pkg/analyzer/lib/src/generated/parser.dart - sdk.git - Git at Google

 // Copyright (c) 2014, 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.

 library analyzer.src.generated.parser;

 import 'dart:collection';
 import "dart:math" as math;

 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_ast_factory.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
 import 'package:analyzer/src/dart/error/syntactic_errors.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
 import 'package:analyzer/src/dart/scanner/scanner.dart';
 import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/generated/engine.dart' show AnalysisEngine;
 import 'package:analyzer/src/generated/java_core.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';

 export 'package:analyzer/src/dart/ast/utilities.dart' show ResolutionCopier;
 export 'package:analyzer/src/dart/error/syntactic_errors.dart';

 /**
  * A simple data-holder for a method that needs to return multiple values.
  */
 class CommentAndMetadata {
   /**
    * The documentation comment that was parsed, or `null` if none was given.
    */
   final Comment comment;

   /**
    * The metadata that was parsed, or `null` if none was given.
    */
   final List<Annotation> metadata;

   /**
    * Initialize a newly created holder with the given [comment] and [metadata].
    */
   CommentAndMetadata(this.comment, this.metadata);

   /**
    * Return `true` if some metadata was parsed.
    */
   bool get hasMetadata => metadata != null && metadata.isNotEmpty;
 }

 /**
  * A simple data-holder for a method that needs to return multiple values.
  */
 class FinalConstVarOrType {
   /**
    * The 'final', 'const' or 'var' keyword, or `null` if none was given.
    */
   final Token keyword;

   /**
    * The type, or `null` if no type was specified.
    */
   final TypeAnnotation type;

   /**
    * Initialize a newly created holder with the given [keyword] and [type].
    */
   FinalConstVarOrType(this.keyword, this.type);
 }

 /**
  * A simple data-holder for a method that needs to return multiple values.
  */
 class Modifiers {
   /**
    * The token representing the keyword 'abstract', or `null` if the keyword was
    * not found.
    */
   Token abstractKeyword;

   /**
    * The token representing the keyword 'const', or `null` if the keyword was
    * not found.
    */
   Token constKeyword;

   /**
    * The token representing the keyword 'covariant', or `null` if the keyword
    * was not found.
    */
   Token covariantKeyword;

   /**
    * The token representing the keyword 'external', or `null` if the keyword was
    * not found.
    */
   Token externalKeyword;

   /**
    * The token representing the keyword 'factory', or `null` if the keyword was
    * not found.
    */
   Token factoryKeyword;

   /**
    * The token representing the keyword 'final', or `null` if the keyword was
    * not found.
    */
   Token finalKeyword;

   /**
    * The token representing the keyword 'static', or `null` if the keyword was
    * not found.
    */
   Token staticKeyword;

   /**
    * The token representing the keyword 'var', or `null` if the keyword was not
    * found.
    */
   Token varKeyword;

   @override
   String toString() {
     StringBuffer buffer = new StringBuffer();
     bool needsSpace = _appendKeyword(buffer, false, abstractKeyword);
     needsSpace = _appendKeyword(buffer, needsSpace, constKeyword);
     needsSpace = _appendKeyword(buffer, needsSpace, externalKeyword);
     needsSpace = _appendKeyword(buffer, needsSpace, factoryKeyword);
     needsSpace = _appendKeyword(buffer, needsSpace, finalKeyword);
     needsSpace = _appendKeyword(buffer, needsSpace, staticKeyword);
     _appendKeyword(buffer, needsSpace, varKeyword);
     return buffer.toString();
   }

   /**
    * If the given [keyword] is not `null`, append it to the given [builder],
    * prefixing it with a space if [needsSpace] is `true`. Return `true` if
    * subsequent keywords need to be prefixed with a space.
    */
   bool _appendKeyword(StringBuffer buffer, bool needsSpace, Token keyword) {
     if (keyword != null) {
       if (needsSpace) {
         buffer.writeCharCode(0x20);
       }
       buffer.write(keyword.lexeme);
       return true;
     }
     return needsSpace;
   }
 }

 /**
  * A parser used to parse tokens into an AST structure.
  */
 class Parser {
   static String ASYNC = "async";

   static String _AWAIT = "await";

   static String _HIDE = "hide";

   static String _OF = "of";

   static String _ON = "on";

   static String _NATIVE = "native";

   static String _SHOW = "show";

   static String SYNC = "sync";

   static String _YIELD = "yield";

   /**
    * The source being parsed.
    */
   final Source _source;

   /**
    * The error listener that will be informed of any errors that are found
    * during the parse.
    */
   final AnalysisErrorListener _errorListener;

   /**
    * An [_errorListener] lock, if more than `0`, then errors are not reported.
    */
   int _errorListenerLock = 0;

   /**
    * A flag indicating whether the parser is to parse asserts in the initializer
    * list of a constructor.
    */
   bool _enableAssertInitializer = false;

   /**
    * A flag indicating whether the parser is to parse the non-nullable modifier
    * in type names.
    */
   bool _enableNnbd = false;

   /**
    * A flag indicating whether the parser is to allow URI's in part-of
    * directives.
    */
   bool _enableUriInPartOf = false;

   /**
    * A flag indicating whether parser is to parse function bodies.
    */
   bool _parseFunctionBodies = true;

   /**
    * The next token to be parsed.
    */
   Token _currentToken;

   /**
    * A flag indicating whether the parser is currently in a function body marked
    * as being 'async'.
    */
   bool _inAsync = false;

   /**
    * A flag indicating whether the parser is currently in a function body marked
    * (by a star) as being a generator.
    */
   bool _inGenerator = false;

   /**
    * A flag indicating whether the parser is currently in the body of a loop.
    */
   bool _inLoop = false;

   /**
    * A flag indicating whether the parser is currently in a switch statement.
    */
   bool _inSwitch = false;

   /**
    * A flag indicating whether the parser is currently in a constructor field
    * initializer, with no intervening parentheses, braces, or brackets.
    */
   bool _inInitializer = false;

   /**
    * A flag indicating whether the parser is to parse generic function type
    * syntax.
    */
   bool parseGenericFunctionTypes = false;

   /**
    * A flag indicating whether the parser is to parse generic method syntax.
    */
   @deprecated
   bool parseGenericMethods = false;

   /**
    * A flag indicating whether to parse generic method comments, of the form
    * `/*=T*/` and `/*<T>*/`.
    */
   bool parseGenericMethodComments = false;

   /**
    * Initialize a newly created parser to parse tokens in the given [_source]
    * and to report any errors that are found to the given [_errorListener].
    */
   Parser(this._source, this._errorListener);

   /**
    * Return the current token.
    */
   Token get currentToken => _currentToken;

   /**
    * Set the token with which the parse is to begin to the given [token].
    */
   void set currentToken(Token token) {
     this._currentToken = token;
   }

   /**
    * Return `true` if the parser is to parse asserts in the initializer list of
    * a constructor.
    */
   bool get enableAssertInitializer => _enableAssertInitializer;

   /**
    * Set whether the parser is to parse asserts in the initializer list of a
    * constructor to match the given [enable] flag.
    */
   void set enableAssertInitializer(bool enable) {
     _enableAssertInitializer = enable;
   }

   /**
    * Return `true` if the parser is to parse the non-nullable modifier in type
    * names.
    */
   bool get enableNnbd => _enableNnbd;

   /**
    * Set whether the parser is to parse the non-nullable modifier in type names
    * to match the given [enable] flag.
    */
   void set enableNnbd(bool enable) {
     _enableNnbd = enable;
   }

   /**
    * Return `true` if the parser is to allow URI's in part-of directives.
    */
   bool get enableUriInPartOf => _enableUriInPartOf;

   /**
    * Set whether the parser is to allow URI's in part-of directives to the given
    * [enable] flag.
    */
   void set enableUriInPartOf(bool enable) {
     _enableUriInPartOf = enable;
   }

   /**
    * Return `true` if the current token is the first token of a return type that
    * is followed by an identifier, possibly followed by a list of type
    * parameters, followed by a left-parenthesis. This is used by
    * [parseTypeAlias] to determine whether or not to parse a return type.
    */
   bool get hasReturnTypeInTypeAlias {
     // TODO(brianwilkerson) This is too expensive as implemented and needs to be
     // re-implemented or removed.
     Token next = skipReturnType(_currentToken);
     if (next == null) {
       return false;
     }
     return _tokenMatchesIdentifier(next);
   }

   /**
    * Set whether the parser is to parse the async support.
    *
    * Support for removing the 'async' library has been removed.
    */
   @deprecated
   void set parseAsync(bool parseAsync) {}

   @deprecated
   bool get parseConditionalDirectives => true;

   @deprecated
   void set parseConditionalDirectives(bool value) {}

   /**
    * Set whether parser is to parse function bodies.
    */
   void set parseFunctionBodies(bool parseFunctionBodies) {
     this._parseFunctionBodies = parseFunctionBodies;
   }

   /**
    * Return the content of a string with the given literal representation. The
    * [lexeme] is the literal representation of the string. The flag [isFirst] is
    * `true` if this is the first token in a string literal. The flag [isLast] is
    * `true` if this is the last token in a string literal.
    */
   String computeStringValue(String lexeme, bool isFirst, bool isLast) {
     StringLexemeHelper helper = new StringLexemeHelper(lexeme, isFirst, isLast);
     int start = helper.start;
     int end = helper.end;
     bool stringEndsAfterStart = end >= start;
     assert(stringEndsAfterStart);
     if (!stringEndsAfterStart) {
       AnalysisEngine.instance.logger.logError(
           "Internal error: computeStringValue($lexeme, $isFirst, $isLast)");
       return "";
     }
     if (helper.isRaw) {
       return lexeme.substring(start, end);
     }
     StringBuffer buffer = new StringBuffer();
     int index = start;
     while (index < end) {
       index = _translateCharacter(buffer, lexeme, index);
     }
     return buffer.toString();
   }

   /**
    * Return a synthetic identifier.
    */
   SimpleIdentifier createSyntheticIdentifier({bool isDeclaration: false}) {
     Token syntheticToken;
     if (_currentToken.type == TokenType.KEYWORD) {
       // Consider current keyword token as an identifier.
       // It is not always true, e.g. "^is T" where "^" is place the place for
       // synthetic identifier. By creating SyntheticStringToken we can
       // distinguish a real identifier from synthetic. In the code completion
       // behavior will depend on a cursor position - before or on "is".
       syntheticToken = _injectToken(new SyntheticStringToken(
           TokenType.IDENTIFIER, _currentToken.lexeme, _currentToken.offset));
     } else {
       syntheticToken = _createSyntheticToken(TokenType.IDENTIFIER);
     }
     return astFactory.simpleIdentifier(syntheticToken,
         isDeclaration: isDeclaration);
   }

   /**
    * Return a synthetic string literal.
    */
   SimpleStringLiteral createSyntheticStringLiteral() => astFactory
       .simpleStringLiteral(_createSyntheticToken(TokenType.STRING), "");

   /**
    * Advance to the next token in the token stream, making it the new current
    * token and return the token that was current before this method was invoked.
    */
   Token getAndAdvance() {
     Token token = _currentToken;
     _currentToken = _currentToken.next;
     return token;
   }

