    var leftBracket = pop() as Token;
    var condition = pop() as _ParenthesizedCondition;
    push(
      SwitchStatementImpl(
        switchKeyword: switchKeyword,
        leftParenthesis: condition.leftParenthesis,
        expression: condition.expression,
        rightParenthesis: condition.rightParenthesis,
        leftBracket: leftBracket,
        members: members,
        rightBracket: rightBracket,
      ),
    );
  }

  @override
  void endThenStatement(Token token) {
    debugEvent("endThenStatement");
  }

  @override
  void endTopLevelDeclaration(Token token) {
    debugEvent("TopLevelDeclaration");
  }

  @override
  void endTopLevelFields(
      Token? externalToken,
      Token? staticToken,
      Token? covariantToken,
      Token? lateToken,
      Token? varFinalOrConst,
      int count,
      Token beginToken,
      Token semicolon) {
    assert(optional(';', semicolon));
    debugEvent("TopLevelFields");

    if (externalToken != null) {
      if (!enableNonNullable) {
        handleRecoverableError(
            messageExternalField, externalToken, externalToken);
      } else if (lateToken != null) {
        handleRecoverableError(
            messageExternalLateField, externalToken, externalToken);
      }
    }

    var variables = popTypedList2<VariableDeclarationImpl>(count);
    var type = pop() as TypeAnnotationImpl?;
    var variableList = VariableDeclarationListImpl(
      comment: null,
      metadata: null,
      lateKeyword: lateToken,
      keyword: varFinalOrConst,
      type: type,
      variables: variables,
    );
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, beginToken);
    declarations.add(
      TopLevelVariableDeclarationImpl(
        comment: comment,
        metadata: metadata,
        externalKeyword: externalToken,
        variableList: variableList,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void endTopLevelMethod(Token beginToken, Token? getOrSet, Token endToken) {
    // TODO(paulberry): set up scopes properly to resolve parameters and type
    // variables.
    assert(getOrSet == null ||
        optional('get', getOrSet) ||
        optional('set', getOrSet));
    debugEvent("TopLevelMethod");

    var body = pop() as FunctionBodyImpl;
    var parameters = pop() as FormalParameterListImpl?;
    var typeParameters = pop() as TypeParameterListImpl?;
    var name = pop() as SimpleIdentifierImpl;
    var returnType = pop() as TypeAnnotationImpl?;
    var modifiers = pop() as _Modifiers?;
    var augmentKeyword = modifiers?.augmentKeyword;
    var externalKeyword = modifiers?.externalKeyword;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, beginToken);
    declarations.add(
      FunctionDeclarationImpl(
        comment: comment,
        metadata: metadata,
        augmentKeyword: augmentKeyword,
        externalKeyword: externalKeyword,
        returnType: returnType,
        propertyKeyword: getOrSet,
        name: name.token,
        functionExpression: FunctionExpressionImpl(
          typeParameters: typeParameters,
          parameters: parameters,
          body: body,
        ),
      ),
    );
  }

  @override
  void endTryStatement(
      int catchCount, Token tryKeyword, Token? finallyKeyword) {
    assert(optional('try', tryKeyword));
    assert(optionalOrNull('finally', finallyKeyword));
    debugEvent("TryStatement");

    var finallyBlock = popIfNotNull(finallyKeyword) as BlockImpl?;
    var catchClauses = popTypedList2<CatchClauseImpl>(catchCount);
    var body = pop() as BlockImpl;
    push(
      TryStatementImpl(
        tryKeyword: tryKeyword,
        body: body,
        catchClauses: catchClauses,
        finallyKeyword: finallyKeyword,
        finallyBlock: finallyBlock,
      ),
    );
  }

  @override
  void endTypeArguments(int count, Token leftBracket, Token rightBracket) {
    assert(optional('<', leftBracket));
    assert(optional('>', rightBracket));
    debugEvent("TypeArguments");

    var arguments = popTypedList2<TypeAnnotationImpl>(count);
    push(
      TypeArgumentListImpl(
        leftBracket: leftBracket,
        arguments: arguments,
        rightBracket: rightBracket,
      ),
    );
  }

  @override
  void endTypedef(Token typedefKeyword, Token? equals, Token semicolon) {
    assert(optional('typedef', typedefKeyword));
    assert(optionalOrNull('=', equals));
    assert(optional(';', semicolon));
    debugEvent("FunctionTypeAlias");

    if (equals == null) {
      var parameters = pop() as FormalParameterListImpl;
      var typeParameters = pop() as TypeParameterListImpl?;
      var name = pop() as SimpleIdentifierImpl;
      var returnType = pop() as TypeAnnotationImpl?;
      var metadata = pop() as List<AnnotationImpl>?;
      var comment = _findComment(metadata, typedefKeyword);
      declarations.add(
        FunctionTypeAliasImpl(
          comment: comment,
          metadata: metadata,
          typedefKeyword: typedefKeyword,
          returnType: returnType,
          name: name.token,
          typeParameters: typeParameters,
          parameters: parameters,
          semicolon: semicolon,
        ),
      );
    } else {
      var type = pop() as TypeAnnotationImpl;
      var templateParameters = pop() as TypeParameterListImpl?;
      var name = pop() as SimpleIdentifierImpl;
      var metadata = pop() as List<AnnotationImpl>?;
      var comment = _findComment(metadata, typedefKeyword);
      if (type is! GenericFunctionTypeImpl && !enableNonFunctionTypeAliases) {
        _reportFeatureNotEnabled(
          feature: ExperimentalFeatures.nonfunction_type_aliases,
          startToken: equals,
        );
      }
      declarations.add(
        GenericTypeAliasImpl(
          comment: comment,
          metadata: metadata,
          typedefKeyword: typedefKeyword,
          name: name.token,
          typeParameters: templateParameters,
          equals: equals,
          type: type,
          semicolon: semicolon,
        ),
      );
    }
  }

  @override
  void endTypeList(int count) {
    debugEvent("TypeList");
    push(popTypedList<TypeAnnotationImpl>(count) ?? NullValues.TypeList);
  }

  @override
  void endTypeVariable(
      Token token, int index, Token? extendsOrSuper, Token? variance) {
    debugEvent("TypeVariable");
    assert(extendsOrSuper == null ||
        optional('extends', extendsOrSuper) ||
        optional('super', extendsOrSuper));

    // TODO (kallentu): Implement variance behaviour for the analyzer.
    assert(variance == null ||
        optional('in', variance) ||
        optional('out', variance) ||
        optional('inout', variance));
    if (!enableVariance) {
      reportVarianceModifierNotEnabled(variance);
    }

    var bound = pop() as TypeAnnotationImpl?;

    // Peek to leave type parameters on top of stack.
    var typeParameters = peek() as List<TypeParameterImpl>;

    typeParameters[index]
      ..extendsKeyword = extendsOrSuper
      ..bound = bound
      ..varianceKeyword = variance;
  }

  @override
  void endTypeVariables(Token beginToken, Token endToken) {
    assert(optional('<', beginToken));
    assert(optional('>', endToken));
    debugEvent("TypeVariables");

    var typeParameters = pop() as List<TypeParameterImpl>;
    push(
      TypeParameterListImpl(
        leftBracket: beginToken,
        typeParameters: typeParameters,
        rightBracket: endToken,
      ),
    );
  }

  @override
  void endVariableInitializer(Token equals) {
    assert(optionalOrNull('=', equals));
    debugEvent("VariableInitializer");

    var initializer = pop() as ExpressionImpl;
    var identifier = pop() as SimpleIdentifierImpl;
    // TODO(ahe): Don't push initializers, instead install them.
    push(
      VariableDeclarationImpl(
        name: identifier.token,
        equals: equals,
        initializer: initializer,
      ),
    );
  }

  @override
  void endVariablesDeclaration(int count, Token? semicolon) {
    assert(optionalOrNull(';', semicolon));
    debugEvent("VariablesDeclaration");

    var variables = popTypedList2<VariableDeclarationImpl>(count);
    var modifiers = pop(NullValues.Modifiers) as _Modifiers?;
    var type = pop() as TypeAnnotationImpl?;
    var keyword = modifiers?.finalConstOrVarKeyword;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, variables[0].beginToken);
    // var comment = _findComment(metadata,
    //     variables[0].beginToken ?? type?.beginToken ?? modifiers.beginToken);
    push(
      VariableDeclarationStatementImpl(
        variableList: VariableDeclarationListImpl(
          comment: comment,
          metadata: metadata,
          lateKeyword: modifiers?.lateToken,
          keyword: keyword,
          type: type,
          variables: variables,
        ),
        semicolon: semicolon ?? Tokens.semicolon(),
      ),
    );
  }

  @override
  void endWhileStatement(Token whileKeyword, Token endToken) {
    assert(optional('while', whileKeyword));
    debugEvent("WhileStatement");

    var body = pop() as StatementImpl;
    var condition = pop() as _ParenthesizedCondition;
    push(
      WhileStatementImpl(
        whileKeyword: whileKeyword,
        leftParenthesis: condition.leftParenthesis,
        condition: condition.expression,
        rightParenthesis: condition.rightParenthesis,
        body: body,
      ),
    );
  }

  @override
  void endWhileStatementBody(Token token) {
    debugEvent("endWhileStatementBody");
  }

  @override
  void endYieldStatement(Token yieldToken, Token? starToken, Token semicolon) {
    assert(optional('yield', yieldToken));
    assert(optionalOrNull('*', starToken));
    assert(optional(';', semicolon));
    debugEvent("YieldStatement");

    var expression = pop() as ExpressionImpl;
    push(
      YieldStatementImpl(
        yieldKeyword: yieldToken,
        star: starToken,
        expression: expression,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void handleAsOperator(Token asOperator) {
    assert(optional('as', asOperator));
    debugEvent("AsOperator");

    var type = pop() as TypeAnnotationImpl;
    var expression = pop() as ExpressionImpl;
    push(
      AsExpressionImpl(
        expression: expression,
        asOperator: asOperator,
        type: type,
      ),
    );
  }

