// 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,
        messageAbstractClassMember,
        messageAbstractLateField,
        messageAbstractStaticField,
        messageConstConstructorWithBody,
        messageConstFactory,
        messageConstructorWithTypeParameters,
        messageDirectiveAfterDeclaration,
        messageExpectedStatement,
        messageExternalField,
        messageExternalLateField,
        messageFieldInitializerOutsideConstructor,
        messageIllegalAssignmentToNonAssignable,
        messageInterpolationInUri,
        messageInvalidInitializer,
        messageInvalidSuperInInitializer,
        messageInvalidThisInInitializer,
        messageMissingAssignableSelector,
        messageNativeClauseShouldBeAnnotation,
        messageOperatorWithTypeParameters,
        messagePositionalAfterNamedArgument,
        templateDuplicateLabelInSwitchStatement,
        templateExpectedButGot,
        templateExpectedIdentifier,
        templateExperimentNotEnabled,
        templateExtraneousModifier,
        templateInternalProblemUnhandled,
        templateUnexpectedToken;
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 NullValue, StackListener;
import 'package:_fe_analyzer_shared/src/scanner/errors.dart'
    show translateErrorToken;
import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' hide StringToken;
import 'package:_fe_analyzer_shared/src/scanner/token.dart'
    show KeywordToken, StringToken, SyntheticStringToken, SyntheticToken;
import 'package:_fe_analyzer_shared/src/scanner/token_constants.dart';
import 'package:analyzer/dart/analysis/features.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/src/dart/analysis/experiments.dart';
import 'package:analyzer/src/dart/ast/ast.dart'
    show
        ClassDeclarationImpl,
        CompilationUnitImpl,
        ConstructorNameImpl,
        EnumConstantArgumentsImpl,
        ConstructorSelectorImpl,
        EnumConstantDeclarationImpl,
        EnumDeclarationImpl,
        ExtensionDeclarationImpl,
        ImportDirectiveImpl,
        MethodInvocationImpl,
        MixinDeclarationImpl,
        SimpleIdentifierImpl,
        TypeArgumentListImpl,
        TypeParameterImpl;
import 'package:analyzer/src/dart/ast/ast_factory.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';

const _invalidCollectionElement = _InvalidCollectionElement._();

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

  final FastaErrorReporter errorReporter;
  final Uri fileUri;
  ScriptTag? scriptTag;
  final List<Directive> directives = <Directive>[];
  final List<CompilationUnitMember> declarations = <CompilationUnitMember>[];

  @override
  final Uri uri;

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

  /// The class currently being parsed, or `null` if no class is being parsed.
  ClassDeclarationImpl? classDeclaration;

  /// The mixin currently being parsed, or `null` if no mixin is being parsed.
  MixinDeclarationImpl? mixinDeclaration;

  /// The extension currently being parsed, or `null` if none.
  ExtensionDeclarationImpl? extensionDeclaration;

  /// The enum currently being parsed, or `null` if none.
  EnumDeclarationImpl? enumDeclaration;

  /// 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;

  StringLiteral? nativeName;

  bool parseFunctionBodies = true;

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

  /// `true` if spread-collections behavior is enabled
  final bool enableSpreadCollections;

  /// `true` if control-flow-collections behavior is enabled
  final bool enableControlFlowCollections;

  /// `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;

  final FeatureSet _featureSet;

  AstBuilder(ErrorReporter? errorReporter, this.fileUri, this.isFullAst,
      this._featureSet,
      [Uri? uri])
      : errorReporter = FastaErrorReporter(errorReporter),
        enableNonNullable = _featureSet.isEnabled(Feature.non_nullable),
        enableSpreadCollections =
            _featureSet.isEnabled(Feature.spread_collections),
        enableControlFlowCollections =
            _featureSet.isEnabled(Feature.control_flow_collections),
        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),
        uri = uri ?? fileUri;

  NodeList<ClassMember> get currentDeclarationMembers {
    if (classDeclaration != null) {
      return classDeclaration!.members;
    } else if (mixinDeclaration != null) {
      return mixinDeclaration!.members;
    } else if (extensionDeclaration != null) {
      return extensionDeclaration!.members;
    } else {
      return enumDeclaration!.members;
    }
  }

  SimpleIdentifier? get currentDeclarationName {
    if (classDeclaration != null) {
      return classDeclaration!.name;
    } else if (mixinDeclaration != null) {
      return mixinDeclaration!.name;
    } else if (extensionDeclaration != null) {
      return extensionDeclaration!.name;
    } else {
      return enumDeclaration!.name;
    }
  }

  @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 Expression;
    push(token);
    if (expression is CascadeExpression) {
      push(expression);
    } else {
      push(ast.cascadeExpression(expression, <Expression>[]));
    }
    push(NullValue.CascadeReceiver);
  }

  @override
  void beginClassDeclaration(
      Token begin, Token? abstractToken, Token? macroToken, Token name) {
    assert(classDeclaration == null &&
        mixinDeclaration == null &&
        extensionDeclaration == null);
    push(_Modifiers()..abstractKeyword = abstractToken);
    if (macroToken != null && !enableMacros) {
      var feature = ExperimentalFeatures.macros;
      handleRecoverableError(
          templateExperimentNotEnabled.withArguments(
            feature.enableString,
            _versionAsString(ExperimentStatus.currentVersion),
          ),
          macroToken,
          macroToken);
      // Pretend that 'macro' didn't occur while this feature is incomplete.
      macroToken = null;
    }
    push(macroToken ?? NullValue.Token);
  }

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

  @override
  void beginEnum(Token enumKeyword) {}

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

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

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

    extensionDeclaration = ast.extensionDeclaration(
      comment: comment,
      metadata: metadata,
      extensionKeyword: extensionKeyword,
      typeKeyword: null,
      name: name,
      typeParameters: typeParameters,
      onKeyword: Tokens.on_(),
      extendedType: ast.namedType(
        name: _tmpSimpleIdentifier(),
      ), // extendedType is set in [endExtensionDeclaration]
      showClause: null,
      hideClause: null,
      leftBracket: Tokens.openCurlyBracket(),
      rightBracket: Tokens.closeCurlyBracket(),
      members: [],
    );

    declarations.add(extensionDeclaration!);
  }

  @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 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? externalToken,
      Token? staticToken,
      Token? covariantToken,
      Token? varFinalOrConst,
      Token? getOrSet,
      Token name) {
    _Modifiers modifiers = _Modifiers();
    if (externalToken != null) {
      assert(externalToken.isModifier);
      modifiers.externalKeyword = externalToken;
    }
    if (staticToken != null) {
      assert(staticToken.isModifier);
      String? className = currentDeclarationName?.name;
      if (name.lexeme != className || 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 mixinKeyword, Token name) {
    assert(classDeclaration == null &&
        mixinDeclaration == null &&
        extensionDeclaration == null);
  }

  @override
  void beginNamedMixinApplication(
      Token begin, Token? abstractToken, Token? macroToken, Token name) {
    push(_Modifiers()..abstractKeyword = abstractToken);
    if (macroToken != null && !enableMacros) {
      var feature = ExperimentalFeatures.macros;
      handleRecoverableError(
          templateExperimentNotEnabled.withArguments(
            feature.enableString,
            _versionAsString(ExperimentStatus.currentVersion),
          ),
          macroToken,
          macroToken);
      // Pretend that 'macro' didn't occur while this feature is incomplete.
      macroToken = null;
    }
    push(macroToken ?? NullValue.Token);
  }

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

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

    var comment = _findComment(metadata, name.beginToken);
    var typeParameter = ast.typeParameter(comment, metadata, name, null, 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(NullValue.Modifiers);
    }
  }

  ConstructorInitializer? buildInitializer(Object initializerObject) {
    if (initializerObject is FunctionExpressionInvocation) {
      Expression function = initializerObject.function;
      if (function is SuperExpression) {
        return ast.superConstructorInvocation(
            function.superKeyword, null, null, initializerObject.argumentList);
      }
      if (function is ThisExpression) {
        return ast.redirectingConstructorInvocation(
            function.thisKeyword, null, null, initializerObject.argumentList);
      }
      return null;
    }

    if (initializerObject is MethodInvocation) {
      var target = initializerObject.target;
      if (target is SuperExpression) {
        return ast.superConstructorInvocation(
            target.superKeyword,
            initializerObject.operator,
            initializerObject.methodName,
            initializerObject.argumentList);
      }
      if (target is ThisExpression) {
        return ast.redirectingConstructorInvocation(
            target.thisKeyword,
            initializerObject.operator,
            initializerObject.methodName,
            initializerObject.argumentList);
      }
      return buildInitializerTargetExpressionRecovery(
          target, initializerObject);
    }

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

    if (initializerObject is AssignmentExpression) {
      Token? thisKeyword;
      Token? period;
      SimpleIdentifier fieldName;
      Expression left = initializerObject.leftHandSide;
      if (left is PropertyAccess) {
        var target = left.target;
        if (target is ThisExpression) {
          thisKeyword = target.thisKeyword;
          period = left.operator;
        } else {
          assert(target is SuperExpression);
          // Recovery:
          // Parser has reported FieldInitializedOutsideDeclaringClass.
        }
        fieldName = left.propertyName;
      } else if (left is SimpleIdentifier) {
        fieldName = left;
      } else {
        // Recovery:
        // Parser has reported invalid assignment.
        var superExpression = left as SuperExpression;
        fieldName = ast.simpleIdentifier(superExpression.superKeyword);
      }
      return ast.constructorFieldInitializer(thisKeyword, period, fieldName,
          initializerObject.operator, initializerObject.rightHandSide);
    }

    if (initializerObject is AssertInitializer) {
      return initializerObject;
    }