   /**
    * Return `true` if the current token appears to be the beginning of a
    * function declaration.
    */
   bool isFunctionDeclaration() {
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.VOID) {
       return true;
     }
     Token afterReturnType = skipTypeName(_currentToken);
     if (afterReturnType == null) {
       // There was no return type, but it is optional, so go back to where we
       // started.
       afterReturnType = _currentToken;
     }
     Token afterIdentifier = skipSimpleIdentifier(afterReturnType);
     if (afterIdentifier == null) {
       // It's possible that we parsed the function name as if it were a type
       // name, so see whether it makes sense if we assume that there is no type.
       afterIdentifier = skipSimpleIdentifier(_currentToken);
     }
     if (afterIdentifier == null) {
       return false;
     }
     if (isFunctionExpression(afterIdentifier)) {
       return true;
     }
     // It's possible that we have found a getter. While this isn't valid at this
     // point we test for it in order to recover better.
     if (keyword == Keyword.GET) {
       Token afterName = skipSimpleIdentifier(_currentToken.next);
       if (afterName == null) {
         return false;
       }
       TokenType type = afterName.type;
       return type == TokenType.FUNCTION || type == TokenType.OPEN_CURLY_BRACKET;
     } else if (_tokenMatchesKeyword(afterReturnType, Keyword.GET)) {
       Token afterName = skipSimpleIdentifier(afterReturnType.next);
       if (afterName == null) {
         return false;
       }
       TokenType type = afterName.type;
       return type == TokenType.FUNCTION || type == TokenType.OPEN_CURLY_BRACKET;
     }
     return false;
   }

   /**
    * Return `true` if the given [token] appears to be the beginning of a
    * function expression.
    */
   bool isFunctionExpression(Token token) {
     // Function expressions aren't allowed in initializer lists.
     if (_inInitializer) {
       return false;
     }
     Token afterTypeParameters = _skipTypeParameterList(token);
     if (afterTypeParameters == null) {
       afterTypeParameters = token;
     }
     Token afterParameters = _skipFormalParameterList(afterTypeParameters);
     if (afterParameters == null) {
       return false;
     }
     if (afterParameters.matchesAny(
         const <TokenType>[TokenType.OPEN_CURLY_BRACKET, TokenType.FUNCTION])) {
       return true;
     }
     String lexeme = afterParameters.lexeme;
     return lexeme == ASYNC || lexeme == SYNC;
   }

   /**
    * Return `true` if the current token is the first token in an initialized
    * variable declaration rather than an expression. This method assumes that we
    * have already skipped past any metadata that might be associated with the
    * declaration.
    *
    *     initializedVariableDeclaration ::=
    *         declaredIdentifier ('=' expression)? (',' initializedIdentifier)*
    *
    *     declaredIdentifier ::=
    *         metadata finalConstVarOrType identifier
    *
    *     finalConstVarOrType ::=
    *         'final' type?
    *       | 'const' type?
    *       | 'var'
    *       | type
    *
    *     type ::=
    *         qualified typeArguments?
    *
    *     initializedIdentifier ::=
    *         identifier ('=' expression)?
    */
   bool isInitializedVariableDeclaration() {
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.FINAL || keyword == Keyword.VAR) {
       // An expression cannot start with a keyword other than 'const',
       // 'rethrow', or 'throw'.
       return true;
     }
     if (keyword == Keyword.CONST) {
       // Look to see whether we might be at the start of a list or map literal,
       // otherwise this should be the start of a variable declaration.
       return !_peek().matchesAny(const <TokenType>[
         TokenType.LT,
         TokenType.OPEN_CURLY_BRACKET,
         TokenType.OPEN_SQUARE_BRACKET,
         TokenType.INDEX
       ]);
     }
     bool allowAdditionalTokens = true;
     // We know that we have an identifier, and need to see whether it might be
     // a type name.
     if (_currentToken.type != TokenType.IDENTIFIER) {
       allowAdditionalTokens = false;
     }
     Token token = skipTypeName(_currentToken);
     if (token == null) {
       // There was no type name, so this can't be a declaration.
       return false;
     }
     if (token.type != TokenType.IDENTIFIER) {
       allowAdditionalTokens = false;
     }
     token = skipSimpleIdentifier(token);
     if (token == null) {
       return false;
     }
     TokenType type = token.type;
     // Usual cases in valid code:
     //     String v = '';
     //     String v, v2;
     //     String v;
     //     for (String item in items) {}
     if (type == TokenType.EQ ||
         type == TokenType.COMMA ||
         type == TokenType.SEMICOLON ||
         token.keyword == Keyword.IN) {
       return true;
     }
     // It is OK to parse as a variable declaration in these cases:
     //     String v }
     //     String v if (true) print('OK');
     //     String v { print(42); }
     // ...but not in these cases:
     //     get getterName {
     //     String get getterName
     if (allowAdditionalTokens) {
       if (type == TokenType.CLOSE_CURLY_BRACKET ||
           type == TokenType.KEYWORD ||
           type == TokenType.IDENTIFIER ||
           type == TokenType.OPEN_CURLY_BRACKET) {
         return true;
       }
     }
     return false;
   }

   /**
    * Return `true` if the current token appears to be the beginning of a switch
    * member.
    */
   bool isSwitchMember() {
     Token token = _currentToken;
     while (_tokenMatches(token, TokenType.IDENTIFIER) &&
         _tokenMatches(token.next, TokenType.COLON)) {
       token = token.next.next;
     }
     Keyword keyword = token.keyword;
     return keyword == Keyword.CASE || keyword == Keyword.DEFAULT;
   }

   /**
    * Parse an additive expression. Return the additive expression that was
    * parsed.
    *
    *     additiveExpression ::=
    *         multiplicativeExpression (additiveOperator multiplicativeExpression)*
    *       | 'super' (additiveOperator multiplicativeExpression)+
    */
   Expression parseAdditiveExpression() {
     Expression expression;
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type.isAdditiveOperator) {
       expression = astFactory.superExpression(getAndAdvance());
     } else {
       expression = parseMultiplicativeExpression();
     }
     while (_currentToken.type.isAdditiveOperator) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseMultiplicativeExpression());
     }
     return expression;
   }

   /**
    * Parse an annotation. Return the annotation that was parsed.
    *
    * This method assumes that the current token matches [TokenType.AT].
    *
    *     annotation ::=
    *         '@' qualified ('.' identifier)? arguments?
    */
   Annotation parseAnnotation() {
     Token atSign = getAndAdvance();
     Identifier name = parsePrefixedIdentifier();
     Token period = null;
     SimpleIdentifier constructorName = null;
     if (_matches(TokenType.PERIOD)) {
       period = getAndAdvance();
       constructorName = parseSimpleIdentifier();
     }
     ArgumentList arguments = null;
     if (_matches(TokenType.OPEN_PAREN)) {
       arguments = parseArgumentList();
     }
     return astFactory.annotation(
         atSign, name, period, constructorName, arguments);
   }

   /**
    * Parse an argument. Return the argument that was parsed.
    *
    *     argument ::=
    *         namedArgument
    *       | expression
    *
    *     namedArgument ::=
    *         label expression
    */
   Expression parseArgument() {
     // TODO(brianwilkerson) Consider returning a wrapper indicating whether the
     // expression is a named expression in order to remove the 'is' check in
     // 'parseArgumentList'.
     //
     // Both namedArgument and expression can start with an identifier, but only
     // namedArgument can have an identifier followed by a colon.
     //
     if (_matchesIdentifier() && _tokenMatches(_peek(), TokenType.COLON)) {
       return astFactory.namedExpression(parseLabel(), parseExpression2());
     } else {
       return parseExpression2();
     }
   }

   /**
    * Parse a list of arguments. Return the argument list that was parsed.
    *
    * This method assumes that the current token matches [TokenType.OPEN_PAREN].
    *
    *     arguments ::=
    *         '(' argumentList? ')'
    *
    *     argumentList ::=
    *         namedArgument (',' namedArgument)*
    *       | expressionList (',' namedArgument)*
    */
   ArgumentList parseArgumentList() {
     Token leftParenthesis = getAndAdvance();
     if (_matches(TokenType.CLOSE_PAREN)) {
       return astFactory.argumentList(leftParenthesis, null, getAndAdvance());
     }
     //
     // Even though unnamed arguments must all appear before any named arguments,
     // we allow them to appear in any order so that we can recover faster.
     //
     bool wasInInitializer = _inInitializer;
     _inInitializer = false;
     try {
       Expression argument = parseArgument();
       List<Expression> arguments = <Expression>[argument];
       bool foundNamedArgument = argument is NamedExpression;
       bool generatedError = false;
       while (_optional(TokenType.COMMA)) {
         if (_matches(TokenType.CLOSE_PAREN)) {
           break;
         }
         argument = parseArgument();
         arguments.add(argument);
         if (argument is NamedExpression) {
           foundNamedArgument = true;
         } else if (foundNamedArgument) {
           if (!generatedError) {
             if (!argument.isSynthetic) {
               // Report the error, once, but allow the arguments to be in any
               // order in the AST.
               _reportErrorForCurrentToken(
                   ParserErrorCode.POSITIONAL_AFTER_NAMED_ARGUMENT);
               generatedError = true;
             }
           }
         }
       }
       // Recovery: If the next token is not a right parenthesis, look at the
       // left parenthesis to see whether there is a matching right parenthesis.
       // If there is, then we're more likely missing a comma and should go back
       // to parsing arguments.
       Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
       return astFactory.argumentList(
           leftParenthesis, arguments, rightParenthesis);
     } finally {
       _inInitializer = wasInInitializer;
     }
   }

   /**
    * Parse an assert statement. Return the assert statement.
    *
    * This method assumes that the current token matches `Keyword.ASSERT`.
    *
    *     assertStatement ::=
    *         'assert' '(' expression [',' expression] ')' ';'
    */
   AssertStatement parseAssertStatement() {
     Token keyword = getAndAdvance();
     Token leftParen = _expect(TokenType.OPEN_PAREN);
     Expression expression = parseExpression2();
     Token comma;
     Expression message;
     if (_matches(TokenType.COMMA)) {
       comma = getAndAdvance();
       message = parseExpression2();
     }
     Token rightParen = _expect(TokenType.CLOSE_PAREN);
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.assertStatement(
         keyword, leftParen, expression, comma, message, rightParen, semicolon);
   }

   /**
    * Parse an assignable expression. The [primaryAllowed] is `true` if the
    * expression is allowed to be a primary without any assignable selector.
    * Return the assignable expression that was parsed.
    *
    *     assignableExpression ::=
    *         primary (arguments* assignableSelector)+
    *       | 'super' unconditionalAssignableSelector
    *       | identifier
    */
   Expression parseAssignableExpression(bool primaryAllowed) {
     if (_matchesKeyword(Keyword.SUPER)) {
       return parseAssignableSelector(
           astFactory.superExpression(getAndAdvance()), false,
           allowConditional: false);
     }
     return _parseAssignableExpressionNotStartingWithSuper(primaryAllowed);
   }

   /**
    * Parse an assignable selector. The [prefix] is the expression preceding the
    * selector. The [optional] is `true` if the selector is optional. Return the
    * assignable selector that was parsed, or the original prefix if there was no
    * assignable selector.  If [allowConditional] is false, then the '?.'
    * operator will still be parsed, but a parse error will be generated.
    *
    *     unconditionalAssignableSelector ::=
    *         '[' expression ']'
    *       | '.' identifier
    *
    *     assignableSelector ::=
    *         unconditionalAssignableSelector
    *       | '?.' identifier
    */
   Expression parseAssignableSelector(Expression prefix, bool optional,
       {bool allowConditional: true}) {
     TokenType type = _currentToken.type;
     if (type == TokenType.OPEN_SQUARE_BRACKET) {
       Token leftBracket = getAndAdvance();
       bool wasInInitializer = _inInitializer;
       _inInitializer = false;
       try {
         Expression index = parseExpression2();
         Token rightBracket = _expect(TokenType.CLOSE_SQUARE_BRACKET);
         return astFactory.indexExpressionForTarget(
             prefix, leftBracket, index, rightBracket);
       } finally {
         _inInitializer = wasInInitializer;
       }
     } else {
       bool isQuestionPeriod = type == TokenType.QUESTION_PERIOD;
       if (type == TokenType.PERIOD || isQuestionPeriod) {
         if (isQuestionPeriod && !allowConditional) {
           _reportErrorForCurrentToken(
               ParserErrorCode.INVALID_OPERATOR_FOR_SUPER,
               [_currentToken.lexeme]);
         }
         Token operator = getAndAdvance();
         return astFactory.propertyAccess(
             prefix, operator, parseSimpleIdentifier());
       } else if (type == TokenType.INDEX) {
         _splitIndex();
         Token leftBracket = getAndAdvance();
         Expression index = parseSimpleIdentifier();
         Token rightBracket = getAndAdvance();
         return astFactory.indexExpressionForTarget(
             prefix, leftBracket, index, rightBracket);
       } else {
         if (!optional) {
           // Report the missing selector.
           _reportErrorForCurrentToken(
               ParserErrorCode.MISSING_ASSIGNABLE_SELECTOR);
         }
         return prefix;
       }
     }
   }