  @override
  void handleAssignmentExpression(Token token) {
    assert(token.type.isAssignmentOperator);
    debugEvent("AssignmentExpression");

    var rhs = pop() as ExpressionImpl;
    var lhs = pop() as ExpressionImpl;
    if (!lhs.isAssignable) {
      // TODO(danrubel): Update the BodyBuilder to report this error.
      handleRecoverableError(
          messageMissingAssignableSelector, lhs.beginToken, lhs.endToken);
    }
    push(
      AssignmentExpressionImpl(
        leftHandSide: lhs,
        operator: token,
        rightHandSide: rhs,
      ),
    );
    if (!enableTripleShift && token.type == TokenType.GT_GT_GT_EQ) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.triple_shift,
        startToken: token,
      );
    }
  }

  @override
  void handleAsyncModifier(Token? asyncToken, Token? starToken) {
    assert(asyncToken == null ||
        optional('async', asyncToken) ||
        optional('sync', asyncToken));
    assert(optionalOrNull('*', starToken));
    debugEvent("AsyncModifier");

    push(asyncToken ?? NullValues.FunctionBodyAsyncToken);
    push(starToken ?? NullValues.FunctionBodyStarToken);
  }

  @override
  void handleAugmentSuperExpression(
      Token augmentKeyword, Token superKeyword, IdentifierContext context) {
    assert(optional('augment', augmentKeyword));
    assert(optional('super', superKeyword));
    debugEvent("AugmentSuperExpression");
    throw UnimplementedError('AstBuilder.handleAugmentSuperExpression');
  }

  @override
  void handleBreakStatement(
      bool hasTarget, Token breakKeyword, Token semicolon) {
    assert(optional('break', breakKeyword));
    assert(optional(';', semicolon));
    debugEvent("BreakStatement");

    var label = hasTarget ? pop() as SimpleIdentifierImpl : null;
    push(
      BreakStatementImpl(
        breakKeyword: breakKeyword,
        label: label,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void handleCastPattern(Token asOperator) {
    assert(optional('as', asOperator));
    debugEvent("CastPattern");

    var type = pop() as TypeAnnotationImpl;
    var pattern = pop() as DartPatternImpl;
    push(CastPatternImpl(pattern: pattern, asToken: asOperator, type: type));
  }

  @override
  void handleCatchBlock(Token? onKeyword, Token? catchKeyword, Token? comma) {
    assert(optionalOrNull('on', onKeyword));
    assert(optionalOrNull('catch', catchKeyword));
    assert(optionalOrNull(',', comma));
    debugEvent("CatchBlock");

    var body = pop() as BlockImpl;
    var catchParameterList =
        popIfNotNull(catchKeyword) as FormalParameterListImpl?;
    var type = popIfNotNull(onKeyword) as TypeAnnotationImpl?;
    Token? exception;
    Token? stackTrace;
    if (catchParameterList != null) {
      var catchParameters = catchParameterList.parameters;
      if (catchParameters.isNotEmpty) {
        exception = catchParameters[0].name;
      }
      if (catchParameters.length > 1) {
        stackTrace = catchParameters[1].name;
      }
    }
    push(
      CatchClauseImpl(
        onKeyword: onKeyword,
        exceptionType: type,
        catchKeyword: catchKeyword,
        leftParenthesis: catchParameterList?.leftParenthesis,
        exceptionParameter: exception != null
            ? CatchClauseParameterImpl(
                name: exception,
              )
            : null,
        comma: comma,
        stackTraceParameter: stackTrace != null
            ? CatchClauseParameterImpl(
                name: stackTrace,
              )
            : null,
        rightParenthesis: catchParameterList?.rightParenthesis,
        body: body,
      ),
    );
  }

  @override
  void handleClassExtends(Token? extendsKeyword, int typeCount) {
    assert(extendsKeyword == null || extendsKeyword.isKeywordOrIdentifier);
    debugEvent("ClassExtends");

    // If more extends clauses was specified (parser has already issued an
    // error) throw them away for now and pick the first one.
    while (typeCount > 1) {
      pop();
      typeCount--;
    }
    var supertype = pop() as TypeAnnotationImpl?;
    if (supertype is NamedTypeImpl) {
      push(
        ExtendsClauseImpl(
          extendsKeyword: extendsKeyword!,
          superclass: supertype,
        ),
      );
    } else {
      push(NullValues.ExtendsClause);
      // TODO(brianwilkerson) Consider (a) extending `ExtendsClause` to accept
      //  any type annotation for recovery purposes, and (b) extending the
      //  parser to parse a generic function type at this location.
      if (supertype != null) {
        errorReporter.errorReporter?.reportErrorForNode(
          ParserErrorCode.EXPECTED_NAMED_TYPE_EXTENDS,
          supertype,
        );
      }
    }
  }

  @override
  void handleClassHeader(Token begin, Token classKeyword, Token? nativeToken) {
    assert(optional('class', classKeyword));
    assert(optionalOrNull('native', nativeToken));
    assert(_classLikeBuilder == null);
    debugEvent("ClassHeader");

    NativeClauseImpl? nativeClause;
    if (nativeToken != null) {
      nativeClause = NativeClauseImpl(
        nativeKeyword: nativeToken,
        name: nativeName,
      );
    }
    var implementsClause =
        pop(NullValues.IdentifierList) as ImplementsClauseImpl?;
    var withClause = pop(NullValues.WithClause) as WithClauseImpl?;
    var extendsClause = pop(NullValues.ExtendsClause) as ExtendsClauseImpl?;
    var mixinKeyword = pop(NullValues.Token) as Token?;
    var augmentKeyword = pop(NullValues.Token) as Token?;
    var finalKeyword = pop(NullValues.Token) as Token?;
    var interfaceKeyword = pop(NullValues.Token) as Token?;
    var baseKeyword = pop(NullValues.Token) as Token?;
    var sealedKeyword = pop(NullValues.Token) as Token?;
    var inlineKeyword = pop(NullValues.Token) as Token?;
    var macroKeyword = pop(NullValues.Token) as Token?;
    var modifiers = pop() as _Modifiers?;
    var typeParameters = pop() as TypeParameterListImpl?;
    var name = pop() as SimpleIdentifierImpl;
    var abstractKeyword = modifiers?.abstractKeyword;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, begin);
    // leftBracket, members, and rightBracket
    // are set in [endClassOrMixinBody].
    _classLikeBuilder = _ClassDeclarationBuilder(
      comment: comment,
      metadata: metadata,
      abstractKeyword: abstractKeyword,
      macroKeyword: macroKeyword,
      inlineKeyword: inlineKeyword,
      sealedKeyword: sealedKeyword,
      baseKeyword: baseKeyword,
      interfaceKeyword: interfaceKeyword,
      finalKeyword: finalKeyword,
      augmentKeyword: augmentKeyword,
      mixinKeyword: mixinKeyword,
      classKeyword: classKeyword,
      name: name.token,
      typeParameters: typeParameters,
      extendsClause: extendsClause,
      withClause: withClause,
      implementsClause: implementsClause,
      nativeClause: nativeClause,
      leftBracket: Tokens.openCurlyBracket(),
      rightBracket: Tokens.closeCurlyBracket(),
    );
  }

  @override
  void handleClassNoWithClause() {
    push(NullValues.WithClause);
  }

  @override
  void handleClassWithClause(Token withKeyword) {
    assert(optional('with', withKeyword));
    var mixinTypes = _popNamedTypeList(
      errorCode: ParserErrorCode.EXPECTED_NAMED_TYPE_WITH,
    );
    push(
      WithClauseImpl(
        withKeyword: withKeyword,
        mixinTypes: mixinTypes,
      ),
    );
  }

  @override
  void handleCommentReference(
    Token? newKeyword,
    Token? firstToken,
    Token? firstPeriod,
    Token? secondToken,
    Token? secondPeriod,
    Token thirdToken,
  ) {
    var identifier = ast.simpleIdentifier(thirdToken);
    if (firstToken != null) {
      var target = PrefixedIdentifierImpl(
        prefix: ast.simpleIdentifier(firstToken),
        period: firstPeriod!,
        identifier: ast.simpleIdentifier(secondToken!),
      );
      var expression = PropertyAccessImpl(
        target: target,
        operator: secondPeriod!,
        propertyName: identifier,
      );
      push(
        CommentReferenceImpl(
          newKeyword: newKeyword,
          expression: expression,
        ),
      );
    } else if (secondToken != null) {
      var expression = PrefixedIdentifierImpl(
        prefix: ast.simpleIdentifier(secondToken),
        period: secondPeriod!,
        identifier: identifier,
      );
      push(
        CommentReferenceImpl(
          newKeyword: newKeyword,
          expression: expression,
        ),
      );
    } else {
      push(
        CommentReferenceImpl(
          newKeyword: newKeyword,
          expression: identifier,
        ),
      );
    }
  }

  @override
  void handleCommentReferenceText(String referenceSource, int referenceOffset) {
    push(referenceSource);
    push(referenceOffset);
  }

  @override
  void handleConstFactory(Token constKeyword) {
    debugEvent("ConstFactory");
    // TODO(kallentu): Removal of const factory error for const function feature
    handleRecoverableError(messageConstFactory, constKeyword, constKeyword);
  }

  @override
  void handleContinueStatement(
      bool hasTarget, Token continueKeyword, Token semicolon) {
    assert(optional('continue', continueKeyword));
    assert(optional(';', semicolon));
    debugEvent("ContinueStatement");

    var label = hasTarget ? pop() as SimpleIdentifierImpl : null;
    push(
      ContinueStatementImpl(
        continueKeyword: continueKeyword,
        label: label,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void handleDottedName(int count, Token firstIdentifier) {
    assert(firstIdentifier.isIdentifier);
    debugEvent("DottedName");

    var components = popTypedList2<SimpleIdentifierImpl>(count);
    push(
      DottedNameImpl(
        components: components,
      ),
    );
  }

  @override
  void handleElseControlFlow(Token elseToken) {
    push(elseToken);
  }