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

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

    return null;
  }

  ConstructorInitializer? buildInitializerTargetExpressionRecovery(
      Expression? target, Object initializerObject) {
    ArgumentList? argumentList;
    while (true) {
      if (target is FunctionExpressionInvocation) {
        argumentList = target.argumentList;
        target = target.function;
      } else if (target is MethodInvocation) {
        argumentList = target.argumentList;
        target = target.target;
      } else if (target is PropertyAccess) {
        argumentList = null;
        target = target.target;
      } else {
        break;
      }
    }
    if (target is SuperExpression) {
      // 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 ast.superConstructorInvocation(target.superKeyword, null, null,
          argumentList ?? _syntheticArgumentList(target.superKeyword));
    } else if (target is ThisExpression) {
      // 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 ast.redirectingConstructorInvocation(target.thisKeyword, null,
          null, argumentList ?? _syntheticArgumentList(target.thisKeyword));
    }
    return null;
  }

  void checkFieldFormalParameters(FormalParameterList? parameterList) {
    var parameters = parameterList?.parameters;
    if (parameters != null) {
      parameters.forEach((FormalParameter param) {
        if (param is FieldFormalParameter) {
          // This error is reported in the BodyBuilder.endFormalParameter.
          handleRecoverableError(messageFieldInitializerOutsideConstructor,
              param.thisKeyword, param.thisKeyword);
        }
      });
    }
  }

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

  void doDotExpression(Token dot) {
    var identifierOrInvoke = pop() as Expression;
    var receiver = pop() as Expression?;
    if (identifierOrInvoke is SimpleIdentifier) {
      if (receiver is SimpleIdentifier && identical('.', dot.stringValue)) {
        push(ast.prefixedIdentifier(receiver, dot, identifierOrInvoke));
      } else {
        push(ast.propertyAccess(receiver, dot, 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);
      SimpleIdentifier identifier =
          ast.simpleIdentifier(token, isDeclaration: false);
      push(ast.propertyAccess(receiver, dot, identifier));
    }
  }

  void doInvocation(
      TypeArgumentList? typeArguments, MethodInvocationImpl arguments) {
    var receiver = pop() as Expression;
    if (receiver is SimpleIdentifierImpl) {
      arguments.methodName = receiver;
      if (typeArguments != null) {
        arguments.typeArguments = typeArguments;
      }
      push(arguments);
    } else {
      push(ast.functionExpressionInvocation(
          receiver, typeArguments, arguments.argumentList));
    }
  }

  void doPropertyGet() {}

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

    var expressions = popTypedList2<Expression>(count);
    ArgumentList arguments =
        ast.argumentList(leftParenthesis, expressions, rightParenthesis);

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

    push(ast.methodInvocation(
        null, null, _tmpSimpleIdentifier(), null, 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 Expression?;
    var condition = pop() as Expression;
    switch (kind) {
      case Assert.Expression:
        // The parser has already reported an error indicating that assert
        // cannot be used in an expression. Insert a placeholder.
        List<Expression> arguments = <Expression>[condition];
        if (message != null) {
          arguments.add(message);
        }
        push(ast.functionExpressionInvocation(
            ast.simpleIdentifier(assertKeyword),
            null,
            ast.argumentList(
                leftParenthesis, arguments, leftParenthesis.endGroup!)));
        break;
      case Assert.Initializer:
        push(ast.assertInitializer(assertKeyword, leftParenthesis, condition,
            comma, message, leftParenthesis.endGroup!));
        break;
      case Assert.Statement:
        push(ast.assertStatement(assertKeyword, leftParenthesis, condition,
            comma, message, leftParenthesis.endGroup!, semicolon));
        break;
    }
  }

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

    var expression = pop() as Expression;
    push(ast.awaitExpression(awaitKeyword, 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 Expression;
      var left = pop() as Expression;
      reportErrorIfSuper(right);
      push(ast.binaryExpression(left, operatorToken, right));
      if (!enableTripleShift && operatorToken.type == TokenType.GT_GT_GT) {
        var feature = ExperimentalFeatures.triple_shift;
        handleRecoverableError(
          templateExperimentNotEnabled.withArguments(
            feature.enableString,
            _versionAsString(ExperimentStatus.currentVersion),
          ),
          operatorToken,
          operatorToken,
        );
      }
    }
  }

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

    var statements = popTypedList2<Statement>(count);
    push(ast.block(leftBracket, statements, rightBracket));
  }

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

    var statements = popTypedList2<Statement>(count);
    Block block = ast.block(leftBracket, statements, rightBracket);
    var star = pop() as Token?;
    var asyncKeyword = pop() as Token?;
    if (parseFunctionBodies) {
      push(ast.blockFunctionBody(asyncKeyword, star, block));
    } else {
      // TODO(danrubel): Skip the block rather than parsing it.
      push(ast.emptyFunctionBody(
          SyntheticToken(TokenType.SEMICOLON, leftBracket.charOffset)));
    }
  }

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

    var expression = pop() as Expression;
    var receiver = pop() as CascadeExpression;
    pop(); // Token.
    receiver.cascadeSections.add(expression);
    push(receiver);
  }

  @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<ConstructorInitializer>?) ?? const [];
    var separator = pop() as Token?;
    var parameters = pop() as FormalParameterList;
    var typeParameters = pop() as TypeParameterList?;
    var name = pop();
    pop(); // return type
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, beginToken);

    ConstructorName? redirectedConstructor;
    FunctionBody body;
    if (bodyObject is FunctionBody) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      separator = bodyObject.equalToken;
      redirectedConstructor = bodyObject.constructorName;
      body = ast.emptyFunctionBody(endToken);
    } else {
      internalProblem(
          templateInternalProblemUnhandled.withArguments(
              "${bodyObject.runtimeType}", "bodyObject"),
          beginToken.charOffset,
          uri);
    }

    SimpleIdentifier prefixOrName;
    Token? period;
    SimpleIdentifier? nameOrNull;
    if (name is SimpleIdentifier) {
      prefixOrName = name;
    } else if (name is PrefixedIdentifier) {
      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);
    }
    ConstructorDeclaration constructor = ast.constructorDeclaration(
        comment,
        metadata,
        modifiers?.externalKeyword,
        modifiers?.finalConstOrVarKeyword,
        null,
        // TODO(paulberry): factoryKeyword
        ast.simpleIdentifier(prefixOrName.token),
        period,
        nameOrNull,
        parameters,
        separator,
        initializers,
        redirectedConstructor,
        body);
    currentDeclarationMembers.add(constructor);
    if (mixinDeclaration != null) {
      // TODO (danrubel): Report an error if this is a mixin declaration.
    }
  }

  @override
  void endClassDeclaration(Token beginToken, Token endToken) {
    debugEvent("ClassDeclaration");
    classDeclaration = null;
  }

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

    FunctionBody body;
    Token? separator;
    ConstructorName? redirectedConstructor;
    var bodyObject = pop();
    if (bodyObject is FunctionBody) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      separator = bodyObject.equalToken;
      redirectedConstructor = bodyObject.constructorName;
      body = ast.emptyFunctionBody(endToken);
    } else {
      internalProblem(
          templateInternalProblemUnhandled.withArguments(
              "${bodyObject.runtimeType}", "bodyObject"),
          beginToken.charOffset,
          uri);
    }

    var parameters = pop() as FormalParameterList;
    var typeParameters = pop() as TypeParameterList?;
    var constructorName = pop() as Identifier;
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<Annotation>?;
    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.
    SimpleIdentifier returnType;
    Token? period;
    SimpleIdentifier? name;
    Identifier typeName = constructorName;
    if (typeName is SimpleIdentifier) {
      returnType = typeName;
    } else if (typeName is PrefixedIdentifier) {
      returnType = typeName.prefix;
      period = typeName.period;
      name =
          ast.simpleIdentifier(typeName.identifier.token, isDeclaration: true);
    } else {
      throw UnimplementedError();
    }

    currentDeclarationMembers.add(ast.constructorDeclaration(
        comment,
        metadata,
        modifiers?.externalKeyword,
        modifiers?.finalConstOrVarKeyword,
        factoryKeyword,
        ast.simpleIdentifier(returnType.token),
        period,
        name,
        parameters,
        separator,
        null,
        redirectedConstructor,
        body));
  }

  @override
  void endClassFields(
      Token? abstractToken,
      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<VariableDeclaration>(count);
    var type = pop() as TypeAnnotation?;
    var variableList = ast.variableDeclarationList2(
      lateKeyword: lateToken,
      keyword: varFinalOrConst,
      type: type,
      variables: variables,
    );
    var covariantKeyword = covariantToken;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, beginToken);
    currentDeclarationMembers.add(ast.fieldDeclaration2(
        comment: comment,
        metadata: metadata,
        abstractKeyword: abstractToken,
        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 FormalParameterList?;
    var typeParameters = pop() as TypeParameterList?;
    var name = pop();
    var returnType = pop() as TypeAnnotation?;
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, beginToken);