   /**
    * Parse a await expression. Return the await expression that was parsed.
    *
    * This method assumes that the current token matches `_AWAIT`.
    *
    *     awaitExpression ::=
    *         'await' unaryExpression
    */
   AwaitExpression parseAwaitExpression() {
     Token awaitToken = getAndAdvance();
     Expression expression = parseUnaryExpression();
     return astFactory.awaitExpression(awaitToken, expression);
   }

   /**
    * Parse a bitwise and expression. Return the bitwise and expression that was
    * parsed.
    *
    *     bitwiseAndExpression ::=
    *         shiftExpression ('&' shiftExpression)*
    *       | 'super' ('&' shiftExpression)+
    */
   Expression parseBitwiseAndExpression() {
     Expression expression;
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type == TokenType.AMPERSAND) {
       expression = astFactory.superExpression(getAndAdvance());
     } else {
       expression = parseShiftExpression();
     }
     while (_currentToken.type == TokenType.AMPERSAND) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseShiftExpression());
     }
     return expression;
   }

   /**
    * Parse a bitwise or expression. Return the bitwise or expression that was
    * parsed.
    *
    *     bitwiseOrExpression ::=
    *         bitwiseXorExpression ('|' bitwiseXorExpression)*
    *       | 'super' ('|' bitwiseXorExpression)+
    */
   Expression parseBitwiseOrExpression() {
     Expression expression;
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type == TokenType.BAR) {
       expression = astFactory.superExpression(getAndAdvance());
     } else {
       expression = parseBitwiseXorExpression();
     }
     while (_currentToken.type == TokenType.BAR) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseBitwiseXorExpression());
     }
     return expression;
   }

   /**
    * Parse a bitwise exclusive-or expression. Return the bitwise exclusive-or
    * expression that was parsed.
    *
    *     bitwiseXorExpression ::=
    *         bitwiseAndExpression ('^' bitwiseAndExpression)*
    *       | 'super' ('^' bitwiseAndExpression)+
    */
   Expression parseBitwiseXorExpression() {
     Expression expression;
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type == TokenType.CARET) {
       expression = astFactory.superExpression(getAndAdvance());
     } else {
       expression = parseBitwiseAndExpression();
     }
     while (_currentToken.type == TokenType.CARET) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseBitwiseAndExpression());
     }
     return expression;
   }

   /**
    * Parse a block. Return the block that was parsed.
    *
    * This method assumes that the current token matches
    * [TokenType.OPEN_CURLY_BRACKET].
    *
    *     block ::=
    *         '{' statements '}'
    */
   Block parseBlock() {
     bool isEndOfBlock() {
       TokenType type = _currentToken.type;
       return type == TokenType.EOF || type == TokenType.CLOSE_CURLY_BRACKET;
     }

     Token leftBracket = getAndAdvance();
     List<Statement> statements = <Statement>[];
     Token statementStart = _currentToken;
     while (!isEndOfBlock()) {
       Statement statement = parseStatement2();
       if (identical(_currentToken, statementStart)) {
         // Ensure that we are making progress and report an error if we're not.
         _reportErrorForToken(ParserErrorCode.UNEXPECTED_TOKEN, _currentToken,
             [_currentToken.lexeme]);
         _advance();
       } else if (statement != null) {
         statements.add(statement);
       }
       statementStart = _currentToken;
     }
     // Recovery: If the next token is not a right curly bracket, look at the
     // left curly bracket to see whether there is a matching right bracket. If
     // there is, then we're more likely missing a semi-colon and should go back
     // to parsing statements.
     Token rightBracket = _expect(TokenType.CLOSE_CURLY_BRACKET);
     return astFactory.block(leftBracket, statements, rightBracket);
   }

   /**
    * Parse a break statement. Return the break statement that was parsed.
    *
    * This method assumes that the current token matches `Keyword.BREAK`.
    *
    *     breakStatement ::=
    *         'break' identifier? ';'
    */
   Statement parseBreakStatement() {
     Token breakKeyword = getAndAdvance();
     SimpleIdentifier label = null;
     if (_matchesIdentifier()) {
       label = _parseSimpleIdentifierUnchecked();
     }
     if (!_inLoop && !_inSwitch && label == null) {
       _reportErrorForToken(ParserErrorCode.BREAK_OUTSIDE_OF_LOOP, breakKeyword);
     }
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.breakStatement(breakKeyword, label, semicolon);
   }

   /**
    * Parse a cascade section. Return the expression representing the cascaded
    * method invocation.
    *
    * This method assumes that the current token matches
    * `TokenType.PERIOD_PERIOD`.
    *
    *     cascadeSection ::=
    *         '..' (cascadeSelector typeArguments? arguments*)
    *         (assignableSelector typeArguments? arguments*)* cascadeAssignment?
    *
    *     cascadeSelector ::=
    *         '[' expression ']'
    *       | identifier
    *
    *     cascadeAssignment ::=
    *         assignmentOperator expressionWithoutCascade
    */
   Expression parseCascadeSection() {
     Token period = getAndAdvance();
     Expression expression = null;
     SimpleIdentifier functionName = null;
     if (_matchesIdentifier()) {
       functionName = _parseSimpleIdentifierUnchecked();
     } else if (_currentToken.type == TokenType.OPEN_SQUARE_BRACKET) {
       Token leftBracket = getAndAdvance();
       bool wasInInitializer = _inInitializer;
       _inInitializer = false;
       try {
         Expression index = parseExpression2();
         Token rightBracket = _expect(TokenType.CLOSE_SQUARE_BRACKET);
         expression = astFactory.indexExpressionForCascade(
             period, leftBracket, index, rightBracket);
         period = null;
       } finally {
         _inInitializer = wasInInitializer;
       }
     } else {
       _reportErrorForToken(ParserErrorCode.MISSING_IDENTIFIER, _currentToken,
           [_currentToken.lexeme]);
       functionName = createSyntheticIdentifier();
     }
     assert((expression == null && functionName != null) ||
         (expression != null && functionName == null));
     if (_isLikelyArgumentList()) {
       do {
         TypeArgumentList typeArguments = _parseOptionalTypeArguments();
         if (functionName != null) {
           expression = astFactory.methodInvocation(expression, period,
               functionName, typeArguments, parseArgumentList());
           period = null;
           functionName = null;
         } else if (expression == null) {
           // It should not be possible to get here.
           expression = astFactory.methodInvocation(expression, period,
               createSyntheticIdentifier(), typeArguments, parseArgumentList());
         } else {
           expression = astFactory.functionExpressionInvocation(
               expression, typeArguments, parseArgumentList());
         }
       } while (_isLikelyArgumentList());
     } else if (functionName != null) {
       expression = astFactory.propertyAccess(expression, period, functionName);
       period = null;
     }
     assert(expression != null);
     bool progress = true;
     while (progress) {
       progress = false;
       Expression selector = parseAssignableSelector(expression, true);
       if (!identical(selector, expression)) {
         expression = selector;
         progress = true;
         while (_isLikelyArgumentList()) {
           TypeArgumentList typeArguments = _parseOptionalTypeArguments();
           Expression currentExpression = expression;
           if (currentExpression is PropertyAccess) {
             expression = astFactory.methodInvocation(
                 currentExpression.target,
                 currentExpression.operator,
                 currentExpression.propertyName,
                 typeArguments,
                 parseArgumentList());
           } else {
             expression = astFactory.functionExpressionInvocation(
                 expression, typeArguments, parseArgumentList());
           }
         }
       }
     }
     if (_currentToken.type.isAssignmentOperator) {
       Token operator = getAndAdvance();
       _ensureAssignable(expression);
       expression = astFactory.assignmentExpression(
           expression, operator, parseExpressionWithoutCascade());
     }
     return expression;
   }

   /**
    * Parse a class declaration. The [commentAndMetadata] is the metadata to be
    * associated with the member. The [abstractKeyword] is the token for the
    * keyword 'abstract', or `null` if the keyword was not given. Return the
    * class declaration that was parsed.
    *
    * This method assumes that the current token matches `Keyword.CLASS`.
    *
    *     classDeclaration ::=
    *         metadata 'abstract'? 'class' name typeParameterList? (extendsClause withClause?)? implementsClause? '{' classMembers '}' |
    *         metadata 'abstract'? 'class' mixinApplicationClass
    */
   CompilationUnitMember parseClassDeclaration(
       CommentAndMetadata commentAndMetadata, Token abstractKeyword) {
     //
     // Parse the name and type parameters.
     //
     Token keyword = getAndAdvance();
     SimpleIdentifier name = parseSimpleIdentifier(isDeclaration: true);
     String className = name.name;
     TypeParameterList typeParameters = null;
     TokenType type = _currentToken.type;
     if (type == TokenType.LT) {
       typeParameters = parseTypeParameterList();
       type = _currentToken.type;
     }
     //
     // Check to see whether this might be a class type alias rather than a class
     // declaration.
     //
     if (type == TokenType.EQ) {
       return _parseClassTypeAliasAfterName(
           commentAndMetadata, abstractKeyword, keyword, name, typeParameters);
     }
     //
     // Parse the clauses. The parser accepts clauses in any order, but will
     // generate errors if they are not in the order required by the
     // specification.
     //
     ExtendsClause extendsClause = null;
     WithClause withClause = null;
     ImplementsClause implementsClause = null;
     bool foundClause = true;
     while (foundClause) {
       Keyword keyword = _currentToken.keyword;
       if (keyword == Keyword.EXTENDS) {
         if (extendsClause == null) {
           extendsClause = parseExtendsClause();
           if (withClause != null) {
             _reportErrorForToken(
                 ParserErrorCode.WITH_BEFORE_EXTENDS, withClause.withKeyword);
           } else if (implementsClause != null) {
             _reportErrorForToken(ParserErrorCode.IMPLEMENTS_BEFORE_EXTENDS,
                 implementsClause.implementsKeyword);
           }
         } else {
           _reportErrorForToken(ParserErrorCode.MULTIPLE_EXTENDS_CLAUSES,
               extendsClause.extendsKeyword);
           parseExtendsClause();
         }
       } else if (keyword == Keyword.WITH) {
         if (withClause == null) {
           withClause = parseWithClause();
           if (implementsClause != null) {
             _reportErrorForToken(ParserErrorCode.IMPLEMENTS_BEFORE_WITH,
                 implementsClause.implementsKeyword);
           }
         } else {
           _reportErrorForToken(
               ParserErrorCode.MULTIPLE_WITH_CLAUSES, withClause.withKeyword);
           parseWithClause();
           // TODO(brianwilkerson) Should we merge the list of applied mixins
           // into a single list?
         }
       } else if (keyword == Keyword.IMPLEMENTS) {
         if (implementsClause == null) {
           implementsClause = parseImplementsClause();
         } else {
           _reportErrorForToken(ParserErrorCode.MULTIPLE_IMPLEMENTS_CLAUSES,
               implementsClause.implementsKeyword);
           parseImplementsClause();
           // TODO(brianwilkerson) Should we merge the list of implemented
           // classes into a single list?
         }
       } else {
         foundClause = false;
       }
     }
     if (withClause != null && extendsClause == null) {
       _reportErrorForToken(
           ParserErrorCode.WITH_WITHOUT_EXTENDS, withClause.withKeyword);
     }
     //
     // Look for and skip over the extra-lingual 'native' specification.
     //
     NativeClause nativeClause = null;
     if (_matchesString(_NATIVE) && _tokenMatches(_peek(), TokenType.STRING)) {
       nativeClause = _parseNativeClause();
     }
     //
     // Parse the body of the class.
     //
     Token leftBracket = null;
     List<ClassMember> members = null;
     Token rightBracket = null;
     if (_matches(TokenType.OPEN_CURLY_BRACKET)) {
       leftBracket = getAndAdvance();
       members = _parseClassMembers(className, _getEndToken(leftBracket));
       rightBracket = _expect(TokenType.CLOSE_CURLY_BRACKET);
     } else {
       // Recovery: Check for an unmatched closing curly bracket and parse
       // members until it is reached.
       leftBracket = _createSyntheticToken(TokenType.OPEN_CURLY_BRACKET);
       rightBracket = _createSyntheticToken(TokenType.CLOSE_CURLY_BRACKET);
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_CLASS_BODY);
     }
     ClassDeclaration classDeclaration = astFactory.classDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         abstractKeyword,
         keyword,
         name,
         typeParameters,
         extendsClause,
         withClause,
         implementsClause,
         leftBracket,
         members,
         rightBracket);
     classDeclaration.nativeClause = nativeClause;
     return classDeclaration;
   }