  @override
  void handleEmptyFunctionBody(Token semicolon) {
    assert(optional(';', semicolon));
    debugEvent("EmptyFunctionBody");

    // TODO(scheglov) Change the parser to not produce these modifiers.
    pop(); // star
    pop(); // async
    push(
      EmptyFunctionBodyImpl(
        semicolon: semicolon,
      ),
    );
  }

  @override
  void handleEmptyStatement(Token semicolon) {
    assert(optional(';', semicolon));
    debugEvent("EmptyStatement");

    push(
      EmptyStatementImpl(
        semicolon: semicolon,
      ),
    );
  }

  @override
  void handleEnumElement(Token beginToken) {
    debugEvent("EnumElement");
    var tmpArguments = pop() as MethodInvocationImpl?;
    var tmpConstructor = pop() as ConstructorNameImpl?;
    var constant = pop() as EnumConstantDeclarationImpl;

    if (!enableEnhancedEnums &&
        (tmpArguments != null ||
            tmpConstructor != null &&
                (tmpConstructor.type.typeArguments != null ||
                    tmpConstructor.name != null))) {
      Token token = tmpArguments != null
          ? tmpArguments.argumentList.beginToken
          : tmpConstructor!.beginToken;
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.enhanced_enums,
        startToken: token,
      );
    }

    var argumentList = tmpArguments?.argumentList;

    TypeArgumentListImpl? typeArguments;
    ConstructorSelectorImpl? constructorSelector;
    if (tmpConstructor != null) {
      typeArguments = tmpConstructor.type.typeArguments;
      var constructorNamePeriod = tmpConstructor.period;
      var constructorNameId = tmpConstructor.name;
      if (constructorNamePeriod != null && constructorNameId != null) {
        constructorSelector = ConstructorSelectorImpl(
          period: constructorNamePeriod,
          name: constructorNameId,
        );
      }
    }

    // Replace the constant to include arguments.
    if (argumentList != null) {
      constant = EnumConstantDeclarationImpl(
        comment: constant.documentationComment,
        metadata: constant.metadata,
        name: constant.name,
        arguments: EnumConstantArgumentsImpl(
          typeArguments: typeArguments,
          constructorSelector: constructorSelector,
          argumentList: argumentList,
        ),
      );
    }

    push(constant);
  }

  @override
  void handleEnumElements(Token elementsEndToken, int elementsCount) {
    debugEvent("EnumElements");
    final builder = _classLikeBuilder as _EnumDeclarationBuilder;

    var constants = popTypedList2<EnumConstantDeclarationImpl>(elementsCount);
    builder.constants.addAll(constants);

    if (optional(';', elementsEndToken)) {
      builder.semicolon = elementsEndToken;
    }

    if (!enableEnhancedEnums && optional(';', elementsEndToken)) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.enhanced_enums,
        startToken: elementsEndToken,
      );
    }
  }

  @override
  void handleEnumHeader(Token enumKeyword, Token leftBrace) {
    assert(optional('enum', enumKeyword));
    assert(optional('{', leftBrace));
    debugEvent("EnumHeader");

    var implementsClause =
        pop(NullValues.IdentifierList) as ImplementsClauseImpl?;
    var withClause = pop(NullValues.WithClause) as WithClauseImpl?;
    var typeParameters = pop() as TypeParameterListImpl?;
    var name = pop() as SimpleIdentifierImpl;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, enumKeyword);

    if (!enableEnhancedEnums &&
        (withClause != null ||
            implementsClause != null ||
            typeParameters != null)) {
      var token = withClause != null
          ? withClause.withKeyword
          : implementsClause != null
              ? implementsClause.implementsKeyword
              : typeParameters!.beginToken;
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.enhanced_enums,
        startToken: token,
      );
    }

    _classLikeBuilder = _EnumDeclarationBuilder(
      comment: comment,
      metadata: metadata,
      enumKeyword: enumKeyword,
      name: name.token,
      typeParameters: typeParameters,
      withClause: withClause,
      implementsClause: implementsClause,
      leftBracket: leftBrace,
      semicolon: null,
      rightBracket: leftBrace.endGroup!,
    );
  }

  @override
  void handleEnumNoWithClause() {
    push(NullValues.WithClause);
  }

  @override
  void handleEnumWithClause(Token withKeyword) {
    assert(optional('with', withKeyword));
    var mixinTypes = _popNamedTypeList(
      errorCode: ParserErrorCode.EXPECTED_NAMED_TYPE_WITH,
    );
    push(
      WithClauseImpl(
        withKeyword: withKeyword,
        mixinTypes: mixinTypes,
      ),
    );
  }

  @override
  void handleErrorToken(ErrorToken token) {
    translateErrorToken(token, errorReporter.reportScannerError);
  }

  @override
  void handleExpressionFunctionBody(Token arrowToken, Token? semicolon) {
    assert(optional('=>', arrowToken) || optional('=', arrowToken));
    assert(optionalOrNull(';', semicolon));
    debugEvent("ExpressionFunctionBody");

    var expression = pop() as ExpressionImpl;
    var star = pop() as Token?;
    var asyncKeyword = pop() as Token?;
    if (parseFunctionBodies) {
      push(ExpressionFunctionBodyImpl(
        keyword: asyncKeyword,
        star: star,
        functionDefinition: arrowToken,
        expression: expression,
        semicolon: semicolon,
      ));
    } else {
      push(
        EmptyFunctionBodyImpl(
          semicolon: semicolon!,
        ),
      );
    }
  }

  @override
  void handleExpressionStatement(Token semicolon) {
    assert(optional(';', semicolon));
    debugEvent("ExpressionStatement");
    var expression = pop() as ExpressionImpl;
    reportErrorIfSuper(expression);
    if (expression is SimpleIdentifierImpl &&
        expression.token.keyword?.isBuiltInOrPseudo == false) {
      // This error is also reported by the body builder.
      handleRecoverableError(
          messageExpectedStatement, expression.beginToken, expression.endToken);
    }
    if (expression is AssignmentExpressionImpl) {
      if (!expression.leftHandSide.isAssignable) {
        // This error is also reported by the body builder.
        handleRecoverableError(
            messageIllegalAssignmentToNonAssignable,
            expression.leftHandSide.beginToken,
            expression.leftHandSide.endToken);
      }
    }
    push(
      ExpressionStatementImpl(
        expression: expression,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void handleFinallyBlock(Token finallyKeyword) {
    debugEvent("FinallyBlock");
    // The finally block is popped in "endTryStatement".
  }

  @override
  void handleForInitializerEmptyStatement(Token token) {
    debugEvent("ForInitializerEmptyStatement");
    push(NullValues.Expression);
  }

  @override
  void handleForInitializerExpressionStatement(Token token, bool forIn) {
    debugEvent("ForInitializerExpressionStatement");
  }

  @override
  void handleForInitializerLocalVariableDeclaration(Token token, bool forIn) {
    debugEvent("ForInitializerLocalVariableDeclaration");
  }

  @override
  void handleForInitializerPatternVariableAssignment(
      Token keyword, Token equals) {
    var expression = pop() as ExpressionImpl;
    var pattern = pop() as DartPatternImpl;
    var metadata = pop() as List<AnnotationImpl>?;
    push(PatternVariableDeclarationImpl(
        keyword: keyword,
        pattern: pattern,
        equals: equals,
        expression: expression,
        comment: null,
        metadata: metadata));
  }

  @override
  void handleForInLoopParts(Token? awaitToken, Token forToken,
      Token leftParenthesis, Token? patternKeyword, Token inKeyword) {
    assert(optionalOrNull('await', awaitToken));
    assert(optional('for', forToken));
    assert(optional('(', leftParenthesis));
    assert(optional('in', inKeyword) || optional(':', inKeyword));

    var iterable = pop() as ExpressionImpl;
    var variableOrDeclaration = pop()!;

    ForEachPartsImpl forLoopParts;
    if (patternKeyword != null) {
      var metadata = pop() as List<AnnotationImpl>?;
      forLoopParts = ForEachPartsWithPatternImpl(
          metadata: metadata,
          keyword: patternKeyword,
          pattern: variableOrDeclaration as DartPatternImpl,
          inKeyword: inKeyword,
          iterable: iterable);
    } else if (variableOrDeclaration is VariableDeclarationStatementImpl) {
      var variableList = variableOrDeclaration.variables;
      forLoopParts = ForEachPartsWithDeclarationImpl(
        loopVariable: DeclaredIdentifierImpl(
          comment: variableList.documentationComment,
          metadata: variableList.metadata,
          keyword: variableList.keyword,
          type: variableList.type,
          name: variableList.variables.first.name,
        ),
        inKeyword: inKeyword,
        iterable: iterable,
      );
    } else {
      if (variableOrDeclaration is! SimpleIdentifierImpl) {
        // Parser has already reported the error.
        if (!leftParenthesis.next!.isIdentifier) {
          parser.rewriter.insertSyntheticIdentifier(leftParenthesis);
        }
        variableOrDeclaration = ast.simpleIdentifier(leftParenthesis.next!);
      }
      forLoopParts = ForEachPartsWithIdentifierImpl(
        identifier: variableOrDeclaration,
        inKeyword: inKeyword,
        iterable: iterable,
      );
    }

    push(awaitToken ?? NullValues.AwaitToken);
    push(forToken);
    push(leftParenthesis);
    push(forLoopParts);
  }

  @override
  void handleForLoopParts(Token forKeyword, Token leftParen,
      Token leftSeparator, int updateExpressionCount) {
    assert(optional('for', forKeyword));
    assert(optional('(', leftParen));
    assert(optional(';', leftSeparator));
    assert(updateExpressionCount >= 0);

    var updates = popTypedList2<ExpressionImpl>(updateExpressionCount);
    var conditionStatement = pop() as StatementImpl;
    var initializerPart = pop();

    ExpressionImpl? condition;
    Token rightSeparator;
    if (conditionStatement is ExpressionStatementImpl) {
      condition = conditionStatement.expression;
      rightSeparator = conditionStatement.semicolon!;
    } else {
      rightSeparator = (conditionStatement as EmptyStatementImpl).semicolon;
    }