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

    FunctionBody body;
    if (bodyObject is FunctionBody) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      body = ast.emptyFunctionBody(endToken);
    } else {
      internalProblem(
          templateInternalProblemUnhandled.withArguments(
              "${bodyObject.runtimeType}", "bodyObject"),
          beginToken.charOffset,
          uri);
    }

    Token? operatorKeyword;
    SimpleIdentifier nameId;
    if (name is SimpleIdentifier) {
      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);
    currentDeclarationMembers.add(ast.methodDeclaration(
        comment,
        metadata,
        modifiers?.externalKeyword,
        modifiers?.abstractKeyword ?? modifiers?.staticKeyword,
        returnType,
        getOrSet,
        operatorKeyword,
        nameId,
        typeParameters,
        parameters,
        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");

    if (classDeclaration != null) {
      classDeclaration!
        ..leftBracket = leftBracket
        ..rightBracket = rightBracket;
    } else if (mixinDeclaration != null) {
      mixinDeclaration!
        ..leftBracket = leftBracket
        ..rightBracket = rightBracket;
    } else {
      extensionDeclaration!
        ..leftBracket = leftBracket
        ..rightBracket = rightBracket;
    }
  }

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

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

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

    CompilationUnitImpl unit = ast.compilationUnit(
        beginToken: beginToken,
        scriptTag: scriptTag,
        directives: directives,
        declarations: declarations,
        endToken: endToken,
        featureSet: _featureSet);
    push(unit);
  }

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

    var elseExpression = pop() as Expression;
    var thenExpression = pop() as Expression;
    var condition = pop() as Expression;
    reportErrorIfSuper(elseExpression);
    reportErrorIfSuper(thenExpression);
    push(ast.conditionalExpression(
        condition, question, thenExpression, colon, 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 StringLiteral;
    var value = popIfNotNull(equalSign) as StringLiteral?;
    if (value is StringInterpolation) {
      for (var child in value.childEntities) {
        if (child is InterpolationExpression) {
          // This error is reported in OutlineBuilder.endLiteralString
          handleRecoverableError(
              messageInterpolationInUri, child.beginToken, child.endToken);
          break;
        }
      }
    }
    var name = pop() as DottedName;
    push(ast.configuration(ifKeyword, leftParen, name, equalSign, value,
        leftParen.endGroup!, libraryUri));
  }

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

    push(popTypedList<Configuration>(count) ?? NullValue.ConditionalUris);
  }

  @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 SimpleIdentifier?;
    var typeArguments = pop() as TypeArgumentList?;
    var typeNameIdentifier = pop() as Identifier;
    push(
      ast.constructorName(
        ast.namedType(
          name: typeNameIdentifier,
          typeArguments: typeArguments,
        ),
        periodBeforeName,
        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 ParenthesizedExpression;
    var body = pop() as Statement;
    push(ast.doStatement(
        doKeyword,
        body,
        whileKeyword,
        condition.leftParenthesis,
        condition.expression,
        condition.rightParenthesis,
        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");
  }

  @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<Combinator>?;
    var configurations = pop() as List<Configuration>?;
    var uri = pop() as StringLiteral;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, exportKeyword);
    directives.add(ast.exportDirective(comment, metadata, exportKeyword, uri,
        configurations, combinators, 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) {
    if (typeKeyword != null && !enableExtensionTypes) {
      var feature = ExperimentalFeatures.extension_types;
      handleRecoverableError(
          templateExperimentNotEnabled.withArguments(
            feature.enableString,
            _versionAsString(ExperimentStatus.currentVersion),
          ),
          typeKeyword,
          typeKeyword);
    }

    if ((showKeyword != null || hideKeyword != null) && !enableExtensionTypes) {
      var feature = ExperimentalFeatures.extension_types;
      handleRecoverableError(
          templateExperimentNotEnabled.withArguments(
            feature.enableString,
            _versionAsString(ExperimentStatus.currentVersion),
          ),
          (showKeyword ?? hideKeyword)!,
          (showKeyword ?? hideKeyword)!);
    }

    ShowClause? showClause = pop(NullValue.ShowClause) as ShowClause?;
    HideClause? hideClause = pop(NullValue.HideClause) as HideClause?;

    var type = pop() as TypeAnnotation;

    extensionDeclaration!
      ..extendedType = type
      ..onKeyword = onKeyword
      ..typeKeyword = typeKeyword
      ..showClause = showClause
      ..hideClause = hideClause;
    extensionDeclaration = 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 FormalParameterList;
    var typeParameters = pop() as TypeParameterList?;
    var constructorName = pop();
    var modifiers = pop() as _Modifiers?;
    var metadata = pop() as List<Annotation>?;

    FunctionBody body;
    if (bodyObject is FunctionBody) {
      body = bodyObject;
    } else if (bodyObject is _RedirectingFactoryBody) {
      body = ast.emptyFunctionBody(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.

    SimpleIdentifier methodName;
    if (constructorName is SimpleIdentifier) {
      methodName = constructorName;
    } else if (constructorName is PrefixedIdentifier) {
      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;
    }
    currentDeclarationMembers.add(ast.methodDeclaration(
        comment,
        metadata,
        modifiers?.externalKeyword,
        modifiers?.abstractKeyword ?? modifiers?.staticKeyword,
        null, // returnType
        null, // getOrSet
        null, // operatorKeyword
        methodName,
        typeParameters,
        parameters,
        body));
  }

  @override
  void endExtensionFields(
      Token? abstractToken,
      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, 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 assignment, Token token) {
    assert(optional('=', assignment));
    debugEvent("FieldInitializer");

    var initializer = pop() as Expression;
    var name = pop() as SimpleIdentifier;
    push(_makeVariableDeclaration(name, assignment, initializer));
  }

  @override
  void endForControlFlow(Token token) {
    debugEvent("endForControlFlow");
    var entry = pop() as Object;
    var forLoopParts = pop() as ForParts;
    var leftParen = pop() as Token;
    var forToken = pop() as Token;

    pushForControlFlowInfo(null, forToken, leftParen, forLoopParts, entry);
  }

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

    var body = pop() as Statement;
    var forLoopParts = pop() as ForEachParts;
    var leftParenthesis = pop() as Token;
    var forToken = pop() as Token;
    var awaitToken = pop(NullValue.AwaitToken) as Token?;

    push(ast.forStatement(
      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 entry = pop() as Object;
    var forLoopParts = pop() as ForEachParts;
    var leftParenthesis = pop() as Token;
    var forToken = pop() as Token;
    var awaitToken = pop(NullValue.AwaitToken) as Token?;

    pushForControlFlowInfo(
        awaitToken, forToken, leftParenthesis, forLoopParts, entry);
  }

  @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) {
      var feature = ExperimentalFeatures.super_parameters;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(ExperimentStatus.currentVersion),
        ),
        superKeyword,
        superKeyword,
      );
    }

    var defaultValue = pop() as _ParameterDefaultValue?;
    var name = pop() as SimpleIdentifier?;
    var typeOrFunctionTypedParameter = pop() as AstNode?;
    var modifiers = pop() as _Modifiers?;
    var keyword = modifiers?.finalConstOrVarKeyword;
    var covariantKeyword = modifiers?.covariantKeyword;
    var requiredKeyword = modifiers?.requiredToken;
    if (!enableNonNullable) {
      reportNonNullableModifierError(requiredKeyword);
    }
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata,
        thisKeyword ?? typeOrFunctionTypedParameter?.beginToken ?? nameToken);

    NormalFormalParameter node;
    if (typeOrFunctionTypedParameter is FunctionTypedFormalParameter) {
      // 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 = ast.superFormalParameter(
            identifier: name!,
            comment: comment,
            metadata: metadata,
            covariantKeyword: covariantKeyword,
            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 = ast.fieldFormalParameter2(
            identifier: name!,
            comment: comment,
            metadata: metadata,
            covariantKeyword: covariantKeyword,
            requiredKeyword: requiredKeyword,
            type: typeOrFunctionTypedParameter.returnType,
            thisKeyword: thisKeyword,
            period: periodAfterThisOrSuper!,
            typeParameters: typeOrFunctionTypedParameter.typeParameters,
            parameters: typeOrFunctionTypedParameter.parameters,
            question: typeOrFunctionTypedParameter.question);
      } else {
        node = ast.functionTypedFormalParameter2(
            identifier: name!,
            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 TypeAnnotation?;
      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 = ast.superFormalParameter(
            comment: comment,
            metadata: metadata,
            covariantKeyword: covariantKeyword,
            requiredKeyword: requiredKeyword,
            keyword: keyword,
            type: type,
            superKeyword: superKeyword,
            period: periodAfterThisOrSuper!,
            identifier: name!);
      } else if (thisKeyword != null) {
        assert(superKeyword == null,
            "Can't have both 'this' and 'super' in a parameter.");
        node = ast.fieldFormalParameter2(
            comment: comment,
            metadata: metadata,
            covariantKeyword: covariantKeyword,
            requiredKeyword: requiredKeyword,
            keyword: keyword,
            type: type,
            thisKeyword: thisKeyword,
            period: thisKeyword.next!,
            identifier: name!);
      } else {
        node = ast.simpleFormalParameter2(
            comment: comment,
            metadata: metadata,
            covariantKeyword: covariantKeyword,
            requiredKeyword: requiredKeyword,
            keyword: keyword,
            type: type,
            identifier: name);
      }
    }