   /**
    * Parse a class member. The [className] is the name of the class containing
    * the member being parsed. Return the class member that was parsed, or `null`
    * if what was found was not a valid class member.
    *
    *     classMemberDefinition ::=
    *         declaration ';'
    *       | methodSignature functionBody
    */
   ClassMember parseClassMember(String className) {
     CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
     Modifiers modifiers = parseModifiers();
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.VOID) {
       TypeName returnType = astFactory.typeName(
           astFactory.simpleIdentifier(getAndAdvance()), null);
       keyword = _currentToken.keyword;
       Token next = _peek();
       bool isFollowedByIdentifier = _tokenMatchesIdentifier(next);
       if (keyword == Keyword.GET && isFollowedByIdentifier) {
         _validateModifiersForGetterOrSetterOrMethod(modifiers);
         return parseGetter(commentAndMetadata, modifiers.externalKeyword,
             modifiers.staticKeyword, returnType);
       } else if (keyword == Keyword.SET && isFollowedByIdentifier) {
         _validateModifiersForGetterOrSetterOrMethod(modifiers);
         return parseSetter(commentAndMetadata, modifiers.externalKeyword,
             modifiers.staticKeyword, returnType);
       } else if (keyword == Keyword.OPERATOR && _isOperator(next)) {
         _validateModifiersForOperator(modifiers);
         return _parseOperatorAfterKeyword(commentAndMetadata,
             modifiers.externalKeyword, returnType, getAndAdvance());
       } else if (_matchesIdentifier() &&
           _peek().matchesAny(const <TokenType>[
             TokenType.OPEN_PAREN,
             TokenType.OPEN_CURLY_BRACKET,
             TokenType.FUNCTION,
             TokenType.LT
           ])) {
         _validateModifiersForGetterOrSetterOrMethod(modifiers);
         return _parseMethodDeclarationAfterReturnType(commentAndMetadata,
             modifiers.externalKeyword, modifiers.staticKeyword, returnType);
       } else {
         //
         // We have found an error of some kind. Try to recover.
         //
         if (_matchesIdentifier()) {
           if (_peek().matchesAny(const <TokenType>[
             TokenType.EQ,
             TokenType.COMMA,
             TokenType.SEMICOLON
           ])) {
             //
             // We appear to have a variable declaration with a type of "void".
             //
             _reportErrorForNode(ParserErrorCode.VOID_VARIABLE, returnType);
             return parseInitializedIdentifierList(
                 commentAndMetadata,
                 modifiers.staticKeyword,
                 modifiers.covariantKeyword,
                 _validateModifiersForField(modifiers),
                 returnType);
           }
         }
         if (_isOperator(_currentToken)) {
           //
           // We appear to have found an operator declaration without the
           // 'operator' keyword.
           //
           _validateModifiersForOperator(modifiers);
           return parseOperator(
               commentAndMetadata, modifiers.externalKeyword, returnType);
         }
         _reportErrorForToken(
             ParserErrorCode.EXPECTED_EXECUTABLE, _currentToken);
         return null;
       }
     }
     Token next = _peek();
     bool isFollowedByIdentifier = _tokenMatchesIdentifier(next);
     if (keyword == Keyword.GET && isFollowedByIdentifier) {
       _validateModifiersForGetterOrSetterOrMethod(modifiers);
       return parseGetter(commentAndMetadata, modifiers.externalKeyword,
           modifiers.staticKeyword, null);
     } else if (keyword == Keyword.SET && isFollowedByIdentifier) {
       _validateModifiersForGetterOrSetterOrMethod(modifiers);
       return parseSetter(commentAndMetadata, modifiers.externalKeyword,
           modifiers.staticKeyword, null);
     } else if (keyword == Keyword.OPERATOR && _isOperator(next)) {
       _validateModifiersForOperator(modifiers);
       return _parseOperatorAfterKeyword(
           commentAndMetadata, modifiers.externalKeyword, null, getAndAdvance());
     } else if (!_matchesIdentifier()) {
       //
       // Recover from an error.
       //
       if (_matchesKeyword(Keyword.CLASS)) {
         _reportErrorForCurrentToken(ParserErrorCode.CLASS_IN_CLASS);
         // TODO(brianwilkerson) We don't currently have any way to capture the
         // class that was parsed.
         parseClassDeclaration(commentAndMetadata, null);
         return null;
       } else if (_matchesKeyword(Keyword.ABSTRACT) &&
           _tokenMatchesKeyword(_peek(), Keyword.CLASS)) {
         _reportErrorForToken(ParserErrorCode.CLASS_IN_CLASS, _peek());
         // TODO(brianwilkerson) We don't currently have any way to capture the
         // class that was parsed.
         parseClassDeclaration(commentAndMetadata, getAndAdvance());
         return null;
       } else if (_matchesKeyword(Keyword.ENUM)) {
         _reportErrorForToken(ParserErrorCode.ENUM_IN_CLASS, _peek());
         // TODO(brianwilkerson) We don't currently have any way to capture the
         // enum that was parsed.
         parseEnumDeclaration(commentAndMetadata);
         return null;
       } else if (_isOperator(_currentToken)) {
         //
         // We appear to have found an operator declaration without the
         // 'operator' keyword.
         //
         _validateModifiersForOperator(modifiers);
         return parseOperator(
             commentAndMetadata, modifiers.externalKeyword, null);
       }
       Token keyword = modifiers.varKeyword ??
           modifiers.finalKeyword ??
           modifiers.constKeyword;
       if (keyword != null) {
         //
         // We appear to have found an incomplete field declaration.
         //
         _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
         VariableDeclaration variable = astFactory.variableDeclaration(
             createSyntheticIdentifier(), null, null);
         List<VariableDeclaration> variables = <VariableDeclaration>[variable];
         FieldDeclarationImpl field = astFactory.fieldDeclaration(
             commentAndMetadata.comment,
             commentAndMetadata.metadata,
             null,
             astFactory.variableDeclarationList(
                 null, null, keyword, null, variables),
             _expect(TokenType.SEMICOLON));
         field.covariantKeyword = modifiers.covariantKeyword;
         return field;
       }
       _reportErrorForToken(
           ParserErrorCode.EXPECTED_CLASS_MEMBER, _currentToken);
       if (commentAndMetadata.comment != null ||
           commentAndMetadata.hasMetadata) {
         //
         // We appear to have found an incomplete declaration at the end of the
         // class. At this point it consists of a metadata, which we don't want
         // to loose, so we'll treat it as a method declaration with a missing
         // name, parameters and empty body.
         //
         return astFactory.methodDeclaration(
             commentAndMetadata.comment,
             commentAndMetadata.metadata,
             null,
             null,
             null,
             null,
             null,
             createSyntheticIdentifier(isDeclaration: true),
             null,
             astFactory.formalParameterList(
                 _createSyntheticToken(TokenType.OPEN_PAREN),
                 <FormalParameter>[],
                 null,
                 null,
                 _createSyntheticToken(TokenType.CLOSE_PAREN)),
             astFactory
                 .emptyFunctionBody(_createSyntheticToken(TokenType.SEMICOLON)));
       }
       return null;
     } else if (_tokenMatches(next, TokenType.PERIOD) &&
         _tokenMatchesIdentifier(_peekAt(2)) &&
         _tokenMatches(_peekAt(3), TokenType.OPEN_PAREN)) {
       return _parseConstructor(
           commentAndMetadata,
           modifiers.externalKeyword,
           _validateModifiersForConstructor(modifiers),
           modifiers.factoryKeyword,
           parseSimpleIdentifier(),
           getAndAdvance(),
           parseSimpleIdentifier(isDeclaration: true),
           parseFormalParameterList());
     } else if (_tokenMatches(next, TokenType.OPEN_PAREN)) {
       TypeName returnType = _parseOptionalTypeNameComment();
       SimpleIdentifier methodName = parseSimpleIdentifier(isDeclaration: true);
       TypeParameterList typeParameters = _parseGenericCommentTypeParameters();
       FormalParameterList parameters = parseFormalParameterList();
       if (_matches(TokenType.COLON) ||
           modifiers.factoryKeyword != null ||
           methodName.name == className) {
         return _parseConstructor(
             commentAndMetadata,
             modifiers.externalKeyword,
             _validateModifiersForConstructor(modifiers),
             modifiers.factoryKeyword,
             astFactory.simpleIdentifier(methodName.token, isDeclaration: false),
             null,
             null,
             parameters);
       }
       _validateModifiersForGetterOrSetterOrMethod(modifiers);
       _validateFormalParameterList(parameters);
       return _parseMethodDeclarationAfterParameters(
           commentAndMetadata,
           modifiers.externalKeyword,
           modifiers.staticKeyword,
           returnType,
           methodName,
           typeParameters,
           parameters);
     } else if (next.matchesAny(const <TokenType>[
       TokenType.EQ,
       TokenType.COMMA,
       TokenType.SEMICOLON
     ])) {
       if (modifiers.constKeyword == null &&
           modifiers.finalKeyword == null &&
           modifiers.varKeyword == null) {
         _reportErrorForCurrentToken(
             ParserErrorCode.MISSING_CONST_FINAL_VAR_OR_TYPE);
       }
       return parseInitializedIdentifierList(
           commentAndMetadata,
           modifiers.staticKeyword,
           modifiers.covariantKeyword,
           _validateModifiersForField(modifiers),
           null);
     } else if (keyword == Keyword.TYPEDEF) {
       _reportErrorForCurrentToken(ParserErrorCode.TYPEDEF_IN_CLASS);
       // TODO(brianwilkerson) We don't currently have any way to capture the
       // function type alias that was parsed.
       _parseFunctionTypeAlias(commentAndMetadata, getAndAdvance());
       return null;
     } else {
       Token token = _skipTypeParameterList(_peek());
       if (token != null && _tokenMatches(token, TokenType.OPEN_PAREN)) {
         return _parseMethodDeclarationAfterReturnType(commentAndMetadata,
             modifiers.externalKeyword, modifiers.staticKeyword, null);
       }
     }
     TypeAnnotation type = _parseTypeAnnotationAfterIdentifier();
     keyword = _currentToken.keyword;
     next = _peek();
     isFollowedByIdentifier = _tokenMatchesIdentifier(next);
     if (keyword == Keyword.GET && isFollowedByIdentifier) {
       _validateModifiersForGetterOrSetterOrMethod(modifiers);
       return parseGetter(commentAndMetadata, modifiers.externalKeyword,
           modifiers.staticKeyword, type);
     } else if (keyword == Keyword.SET && isFollowedByIdentifier) {
       _validateModifiersForGetterOrSetterOrMethod(modifiers);
       return parseSetter(commentAndMetadata, modifiers.externalKeyword,
           modifiers.staticKeyword, type);
     } else if (keyword == Keyword.OPERATOR && _isOperator(next)) {
       _validateModifiersForOperator(modifiers);
       return _parseOperatorAfterKeyword(
           commentAndMetadata, modifiers.externalKeyword, type, getAndAdvance());
     } else if (!_matchesIdentifier()) {
       if (_matches(TokenType.CLOSE_CURLY_BRACKET)) {
         //
         // We appear to have found an incomplete declaration at the end of the
         // class. At this point it consists of a type name, so we'll treat it as
         // a field declaration with a missing field name and semicolon.
         //
         return parseInitializedIdentifierList(
             commentAndMetadata,
             modifiers.staticKeyword,
             modifiers.covariantKeyword,
             _validateModifiersForField(modifiers),
             type);
       }
       if (_isOperator(_currentToken)) {
         //
         // We appear to have found an operator declaration without the
         // 'operator' keyword.
         //
         _validateModifiersForOperator(modifiers);
         return parseOperator(
             commentAndMetadata, modifiers.externalKeyword, type);
       }
       //
       // We appear to have found an incomplete declaration before another
       // declaration. At this point it consists of a type name, so we'll treat
       // it as a field declaration with a missing field name and semicolon.
       //
       _reportErrorForToken(
           ParserErrorCode.EXPECTED_CLASS_MEMBER, _currentToken);
       try {
         _lockErrorListener();
         return parseInitializedIdentifierList(
             commentAndMetadata,
             modifiers.staticKeyword,
             modifiers.covariantKeyword,
             _validateModifiersForField(modifiers),
             type);
       } finally {
         _unlockErrorListener();
       }
     } else if (_tokenMatches(next, TokenType.OPEN_PAREN)) {
       SimpleIdentifier methodName =
           _parseSimpleIdentifierUnchecked(isDeclaration: true);
       TypeParameterList typeParameters = _parseGenericCommentTypeParameters();
       FormalParameterList parameters = parseFormalParameterList();
       if (methodName.name == className) {
         _reportErrorForNode(ParserErrorCode.CONSTRUCTOR_WITH_RETURN_TYPE, type);
         return _parseConstructor(
             commentAndMetadata,
             modifiers.externalKeyword,
             _validateModifiersForConstructor(modifiers),
             modifiers.factoryKeyword,
             astFactory.simpleIdentifier(methodName.token, isDeclaration: true),
             null,
             null,
             parameters);
       }
       _validateModifiersForGetterOrSetterOrMethod(modifiers);
       _validateFormalParameterList(parameters);
       return _parseMethodDeclarationAfterParameters(
           commentAndMetadata,
           modifiers.externalKeyword,
           modifiers.staticKeyword,
           type,
           methodName,
           typeParameters,
           parameters);
     } else if (_tokenMatches(next, TokenType.LT)) {
       return _parseMethodDeclarationAfterReturnType(commentAndMetadata,
           modifiers.externalKeyword, modifiers.staticKeyword, type);
     } else if (_tokenMatches(next, TokenType.OPEN_CURLY_BRACKET)) {
       // We have found "TypeName identifier {", and are guessing that this is a
       // getter without the keyword 'get'.
       _validateModifiersForGetterOrSetterOrMethod(modifiers);
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_GET);
       _currentToken = _injectToken(
           new Parser_SyntheticKeywordToken(Keyword.GET, _currentToken.offset));
       return parseGetter(commentAndMetadata, modifiers.externalKeyword,
           modifiers.staticKeyword, type);
     }
     return parseInitializedIdentifierList(
         commentAndMetadata,
         modifiers.staticKeyword,
         modifiers.covariantKeyword,
         _validateModifiersForField(modifiers),
         type);
   }