    ForPartsImpl forLoopParts;
    if (initializerPart is VariableDeclarationStatementImpl) {
      forLoopParts = ForPartsWithDeclarationsImpl(
        variableList: initializerPart.variables,
        leftSeparator: leftSeparator,
        condition: condition,
        rightSeparator: rightSeparator,
        updaters: updates,
      );
    } else if (initializerPart is PatternVariableDeclarationImpl) {
      forLoopParts = ForPartsWithPatternImpl(
          variables: initializerPart,
          leftSeparator: leftSeparator,
          condition: condition,
          rightSeparator: rightSeparator,
          updaters: updates);
    } else {
      forLoopParts = ForPartsWithExpressionImpl(
        initialization: initializerPart as ExpressionImpl?,
        leftSeparator: leftSeparator,
        condition: condition,
        rightSeparator: rightSeparator,
        updaters: updates,
      );
    }

    push(forKeyword);
    push(leftParen);
    push(forLoopParts);
  }

  @override
  void handleFormalParameterWithoutValue(Token token) {
    debugEvent("FormalParameterWithoutValue");

    push(NullValues.ParameterDefaultValue);
  }

  @override
  void handleIdentifier(Token token, IdentifierContext context) {
    assert(token.isKeywordOrIdentifier);
    debugEvent("handleIdentifier");

    if (context.inSymbol) {
      push(token);
      return;
    }

    final identifier =
        ast.simpleIdentifier(token, isDeclaration: context.inDeclaration);
    if (context.inLibraryOrPartOfDeclaration) {
      if (!context.isContinuation) {
        push([identifier]);
      } else {
        push(identifier);
      }
    } else if (context == IdentifierContext.enumValueDeclaration) {
      var metadata = pop() as List<AnnotationImpl>?;
      var comment = _findComment(metadata, token);
      push(
        EnumConstantDeclarationImpl(
          comment: comment,
          metadata: metadata,
          name: token,
          arguments: null,
        ),
      );
    } else {
      push(identifier);
    }
  }

  @override
  void handleIdentifierList(int count) {
    debugEvent("IdentifierList");

    push(
        popTypedList<SimpleIdentifierImpl>(count) ?? NullValues.IdentifierList);
  }

  @override
  void handleImplements(Token? implementsKeyword, int interfacesCount) {
    assert(optionalOrNull('implements', implementsKeyword));
    debugEvent("Implements");

    if (implementsKeyword != null) {
      endTypeList(interfacesCount);
      final interfaces = _popNamedTypeList(
        errorCode: ParserErrorCode.EXPECTED_NAMED_TYPE_IMPLEMENTS,
      );
      push(
        ImplementsClauseImpl(
          implementsKeyword: implementsKeyword,
          interfaces: interfaces,
        ),
      );
    } else {
      push(NullValues.IdentifierList);
    }
  }

  @override
  void handleImportPrefix(Token? deferredKeyword, Token? asKeyword) {
    assert(optionalOrNull('deferred', deferredKeyword));
    assert(optionalOrNull('as', asKeyword));
    debugEvent("ImportPrefix");

    if (asKeyword == null) {
      // If asKeyword is null, then no prefix has been pushed on the stack.
      // Push a placeholder indicating that there is no prefix.
      push(NullValues.Prefix);
      push(NullValues.As);
    } else {
      push(asKeyword);
    }
    push(deferredKeyword ?? NullValues.Deferred);
  }

  @override
  void handleIndexedExpression(
      Token? question, Token leftBracket, Token rightBracket) {
    assert(optional('[', leftBracket) ||
        (enableNonNullable && optional('?.[', leftBracket)));
    assert(optional(']', rightBracket));
    debugEvent("IndexedExpression");

    if (!enableNonNullable) {
      reportErrorIfNullableType(question);
    }

    var index = pop() as ExpressionImpl;
    var target = pop() as ExpressionImpl?;
    if (target == null) {
      var receiver = pop() as CascadeExpressionImpl;
      var token = peek() as Token;
      push(receiver);
      var expression = IndexExpressionImpl.forCascade(
        period: token,
        question: question,
        leftBracket: leftBracket,
        index: index,
        rightBracket: rightBracket,
      );
      assert(expression.isCascaded);
      push(expression);
    } else {
      push(
        IndexExpressionImpl.forTarget(
          target: target,
          question: question,
          leftBracket: leftBracket,
          index: index,
          rightBracket: rightBracket,
        ),
      );
    }
  }

  @override
  void handleInterpolationExpression(Token leftBracket, Token? rightBracket) {
    var expression = pop() as ExpressionImpl;
    push(
      InterpolationExpressionImpl(
        leftBracket: leftBracket,
        expression: expression,
        rightBracket: rightBracket,
      ),
    );
  }

  @override
  void handleInvalidExpression(Token token) {
    debugEvent("InvalidExpression");
  }

  @override
  void handleInvalidFunctionBody(Token leftBracket) {
    assert(optional('{', leftBracket));
    assert(optional('}', leftBracket.endGroup!));
    debugEvent("InvalidFunctionBody");
    final block = BlockImpl(
      leftBracket: leftBracket,
      statements: [],
      rightBracket: leftBracket.endGroup!,
    );
    var star = pop() as Token?;
    var asyncKeyword = pop() as Token?;
    push(
      BlockFunctionBodyImpl(
        keyword: asyncKeyword,
        star: star,
        block: block,
      ),
    );
  }

  @override
  void handleInvalidMember(Token endToken) {
    debugEvent("InvalidMember");
    pop(); // metadata star
  }

  @override
  void handleInvalidOperatorName(Token operatorKeyword, Token token) {
    assert(optional('operator', operatorKeyword));
    debugEvent("InvalidOperatorName");

    push(_OperatorName(
        operatorKeyword, ast.simpleIdentifier(token, isDeclaration: true)));
  }

  @override
  void handleInvalidTopLevelBlock(Token token) {
    // TODO(danrubel): Consider improved recovery by adding this block
    // as part of a synthetic top level function.
    pop(); // block
  }

  @override
  void handleInvalidTopLevelDeclaration(Token endToken) {
    debugEvent("InvalidTopLevelDeclaration");

    pop(); // metadata star
    // TODO(danrubel): consider creating a AST node
    // representing the invalid declaration to better support code completion,
    // quick fixes, etc, rather than discarding the metadata and token
  }

  @override
  void handleInvalidTypeArguments(Token token) {
    var invalidTypeArgs = pop() as TypeArgumentListImpl;
    var node = pop();
    if (node is ConstructorNameImpl) {
      push(_ConstructorNameWithInvalidTypeArgs(node, invalidTypeArgs));
    } else {
      throw UnimplementedError(
          'node is an instance of ${node.runtimeType} in handleInvalidTypeArguments');
    }
  }

  @override
  void handleIsOperator(Token isOperator, Token? not) {
    assert(optional('is', isOperator));
    assert(optionalOrNull('!', not));
    debugEvent("IsOperator");

    var type = pop() as TypeAnnotationImpl;
    var expression = pop() as ExpressionImpl;
    push(
      IsExpressionImpl(
        expression: expression,
        isOperator: isOperator,
        notOperator: not,
        type: type,
      ),
    );
  }

  @override
  void handleLabel(Token colon) {
    assert(optionalOrNull(':', colon));
    debugEvent("Label");

    var name = pop() as SimpleIdentifierImpl;
    push(
      LabelImpl(
        label: name,
        colon: colon,
      ),
    );
  }

  @override
  void handleListPattern(int count, Token leftBracket, Token rightBracket) {
    assert(optional('[', leftBracket));
    assert(optional(']', rightBracket));
    debugEvent("ListPattern");

    var elements = popTypedList2<ListPatternElementImpl>(count);
    var typeArguments = pop() as TypeArgumentListImpl?;
    push(
      ListPatternImpl(
        typeArguments: typeArguments,
        leftBracket: leftBracket,
        elements: elements,
        rightBracket: rightBracket,
      ),
    );
  }

  @override
  void handleLiteralBool(Token token) {
    bool value = identical(token.stringValue, "true");
    assert(value || identical(token.stringValue, "false"));
    debugEvent("LiteralBool");

    push(
      BooleanLiteralImpl(
        literal: token,
        value: value,
      ),
    );
  }

  @override
  void handleLiteralDouble(Token token) {
    assert(token.type == TokenType.DOUBLE);
    debugEvent("LiteralDouble");

    push(
      DoubleLiteralImpl(
        literal: token,
        value: double.parse(token.lexeme),
      ),
    );
  }

  @override
  void handleLiteralInt(Token token) {
    assert(identical(token.kind, INT_TOKEN) ||
        identical(token.kind, HEXADECIMAL_TOKEN));
    debugEvent("LiteralInt");

    push(
      IntegerLiteralImpl(
        literal: token,
        value: int.tryParse(token.lexeme),
      ),
    );
  }

  @override
  void handleLiteralList(
      int count, Token leftBracket, Token? constKeyword, Token rightBracket) {
    assert(optional('[', leftBracket));
    assert(optionalOrNull('const', constKeyword));
    assert(optional(']', rightBracket));
    debugEvent("LiteralList");

    var elements = popCollectionElements(count);
    var typeArguments = pop() as TypeArgumentListImpl?;

    push(
      ListLiteralImpl(
        constKeyword: constKeyword,
        typeArguments: typeArguments,
        leftBracket: leftBracket,
        elements: elements,
        rightBracket: rightBracket,
      ),
    );
  }

  @override
  void handleLiteralMapEntry(Token colon, Token endToken) {
    assert(optional(':', colon));
    debugEvent("LiteralMapEntry");

    var value = pop() as ExpressionImpl;
    var key = pop() as ExpressionImpl;
    push(
      MapLiteralEntryImpl(
        key: key,
        separator: colon,
        value: value,
      ),
    );
  }