    ParameterKind analyzerKind =
        _toAnalyzerParameterKind(kind, requiredKeyword);
    FormalParameter parameter = node;
    if (analyzerKind != ParameterKind.REQUIRED) {
      parameter = ast.defaultFormalParameter(
          node, analyzerKind, defaultValue?.separator, 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 = ast.defaultFormalParameter(node, ParameterKind.NAMED,
          defaultValue.separator, defaultValue.value);
    }
    push(parameter);
  }

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

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

    var rawParameters = popTypedList(count) ?? const <Object>[];
    List<FormalParameter> parameters = <FormalParameter>[];
    Token? leftDelimiter;
    Token? rightDelimiter;
    for (Object raw in rawParameters) {
      if (raw is _OptionalFormalParameters) {
        parameters.addAll(raw.parameters ?? const <FormalParameter>[]);
        leftDelimiter = raw.leftDelimiter;
        rightDelimiter = raw.rightDelimiter;
      } else {
        parameters.add(raw as FormalParameter);
      }
    }
    push(ast.formalParameterList(
        leftParen, parameters, leftDelimiter, rightDelimiter, rightParen));
  }

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

    push(ast.forStatement(
      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 FunctionBody;
    var parameters = pop() as FormalParameterList?;
    var typeParameters = pop() as TypeParameterList?;
    push(ast.functionExpression(typeParameters, parameters, 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 FormalParameterList;
    var returnType = pop() as TypeAnnotation?;
    var typeParameters = pop() as TypeParameterList?;
    push(ast.genericFunctionType(
        returnType, functionToken, typeParameters, parameters,
        question: questionMark));
  }

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

    var formalParameters = pop() as FormalParameterList;
    var returnType = pop() as TypeAnnotation?;
    var typeParameters = pop() as TypeParameterList?;

    // Create a temporary formal parameter that will be dissected later in
    // [endFormalParameter].
    push(ast.functionTypedFormalParameter2(
        identifier: ast.simpleIdentifier(
          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<SimpleIdentifier>;
    push(ast.hideCombinator(hideKeyword, hiddenNames));
  }

  @override
  void endIfControlFlow(Token token) {
    var thenElement = pop() as CollectionElement;
    var condition = pop() as ParenthesizedExpression;
    var ifToken = pop() as Token;
    pushIfControlFlowInfo(ifToken, condition, thenElement, null, null);
  }

  @override
  void endIfElseControlFlow(Token token) {
    var elseElement = pop() as CollectionElement;
    var elseToken = pop() as Token;
    var thenElement = pop() as CollectionElement;
    var condition = pop() as ParenthesizedExpression;
    var ifToken = pop() as Token;
    pushIfControlFlowInfo(
        ifToken, condition, thenElement, elseToken, elseElement);
  }

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

    var elsePart = popIfNotNull(elseToken) as Statement?;
    var thenPart = pop() as Statement;
    var condition = pop() as ParenthesizedExpression;
    push(ast.ifStatement(
        ifToken,
        condition.leftParenthesis,
        condition.expression,
        condition.rightParenthesis,
        thenPart,
        elseToken,
        elsePart));
  }

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

    _handleInstanceCreation(null);
  }

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

    var combinators = pop() as List<Combinator>?;
    var deferredKeyword = pop(NullValue.Deferred) as Token?;
    var asKeyword = pop(NullValue.As) as Token?;
    var prefix = pop(NullValue.Prefix) as SimpleIdentifier?;
    var configurations = pop() as List<Configuration>?;
    var uri = pop() as StringLiteral;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, importKeyword);

    directives.add(ast.importDirective(
        comment,
        metadata,
        importKeyword,
        uri,
        configurations,
        deferredKeyword,
        asKeyword,
        prefix,
        combinators,
        semicolon ?? Tokens.semicolon()));
  }

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

    var node = pop() as AstNode?;
    VariableDeclaration 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 VariableDeclaration) {
      variable = node;
    } else if (node is SimpleIdentifier) {
      variable = _makeVariableDeclaration(node, null, 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 = <ConstructorInitializer>[];
    for (Object initializerObject in initializerObjects) {
      var initializer = buildInitializer(initializerObject);
      if (initializer != null) {
        initializers.add(initializer);
      } else {
        handleRecoverableError(
            messageInvalidInitializer,
            initializerObject is AstNode ? initializerObject.beginToken : colon,
            initializerObject is AstNode ? 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 Statement;
    var labels = popTypedList2<Label>(labelCount);
    push(ast.labeledStatement(labels, statement));
  }

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

    var libraryName = pop() as List<SimpleIdentifier>;
    var name = ast.libraryIdentifier(libraryName);
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, libraryKeyword);
    directives.add(ast.libraryDirective(
        comment, metadata, libraryKeyword, name, 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(ast.simpleStringLiteral(token, 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);
      List<InterpolationElement> elements = <InterpolationElement>[];
      elements.add(ast.interpolationString(
          first, 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(ast.interpolationString(
              part, unescape(part.lexeme, quote, part, this)));
        } else if (part is InterpolationExpression) {
          elements.add(part);
        } else {
          internalProblem(
              templateInternalProblemUnhandled.withArguments(
                  "${part.runtimeType}", "string interpolation"),
              first.charOffset,
              uri);
        }
      }
      elements.add(ast.interpolationString(
          last,
          unescapeLastStringPart(
              last.lexeme, quote, last, last.isSynthetic, this)));
      push(ast.stringInterpolation(elements));
    }
  }

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

    var components = popTypedList2<Token>(tokenCount);
    push(ast.symbolLiteral(hashToken, components));
  }

  @override
  void endLocalFunctionDeclaration(Token token) {
    debugEvent("LocalFunctionDeclaration");
    var body = pop() as FunctionBody;
    if (isFullAst) {
      pop(); // constructor initializers
      pop(); // separator before constructor initializers
    }
    var parameters = pop() as FormalParameterList;
    checkFieldFormalParameters(parameters);
    var name = pop() as SimpleIdentifier;
    var returnType = pop() as TypeAnnotation?;
    var typeParameters = pop() as TypeParameterList?;
    var metadata = pop(NullValue.Metadata) as List<Annotation>?;
    FunctionExpression functionExpression =
        ast.functionExpression(typeParameters, parameters, body);
    var functionDeclaration = ast.functionDeclaration(
        null, metadata, null, returnType, null, name, functionExpression);
    push(ast.functionDeclarationStatement(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 MethodInvocation?;
    var constructorName =
        periodBeforeName != null ? pop() as SimpleIdentifier : null;
    var typeArguments = pop() as TypeArgumentList?;
    if (typeArguments != null &&
        !_featureSet.isEnabled(Feature.generic_metadata)) {
      var feature = Feature.generic_metadata;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(feature.releaseVersion!),
        ),
        typeArguments.beginToken,
        typeArguments.beginToken,
      );
    }
    var name = pop() as Identifier;
    push(ast.annotation(
        atSign: atSign,
        name: name,
        typeArguments: typeArguments,
        period: periodBeforeName,
        constructorName: constructorName,
        arguments: invocation?.argumentList));
  }

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

    push(popTypedList<Annotation>(count) ?? NullValue.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");
    mixinDeclaration = null;
  }

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

  @override
  void endMixinFields(
      Token? abstractToken,
      Token? externalToken,
      Token? staticToken,
      Token? covariantToken,
      Token? lateToken,
      Token? varFinalOrConst,
      int count,
      Token beginToken,
      Token endToken) {
    endClassFields(abstractToken, 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 FunctionBody;
    if (isFullAst) {
      pop(); // constructor initializers
      pop(); // separator before constructor initializers
    }
    var parameters = pop() as FormalParameterList;
    pop(); // name
    pop(); // returnType
    var typeParameters = pop() as TypeParameterList?;
    push(ast.functionExpression(typeParameters, parameters, 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");

    ImplementsClause? implementsClause;
    if (implementsKeyword != null) {
      var interfaces = pop() as List<NamedType>;
      implementsClause = ast.implementsClause(implementsKeyword, interfaces);
    }
    var withClause = pop(NullValue.WithClause) as WithClause;
    var superclass = pop() as NamedType;
    var macroKeyword = pop(NullValue.Token) as Token?;
    var modifiers = pop() as _Modifiers?;
    var typeParameters = pop() as TypeParameterList?;
    var name = pop() as SimpleIdentifier;
    var abstractKeyword = modifiers?.abstractKeyword;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, beginToken);
    declarations.add(ast.classTypeAlias(
        comment,
        metadata,
        classKeyword,
        name,
        typeParameters,
        equalsToken,
        abstractKeyword,
        macroKeyword,
        superclass,
        withClause,
        implementsClause,
        semicolon));
  }

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

    _handleInstanceCreation(newKeyword);
  }

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

    push(_OptionalFormalParameters(
        popTypedList2<FormalParameter>(count), leftDelimeter, rightDelimeter));
  }

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

    var uri = pop() as StringLiteral;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, partKeyword);
    directives
        .add(ast.partDirective(comment, metadata, partKeyword, uri, 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();
    LibraryIdentifier? name;
    StringLiteral? uri;
    if (libraryNameOrUri is StringLiteral) {
      uri = libraryNameOrUri;
    } else {
      name = ast.libraryIdentifier(libraryNameOrUri as List<SimpleIdentifier>);
    }
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, partKeyword);
    directives.add(ast.partOfDirective(
        comment, metadata, partKeyword, ofKeyword, uri, name, semicolon));
  }