   /**
    * Parse a single combinator. Return the combinator that was parsed, or `null`
    * if no combinator is found.
    *
    *     combinator ::=
    *         'show' identifier (',' identifier)*
    *       | 'hide' identifier (',' identifier)*
    */
   Combinator parseCombinator() {
     if (_matchesString(_SHOW)) {
       return astFactory.showCombinator(getAndAdvance(), parseIdentifierList());
     } else if (_matchesString(_HIDE)) {
       return astFactory.hideCombinator(getAndAdvance(), parseIdentifierList());
     }
     return null;
   }

   /**
    * Parse a list of combinators in a directive. Return the combinators that
    * were parsed, or `null` if there are no combinators.
    *
    *     combinator ::=
    *         'show' identifier (',' identifier)*
    *       | 'hide' identifier (',' identifier)*
    */
   List<Combinator> parseCombinators() {
     List<Combinator> combinators = null;
     while (true) {
       Combinator combinator = parseCombinator();
       if (combinator == null) {
         break;
       }
       combinators ??= <Combinator>[];
       combinators.add(combinator);
     }
     return combinators;
   }

   /**
    * Parse the documentation comment and metadata preceding a declaration. This
    * method allows any number of documentation comments to occur before, after
    * or between the metadata, but only returns the last (right-most)
    * documentation comment that is found. Return the documentation comment and
    * metadata that were parsed.
    *
    *     metadata ::=
    *         annotation*
    */
   CommentAndMetadata parseCommentAndMetadata() {
     // TODO(brianwilkerson) Consider making the creation of documentation
     // comments be lazy.
     List<DocumentationCommentToken> tokens = parseDocumentationCommentTokens();
     List<Annotation> metadata = null;
     while (_matches(TokenType.AT)) {
       metadata ??= <Annotation>[];
       metadata.add(parseAnnotation());
       List<DocumentationCommentToken> optionalTokens =
           parseDocumentationCommentTokens();
       if (optionalTokens != null) {
         tokens = optionalTokens;
       }
     }
     return new CommentAndMetadata(parseDocumentationComment(tokens), metadata);
   }

   /**
    * Parse a comment reference from the source between square brackets. The
    * [referenceSource] is the source occurring between the square brackets
    * within a documentation comment. The [sourceOffset] is the offset of the
    * first character of the reference source. Return the comment reference that
    * was parsed, or `null` if no reference could be found.
    *
    *     commentReference ::=
    *         'new'? prefixedIdentifier
    */
   CommentReference parseCommentReference(
       String referenceSource, int sourceOffset) {
     // TODO(brianwilkerson) The errors are not getting the right offset/length
     // and are being duplicated.
     try {
       BooleanErrorListener listener = new BooleanErrorListener();
       Scanner scanner = new Scanner(
           null, new SubSequenceReader(referenceSource, sourceOffset), listener);
       scanner.setSourceStart(1, 1);
       Token firstToken = scanner.tokenize();
       if (listener.errorReported) {
         return null;
       }
       if (firstToken.type == TokenType.EOF) {
         Token syntheticToken =
             new SyntheticStringToken(TokenType.IDENTIFIER, "", sourceOffset);
         syntheticToken.setNext(firstToken);
         return astFactory.commentReference(
             null, astFactory.simpleIdentifier(syntheticToken));
       }
       Token newKeyword = null;
       if (_tokenMatchesKeyword(firstToken, Keyword.NEW)) {
         newKeyword = firstToken;
         firstToken = firstToken.next;
       }
       if (firstToken.isUserDefinableOperator) {
         if (firstToken.next.type != TokenType.EOF) {
           return null;
         }
         Identifier identifier = astFactory.simpleIdentifier(firstToken);
         return astFactory.commentReference(null, identifier);
       } else if (_tokenMatchesKeyword(firstToken, Keyword.OPERATOR)) {
         Token secondToken = firstToken.next;
         if (secondToken.isUserDefinableOperator) {
           if (secondToken.next.type != TokenType.EOF) {
             return null;
           }
           Identifier identifier = astFactory.simpleIdentifier(secondToken);
           return astFactory.commentReference(null, identifier);
         }
         return null;
       } else if (_tokenMatchesIdentifier(firstToken)) {
         Token secondToken = firstToken.next;
         Token thirdToken = secondToken.next;
         Token nextToken;
         Identifier identifier;
         if (_tokenMatches(secondToken, TokenType.PERIOD)) {
           if (thirdToken.isUserDefinableOperator) {
             identifier = astFactory.prefixedIdentifier(
                 astFactory.simpleIdentifier(firstToken),
                 secondToken,
                 astFactory.simpleIdentifier(thirdToken));
             nextToken = thirdToken.next;
           } else if (_tokenMatchesKeyword(thirdToken, Keyword.OPERATOR)) {
             Token fourthToken = thirdToken.next;
             if (fourthToken.isUserDefinableOperator) {
               identifier = astFactory.prefixedIdentifier(
                   astFactory.simpleIdentifier(firstToken),
                   secondToken,
                   astFactory.simpleIdentifier(fourthToken));
               nextToken = fourthToken.next;
             } else {
               return null;
             }
           } else if (_tokenMatchesIdentifier(thirdToken)) {
             identifier = astFactory.prefixedIdentifier(
                 astFactory.simpleIdentifier(firstToken),
                 secondToken,
                 astFactory.simpleIdentifier(thirdToken));
             nextToken = thirdToken.next;
           }
         } else {
           identifier = astFactory.simpleIdentifier(firstToken);
           nextToken = firstToken.next;
         }
         if (nextToken.type != TokenType.EOF) {
           return null;
         }
         return astFactory.commentReference(newKeyword, identifier);
       } else {
         Keyword keyword = firstToken.keyword;
         if (keyword == Keyword.THIS ||
             keyword == Keyword.NULL ||
             keyword == Keyword.TRUE ||
             keyword == Keyword.FALSE) {
           // TODO(brianwilkerson) If we want to support this we will need to
           // extend the definition of CommentReference to take an expression
           // rather than an identifier. For now we just ignore it to reduce the
           // number of errors produced, but that's probably not a valid long term
           // approach.
           return null;
         }
       }
     } catch (exception) {
       // Ignored because we assume that it wasn't a real comment reference.
     }
     return null;
   }

   /**
    * Parse all of the comment references occurring in the given array of
    * documentation comments. The [tokens] are the comment tokens representing
    * the documentation comments to be parsed. Return the comment references that
    * were parsed.
    *
    *     commentReference ::=
    *         '[' 'new'? qualified ']' libraryReference?
    *
    *     libraryReference ::=
    *          '(' stringLiteral ')'
    */
   List<CommentReference> parseCommentReferences(
       List<DocumentationCommentToken> tokens) {
     List<CommentReference> references = <CommentReference>[];
     bool isInGitHubCodeBlock = false;
     for (DocumentationCommentToken token in tokens) {
       String comment = token.lexeme;
       // Skip GitHub code blocks.
       // https://help.github.com/articles/creating-and-highlighting-code-blocks/
       if (tokens.length != 1) {
         if (comment.indexOf('```') != -1) {
           isInGitHubCodeBlock = !isInGitHubCodeBlock;
         }
         if (isInGitHubCodeBlock) {
           continue;
         }
       }
       // Remove GitHub include code.
       comment = _removeGitHubInlineCode(comment);
       // Find references.
       int length = comment.length;
       List<List<int>> codeBlockRanges = _getCodeBlockRanges(comment);
       int leftIndex = comment.indexOf('[');
       while (leftIndex >= 0 && leftIndex + 1 < length) {
         List<int> range = _findRange(codeBlockRanges, leftIndex);
         if (range == null) {
           int nameOffset = token.offset + leftIndex + 1;
           int rightIndex = comment.indexOf(']', leftIndex);
           if (rightIndex >= 0) {
             int firstChar = comment.codeUnitAt(leftIndex + 1);
             if (firstChar != 0x27 && firstChar != 0x22) {
               if (_isLinkText(comment, rightIndex)) {
                 // TODO(brianwilkerson) Handle the case where there's a library
                 // URI in the link text.
               } else {
                 CommentReference reference = parseCommentReference(
                     comment.substring(leftIndex + 1, rightIndex), nameOffset);
                 if (reference != null) {
                   references.add(reference);
                   token.references.add(reference.beginToken);
                 }
               }
             }
           } else {
             // terminating ']' is not typed yet
             int charAfterLeft = comment.codeUnitAt(leftIndex + 1);
             Token nameToken;
             if (Character.isLetterOrDigit(charAfterLeft)) {
               int nameEnd = StringUtilities.indexOfFirstNotLetterDigit(
                   comment, leftIndex + 1);
               String name = comment.substring(leftIndex + 1, nameEnd);
               nameToken =
                   new StringToken(TokenType.IDENTIFIER, name, nameOffset);
             } else {
               nameToken = new SyntheticStringToken(
                   TokenType.IDENTIFIER, '', nameOffset);
             }
             nameToken.setNext(new SimpleToken(TokenType.EOF, nameToken.end));
             references.add(astFactory.commentReference(
                 null, astFactory.simpleIdentifier(nameToken)));
             token.references.add(nameToken);
             // next character
             rightIndex = leftIndex + 1;
           }
           leftIndex = comment.indexOf('[', rightIndex);
         } else {
           leftIndex = comment.indexOf('[', range[1]);
         }
       }
     }
     return references;
   }