  @override
  void handleLiteralNull(Token token) {
    assert(optional('null', token));
    debugEvent("LiteralNull");

    push(
      NullLiteralImpl(
        literal: token,
      ),
    );
  }

  @override
  void handleLiteralSetOrMap(
    int count,
    Token leftBrace,
    Token? constKeyword,
    Token rightBrace,
    // TODO(danrubel): hasSetEntry parameter exists for replicating existing
    // behavior and will be removed once unified collection has been enabled
    bool hasSetEntry,
  ) {
    var elements = popCollectionElements(count);

    var typeArguments = pop() as TypeArgumentListImpl?;
    push(
      SetOrMapLiteralImpl(
        constKeyword: constKeyword,
        typeArguments: typeArguments,
        leftBracket: leftBrace,
        elements: elements,
        rightBracket: rightBrace,
      ),
    );
  }

  @override
  void handleMapPattern(int count, Token leftBrace, Token rightBrace) {
    debugEvent('MapPattern');

    var elements = popTypedList2<MapPatternElementImpl>(count);
    var typeArguments = pop() as TypeArgumentListImpl?;
    push(
      MapPatternImpl(
        typeArguments: typeArguments,
        leftBracket: leftBrace,
        elements: elements,
        rightBracket: rightBrace,
      ),
    );
  }

  @override
  void handleMapPatternEntry(Token colon, Token endToken) {
    assert(optional(':', colon));
    debugEvent("MapPatternEntry");

    var value = pop() as DartPatternImpl;
    var key = pop() as ExpressionImpl;
    push(MapPatternEntryImpl(key: key, separator: colon, value: value));
  }

  @override
  void handleMixinHeader(Token mixinKeyword) {
    assert(optional('mixin', mixinKeyword));
    assert(_classLikeBuilder == null);
    debugEvent("MixinHeader");

    var implementsClause =
        pop(NullValues.IdentifierList) as ImplementsClauseImpl?;
    var onClause = pop(NullValues.IdentifierList) as OnClauseImpl?;
    var finalKeyword = pop(NullValues.Token) as Token?;
    var interfaceKeyword = pop(NullValues.Token) as Token?;
    var baseKeyword = pop(NullValues.Token) as Token?;
    var sealedKeyword = pop(NullValues.Token) as Token?;
    var augmentKeyword = pop(NullValues.Token) as Token?;
    var typeParameters = pop() as TypeParameterListImpl?;
    var name = pop() as SimpleIdentifierImpl;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, mixinKeyword);

    _classLikeBuilder = _MixinDeclarationBuilder(
      comment: comment,
      metadata: metadata,
      augmentKeyword: augmentKeyword,
      sealedKeyword: sealedKeyword,
      baseKeyword: baseKeyword,
      interfaceKeyword: interfaceKeyword,
      finalKeyword: finalKeyword,
      mixinKeyword: mixinKeyword,
      name: name.token,
      typeParameters: typeParameters,
      onClause: onClause,
      implementsClause: implementsClause,
      leftBracket: Tokens.openCurlyBracket(),
      rightBracket: Tokens.closeCurlyBracket(),
    );
  }

  @override
  void handleMixinOn(Token? onKeyword, int typeCount) {
    assert(onKeyword == null || onKeyword.isKeywordOrIdentifier);
    debugEvent("MixinOn");

    if (onKeyword != null) {
      endTypeList(typeCount);
      final onTypes = _popNamedTypeList(
        errorCode: ParserErrorCode.EXPECTED_NAMED_TYPE_ON,
      );
      push(
        OnClauseImpl(
          onKeyword: onKeyword,
          superclassConstraints: onTypes,
        ),
      );
    } else {
      push(NullValues.IdentifierList);
    }
  }

  @override
  void handleNamedArgument(Token colon) {
    assert(optional(':', colon));
    debugEvent("NamedArgument");

    var expression = pop() as ExpressionImpl;
    var name = pop() as SimpleIdentifierImpl;
    push(
      NamedExpressionImpl(
        name: LabelImpl(
          label: name,
          colon: colon,
        ),
        expression: expression,
      ),
    );
  }

  @override
  void handleNamedMixinApplicationWithClause(Token withKeyword) {
    assert(optionalOrNull('with', withKeyword));
    var mixinTypes = _popNamedTypeList(
      errorCode: ParserErrorCode.EXPECTED_NAMED_TYPE_WITH,
    );
    push(
      WithClauseImpl(
        withKeyword: withKeyword,
        mixinTypes: mixinTypes,
      ),
    );
  }

  @override
  void handleNamedRecordField(Token colon) => handleNamedArgument(colon);

  @override
  void handleNativeClause(Token nativeToken, bool hasName) {
    debugEvent("NativeClause");

    if (hasName) {
      nativeName = pop() as StringLiteralImpl;
    } else {
      nativeName = null;
    }
  }

  @override
  void handleNativeFunctionBody(Token nativeToken, Token semicolon) {
    assert(optional('native', nativeToken));
    assert(optional(';', semicolon));
    debugEvent("NativeFunctionBody");

    // TODO(danrubel) Change the parser to not produce these modifiers.
    pop(); // star
    pop(); // async
    push(
      NativeFunctionBodyImpl(
        nativeKeyword: nativeToken,
        stringLiteral: nativeName,
        semicolon: semicolon,
      ),
    );
  }

  @override
  void handleNewAsIdentifier(Token token) {
    if (!enableConstructorTearoffs) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.constructor_tearoffs,
        startToken: token,
      );
    }
  }

  @override
  void handleNoConstructorReferenceContinuationAfterTypeArguments(Token token) {
    debugEvent("NoConstructorReferenceContinuationAfterTypeArguments");

    push(NullValues.ConstructorReferenceContinuationAfterTypeArguments);
  }

  @override
  void handleNoFieldInitializer(Token token) {
    debugEvent("NoFieldInitializer");

    var name = pop() as SimpleIdentifierImpl;
    push(
      VariableDeclarationImpl(
        name: name.token,
        equals: null,
        initializer: null,
      ),
    );
  }

  @override
  void handleNoInitializers() {
    debugEvent("NoInitializers");

    if (!isFullAst) return;
    push(NullValues.ConstructorInitializerSeparator);
    push(NullValues.ConstructorInitializers);
  }

  @override
  void handleNonNullAssertExpression(Token bang) {
    debugEvent('NonNullAssertExpression');
    if (!enableNonNullable) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.non_nullable,
        startToken: bang,
      );
    } else {
      push(
        PostfixExpressionImpl(
          operand: pop() as ExpressionImpl,
          operator: bang,
        ),
      );
    }
  }

  @override
  void handleNoTypeNameInConstructorReference(Token token) {
    debugEvent("NoTypeNameInConstructorReference");
    final builder = _classLikeBuilder as _EnumDeclarationBuilder;

    push(ast.simpleIdentifier(builder.name));
  }

  @override
  void handleNoVariableInitializer(Token token) {
    debugEvent("NoVariableInitializer");
  }

  @override
  void handleNullAssertPattern(Token bang) {
    debugEvent("NullAssertPattern");
    push(
      NullAssertPatternImpl(
        pattern: pop() as DartPatternImpl,
        operator: bang,
      ),
    );
  }

  @override
  void handleNullCheckPattern(Token question) {
    debugEvent('NullCheckPattern');
    if (!_featureSet.isEnabled(Feature.patterns)) {
      // TODO(paulberry): report the appropriate error
      throw UnimplementedError('Patterns not enabled');
    }
    push(
      NullCheckPatternImpl(
        pattern: pop() as DartPatternImpl,
        operator: question,
      ),
    );
  }

  @override
  void handleObjectPattern(
      Token firstIdentifierToken, Token? dot, Token? secondIdentifierToken) {
    debugEvent("ExtractorPattern");

    var arguments = pop() as _ObjectPatternFields;
    var typeArguments = pop() as TypeArgumentListImpl?;
    var firstIdentifier = SimpleIdentifierImpl(firstIdentifierToken);
    var typeName = dot == null
        ? firstIdentifier
        : PrefixedIdentifierImpl(
            prefix: firstIdentifier,
            period: dot,
            identifier: SimpleIdentifierImpl(secondIdentifierToken!),
          );
    push(
      ObjectPatternImpl(
        type: NamedTypeImpl(
          name: typeName,
          typeArguments: typeArguments,
          question: null,
        ),
        leftParenthesis: arguments.leftParenthesis,
        fields: arguments.fields,
        rightParenthesis: arguments.rightParenthesis,
      ),
    );
  }

  @override
  void handleObjectPatternFields(int count, Token beginToken, Token endToken) {
    debugEvent("ExtractorPatternFields");
    var fields = popTypedList2<PatternFieldImpl>(count);
    push(_ObjectPatternFields(beginToken, endToken, fields));
  }

  @override
  void handleOperator(Token operatorToken) {
    assert(operatorToken.isUserDefinableOperator);
    debugEvent("Operator");

    push(operatorToken);
  }

  @override
  void handleOperatorName(Token operatorKeyword, Token token) {
    assert(optional('operator', operatorKeyword));
    assert(token.type.isUserDefinableOperator);
    debugEvent("OperatorName");

    push(_OperatorName(
        operatorKeyword, ast.simpleIdentifier(token, isDeclaration: true)));
  }

  @override
  void handleParenthesizedCondition(
      Token leftParenthesis, Token? case_, Token? when) {
    ExpressionImpl condition;
    CaseClauseImpl? caseClause;
    if (case_ != null) {
      var whenClause = when != null ? pop() as WhenClauseImpl : null;
      var pattern = pop() as DartPatternImpl;
      caseClause = CaseClauseImpl(
        caseKeyword: case_,
        guardedPattern: GuardedPatternImpl(
          pattern: pattern,
          whenClause: whenClause,
        ),
      );
    }
    condition = pop() as ExpressionImpl;
    push(_ParenthesizedCondition(leftParenthesis, condition, caseClause));
  }

  @override
  void handleParenthesizedPattern(Token leftParenthesis) {
    assert(optional('(', leftParenthesis));
    debugEvent("ParenthesizedPattern");

    var pattern = pop() as DartPatternImpl;
    push(ParenthesizedPatternImpl(
        leftParenthesis: leftParenthesis,
        pattern: pattern,
        rightParenthesis: leftParenthesis.endGroup!));
  }