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

    var constructorName = pop() as ConstructorName;
    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");

    RethrowExpression expression = ast.rethrowExpression(rethrowToken);
    // TODO(scheglov) According to the specification, 'rethrow' is a statement.
    push(ast.expressionStatement(expression, semicolon));
  }

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

    var expression = hasExpression ? pop() as Expression : null;
    push(ast.returnStatement(returnKeyword, expression, semicolon));
  }

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

    var shownNames = pop() as List<SimpleIdentifier>;
    push(ast.showCombinator(showKeyword, shownNames));
  }

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

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

    Set<String> labels = <String>{};
    for (SwitchMember member in members) {
      for (Label 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<Statement>(statementCount);
    List<SwitchMember?> members;

    if (labelCount == 0 && defaultKeyword == null) {
      // Common situation: case with no default and no labels.
      members = popTypedList2<SwitchMember>(expressionCount);
    } else {
      // Labels and case statements may be intertwined
      if (defaultKeyword != null) {
        SwitchDefault member = ast.switchDefault(
            <Label>[], defaultKeyword, colonAfterDefault!, <Statement>[]);
        while (peek() is Label) {
          member.labels.insert(0, pop() as Label);
          --labelCount;
        }
        members = List<SwitchMember?>.filled(expressionCount + 1, null);
        members[expressionCount] = member;
      } else {
        members = List<SwitchMember?>.filled(expressionCount, null);
      }
      for (int index = expressionCount - 1; index >= 0; --index) {
        var member = pop() as SwitchMember;
        while (peek() is Label) {
          member.labels.insert(0, pop() as Label);
          --labelCount;
        }
        members[index] = member;
      }
      assert(labelCount == 0);
    }
    var members2 = members.whereNotNull().toList();
    if (members2.isNotEmpty) {
      members2.last.statements.addAll(statements);
    }
    push(members2);
  }

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

    var rightBracket = pop() as Token;
    var members = pop() as List<SwitchMember>;
    var leftBracket = pop() as Token;
    var expression = pop() as ParenthesizedExpression;
    push(ast.switchStatement(
        switchKeyword,
        expression.leftParenthesis,
        expression.expression,
        expression.rightParenthesis,
        leftBracket,
        members,
        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<VariableDeclaration>(count);
    var type = pop() as TypeAnnotation?;
    var variableList = ast.variableDeclarationList2(
      lateKeyword: lateToken,
      keyword: varFinalOrConst,
      type: type,
      variables: variables,
    );
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, beginToken);
    declarations.add(ast.topLevelVariableDeclaration(
        comment, metadata, variableList, semicolon,
        externalKeyword: externalToken));
  }

  @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 FunctionBody;
    var parameters = pop() as FormalParameterList?;
    var typeParameters = pop() as TypeParameterList?;
    var name = pop() as SimpleIdentifier;
    var returnType = pop() as TypeAnnotation?;
    var modifiers = pop() as _Modifiers?;
    var externalKeyword = modifiers?.externalKeyword;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, beginToken);
    declarations.add(ast.functionDeclaration(
        comment,
        metadata,
        externalKeyword,
        returnType,
        getOrSet,
        name,
        ast.functionExpression(typeParameters, parameters, 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 Block?;
    var catchClauses = popTypedList2<CatchClause>(catchCount);
    var body = pop() as Block;
    push(ast.tryStatement(
        tryKeyword, body, catchClauses, finallyKeyword, finallyBlock));
  }

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

    var arguments = popTypedList2<TypeAnnotation>(count);
    push(ast.typeArgumentList(leftBracket, arguments, 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 FormalParameterList;
      var typeParameters = pop() as TypeParameterList?;
      var name = pop() as SimpleIdentifier;
      var returnType = pop() as TypeAnnotation?;
      var metadata = pop() as List<Annotation>?;
      var comment = _findComment(metadata, typedefKeyword);
      declarations.add(ast.functionTypeAlias(comment, metadata, typedefKeyword,
          returnType, name, typeParameters, parameters, semicolon));
    } else {
      var type = pop() as TypeAnnotation;
      var templateParameters = pop() as TypeParameterList?;
      var name = pop() as SimpleIdentifier;
      var metadata = pop() as List<Annotation>?;
      var comment = _findComment(metadata, typedefKeyword);
      if (type is! GenericFunctionType && !enableNonFunctionTypeAliases) {
        var feature = Feature.nonfunction_type_aliases;
        handleRecoverableError(
          templateExperimentNotEnabled.withArguments(
            feature.enableString,
            _versionAsString(ExperimentStatus.currentVersion),
          ),
          equals,
          equals,
        );
      }
      declarations.add(ast.genericTypeAlias(comment, metadata, typedefKeyword,
          name, templateParameters, equals, type, semicolon));
    }
  }

  @override
  void endTypeList(int count) {
    debugEvent("TypeList");
    push(popTypedList<NamedType>(count) ?? NullValue.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 TypeAnnotation?;

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

    // TODO (kallentu) : Clean up TypeParameterImpl casting once variance is
    // added to the interface.
    (typeParameters[index] as TypeParameterImpl)
      ..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<TypeParameter>;
    push(ast.typeParameterList(beginToken, typeParameters, endToken));
  }

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

    var initializer = pop() as Expression;
    var identifier = pop() as SimpleIdentifier;
    // TODO(ahe): Don't push initializers, instead install them.
    push(_makeVariableDeclaration(identifier, assignmentOperator, initializer));
  }

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

    var variables = popTypedList2<VariableDeclaration>(count);
    var modifiers = pop(NullValue.Modifiers) as _Modifiers?;
    var type = pop() as TypeAnnotation?;
    var keyword = modifiers?.finalConstOrVarKeyword;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, variables[0].beginToken);
    // var comment = _findComment(metadata,
    //     variables[0].beginToken ?? type?.beginToken ?? modifiers.beginToken);
    push(ast.variableDeclarationStatement(
        ast.variableDeclarationList2(
          comment: comment,
          metadata: metadata,
          lateKeyword: modifiers?.lateToken,
          keyword: keyword,
          type: type,
          variables: variables,
        ),
        semicolon ?? Tokens.semicolon()));
  }

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

    var body = pop() as Statement;
    var condition = pop() as ParenthesizedExpression;
    push(ast.whileStatement(whileKeyword, condition.leftParenthesis,
        condition.expression, condition.rightParenthesis, 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 Expression;
    push(ast.yieldStatement(yieldToken, starToken, expression, semicolon));
  }

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

    var type = pop() as TypeAnnotation;
    var expression = pop() as Expression;
    push(ast.asExpression(expression, asOperator, type));
  }

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

    var rhs = pop() as Expression;
    var lhs = pop() as Expression;
    if (!lhs.isAssignable) {
      // TODO(danrubel): Update the BodyBuilder to report this error.
      handleRecoverableError(
          messageMissingAssignableSelector, lhs.beginToken, lhs.endToken);
    }
    push(ast.assignmentExpression(lhs, token, rhs));
    if (!enableTripleShift && token.type == TokenType.GT_GT_GT_EQ) {
      var feature = ExperimentalFeatures.triple_shift;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(ExperimentStatus.currentVersion),
        ),
        token,
        token,
      );
    }
  }

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

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

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

    var label = hasTarget ? pop() as SimpleIdentifier : null;
    push(ast.breakStatement(breakKeyword, label, semicolon));
  }

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

    var expression = pop() as Expression;
    push(ast.switchCase(
        <Label>[], caseKeyword, expression, colon, <Statement>[]));
  }

  @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 Block;
    var catchParameterList = popIfNotNull(catchKeyword) as FormalParameterList?;
    var type = popIfNotNull(onKeyword) as TypeAnnotation?;
    SimpleIdentifier? exception;
    SimpleIdentifier? stackTrace;
    if (catchParameterList != null) {
      List<FormalParameter> catchParameters = catchParameterList.parameters;
      if (catchParameters.isNotEmpty) {
        exception = catchParameters[0].identifier;
      }
      if (catchParameters.length > 1) {
        stackTrace = catchParameters[1].identifier;
      }
    }
    push(ast.catchClause(
        onKeyword,
        type,
        catchKeyword,
        catchParameterList?.leftParenthesis,
        exception,
        comma,
        stackTrace,
        catchParameterList?.rightParenthesis,
        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 NamedType?;
    if (supertype != null) {
      push(ast.extendsClause(extendsKeyword!, supertype));
    } else {
      push(NullValue.ExtendsClause);
    }
  }

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

    NativeClause? nativeClause;
    if (nativeToken != null) {
      nativeClause = ast.nativeClause(nativeToken, nativeName);
    }
    var implementsClause = pop(NullValue.IdentifierList) as ImplementsClause?;
    var withClause = pop(NullValue.WithClause) as WithClause?;
    var extendsClause = pop(NullValue.ExtendsClause) as ExtendsClause?;
    var macroKeyword = pop(NullValue.Token) as Token?;
    var modifiers = pop() as _Modifiers?;
    var typeParameters = pop() as TypeParameterList?;
    var name = pop() as SimpleIdentifier;
    var abstractKeyword = modifiers?.abstractKeyword;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, begin);
    // leftBracket, members, and rightBracket
    // are set in [endClassOrMixinBody].
    classDeclaration = ast.classDeclaration(
      comment,
      metadata,
      abstractKeyword,
      macroKeyword,
      classKeyword,
      name,
      typeParameters,
      extendsClause,
      withClause,
      implementsClause,
      Tokens.openCurlyBracket(), // leftBracket
      <ClassMember>[],
      Tokens.closeCurlyBracket(), // rightBracket
    );

    classDeclaration!.nativeClause = nativeClause;
    declarations.add(classDeclaration!);
  }