   /**
    * Parse a compilation unit, starting with the given [token]. Return the
    * compilation unit that was parsed.
    */
   CompilationUnit parseCompilationUnit(Token token) {
     _currentToken = token;
     return parseCompilationUnit2();
   }

   /**
    * Parse a compilation unit. Return the compilation unit that was parsed.
    *
    * Specified:
    *
    *     compilationUnit ::=
    *         scriptTag? directive* topLevelDeclaration*
    *
    * Actual:
    *
    *     compilationUnit ::=
    *         scriptTag? topLevelElement*
    *
    *     topLevelElement ::=
    *         directive
    *       | topLevelDeclaration
    */
   CompilationUnit parseCompilationUnit2() {
     Token firstToken = _currentToken;
     ScriptTag scriptTag = null;
     if (_matches(TokenType.SCRIPT_TAG)) {
       scriptTag = astFactory.scriptTag(getAndAdvance());
     }
     //
     // Even though all directives must appear before declarations and must occur
     // in a given order, we allow directives and declarations to occur in any
     // order so that we can recover better.
     //
     bool libraryDirectiveFound = false;
     bool partOfDirectiveFound = false;
     bool partDirectiveFound = false;
     bool directiveFoundAfterDeclaration = false;
     List<Directive> directives = <Directive>[];
     List<CompilationUnitMember> declarations = <CompilationUnitMember>[];
     Token memberStart = _currentToken;
     TokenType type = _currentToken.type;
     while (type != TokenType.EOF) {
       CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
       Keyword keyword = _currentToken.keyword;
       TokenType nextType = _currentToken.next.type;
       if ((keyword == Keyword.IMPORT ||
               keyword == Keyword.EXPORT ||
               keyword == Keyword.LIBRARY ||
               keyword == Keyword.PART) &&
           nextType != TokenType.PERIOD &&
           nextType != TokenType.LT &&
           nextType != TokenType.OPEN_PAREN) {
         Directive parseDirective() {
           if (keyword == Keyword.IMPORT) {
             if (partDirectiveFound) {
               _reportErrorForCurrentToken(
                   ParserErrorCode.IMPORT_DIRECTIVE_AFTER_PART_DIRECTIVE);
             }
             return parseImportDirective(commentAndMetadata);
           } else if (keyword == Keyword.EXPORT) {
             if (partDirectiveFound) {
               _reportErrorForCurrentToken(
                   ParserErrorCode.EXPORT_DIRECTIVE_AFTER_PART_DIRECTIVE);
             }
             return parseExportDirective(commentAndMetadata);
           } else if (keyword == Keyword.LIBRARY) {
             if (libraryDirectiveFound) {
               _reportErrorForCurrentToken(
                   ParserErrorCode.MULTIPLE_LIBRARY_DIRECTIVES);
             } else {
               if (directives.length > 0) {
                 _reportErrorForCurrentToken(
                     ParserErrorCode.LIBRARY_DIRECTIVE_NOT_FIRST);
               }
               libraryDirectiveFound = true;
             }
             return parseLibraryDirective(commentAndMetadata);
           } else if (keyword == Keyword.PART) {
             if (_tokenMatchesString(_peek(), _OF)) {
               partOfDirectiveFound = true;
               return _parsePartOfDirective(commentAndMetadata);
             } else {
               partDirectiveFound = true;
               return _parsePartDirective(commentAndMetadata);
             }
           } else {
             // Internal error: this method should not have been invoked if the
             // current token was something other than one of the above.
             throw new StateError(
                 "parseDirective invoked in an invalid state (currentToken = $_currentToken)");
           }
         }

         Directive directive = parseDirective();
         if (declarations.length > 0 && !directiveFoundAfterDeclaration) {
           _reportErrorForToken(ParserErrorCode.DIRECTIVE_AFTER_DECLARATION,
               directive.beginToken);
           directiveFoundAfterDeclaration = true;
         }
         directives.add(directive);
       } else if (type == TokenType.SEMICOLON) {
         // TODO(brianwilkerson) Consider moving this error detection into
         // _parseCompilationUnitMember (in the places where EXPECTED_EXECUTABLE
         // is being generated).
         _reportErrorForToken(ParserErrorCode.UNEXPECTED_TOKEN, _currentToken,
             [_currentToken.lexeme]);
         _advance();
       } else {
         CompilationUnitMember member =
             parseCompilationUnitMember(commentAndMetadata);
         if (member != null) {
           declarations.add(member);
         }
       }
       if (identical(_currentToken, memberStart)) {
         _reportErrorForToken(ParserErrorCode.UNEXPECTED_TOKEN, _currentToken,
             [_currentToken.lexeme]);
         _advance();
         while (!_matches(TokenType.EOF) &&
             !_couldBeStartOfCompilationUnitMember()) {
           _advance();
         }
       }
       memberStart = _currentToken;
       type = _currentToken.type;
     }
     if (partOfDirectiveFound && directives.length > 1) {
       // TODO(brianwilkerson) Improve error reporting when both a library and
       // part-of directive are found.
 //      if (libraryDirectiveFound) {
 //        int directiveCount = directives.length;
 //        for (int i = 0; i < directiveCount; i++) {
 //          Directive directive = directives[i];
 //          if (directive is PartOfDirective) {
 //            _reportErrorForToken(
 //                ParserErrorCode.PART_OF_IN_LIBRARY, directive.partKeyword);
 //          }
 //        }
 //      } else {
       bool firstPartOf = true;
       int directiveCount = directives.length;
       for (int i = 0; i < directiveCount; i++) {
         Directive directive = directives[i];
         if (directive is PartOfDirective) {
           if (firstPartOf) {
             firstPartOf = false;
           } else {
             _reportErrorForToken(ParserErrorCode.MULTIPLE_PART_OF_DIRECTIVES,
                 directive.partKeyword);
           }
         } else {
           _reportErrorForToken(ParserErrorCode.NON_PART_OF_DIRECTIVE_IN_PART,
               directives[i].keyword);
         }
 //        }
       }
     }
     return astFactory.compilationUnit(
         firstToken, scriptTag, directives, declarations, _currentToken);
   }

   /**
    * Parse a compilation unit member. The [commentAndMetadata] is the metadata
    * to be associated with the member. Return the compilation unit member that
    * was parsed, or `null` if what was parsed could not be represented as a
    * compilation unit member.
    *
    *     compilationUnitMember ::=
    *         classDefinition
    *       | functionTypeAlias
    *       | external functionSignature
    *       | external getterSignature
    *       | external setterSignature
    *       | functionSignature functionBody
    *       | returnType? getOrSet identifier formalParameterList functionBody
    *       | (final | const) type? staticFinalDeclarationList ';'
    *       | variableDeclaration ';'
    */
   CompilationUnitMember parseCompilationUnitMember(
       CommentAndMetadata commentAndMetadata) {
     Modifiers modifiers = parseModifiers();
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.CLASS) {
       return parseClassDeclaration(
           commentAndMetadata, _validateModifiersForClass(modifiers));
     }
     Token next = _peek();
     TokenType nextType = next.type;
     if (keyword == Keyword.TYPEDEF &&
         nextType != TokenType.PERIOD &&
         nextType != TokenType.LT &&
         nextType != TokenType.OPEN_PAREN) {
       _validateModifiersForTypedef(modifiers);
       return parseTypeAlias(commentAndMetadata);
     } else if (keyword == Keyword.ENUM) {
       _validateModifiersForEnum(modifiers);
       return parseEnumDeclaration(commentAndMetadata);
     } else if (keyword == Keyword.VOID) {
       TypeName returnType = astFactory.typeName(
           astFactory.simpleIdentifier(getAndAdvance()), null);
       keyword = _currentToken.keyword;
       next = _peek();
       if ((keyword == Keyword.GET || keyword == Keyword.SET) &&
           _tokenMatchesIdentifier(next)) {
         _validateModifiersForTopLevelFunction(modifiers);
         return parseFunctionDeclaration(
             commentAndMetadata, modifiers.externalKeyword, returnType);
       } else if (keyword == Keyword.OPERATOR && _isOperator(next)) {
         _reportErrorForToken(ParserErrorCode.TOP_LEVEL_OPERATOR, _currentToken);
         return _convertToFunctionDeclaration(_parseOperatorAfterKeyword(
             commentAndMetadata,
             modifiers.externalKeyword,
             returnType,
             getAndAdvance()));
       } else if (_matchesIdentifier() &&
           next.matchesAny(const <TokenType>[
             TokenType.OPEN_PAREN,
             TokenType.OPEN_CURLY_BRACKET,
             TokenType.FUNCTION,
             TokenType.LT
           ])) {
         _validateModifiersForTopLevelFunction(modifiers);
         return parseFunctionDeclaration(
             commentAndMetadata, modifiers.externalKeyword, returnType);
       } else {
         //
         // We have found an error of some kind. Try to recover.
         //
         if (_matchesIdentifier()) {
           if (next.matchesAny(const <TokenType>[
             TokenType.EQ,
             TokenType.COMMA,
             TokenType.SEMICOLON
           ])) {
             //
             // We appear to have a variable declaration with a type of "void".
             //
             _reportErrorForNode(ParserErrorCode.VOID_VARIABLE, returnType);
             return astFactory.topLevelVariableDeclaration(
                 commentAndMetadata.comment,
                 commentAndMetadata.metadata,
                 parseVariableDeclarationListAfterType(null,
                     _validateModifiersForTopLevelVariable(modifiers), null),
                 _expect(TokenType.SEMICOLON));
           }
         }
         _reportErrorForToken(
             ParserErrorCode.EXPECTED_EXECUTABLE, _currentToken);
         return null;
       }
     } else if ((keyword == Keyword.GET || keyword == Keyword.SET) &&
         _tokenMatchesIdentifier(next)) {
       _validateModifiersForTopLevelFunction(modifiers);
       return parseFunctionDeclaration(
           commentAndMetadata, modifiers.externalKeyword, null);
     } else if (keyword == Keyword.OPERATOR && _isOperator(next)) {
       _reportErrorForToken(ParserErrorCode.TOP_LEVEL_OPERATOR, _currentToken);
       return _convertToFunctionDeclaration(_parseOperatorAfterKeyword(
           commentAndMetadata,
           modifiers.externalKeyword,
           null,
           getAndAdvance()));
     } else if (!_matchesIdentifier()) {
       Token keyword = modifiers.varKeyword;
       if (keyword == null) {
         keyword = modifiers.finalKeyword;
       }
       if (keyword == null) {
         keyword = modifiers.constKeyword;
       }
       if (keyword != null) {
         //
         // We appear to have found an incomplete top-level variable declaration.
         //
         _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
         VariableDeclaration variable = astFactory.variableDeclaration(
             createSyntheticIdentifier(), null, null);
         List<VariableDeclaration> variables = <VariableDeclaration>[variable];
         return astFactory.topLevelVariableDeclaration(
             commentAndMetadata.comment,
             commentAndMetadata.metadata,
             astFactory.variableDeclarationList(
                 null, null, keyword, null, variables),
             _expect(TokenType.SEMICOLON));
       }
       _reportErrorForToken(ParserErrorCode.EXPECTED_EXECUTABLE, _currentToken);
       return null;
     } else if (_isPeekGenericTypeParametersAndOpenParen()) {
       return parseFunctionDeclaration(
           commentAndMetadata, modifiers.externalKeyword, null);
     } else if (_tokenMatches(next, TokenType.OPEN_PAREN)) {
       TypeName returnType = _parseOptionalTypeNameComment();
       _validateModifiersForTopLevelFunction(modifiers);
       return parseFunctionDeclaration(
           commentAndMetadata, modifiers.externalKeyword, returnType);
     } else if (next.matchesAny(const <TokenType>[
       TokenType.EQ,
       TokenType.COMMA,
       TokenType.SEMICOLON
     ])) {
       if (modifiers.constKeyword == null &&
           modifiers.finalKeyword == null &&
           modifiers.varKeyword == null) {
         _reportErrorForCurrentToken(
             ParserErrorCode.MISSING_CONST_FINAL_VAR_OR_TYPE);
       }
       return astFactory.topLevelVariableDeclaration(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           parseVariableDeclarationListAfterType(
               null, _validateModifiersForTopLevelVariable(modifiers), null),
           _expect(TokenType.SEMICOLON));
     }
     TypeAnnotation returnType = parseReturnType(false);
     keyword = _currentToken.keyword;
     next = _peek();
     if ((keyword == Keyword.GET || keyword == Keyword.SET) &&
         _tokenMatchesIdentifier(next)) {
       _validateModifiersForTopLevelFunction(modifiers);
       return parseFunctionDeclaration(
           commentAndMetadata, modifiers.externalKeyword, returnType);
     } else if (keyword == Keyword.OPERATOR && _isOperator(next)) {
       _reportErrorForToken(ParserErrorCode.TOP_LEVEL_OPERATOR, _currentToken);
       return _convertToFunctionDeclaration(_parseOperatorAfterKeyword(
           commentAndMetadata,
           modifiers.externalKeyword,
           returnType,
           getAndAdvance()));
     } else if (_matches(TokenType.AT)) {
       return astFactory.topLevelVariableDeclaration(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           parseVariableDeclarationListAfterType(null,
               _validateModifiersForTopLevelVariable(modifiers), returnType),
           _expect(TokenType.SEMICOLON));
     } else if (!_matchesIdentifier()) {
       // TODO(brianwilkerson) Generalize this error. We could also be parsing a
       // top-level variable at this point.
       _reportErrorForToken(ParserErrorCode.EXPECTED_EXECUTABLE, _currentToken);
       Token semicolon;
       if (_matches(TokenType.SEMICOLON)) {
         semicolon = getAndAdvance();
       } else {
         semicolon = _createSyntheticToken(TokenType.SEMICOLON);
       }
       VariableDeclaration variable = astFactory.variableDeclaration(
           createSyntheticIdentifier(), null, null);
       List<VariableDeclaration> variables = <VariableDeclaration>[variable];
       return astFactory.topLevelVariableDeclaration(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           astFactory.variableDeclarationList(
               null, null, null, returnType, variables),
           semicolon);
     } else if (next.matchesAny(const <TokenType>[
       TokenType.OPEN_PAREN,
       TokenType.FUNCTION,
       TokenType.OPEN_CURLY_BRACKET,
       TokenType.LT
     ])) {
       _validateModifiersForTopLevelFunction(modifiers);
       return parseFunctionDeclaration(
           commentAndMetadata, modifiers.externalKeyword, returnType);
     }
     return astFactory.topLevelVariableDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         parseVariableDeclarationListAfterType(
             null, _validateModifiersForTopLevelVariable(modifiers), returnType),
         _expect(TokenType.SEMICOLON));
   }