  @override
  void handlePatternAssignment(Token equals) {
    var expression = pop() as ExpressionImpl;
    var pattern = pop() as DartPatternImpl;
    push(PatternAssignmentImpl(
        pattern: pattern, equals: equals, expression: expression));
  }

  @override
  void handlePatternField(Token? colon) {
    debugEvent("PatternField");

    var pattern = pop() as DartPatternImpl;
    PatternFieldNameImpl? fieldName;
    if (colon != null) {
      var name = (pop() as SimpleIdentifierImpl?)?.token;
      fieldName = PatternFieldNameImpl(name: name, colon: colon);
    }
    push(PatternFieldImpl(name: fieldName, pattern: pattern));
  }

  @override
  void handlePatternVariableDeclarationStatement(
      Token keyword, Token equals, Token semicolon) {
    var expression = pop() as ExpressionImpl;
    var pattern = pop() as DartPatternImpl;
    var metadata = pop() as List<AnnotationImpl>?;
    var comment = _findComment(metadata, keyword);
    push(PatternVariableDeclarationStatementImpl(
        declaration: PatternVariableDeclarationImpl(
            keyword: keyword,
            pattern: pattern,
            equals: equals,
            expression: expression,
            comment: comment,
            metadata: metadata),
        semicolon: semicolon));
  }

  @override
  void handleQualified(Token period) {
    assert(optional('.', period));

    var identifier = pop() as SimpleIdentifierImpl;
    var prefix = pop();
    if (prefix is List) {
      // We're just accumulating components into a list.
      prefix.add(identifier);
      push(prefix);
    } else if (prefix is SimpleIdentifierImpl) {
      // TODO(paulberry): resolve [identifier].  Note that BodyBuilder handles
      // this situation using SendAccessGenerator.
      push(
        PrefixedIdentifierImpl(
          prefix: prefix,
          period: period,
          identifier: identifier,
        ),
      );
    } else {
      // TODO(paulberry): implement.
      logEvent('Qualified with >1 dot');
    }
  }

  @override
  void handleRecordPattern(Token token, int count) {
    debugEvent("RecordPattern");

    var fields = popTypedList2<PatternFieldImpl>(count);
    push(
      RecordPatternImpl(
        leftParenthesis: token,
        fields: fields,
        rightParenthesis: token.endGroup!,
      ),
    );
  }

  @override
  void handleRecoverableError(
      Message message, Token startToken, Token endToken) {
    /// TODO(danrubel): Ignore this error until we deprecate `native` support.
    if (message == messageNativeClauseShouldBeAnnotation && allowNativeClause) {
      return;
    } else if (message.code == codeBuiltInIdentifierInDeclaration) {
      // Allow e.g. 'class Function' in sdk.
      if (importUri.isScheme("dart")) return;
      if (uri.isScheme("org-dartlang-sdk")) return;
    }
    debugEvent("Error: ${message.problemMessage}");
    if (message.code.analyzerCodes == null && startToken is ErrorToken) {
      translateErrorToken(startToken, errorReporter.reportScannerError);
    } else {
      int offset = startToken.offset;
      int length = endToken.end - offset;
      addProblem(message, offset, length);
    }
  }

  @override
  void handleRecoverClassHeader() {
    debugEvent("RecoverClassHeader");

    var implementsClause =
        pop(NullValues.IdentifierList) as ImplementsClauseImpl?;
    var withClause = pop(NullValues.WithClause) as WithClauseImpl?;
    var extendsClause = pop(NullValues.ExtendsClause) as ExtendsClauseImpl?;
    var declaration = _classLikeBuilder as _ClassDeclarationBuilder;
    if (extendsClause != null) {
      if (declaration.extendsClause?.superclass == null) {
        declaration.extendsClause = extendsClause;
      }
    }
    if (withClause != null) {
      final existingClause = declaration.withClause;
      if (existingClause == null) {
        declaration.withClause = withClause;
      } else {
        declaration.withClause = WithClauseImpl(
          withKeyword: existingClause.withKeyword,
          mixinTypes: [
            ...existingClause.mixinTypes,
            ...withClause.mixinTypes,
          ],
        );
      }
    }
    if (implementsClause != null) {
      final existingClause = declaration.implementsClause;
      if (existingClause == null) {
        declaration.implementsClause = implementsClause;
      } else {
        declaration.implementsClause = ImplementsClauseImpl(
          implementsKeyword: existingClause.implementsKeyword,
          interfaces: [
            ...existingClause.interfaces,
            ...implementsClause.interfaces,
          ],
        );
      }
    }
  }

  @override
  void handleRecoverImport(Token? semicolon) {
    assert(optionalOrNull(';', semicolon));
    debugEvent("RecoverImport");

    var combinators = pop() as List<CombinatorImpl>?;
    var deferredKeyword = pop(NullValues.Deferred) as Token?;
    var asKeyword = pop(NullValues.As) as Token?;
    var prefix = pop(NullValues.Prefix) as SimpleIdentifierImpl?;
    var configurations = pop() as List<ConfigurationImpl>?;

    final directive = directives.last as ImportDirectiveImpl;

    // TODO(scheglov) This code would be easier if we used one object.
    var mergedAsKeyword = directive.asKeyword;
    var mergedPrefix = directive.prefix;
    if (directive.asKeyword == null && asKeyword != null) {
      mergedAsKeyword = asKeyword;
      mergedPrefix = prefix;
    }

    directives.last = ImportDirectiveImpl(
      comment: directive.documentationComment,
      metadata: directive.metadata,
      importKeyword: directive.importKeyword,
      uri: directive.uri,
      configurations: [
        ...directive.configurations,
        ...?configurations,
      ],
      deferredKeyword: directive.deferredKeyword ?? deferredKeyword,
      asKeyword: mergedAsKeyword,
      prefix: mergedPrefix,
      combinators: [
        ...directive.combinators,
        ...?combinators,
      ],
      semicolon: semicolon ?? directive.semicolon,
    );
  }

  @override
  void handleRecoverMixinHeader() {
    final builder = _classLikeBuilder as _MixinDeclarationBuilder;
    var implementsClause =
        pop(NullValues.IdentifierList) as ImplementsClauseImpl?;
    var onClause = pop(NullValues.IdentifierList) as OnClauseImpl?;

    if (onClause != null) {
      final existingClause = builder.onClause;
      if (existingClause == null) {
        builder.onClause = onClause;
      } else {
        builder.onClause = OnClauseImpl(
          onKeyword: existingClause.onKeyword,
          superclassConstraints: [
            ...existingClause.superclassConstraints,
            ...onClause.superclassConstraints,
          ],
        );
      }
    }
    if (implementsClause != null) {
      final existingClause = builder.implementsClause;
      if (existingClause == null) {
        builder.implementsClause = implementsClause;
      } else {
        builder.implementsClause = ImplementsClauseImpl(
          implementsKeyword: implementsClause.implementsKeyword,
          interfaces: [
            ...existingClause.interfaces,
            ...implementsClause.interfaces,
          ],
        );
      }
    }
  }

  @override
  void handleRelationalPattern(Token token) {
    debugEvent("RelationalPattern");
    push(RelationalPatternImpl(
        operator: token, operand: pop() as ExpressionImpl));
  }

  @override
  void handleRestPattern(Token dots, {required bool hasSubPattern}) {
    var subPattern = hasSubPattern ? pop() as DartPatternImpl : null;
    push(RestPatternElementImpl(operator: dots, pattern: subPattern));
  }

  @override
  void handleScript(Token token) {
    assert(identical(token.type, TokenType.SCRIPT_TAG));
    debugEvent("Script");

    scriptTag = ScriptTagImpl(
      scriptTag: token,
    );
  }

  @override
  void handleSend(Token beginToken, Token endToken) {
    debugEvent("Send");

    var arguments = pop() as MethodInvocationImpl?;
    var typeArguments = pop() as TypeArgumentListImpl?;
    if (arguments != null) {
      doInvocation(typeArguments, arguments);
    } else {
      doPropertyGet();
    }
  }

  @override
  void handleSpreadExpression(Token spreadToken) {
    var expression = pop() as ExpressionImpl;
    push(
      SpreadElementImpl(
        spreadOperator: spreadToken,
        expression: expression,
      ),
    );
  }

  @override
  void handleStringJuxtaposition(Token startToken, int literalCount) {
    debugEvent("StringJuxtaposition");

    var strings = popTypedList2<StringLiteralImpl>(literalCount);
    push(AdjacentStringsImpl(strings: strings));
  }

  @override
  void handleStringPart(Token literalString) {
    assert(identical(literalString.kind, STRING_TOKEN));
    debugEvent("StringPart");

    push(literalString);
  }

  @override
  void handleSuperExpression(Token superKeyword, IdentifierContext context) {
    assert(optional('super', superKeyword));
    debugEvent("SuperExpression");
    push(
      SuperExpressionImpl(
        superKeyword: superKeyword,
      ),
    );
  }

  @override
  void handleSwitchCaseNoWhenClause(Token token) {
    debugEvent("SwitchCaseNoWhenClause");
  }

  @override
  void handleSwitchExpressionCasePattern(Token token) {
    debugEvent("SwitchExpressionCasePattern");
  }

  @override
  void handleSymbolVoid(Token voidKeyword) {
    assert(optional('void', voidKeyword));
    debugEvent("SymbolVoid");

    push(voidKeyword);
  }

  @override
  void handleThisExpression(Token thisKeyword, IdentifierContext context) {
    assert(optional('this', thisKeyword));
    debugEvent("ThisExpression");

    push(
      ThisExpressionImpl(
        thisKeyword: thisKeyword,
      ),
    );
  }

  @override
  void handleThrowExpression(Token throwToken, Token endToken) {
    assert(optional('throw', throwToken));
    debugEvent("ThrowExpression");

    push(
      ThrowExpressionImpl(
        throwKeyword: throwToken,
        expression: pop() as ExpressionImpl,
      ),
    );
  }