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

  @override
  void handleClassWithClause(Token withKeyword) {
    assert(optional('with', withKeyword));
    var mixinTypes = pop() as List<NamedType>;
    push(ast.withClause(withKeyword, 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 = ast.prefixedIdentifier(ast.simpleIdentifier(firstToken),
          firstPeriod!, ast.simpleIdentifier(secondToken!));
      var expression = ast.propertyAccess(target, secondPeriod!, identifier);
      push(ast.commentReference(newKeyword, expression));
    } else if (secondToken != null) {
      var expression = ast.prefixedIdentifier(
          ast.simpleIdentifier(secondToken), secondPeriod!, identifier);
      push(ast.commentReference(newKeyword, expression));
    } else {
      push(ast.commentReference(newKeyword, 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 SimpleIdentifier : null;
    push(ast.continueStatement(continueKeyword, label, semicolon));
  }

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

    var components = popTypedList2<SimpleIdentifier>(count);
    push(ast.dottedName(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(ast.emptyFunctionBody(semicolon));
  }

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

    push(ast.emptyStatement(semicolon));
  }

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

    if (!enableEnhancedEnums &&
        (tmpArguments != null ||
            tmpConstructor != null &&
                (tmpConstructor.type2.typeArguments != null ||
                    tmpConstructor.name != null))) {
      Token token = tmpArguments != null
          ? tmpArguments.argumentList.beginToken
          : tmpConstructor!.beginToken;
      var feature = ExperimentalFeatures.enhanced_enums;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(ExperimentStatus.currentVersion),
        ),
        token,
        token,
      );
    }

    var constant = pop() as EnumConstantDeclarationImpl;

    // Replace the constant to include arguments.
    if (tmpArguments != null) {
      TypeArgumentListImpl? typeArguments;
      ConstructorSelectorImpl? constructorName;
      if (tmpConstructor != null) {
        typeArguments = tmpConstructor.type2.typeArguments;
        var constructorNamePeriod = tmpConstructor.period;
        var constructorNameId = tmpConstructor.name;
        if (constructorNamePeriod != null && constructorNameId != null) {
          constructorName = ConstructorSelectorImpl(
            period: constructorNamePeriod,
            name: constructorNameId,
          );
        }
      }
      constant = EnumConstantDeclarationImpl(
        documentationComment: constant.documentationComment,
        metadata: constant.metadata,
        name: constant.name,
        arguments: EnumConstantArgumentsImpl(
          typeArguments: typeArguments,
          constructorSelector: constructorName,
          argumentList: tmpArguments.argumentList,
        ),
      );
    }

    push(constant);
  }

  @override
  void handleEnumElements(Token elementsEndToken, int elementsCount) {
    debugEvent("EnumElements");

    var constants = popTypedList2<EnumConstantDeclaration>(elementsCount);
    enumDeclaration!.constants.addAll(constants);

    if (!enableEnhancedEnums && optional(';', elementsEndToken)) {
      var feature = ExperimentalFeatures.enhanced_enums;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(ExperimentStatus.currentVersion),
        ),
        elementsEndToken,
        elementsEndToken,
      );
    }
  }

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

    var implementsClause = pop(NullValue.IdentifierList) as ImplementsClause?;
    var withClause = pop(NullValue.WithClause) as WithClause?;
    var typeParameters = pop() as TypeParameterList?;
    var name = pop() as SimpleIdentifier;
    var metadata = pop() as List<Annotation>?;
    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;
      var feature = ExperimentalFeatures.enhanced_enums;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(ExperimentStatus.currentVersion),
        ),
        token,
        token,
      );
    }

    declarations.add(
      enumDeclaration = ast.enumDeclaration2(
        comment: comment,
        metadata: metadata,
        enumKeyword: enumKeyword,
        name: name,
        typeParameters: typeParameters,
        withClause: withClause,
        implementsClause: implementsClause,
        leftBracket: leftBrace,
        constants: [],
        members: [],
        rightBracket: leftBrace.endGroup!,
      ),
    );
  }

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

  @override
  void handleEnumWithClause(Token withKeyword) {
    assert(optional('with', withKeyword));
    var mixinTypes = pop() as List<NamedType>;
    push(ast.withClause(withKeyword, 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 Expression;
    var star = pop() as Token?;
    var asyncKeyword = pop() as Token?;
    if (parseFunctionBodies) {
      push(ast.expressionFunctionBody2(
        keyword: asyncKeyword,
        star: star,
        functionDefinition: arrowToken,
        expression: expression,
        semicolon: semicolon,
      ));
    } else {
      push(ast.emptyFunctionBody(semicolon!));
    }
  }

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

  @override
  void handleExtensionShowHide(Token? showKeyword, int showElementCount,
      Token? hideKeyword, int hideElementCount) {
    assert(optionalOrNull('hide', hideKeyword));
    assert(optionalOrNull('show', showKeyword));
    debugEvent("ExtensionShowHide");

    HideClause? hideClause;
    if (hideKeyword != null) {
      var elements = popTypedList2<ShowHideClauseElement>(hideElementCount);
      hideClause = ast.hideClause(hideKeyword: hideKeyword, elements: elements);
    }

    ShowClause? showClause;
    if (showKeyword != null) {
      var elements = popTypedList2<ShowHideClauseElement>(showElementCount);
      showClause = ast.showClause(showKeyword: showKeyword, elements: elements);
    }

    push(hideClause ?? NullValue.HideClause);
    push(showClause ?? NullValue.ShowClause);
  }

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

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

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

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

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

    var iterator = pop() as Expression;
    var variableOrDeclaration = pop()!;

    ForEachParts forLoopParts;
    if (variableOrDeclaration is VariableDeclarationStatement) {
      VariableDeclarationList variableList = variableOrDeclaration.variables;
      forLoopParts = ast.forEachPartsWithDeclaration(
        loopVariable: ast.declaredIdentifier(
            variableList.documentationComment,
            variableList.metadata,
            variableList.keyword,
            variableList.type,
            variableList.variables.first.name),
        inKeyword: inKeyword,
        iterable: iterator,
      );
    } else {
      if (variableOrDeclaration is! SimpleIdentifier) {
        // Parser has already reported the error.
        if (!leftParenthesis.next!.isIdentifier) {
          parser.rewriter.insertSyntheticIdentifier(leftParenthesis);
        }
        variableOrDeclaration = ast.simpleIdentifier(leftParenthesis.next!);
      }
      forLoopParts = ast.forEachPartsWithIdentifier(
        identifier: variableOrDeclaration,
        inKeyword: inKeyword,
        iterable: iterator,
      );
    }

    push(awaitToken ?? NullValue.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<Expression>(updateExpressionCount);
    var conditionStatement = pop() as Statement;
    var initializerPart = pop();

    Expression? condition;
    Token rightSeparator;
    if (conditionStatement is ExpressionStatement) {
      condition = conditionStatement.expression;
      rightSeparator = conditionStatement.semicolon!;
    } else {
      rightSeparator = (conditionStatement as EmptyStatement).semicolon;
    }

    ForParts forLoopParts;
    if (initializerPart is VariableDeclarationStatement) {
      forLoopParts = ast.forPartsWithDeclarations(
        variables: initializerPart.variables,
        leftSeparator: leftSeparator,
        condition: condition,
        rightSeparator: rightSeparator,
        updaters: updates,
      );
    } else {
      forLoopParts = ast.forPartsWithExpression(
        initialization: initializerPart as Expression?,
        leftSeparator: leftSeparator,
        condition: condition,
        rightSeparator: rightSeparator,
        updaters: updates,
      );
    }

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

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

    push(NullValue.ParameterDefaultValue);
  }

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

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

    SimpleIdentifier 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<Annotation>?;
      var comment = _findComment(metadata, token);
      push(ast.enumConstantDeclaration(comment, metadata, identifier));
    } else {
      push(identifier);
    }
  }

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

    push(popTypedList<SimpleIdentifier>(count) ?? NullValue.IdentifierList);
  }

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

    if (implementsKeyword != null) {
      var interfaces = popTypedList2<NamedType>(interfacesCount);
      push(ast.implementsClause(implementsKeyword, interfaces));
    } else {
      push(NullValue.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(NullValue.Prefix);
      push(NullValue.As);
    } else {
      push(asKeyword);
    }
    push(deferredKeyword ?? NullValue.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 Expression;
    var target = pop() as Expression?;
    if (target == null) {
      var receiver = pop() as CascadeExpression;
      var token = peek() as Token;
      push(receiver);
      IndexExpression expression = ast.indexExpressionForCascade2(
          period: token,
          question: question,
          leftBracket: leftBracket,
          index: index,
          rightBracket: rightBracket);
      assert(expression.isCascaded);
      push(expression);
    } else {
      push(ast.indexExpressionForTarget2(
          target: target,
          question: question,
          leftBracket: leftBracket,
          index: index,
          rightBracket: rightBracket));
    }
  }