   /**
    * Parse a conditional expression. Return the conditional expression that was
    * parsed.
    *
    *     conditionalExpression ::=
    *         ifNullExpression ('?' expressionWithoutCascade ':' expressionWithoutCascade)?
    */
   Expression parseConditionalExpression() {
     Expression condition = parseIfNullExpression();
     if (_currentToken.type != TokenType.QUESTION) {
       return condition;
     }
     Token question = getAndAdvance();
     Expression thenExpression = parseExpressionWithoutCascade();
     Token colon = _expect(TokenType.COLON);
     Expression elseExpression = parseExpressionWithoutCascade();
     return astFactory.conditionalExpression(
         condition, question, thenExpression, colon, elseExpression);
   }

   /**
    * Parse a configuration in either an import or export directive.
    *
    * This method assumes that the current token matches `Keyword.IF`.
    *
    *     configuration ::=
    *         'if' '(' test ')' uri
    *
    *     test ::=
    *         dottedName ('==' stringLiteral)?
    *
    *     dottedName ::=
    *         identifier ('.' identifier)*
    */
   Configuration parseConfiguration() {
     Token ifKeyword = getAndAdvance();
     Token leftParenthesis = _expect(TokenType.OPEN_PAREN);
     DottedName name = parseDottedName();
     Token equalToken = null;
     StringLiteral value = null;
     if (_matches(TokenType.EQ_EQ)) {
       equalToken = getAndAdvance();
       value = parseStringLiteral();
       if (value is StringInterpolation) {
         _reportErrorForNode(
             ParserErrorCode.INVALID_LITERAL_IN_CONFIGURATION, value);
       }
     }
     Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
     StringLiteral libraryUri = _parseUri();
     return astFactory.configuration(ifKeyword, leftParenthesis, name,
         equalToken, value, rightParenthesis, libraryUri);
   }

   /**
    * Parse a const expression. Return the const expression that was parsed.
    *
    * This method assumes that the current token matches `Keyword.CONST`.
    *
    *     constExpression ::=
    *         instanceCreationExpression
    *       | listLiteral
    *       | mapLiteral
    */
   Expression parseConstExpression() {
     Token keyword = getAndAdvance();
     TokenType type = _currentToken.type;
     if (type == TokenType.LT || _injectGenericCommentTypeList()) {
       return parseListOrMapLiteral(keyword);
     } else if (type == TokenType.OPEN_SQUARE_BRACKET ||
         type == TokenType.INDEX) {
       return parseListLiteral(keyword, null);
     } else if (type == TokenType.OPEN_CURLY_BRACKET) {
       return parseMapLiteral(keyword, null);
     }
     return parseInstanceCreationExpression(keyword);
   }

   /**
    * Parse a field initializer within a constructor. The flag [hasThis] should
    * be true if the current token is `this`. Return the field initializer that
    * was parsed.
    *
    *     fieldInitializer:
    *         ('this' '.')? identifier '=' conditionalExpression cascadeSection*
    */
   ConstructorFieldInitializer parseConstructorFieldInitializer(bool hasThis) {
     Token keywordToken = null;
     Token period = null;
     if (hasThis) {
       keywordToken = getAndAdvance();
       period = _expect(TokenType.PERIOD);
     }
     SimpleIdentifier fieldName = parseSimpleIdentifier();
     Token equals = null;
     TokenType type = _currentToken.type;
     if (type == TokenType.EQ) {
       equals = getAndAdvance();
     } else {
       _reportErrorForCurrentToken(
           ParserErrorCode.MISSING_ASSIGNMENT_IN_INITIALIZER);
       Keyword keyword = _currentToken.keyword;
       if (keyword != Keyword.THIS &&
           keyword != Keyword.SUPER &&
           type != TokenType.OPEN_CURLY_BRACKET &&
           type != TokenType.FUNCTION) {
         equals = _createSyntheticToken(TokenType.EQ);
       } else {
         return astFactory.constructorFieldInitializer(
             keywordToken,
             period,
             fieldName,
             _createSyntheticToken(TokenType.EQ),
             createSyntheticIdentifier());
       }
     }
     bool wasInInitializer = _inInitializer;
     _inInitializer = true;
     try {
       Expression expression = parseConditionalExpression();
       if (_matches(TokenType.PERIOD_PERIOD)) {
         List<Expression> cascadeSections = <Expression>[];
         do {
           Expression section = parseCascadeSection();
           if (section != null) {
             cascadeSections.add(section);
           }
         } while (_matches(TokenType.PERIOD_PERIOD));
         expression = astFactory.cascadeExpression(expression, cascadeSections);
       }
       return astFactory.constructorFieldInitializer(
           keywordToken, period, fieldName, equals, expression);
     } finally {
       _inInitializer = wasInInitializer;
     }
   }

   /**
    * Parse the name of a constructor. Return the constructor name that was
    * parsed.
    *
    *     constructorName:
    *         type ('.' identifier)?
    */
   ConstructorName parseConstructorName() {
     TypeName type = parseTypeName(false);
     Token period = null;
     SimpleIdentifier name = null;
     if (_matches(TokenType.PERIOD)) {
       period = getAndAdvance();
       name = parseSimpleIdentifier();
     }
     return astFactory.constructorName(type, period, name);
   }

   /**
    * Parse a continue statement. Return the continue statement that was parsed.
    *
    * This method assumes that the current token matches `Keyword.CONTINUE`.
    *
    *     continueStatement ::=
    *         'continue' identifier? ';'
    */
   Statement parseContinueStatement() {
     Token continueKeyword = getAndAdvance();
     if (!_inLoop && !_inSwitch) {
       _reportErrorForToken(
           ParserErrorCode.CONTINUE_OUTSIDE_OF_LOOP, continueKeyword);
     }
     SimpleIdentifier label = null;
     if (_matchesIdentifier()) {
       label = _parseSimpleIdentifierUnchecked();
     }
     if (_inSwitch && !_inLoop && label == null) {
       _reportErrorForToken(
           ParserErrorCode.CONTINUE_WITHOUT_LABEL_IN_CASE, continueKeyword);
     }
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.continueStatement(continueKeyword, label, semicolon);
   }

   /**
    * Parse a directive. The [commentAndMetadata] is the metadata to be
    * associated with the directive. Return the directive that was parsed.
    *
    *     directive ::=
    *         exportDirective
    *       | libraryDirective
    *       | importDirective
    *       | partDirective
    */
   Directive parseDirective(CommentAndMetadata commentAndMetadata) {
     if (_matchesKeyword(Keyword.IMPORT)) {
       return parseImportDirective(commentAndMetadata);
     } else if (_matchesKeyword(Keyword.EXPORT)) {
       return parseExportDirective(commentAndMetadata);
     } else if (_matchesKeyword(Keyword.LIBRARY)) {
       return parseLibraryDirective(commentAndMetadata);
     } else if (_matchesKeyword(Keyword.PART)) {
       return parsePartOrPartOfDirective(commentAndMetadata);
     } else {
       // Internal error: this method should not have been invoked if the current
       // token was something other than one of the above.
       throw new StateError(
           "parseDirective invoked in an invalid state; currentToken = $_currentToken");
     }
   }

   /**
    * Parse the script tag and directives in a compilation unit, starting with
    * the given [token], until the first non-directive is encountered. The
    * remainder of the compilation unit will not be parsed. Specifically, if
    * there are directives later in the file, they will not be parsed. Return the
    * compilation unit that was parsed.
    */
   CompilationUnit parseDirectives(Token token) {
     _currentToken = token;
     return parseDirectives2();
   }