  @override
  void handleType(Token beginToken, Token? questionMark) {
    debugEvent("Type");
    if (!enableNonNullable) {
      reportErrorIfNullableType(questionMark);
    }

    var arguments = pop() as TypeArgumentListImpl?;
    var name = pop() as IdentifierImpl;
    push(
      NamedTypeImpl(
        name: name,
        typeArguments: arguments,
        question: questionMark,
      ),
    );
  }

  @override
  void handleTypeArgumentApplication(Token openAngleBracket) {
    var typeArguments = pop() as TypeArgumentListImpl;
    var receiver = pop() as ExpressionImpl;
    if (!enableConstructorTearoffs) {
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.constructor_tearoffs,
        startToken: typeArguments.leftBracket,
        endToken: typeArguments.rightBracket,
      );
    }
    push(
      FunctionReferenceImpl(
        function: receiver,
        typeArguments: typeArguments,
      ),
    );
  }

  @override
  void handleTypeVariablesDefined(Token token, int count) {
    debugEvent("handleTypeVariablesDefined");
    assert(count > 0);
    push(popTypedList<TypeParameterImpl>(count));
  }

  @override
  void handleUnaryPostfixAssignmentExpression(Token operator) {
    assert(operator.type.isUnaryPostfixOperator);
    debugEvent("UnaryPostfixAssignmentExpression");

    var expression = pop() as ExpressionImpl;
    if (!expression.isAssignable) {
      // This error is also reported by the body builder.
      handleRecoverableError(
          messageIllegalAssignmentToNonAssignable, operator, operator);
    }
    push(
      PostfixExpressionImpl(
        operand: expression,
        operator: operator,
      ),
    );
  }

  @override
  void handleUnaryPrefixAssignmentExpression(Token operator) {
    assert(operator.type.isUnaryPrefixOperator);
    debugEvent("UnaryPrefixAssignmentExpression");

    var expression = pop() as ExpressionImpl;
    if (!expression.isAssignable) {
      // This error is also reported by the body builder.
      handleRecoverableError(messageMissingAssignableSelector,
          expression.endToken, expression.endToken);
    }
    push(
      PrefixExpressionImpl(
        operator: operator,
        operand: expression,
      ),
    );
  }

  @override
  void handleUnaryPrefixExpression(Token operator) {
    assert(operator.type.isUnaryPrefixOperator);
    debugEvent("UnaryPrefixExpression");

    push(
      PrefixExpressionImpl(
        operator: operator,
        operand: pop() as ExpressionImpl,
      ),
    );
  }

  @override
  void handleValuedFormalParameter(Token equals, Token token) {
    assert(optional('=', equals) || optional(':', equals));
    debugEvent("ValuedFormalParameter");

    var value = pop() as ExpressionImpl;
    push(_ParameterDefaultValue(equals, value));
  }

  @override
  void handleVariablePattern(Token? keyword, Token variable,
      {required bool inAssignmentPattern}) {
    debugEvent('VariablePattern');
    if (!_featureSet.isEnabled(Feature.patterns)) {
      // TODO(paulberry): report the appropriate error
      throw UnimplementedError('Patterns not enabled');
    }
    var type = pop() as TypeAnnotationImpl?;
    if (variable.lexeme == '_') {
      push(
        WildcardPatternImpl(
          keyword: keyword,
          type: type,
          name: variable,
        ),
      );
    } else if (inAssignmentPattern) {
      push(
        AssignedVariablePatternImpl(
          name: variable,
        ),
      );
    } else {
      push(
        DeclaredVariablePatternImpl(
          keyword: keyword,
          type: type,
          name: variable,
        ),
      );
    }
  }

  @override
  void handleVoidKeyword(Token voidKeyword) {
    assert(optional('void', voidKeyword));
    debugEvent("VoidKeyword");

    // TODO(paulberry): is this sufficient, or do we need to hook the "void"
    // keyword up to an element?
    handleIdentifier(voidKeyword, IdentifierContext.typeReference);
    handleNoTypeArguments(voidKeyword);
    handleType(voidKeyword, null);
  }

  @override
  void handleVoidKeywordWithTypeArguments(Token voidKeyword) {
    assert(optional('void', voidKeyword));
    debugEvent("VoidKeywordWithTypeArguments");
    var arguments = pop() as TypeArgumentListImpl;

    // TODO(paulberry): is this sufficient, or do we need to hook the "void"
    // keyword up to an element?
    handleIdentifier(voidKeyword, IdentifierContext.typeReference);
    push(arguments);
    handleType(voidKeyword, null);
  }

  @override
  Never internalProblem(Message message, int charOffset, Uri uri) {
    throw UnsupportedError(message.problemMessage);
  }

  /// Return `true` if [token] is either `null` or is the symbol or keyword
  /// [value].
  bool optionalOrNull(String value, Token? token) {
    return token == null || identical(value, token.stringValue);
  }

  List<CommentReferenceImpl> parseCommentReferences(Token dartdoc) {
    // Parse dartdoc into potential comment reference source/offset pairs
    int count = parser.parseCommentReferences(dartdoc);
    List sourcesAndOffsets = List.filled(count * 2, null);
    popList(count * 2, sourcesAndOffsets);

    // Parse each of the source/offset pairs into actual comment references
    count = 0;
    int index = 0;
    while (index < sourcesAndOffsets.length) {
      var referenceSource = sourcesAndOffsets[index++] as String;
      var referenceOffset = sourcesAndOffsets[index++] as int;
      ScannerResult result = scanString(referenceSource);
      if (!result.hasErrors) {
        Token token = result.tokens;
        if (parser.parseOneCommentReference(token, referenceOffset)) {
          ++count;
        }
      }
    }

    return popTypedList<CommentReferenceImpl>(count) ?? const [];
  }

  List<CollectionElementImpl> popCollectionElements(int count) {
    // TODO(scheglov) Not efficient.
    final elements = <CollectionElementImpl>[];
    for (int index = count - 1; index >= 0; --index) {
      var element = pop();
      elements.add(element as CollectionElementImpl);
    }
    return elements.reversed.toList();
  }

  List? popList(int n, List list) {
    if (n == 0) return null;
    return stack.popList(n, list, null);
  }

  List<T>? popTypedList<T extends Object>(int count) {
    if (count == 0) return null;
    assert(stack.length >= count);

    final tailList = List<T?>.filled(count, null, growable: true);
    stack.popList(count, tailList, null);
    return tailList.whereNotNull().toList();
  }

  /// TODO(scheglov) This is probably not optimal.
  List<T> popTypedList2<T>(int count) {
    var result = <T>[];
    for (var i = 0; i < count; i++) {
      var element = stack.pop(null) as T;
      result.add(element);
    }
    return result.reversed.toList();
  }

  void reportErrorIfNullableType(Token? questionMark) {
    if (questionMark != null) {
      assert(optional('?', questionMark));
      _reportFeatureNotEnabled(
        feature: ExperimentalFeatures.non_nullable,
        startToken: questionMark,
      );
    }
  }

  void reportErrorIfSuper(ExpressionImpl expression) {
    if (expression is SuperExpressionImpl) {
      // This error is also reported by the body builder.
      handleRecoverableError(messageMissingAssignableSelector,
          expression.beginToken, expression.endToken);
    }
  }

  CommentImpl? _findComment(
      List<AnnotationImpl>? metadata, Token tokenAfterMetadata) {
    // Find the dartdoc tokens
    var dartdoc = parser.findDartDoc(tokenAfterMetadata);
    if (dartdoc == null) {
      if (metadata == null) {
        return null;
      }
      int index = metadata.length;
      while (true) {
        if (index == 0) {
          return null;
        }
        --index;
        dartdoc = parser.findDartDoc(metadata[index].beginToken);
        if (dartdoc != null) {
          break;
        }
      }
    }

    // Build and return the comment
    var references = parseCommentReferences(dartdoc);
    List<Token> tokens = <Token>[dartdoc];
    if (dartdoc.lexeme.startsWith('///')) {
      dartdoc = dartdoc.next;
      while (dartdoc != null) {
        if (dartdoc.lexeme.startsWith('///')) {
          tokens.add(dartdoc);
        }
        dartdoc = dartdoc.next;
      }
    }
    return CommentImpl(
      tokens: tokens,
      type: CommentType.DOCUMENTATION,
      references: references,
    );
  }

  void _handleInstanceCreation(Token? token) {
    var arguments = pop() as MethodInvocationImpl;
    ConstructorNameImpl constructorName;
    TypeArgumentListImpl? typeArguments;
    var object = pop();
    if (object is _ConstructorNameWithInvalidTypeArgs) {
      constructorName = object.name;
      typeArguments = object.invalidTypeArgs;
    } else {
      constructorName = object as ConstructorNameImpl;
    }
    push(
      InstanceCreationExpressionImpl(
        keyword: token,
        constructorName: constructorName,
        argumentList: arguments.argumentList,
        typeArguments: typeArguments,
      ),
    );
  }

  List<NamedTypeImpl> _popNamedTypeList({
    required ErrorCode errorCode,
  }) {
    final types = pop() as List<TypeAnnotationImpl>;
    final namedTypes = <NamedTypeImpl>[];
    for (final type in types) {
      if (type is NamedTypeImpl) {
        namedTypes.add(type);
      } else {
        errorReporter.errorReporter?.reportErrorForNode(errorCode, type);
      }
    }
    return namedTypes;
  }

  void _reportFeatureNotEnabled({
    required ExperimentalFeature feature,
    required Token startToken,
    Token? endToken,
  }) {
    final requiredVersion =
        feature.releaseVersion ?? ExperimentStatus.currentVersion;
    handleRecoverableError(
      templateExperimentNotEnabled.withArguments(
        feature.enableString,
        _versionAsString(requiredVersion),
      ),
      startToken,
      endToken ?? startToken,
    );
  }

  ArgumentListImpl _syntheticArgumentList(Token precedingToken) {
    var syntheticOffset = precedingToken.end;
    var left = SyntheticToken(TokenType.OPEN_PAREN, syntheticOffset)
      ..previous = precedingToken;
    var right = SyntheticToken(TokenType.CLOSE_PAREN, syntheticOffset)
      ..previous = left;
    return ArgumentListImpl(
      leftParenthesis: left,
      arguments: [],
      rightParenthesis: right,
    );
  }