  @override
  void handleInterpolationExpression(Token leftBracket, Token? rightBracket) {
    var expression = pop() as Expression;
    push(ast.interpolationExpression(leftBracket, expression, rightBracket));
  }

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

  @override
  void handleInvalidFunctionBody(Token leftBracket) {
    assert(optional('{', leftBracket));
    assert(optional('}', leftBracket.endGroup!));
    debugEvent("InvalidFunctionBody");
    Block block = ast.block(leftBracket, [], leftBracket.endGroup!);
    var star = pop() as Token?;
    var asyncKeyword = pop() as Token?;
    push(ast.blockFunctionBody(asyncKeyword, star, 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 TypeArgumentList;
    var node = pop();
    if (node is ConstructorName) {
      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 TypeAnnotation;
    var expression = pop() as Expression;
    push(ast.isExpression(expression, isOperator, not, type));
  }

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

    var name = pop() as SimpleIdentifier;
    push(ast.label(name, colon));
  }

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

    push(ast.booleanLiteral(token, value));
  }

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

    push(ast.doubleLiteral(token, double.parse(token.lexeme)));
  }

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

    push(ast.integerLiteral(token, 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");

    if (enableControlFlowCollections || enableSpreadCollections) {
      List<CollectionElement> elements = popCollectionElements(count);
      var typeArguments = pop() as TypeArgumentList?;

      // TODO(danrubel): Remove this and _InvalidCollectionElement
      // once control flow and spread collection support is enabled by default
      elements.removeWhere((e) => e == _invalidCollectionElement);

      push(ast.listLiteral(
          constKeyword, typeArguments, leftBracket, elements, rightBracket));
    } else {
      var elements = popTypedList<Expression>(count) ?? const [];
      var typeArguments = pop() as TypeArgumentList?;

      List<Expression> expressions = <Expression>[];
      for (var elem in elements) {
        expressions.add(elem);
      }

      push(ast.listLiteral(
          constKeyword, typeArguments, leftBracket, expressions, rightBracket));
    }
  }

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

    var value = pop() as Expression;
    var key = pop() as Expression;
    push(ast.mapLiteralEntry(key, colon, value));
  }

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

    push(ast.nullLiteral(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,
  ) {
    if (enableControlFlowCollections || enableSpreadCollections) {
      List<CollectionElement> elements = popCollectionElements(count);

      // TODO(danrubel): Remove this and _InvalidCollectionElement
      // once control flow and spread collection support is enabled by default
      elements.removeWhere((e) => e == _invalidCollectionElement);

      var typeArguments = pop() as TypeArgumentList?;
      push(ast.setOrMapLiteral(
        constKeyword: constKeyword,
        typeArguments: typeArguments,
        leftBracket: leftBrace,
        elements: elements,
        rightBracket: rightBrace,
      ));
    } else {
      var elements = popTypedList(count);
      var typeArguments = pop() as TypeArgumentList?;

      // Replicate existing behavior that has been removed from the parser.
      // This will be removed once control flow collections
      // and spread collections are enabled by default.

      // Determine if this is a set or map based on type args and content
      final typeArgCount = typeArguments?.arguments.length;
      bool? isSet = typeArgCount == 1
          ? true
          : typeArgCount != null
              ? false
              : null;
      isSet ??= hasSetEntry;

      // Build the set or map
      if (isSet) {
        final setEntries = <Expression>[];
        if (elements != null) {
          for (var elem in elements) {
            if (elem is MapLiteralEntry) {
              setEntries.add(elem.key);
              handleRecoverableError(
                  templateUnexpectedToken.withArguments(elem.separator),
                  elem.separator,
                  elem.separator);
            } else if (elem is Expression) {
              setEntries.add(elem);
            }
          }
        }
        push(ast.setOrMapLiteral(
          constKeyword: constKeyword,
          typeArguments: typeArguments,
          leftBracket: leftBrace,
          elements: setEntries,
          rightBracket: rightBrace,
        ));
      } else {
        final mapEntries = <MapLiteralEntry>[];
        if (elements != null) {
          for (var elem in elements) {
            if (elem is MapLiteralEntry) {
              mapEntries.add(elem);
            } else if (elem is Expression) {
              Token next = elem.endToken.next!;
              int offset = next.offset;
              handleRecoverableError(
                  templateExpectedButGot.withArguments(':'), next, next);
              handleRecoverableError(
                  templateExpectedIdentifier.withArguments(next), next, next);
              Token separator = SyntheticToken(TokenType.COLON, offset);
              Expression value = ast.simpleIdentifier(
                  SyntheticStringToken(TokenType.IDENTIFIER, '', offset));
              mapEntries.add(ast.mapLiteralEntry(elem, separator, value));
            }
          }
        }
        push(ast.setOrMapLiteral(
          constKeyword: constKeyword,
          typeArguments: typeArguments,
          leftBracket: leftBrace,
          elements: mapEntries,
          rightBracket: rightBrace,
        ));
      }
    }
  }

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

    var implementsClause = pop(NullValue.IdentifierList) as ImplementsClause?;
    var onClause = pop(NullValue.IdentifierList) as OnClause?;
    var typeParameters = pop() as TypeParameterList?;
    var name = pop() as SimpleIdentifier;
    var metadata = pop() as List<Annotation>?;
    var comment = _findComment(metadata, mixinKeyword);

    mixinDeclaration = ast.mixinDeclaration(
      comment,
      metadata,
      mixinKeyword,
      name,
      typeParameters,
      onClause,
      implementsClause,
      Tokens.openCurlyBracket(), // leftBracket
      <ClassMember>[],
      Tokens.closeCurlyBracket(), // rightBracket
    );
    declarations.add(mixinDeclaration!);
  }

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

    if (onKeyword != null) {
      var types = popTypedList2<NamedType>(typeCount);
      push(ast.onClause(onKeyword, types));
    } else {
      push(NullValue.IdentifierList);
    }
  }

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

    var expression = pop() as Expression;
    var name = pop() as SimpleIdentifier;
    push(ast.namedExpression(ast.label(name, colon), expression));
  }

  @override
  void handleNamedMixinApplicationWithClause(Token withKeyword) {
    assert(optionalOrNull('with', withKeyword));
    var mixinTypes = pop() as List<NamedType>;
    push(ast.withClause(withKeyword, mixinTypes));
  }

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

    if (hasName) {
      nativeName = pop() as StringLiteral; // StringLiteral
    } 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(ast.nativeFunctionBody(nativeToken, nativeName, semicolon));
  }

  @override
  void handleNewAsIdentifier(Token token) {
    if (!enableConstructorTearoffs) {
      var feature = ExperimentalFeatures.constructor_tearoffs;
      handleRecoverableError(
          templateExperimentNotEnabled.withArguments(
            feature.enableString,
            _versionAsString(ExperimentStatus.currentVersion),
          ),
          token,
          token);
    }
  }

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

    push(NullValue.ConstructorReferenceContinuationAfterTypeArguments);
  }

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

    var name = pop() as SimpleIdentifier;
    push(_makeVariableDeclaration(name, null, null));
  }

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

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

  @override
  void handleNonNullAssertExpression(Token bang) {
    debugEvent('NonNullAssertExpression');
    if (!enableNonNullable) {
      reportNonNullAssertExpressionNotEnabled(bang);
    } else {
      push(ast.postfixExpression(pop() as Expression, bang));
    }
  }

  @override
  void handleNoTypeNameInConstructorReference(Token token) {
    debugEvent("NoTypeNameInConstructorReference");
    assert(enumDeclaration != null);

    push(ast.simpleIdentifier(enumDeclaration!.name.token));
  }

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

  @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) {
    // TODO(danrubel): Implement rather than forwarding.
    handleParenthesizedExpression(leftParenthesis);
  }

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

    var expression = pop() as Expression;
    push(ast.parenthesizedExpression(
        leftParenthesis, expression, leftParenthesis.endGroup!));
  }

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

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

  @override
  void handleRecoverableError(
      Message message, Token startToken, Token endToken) {
    /// TODO(danrubel): Ignore this error until we deprecate `native` support.
    if (message == messageNativeClauseShouldBeAnnotation && allowNativeClause) {
      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(NullValue.IdentifierList) as ImplementsClause?;
    var withClause = pop(NullValue.WithClause) as WithClause?;
    var extendsClause = pop(NullValue.ExtendsClause) as ExtendsClause?;
    var declaration = declarations.last as ClassDeclarationImpl;
    if (extendsClause != null) {
      if (declaration.extendsClause?.superclass2 == null) {
        declaration.extendsClause = extendsClause;
      }
    }
    if (withClause != null) {
      if (declaration.withClause == null) {
        declaration.withClause = withClause;
      } else {
        declaration.withClause!.mixinTypes2.addAll(withClause.mixinTypes2);
      }
    }
    if (implementsClause != null) {
      if (declaration.implementsClause == null) {
        declaration.implementsClause = implementsClause;
      } else {
        declaration.implementsClause!.interfaces2
            .addAll(implementsClause.interfaces2);
      }
    }
  }