  SimpleIdentifierImpl _tmpSimpleIdentifier() {
    return ast.simpleIdentifier(
      StringToken(TokenType.STRING, '__tmp', -1),
    );
  }

  ParameterKind _toAnalyzerParameterKind(FormalParameterKind type) {
    switch (type) {
      case FormalParameterKind.requiredPositional:
        return ParameterKind.REQUIRED;
      case FormalParameterKind.requiredNamed:
        return ParameterKind.NAMED_REQUIRED;
      case FormalParameterKind.optionalNamed:
        return ParameterKind.NAMED;
      case FormalParameterKind.optionalPositional:
        return ParameterKind.POSITIONAL;
    }
  }

  static String _versionAsString(Version version) {
    return '${version.major}.${version.minor}.${version.patch}';
  }
}

class _ClassDeclarationBuilder extends _ClassLikeDeclarationBuilder {
  final Token? abstractKeyword;
  final Token? macroKeyword;
  final Token? inlineKeyword;
  final Token? sealedKeyword;
  final Token? baseKeyword;
  final Token? interfaceKeyword;
  final Token? finalKeyword;
  final Token? augmentKeyword;
  final Token? mixinKeyword;
  final Token classKeyword;
  final Token name;
  ExtendsClauseImpl? extendsClause;
  WithClauseImpl? withClause;
  ImplementsClauseImpl? implementsClause;
  final NativeClauseImpl? nativeClause;

  _ClassDeclarationBuilder({
    required super.comment,
    required super.metadata,
    required super.typeParameters,
    required super.leftBracket,
    required super.rightBracket,
    required this.abstractKeyword,
    required this.macroKeyword,
    required this.inlineKeyword,
    required this.sealedKeyword,
    required this.baseKeyword,
    required this.interfaceKeyword,
    required this.finalKeyword,
    required this.augmentKeyword,
    required this.mixinKeyword,
    required this.classKeyword,
    required this.name,
    required this.extendsClause,
    required this.withClause,
    required this.implementsClause,
    required this.nativeClause,
  });

  ClassDeclarationImpl build() {
    return ClassDeclarationImpl(
      comment: comment,
      metadata: metadata,
      abstractKeyword: abstractKeyword,
      macroKeyword: macroKeyword,
      inlineKeyword: inlineKeyword,
      sealedKeyword: sealedKeyword,
      baseKeyword: baseKeyword,
      interfaceKeyword: interfaceKeyword,
      finalKeyword: finalKeyword,
      augmentKeyword: augmentKeyword,
      mixinKeyword: mixinKeyword,
      classKeyword: classKeyword,
      name: name,
      typeParameters: typeParameters,
      extendsClause: extendsClause,
      withClause: withClause,
      implementsClause: implementsClause,
      nativeClause: nativeClause,
      leftBracket: leftBracket,
      members: members,
      rightBracket: rightBracket,
    );
  }
}

class _ClassLikeDeclarationBuilder {
  final CommentImpl? comment;
  final List<AnnotationImpl>? metadata;
  final TypeParameterListImpl? typeParameters;

  Token leftBracket;
  final List<ClassMemberImpl> members = [];
  Token rightBracket;

  _ClassLikeDeclarationBuilder({
    required this.comment,
    required this.metadata,
    required this.typeParameters,
    required this.leftBracket,
    required this.rightBracket,
  });
}

class _ConstructorNameWithInvalidTypeArgs {
  final ConstructorNameImpl name;
  final TypeArgumentListImpl invalidTypeArgs;

  _ConstructorNameWithInvalidTypeArgs(this.name, this.invalidTypeArgs);
}

class _EnumDeclarationBuilder extends _ClassLikeDeclarationBuilder {
  final Token enumKeyword;
  final Token name;
  final WithClauseImpl? withClause;
  final ImplementsClauseImpl? implementsClause;
  final List<EnumConstantDeclarationImpl> constants = [];
  Token? semicolon;

  _EnumDeclarationBuilder({
    required super.comment,
    required super.metadata,
    required super.typeParameters,
    required super.leftBracket,
    required super.rightBracket,
    required this.enumKeyword,
    required this.name,
    required this.withClause,
    required this.implementsClause,
    required this.semicolon,
  });

  EnumDeclarationImpl build() {
    return EnumDeclarationImpl(
      comment: comment,
      metadata: metadata,
      enumKeyword: enumKeyword,
      name: name,
      typeParameters: typeParameters,
      withClause: withClause,
      implementsClause: implementsClause,
      leftBracket: leftBracket,
      constants: constants,
      semicolon: semicolon,
      members: members,
      rightBracket: rightBracket,
    );
  }
}

class _ExtensionDeclarationBuilder extends _ClassLikeDeclarationBuilder {
  final Token extensionKeyword;
  final Token? name;

  _ExtensionDeclarationBuilder({
    required super.comment,
    required super.metadata,
    required super.typeParameters,
    required super.leftBracket,
    required super.rightBracket,
    required this.extensionKeyword,
    required this.name,
  });

  ExtensionDeclarationImpl build({
    required Token? typeKeyword,
    required Token onKeyword,
    required TypeAnnotationImpl extendedType,
  }) {
    return ExtensionDeclarationImpl(
      comment: comment,
      metadata: metadata,
      extensionKeyword: extensionKeyword,
      typeKeyword: typeKeyword,
      name: name,
      typeParameters: typeParameters,
      onKeyword: onKeyword,
      extendedType: extendedType,
      leftBracket: leftBracket,
      members: members,
      rightBracket: rightBracket,
    );
  }
}

class _MixinDeclarationBuilder extends _ClassLikeDeclarationBuilder {
  final Token? augmentKeyword;
  final Token? sealedKeyword;
  final Token? baseKeyword;
  final Token? interfaceKeyword;
  final Token? finalKeyword;
  final Token mixinKeyword;
  final Token name;
  OnClauseImpl? onClause;
  ImplementsClauseImpl? implementsClause;

  _MixinDeclarationBuilder({
    required super.comment,
    required super.metadata,
    required super.typeParameters,
    required super.leftBracket,
    required super.rightBracket,
    required this.augmentKeyword,
    required this.sealedKeyword,
    required this.baseKeyword,
    required this.interfaceKeyword,
    required this.finalKeyword,
    required this.mixinKeyword,
    required this.name,
    required this.onClause,
    required this.implementsClause,
  });

  MixinDeclarationImpl build() {
    return MixinDeclarationImpl(
      comment: comment,
      metadata: metadata,
      augmentKeyword: augmentKeyword,
      sealedKeyword: sealedKeyword,
      baseKeyword: baseKeyword,
      interfaceKeyword: interfaceKeyword,
      finalKeyword: finalKeyword,
      mixinKeyword: mixinKeyword,
      name: name,
      typeParameters: typeParameters,
      onClause: onClause,
      implementsClause: implementsClause,
      leftBracket: leftBracket,
      members: members,
      rightBracket: rightBracket,
    );
  }
}

/// Data structure placed on the stack to represent a non-empty sequence
/// of modifiers.
class _Modifiers {
  Token? abstractKeyword;
  Token? augmentKeyword;
  Token? externalKeyword;
  Token? finalConstOrVarKeyword;
  Token? staticKeyword;
  Token? covariantKeyword;
  Token? requiredToken;
  Token? lateToken;

  /// Return the token that is lexically first.
  Token? get beginToken {
    Token? firstToken;
    for (Token? token in [
      abstractKeyword,
      externalKeyword,
      finalConstOrVarKeyword,
      staticKeyword,
      covariantKeyword,
      requiredToken,
      lateToken,
    ]) {
      if (firstToken == null) {
        firstToken = token;
      } else if (token != null) {
        if (token.offset < firstToken.offset) {
          firstToken = token;
        }
      }
    }
    return firstToken;
  }

  /// Return the `const` keyword or `null`.
  Token? get constKeyword {
    return identical('const', finalConstOrVarKeyword?.lexeme)
        ? finalConstOrVarKeyword
        : null;
  }
}

/// Temporary representation of the fields of an extractor used internally by
/// the [AstBuilder].
class _ObjectPatternFields {
  final Token leftParenthesis;
  final Token rightParenthesis;
  final List<PatternFieldImpl> fields;

  _ObjectPatternFields(
      this.leftParenthesis, this.rightParenthesis, this.fields);
}

/// Data structure placed on the stack to represent the keyword "operator"
/// followed by a token.
class _OperatorName {
  final Token operatorKeyword;
  final SimpleIdentifierImpl name;

  _OperatorName(this.operatorKeyword, this.name);
}

/// Data structure placed on the stack as a container for optional parameters.
class _OptionalFormalParameters {
  final List<FormalParameterImpl>? parameters;
  final Token leftDelimiter;
  final Token rightDelimiter;

  _OptionalFormalParameters(
      this.parameters, this.leftDelimiter, this.rightDelimiter);
}

/// Data structure placed on the stack to represent the default parameter
/// value with the separator token.
class _ParameterDefaultValue {
  final Token separator;
  final ExpressionImpl value;

  _ParameterDefaultValue(this.separator, this.value);
}

/// Data structure placed on the stack to represent the parenthesized condition
/// part of an if-statement, if-control-flow, switch-statement, while-statement,
/// or do-while-statement.
class _ParenthesizedCondition {
  final Token leftParenthesis;
  final ExpressionImpl expression;
  final CaseClauseImpl? caseClause;

  _ParenthesizedCondition(
      this.leftParenthesis, this.expression, this.caseClause);

  Token get rightParenthesis => leftParenthesis.endGroup!;
}

/// Data structure placed on stack to represent the redirected constructor.
class _RedirectingFactoryBody {
  final Token? asyncKeyword;
  final Token? starKeyword;
  final Token equalToken;
  final ConstructorNameImpl constructorName;

  _RedirectingFactoryBody(this.asyncKeyword, this.starKeyword, this.equalToken,
      this.constructorName);
}