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

    var combinators = pop() as List<Combinator>?;
    var deferredKeyword = pop(NullValue.Deferred) as Token?;
    var asKeyword = pop(NullValue.As) as Token?;
    var prefix = pop(NullValue.Prefix) as SimpleIdentifier?;
    var configurations = pop() as List<Configuration>?;

    var directive = directives.last as ImportDirectiveImpl;
    if (combinators != null) {
      directive.combinators.addAll(combinators);
    }
    directive.deferredKeyword ??= deferredKeyword;
    if (directive.asKeyword == null && asKeyword != null) {
      directive.asKeyword = asKeyword;
      directive.prefix = prefix;
    }
    if (configurations != null) {
      directive.configurations.addAll(configurations);
    }
    if (semicolon != null) {
      directive.semicolon = semicolon;
    }
  }

  @override
  void handleRecoverMixinHeader() {
    var implementsClause = pop(NullValue.IdentifierList) as ImplementsClause?;
    var onClause = pop(NullValue.IdentifierList) as OnClause?;

    if (onClause != null) {
      if (mixinDeclaration!.onClause == null) {
        mixinDeclaration!.onClause = onClause;
      } else {
        mixinDeclaration!.onClause!.superclassConstraints2
            .addAll(onClause.superclassConstraints2);
      }
    }
    if (implementsClause != null) {
      if (mixinDeclaration!.implementsClause == null) {
        mixinDeclaration!.implementsClause = implementsClause;
      } else {
        mixinDeclaration!.implementsClause!.interfaces2
            .addAll(implementsClause.interfaces2);
      }
    }
  }

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

    scriptTag = ast.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 handleShowHideIdentifier(Token? modifier, Token identifier) {
    debugEvent("handleShowHideIdentifier");

    assert(modifier == null ||
        modifier.stringValue! == "get" ||
        modifier.stringValue! == "set" ||
        modifier.stringValue! == "operator");

    SimpleIdentifier name = ast.simpleIdentifier(identifier);
    ShowHideElement element =
        ast.showHideElement(modifier: modifier, name: name);

    push(element);
  }

  @override
  void handleSpreadExpression(Token spreadToken) {
    var expression = pop() as Expression;
    if (enableSpreadCollections) {
      push(ast.spreadElement(
          spreadOperator: spreadToken, expression: expression));
    } else {
      var feature = Feature.spread_collections;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(feature.releaseVersion!),
        ),
        spreadToken,
        spreadToken,
      );
      push(_invalidCollectionElement);
    }
  }

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

    var strings = popTypedList2<StringLiteral>(literalCount);
    push(ast.adjacentStrings(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(ast.superExpression(superKeyword));
  }

  @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(ast.thisExpression(thisKeyword));
  }

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

    push(ast.throwExpression(throwToken, pop() as Expression));
  }

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

    var arguments = pop() as TypeArgumentList?;
    var name = pop() as Identifier;
    push(
      ast.namedType(
        name: name,
        typeArguments: arguments,
        question: questionMark,
      ),
    );
  }

  @override
  void handleTypeArgumentApplication(Token openAngleBracket) {
    var typeArguments = pop() as TypeArgumentList;
    var receiver = pop() as Expression;
    if (!enableConstructorTearoffs) {
      var feature = ExperimentalFeatures.constructor_tearoffs;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(ExperimentStatus.currentVersion),
        ),
        typeArguments.leftBracket,
        typeArguments.rightBracket,
      );
    }
    push(ast.functionReference(
        function: receiver, typeArguments: typeArguments));
  }

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

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

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

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

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

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

    push(ast.prefixExpression(operator, pop() as Expression));
  }

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

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

  @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 TypeArgumentList;

    // 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<CommentReference> 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) {
      String referenceSource = sourcesAndOffsets[index++];
      int referenceOffset = sourcesAndOffsets[index++];
      ScannerResult result = scanString(referenceSource);
      if (!result.hasErrors) {
        Token token = result.tokens;
        if (parser.parseOneCommentReference(token, referenceOffset)) {
          ++count;
        }
      }
    }

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

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

  // List<T?>? popTypedList<T>(int count, [List<T>? list]) {
  //   if (count == 0) return null;
  //   assert(stack.length >= count);
  //
  //   final tailList = list ?? List<T?>.filled(count, null, growable: true);
  //   stack.popList(count, tailList, null);
  //   return tailList;
  // }

  /// 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 pushForControlFlowInfo(Token? awaitToken, Token forToken,
      Token leftParenthesis, ForLoopParts forLoopParts, Object entry) {
    if (entry == _invalidCollectionElement) {
      push(_invalidCollectionElement);
    } else if (enableControlFlowCollections) {
      push(ast.forElement(
        awaitKeyword: awaitToken,
        forKeyword: forToken,
        leftParenthesis: leftParenthesis,
        forLoopParts: forLoopParts,
        rightParenthesis: leftParenthesis.endGroup!,
        body: entry as CollectionElement,
      ));
    } else {
      var feature = Feature.control_flow_collections;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(feature.releaseVersion!),
        ),
        forToken,
        forToken,
      );
      push(_invalidCollectionElement);
    }
  }

  void pushIfControlFlowInfo(
      Token ifToken,
      ParenthesizedExpression condition,
      CollectionElement thenElement,
      Token? elseToken,
      CollectionElement? elseElement) {
    if (thenElement == _invalidCollectionElement ||
        elseElement == _invalidCollectionElement) {
      push(_invalidCollectionElement);
    } else if (enableControlFlowCollections) {
      push(ast.ifElement(
        ifKeyword: ifToken,
        leftParenthesis: condition.leftParenthesis,
        condition: condition.expression,
        rightParenthesis: condition.rightParenthesis,
        thenElement: thenElement,
        elseKeyword: elseToken,
        elseElement: elseElement,
      ));
    } else {
      var feature = ExperimentalFeatures.control_flow_collections;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(feature.releaseVersion!),
        ),
        ifToken,
        ifToken,
      );
      push(_invalidCollectionElement);
    }
  }

  void reportErrorIfNullableType(Token? questionMark) {
    if (questionMark != null) {
      assert(optional('?', questionMark));
      var feature = ExperimentalFeatures.non_nullable;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(feature.releaseVersion!),
        ),
        questionMark,
        questionMark,
      );
    }
  }

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

  void reportNonNullableModifierError(Token? modifierToken) {
    if (modifierToken != null) {
      var feature = ExperimentalFeatures.non_nullable;
      handleRecoverableError(
        templateExperimentNotEnabled.withArguments(
          feature.enableString,
          _versionAsString(feature.releaseVersion!),
        ),
        modifierToken,
        modifierToken,
      );
    }
  }

  void reportNonNullAssertExpressionNotEnabled(Token bang) {
    var feature = ExperimentalFeatures.non_nullable;
    handleRecoverableError(
      templateExperimentNotEnabled.withArguments(
        feature.enableString,
        _versionAsString(feature.releaseVersion!),
      ),
      bang,
      bang,
    );
  }

  Comment? _findComment(List<Annotation>? 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
    List<CommentReference> 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 ast.documentationComment(tokens, references);
  }

  void _handleInstanceCreation(Token? token) {
    var arguments = pop() as MethodInvocation;
    ConstructorName constructorName;
    TypeArgumentList? typeArguments;
    var object = pop();
    if (object is _ConstructorNameWithInvalidTypeArgs) {
      constructorName = object.name;
      typeArguments = object.invalidTypeArgs;
    } else {
      constructorName = object as ConstructorName;
    }
    push(ast.instanceCreationExpression(
        token, constructorName, arguments.argumentList,
        typeArguments: typeArguments));
  }

  VariableDeclaration _makeVariableDeclaration(
      SimpleIdentifier name, Token? equals, Expression? initializer) {
    return ast.variableDeclaration(name, equals, initializer);
  }

  ArgumentList _syntheticArgumentList(Token precedingToken) {
    int syntheticOffset = precedingToken.end;
    return ast.argumentList(
        SyntheticToken(TokenType.OPEN_PAREN, syntheticOffset),
        [],
        SyntheticToken(TokenType.CLOSE_PAREN, syntheticOffset));
  }

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

  ParameterKind _toAnalyzerParameterKind(
      FormalParameterKind type, Token? requiredKeyword) {
    if (type == FormalParameterKind.optionalPositional) {
      return ParameterKind.POSITIONAL;
    } else if (type == FormalParameterKind.optionalNamed) {
      if (requiredKeyword != null) {
        return ParameterKind.NAMED_REQUIRED;
      }
      return ParameterKind.NAMED;
    } else {
      return ParameterKind.REQUIRED;
    }
  }

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

class _ConstructorNameWithInvalidTypeArgs {
  final ConstructorName name;
  final TypeArgumentList invalidTypeArgs;

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

/// When [enableSpreadCollections] and/or [enableControlFlowCollections]
/// are false, this class is pushed on the stack when a disabled
/// [CollectionElement] has been parsed.
class _InvalidCollectionElement implements CollectionElement {
  // TODO(danrubel): Remove this once control flow and spread collections
  // have been enabled by default.

  const _InvalidCollectionElement._();

  @override
  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}

/// Data structure placed on the stack to represent a non-empty sequence
/// of modifiers.
class _Modifiers {
  Token? abstractKeyword;
  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;
  }
}

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

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

/// Data structure placed on the stack as a container for optional parameters.
class _OptionalFormalParameters {
  final List<FormalParameter>? 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 Expression value;

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

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

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