   /**
    * Parse the script tag and directives in a compilation unit until the first
    * non-directive is encountered. Return the compilation unit that was parsed.
    *
    *     compilationUnit ::=
    *         scriptTag? directive*
    */
   CompilationUnit parseDirectives2() {
     Token firstToken = _currentToken;
     ScriptTag scriptTag = null;
     if (_matches(TokenType.SCRIPT_TAG)) {
       scriptTag = astFactory.scriptTag(getAndAdvance());
     }
     List<Directive> directives = <Directive>[];
     while (!_matches(TokenType.EOF)) {
       CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
       Keyword keyword = _currentToken.keyword;
       TokenType type = _peek().type;
       if ((keyword == Keyword.IMPORT ||
               keyword == Keyword.EXPORT ||
               keyword == Keyword.LIBRARY ||
               keyword == Keyword.PART) &&
           type != TokenType.PERIOD &&
           type != TokenType.LT &&
           type != TokenType.OPEN_PAREN) {
         directives.add(parseDirective(commentAndMetadata));
       } else if (_matches(TokenType.SEMICOLON)) {
         _advance();
       } else {
         while (!_matches(TokenType.EOF)) {
           _advance();
         }
         return astFactory.compilationUnit(
             firstToken, scriptTag, directives, null, _currentToken);
       }
     }
     return astFactory.compilationUnit(
         firstToken, scriptTag, directives, null, _currentToken);
   }

   /**
    * Parse a documentation comment based on the given list of documentation
    * comment tokens. Return the documentation comment that was parsed, or `null`
    * if there was no comment.
    *
    *     documentationComment ::=
    *         multiLineComment?
    *       | singleLineComment*
    */
   Comment parseDocumentationComment(List<DocumentationCommentToken> tokens) {
     if (tokens == null) {
       return null;
     }
     List<CommentReference> references = parseCommentReferences(tokens);
     return astFactory.documentationComment(tokens, references);
   }

   /**
    * Parse a documentation comment. Return the documentation comment that was
    * parsed, or `null` if there was no comment.
    *
    *     documentationComment ::=
    *         multiLineComment?
    *       | singleLineComment*
    */
   List<DocumentationCommentToken> parseDocumentationCommentTokens() {
     List<DocumentationCommentToken> tokens = <DocumentationCommentToken>[];
     CommentToken commentToken = _currentToken.precedingComments;
     while (commentToken != null) {
       if (commentToken is DocumentationCommentToken) {
         if (tokens.isNotEmpty) {
           if (commentToken.type == TokenType.SINGLE_LINE_COMMENT) {
             if (tokens[0].type != TokenType.SINGLE_LINE_COMMENT) {
               tokens.clear();
             }
           } else {
             tokens.clear();
           }
         }
         tokens.add(commentToken);
       }
       commentToken = commentToken.next;
     }
     return tokens.isEmpty ? null : tokens;
   }

   /**
    * Parse a do statement. Return the do statement that was parsed.
    *
    * This method assumes that the current token matches `Keyword.DO`.
    *
    *     doStatement ::=
    *         'do' statement 'while' '(' expression ')' ';'
    */
   Statement parseDoStatement() {
     bool wasInLoop = _inLoop;
     _inLoop = true;
     try {
       Token doKeyword = getAndAdvance();
       Statement body = parseStatement2();
       Token whileKeyword = _expectKeyword(Keyword.WHILE);
       Token leftParenthesis = _expect(TokenType.OPEN_PAREN);
       Expression condition = parseExpression2();
       Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
       Token semicolon = _expect(TokenType.SEMICOLON);
       return astFactory.doStatement(doKeyword, body, whileKeyword,
           leftParenthesis, condition, rightParenthesis, semicolon);
     } finally {
       _inLoop = wasInLoop;
     }
   }

   /**
    * Parse a dotted name. Return the dotted name that was parsed.
    *
    *     dottedName ::=
    *         identifier ('.' identifier)*
    */
   DottedName parseDottedName() {
     List<SimpleIdentifier> components = <SimpleIdentifier>[
       parseSimpleIdentifier()
     ];
     while (_optional(TokenType.PERIOD)) {
       components.add(parseSimpleIdentifier());
     }
     return astFactory.dottedName(components);
   }

   /**
    * Parse an empty statement. Return the empty statement that was parsed.
    *
    * This method assumes that the current token matches `TokenType.SEMICOLON`.
    *
    *     emptyStatement ::=
    *         ';'
    */
   Statement parseEmptyStatement() => astFactory.emptyStatement(getAndAdvance());

   /**
    * Parse an enum declaration. The [commentAndMetadata] is the metadata to be
    * associated with the member. Return the enum declaration that was parsed.
    *
    * This method assumes that the current token matches `Keyword.ENUM`.
    *
    *     enumType ::=
    *         metadata 'enum' id '{' id (',' id)* (',')? '}'
    */
   EnumDeclaration parseEnumDeclaration(CommentAndMetadata commentAndMetadata) {
     Token keyword = getAndAdvance();
     SimpleIdentifier name = parseSimpleIdentifier(isDeclaration: true);
     Token leftBracket = null;
     List<EnumConstantDeclaration> constants = <EnumConstantDeclaration>[];
     Token rightBracket = null;
     if (_matches(TokenType.OPEN_CURLY_BRACKET)) {
       leftBracket = getAndAdvance();
       if (_matchesIdentifier() || _matches(TokenType.AT)) {
         constants.add(_parseEnumConstantDeclaration());
       } else if (_matches(TokenType.COMMA) &&
           _tokenMatchesIdentifier(_peek())) {
         constants.add(_parseEnumConstantDeclaration());
         _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
       } else {
         constants.add(_parseEnumConstantDeclaration());
         _reportErrorForCurrentToken(ParserErrorCode.EMPTY_ENUM_BODY);
       }
       while (_optional(TokenType.COMMA)) {
         if (_matches(TokenType.CLOSE_CURLY_BRACKET)) {
           break;
         }
         constants.add(_parseEnumConstantDeclaration());
       }
       rightBracket = _expect(TokenType.CLOSE_CURLY_BRACKET);
     } else {
       leftBracket = _createSyntheticToken(TokenType.OPEN_CURLY_BRACKET);
       rightBracket = _createSyntheticToken(TokenType.CLOSE_CURLY_BRACKET);
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_ENUM_BODY);
     }
     return astFactory.enumDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         keyword,
         name,
         leftBracket,
         constants,
         rightBracket);
   }

   /**
    * Parse an equality expression. Return the equality expression that was
    * parsed.
    *
    *     equalityExpression ::=
    *         relationalExpression (equalityOperator relationalExpression)?
    *       | 'super' equalityOperator relationalExpression
    */
   Expression parseEqualityExpression() {
     Expression expression;
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type.isEqualityOperator) {
       expression = astFactory.superExpression(getAndAdvance());
     } else {
       expression = parseRelationalExpression();
     }
     bool leftEqualityExpression = false;
     while (_currentToken.type.isEqualityOperator) {
       if (leftEqualityExpression) {
         _reportErrorForNode(
             ParserErrorCode.EQUALITY_CANNOT_BE_EQUALITY_OPERAND, expression);
       }
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseRelationalExpression());
       leftEqualityExpression = true;
     }
     return expression;
   }

   /**
    * Parse an export directive. The [commentAndMetadata] is the metadata to be
    * associated with the directive. Return the export directive that was parsed.
    *
    * This method assumes that the current token matches `Keyword.EXPORT`.
    *
    *     exportDirective ::=
    *         metadata 'export' stringLiteral configuration* combinator*';'
    */
   ExportDirective parseExportDirective(CommentAndMetadata commentAndMetadata) {
     Token exportKeyword = getAndAdvance();
     StringLiteral libraryUri = _parseUri();
     List<Configuration> configurations = _parseConfigurations();
     List<Combinator> combinators = parseCombinators();
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.exportDirective(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         exportKeyword,
         libraryUri,
         configurations,
         combinators,
         semicolon);
   }

   /**
    * Parse an expression, starting with the given [token]. Return the expression
    * that was parsed, or `null` if the tokens do not represent a recognizable
    * expression.
    */
   Expression parseExpression(Token token) {
     _currentToken = token;
     return parseExpression2();
   }

   /**
    * Parse an expression that might contain a cascade. Return the expression
    * that was parsed.
    *
    *     expression ::=
    *         assignableExpression assignmentOperator expression
    *       | conditionalExpression cascadeSection*
    *       | throwExpression
    */
   Expression parseExpression2() {
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.THROW) {
       return parseThrowExpression();
     } else if (keyword == Keyword.RETHROW) {
       // TODO(brianwilkerson) Rethrow is a statement again.
       return parseRethrowExpression();
     }
     //
     // assignableExpression is a subset of conditionalExpression, so we can
     // parse a conditional expression and then determine whether it is followed
     // by an assignmentOperator, checking for conformance to the restricted
     // grammar after making that determination.
     //
     Expression expression = parseConditionalExpression();
     TokenType type = _currentToken.type;
     if (type == TokenType.PERIOD_PERIOD) {
       List<Expression> cascadeSections = <Expression>[];
       do {
         Expression section = parseCascadeSection();
         if (section != null) {
           cascadeSections.add(section);
         }
       } while (_currentToken.type == TokenType.PERIOD_PERIOD);
       return astFactory.cascadeExpression(expression, cascadeSections);
     } else if (type.isAssignmentOperator) {
       Token operator = getAndAdvance();
       _ensureAssignable(expression);
       return astFactory.assignmentExpression(
           expression, operator, parseExpression2());
     }
     return expression;
   }

   /**
    * Parse a list of expressions. Return the expression that was parsed.
    *
    *     expressionList ::=
    *         expression (',' expression)*
    */
   List<Expression> parseExpressionList() {
     List<Expression> expressions = <Expression>[parseExpression2()];
     while (_optional(TokenType.COMMA)) {
       expressions.add(parseExpression2());
     }
     return expressions;
   }

   /**
    * Parse an expression that does not contain any cascades. Return the
    * expression that was parsed.
    *
    *     expressionWithoutCascade ::=
    *         assignableExpression assignmentOperator expressionWithoutCascade
    *       | conditionalExpression
    *       | throwExpressionWithoutCascade
    */
   Expression parseExpressionWithoutCascade() {
     if (_matchesKeyword(Keyword.THROW)) {
       return parseThrowExpressionWithoutCascade();
     } else if (_matchesKeyword(Keyword.RETHROW)) {
       return parseRethrowExpression();
     }
     //
     // assignableExpression is a subset of conditionalExpression, so we can
     // parse a conditional expression and then determine whether it is followed
     // by an assignmentOperator, checking for conformance to the restricted
     // grammar after making that determination.
     //
     Expression expression = parseConditionalExpression();
     if (_currentToken.type.isAssignmentOperator) {
       Token operator = getAndAdvance();
       _ensureAssignable(expression);
       expression = astFactory.assignmentExpression(
           expression, operator, parseExpressionWithoutCascade());
     }
     return expression;
   }

   /**
    * Parse a class extends clause. Return the class extends clause that was
    * parsed.
    *
    * This method assumes that the current token matches `Keyword.EXTENDS`.
    *
    *     classExtendsClause ::=
    *         'extends' type
    */
   ExtendsClause parseExtendsClause() {
     Token keyword = getAndAdvance();
     TypeName superclass = parseTypeName(false);
     _mustNotBeNullable(superclass, ParserErrorCode.NULLABLE_TYPE_IN_EXTENDS);
     return astFactory.extendsClause(keyword, superclass);
   }

   /**
    * Parse the 'final', 'const', 'var' or type preceding a variable declaration.
    * The [optional] is `true` if the keyword and type are optional. Return the
    * 'final', 'const', 'var' or type that was parsed.
    *
    *     finalConstVarOrType ::=
    *         'final' type?
    *       | 'const' type?
    *       | 'var'
    *       | type
    */
   FinalConstVarOrType parseFinalConstVarOrType(bool optional,
       {bool inFunctionType: false}) {
     Token keywordToken = null;
     TypeAnnotation type = null;
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.FINAL || keyword == Keyword.CONST) {
       keywordToken = getAndAdvance();
       if (_isTypedIdentifier(_currentToken)) {
         type = parseTypeAnnotation(false);
       } else {
         // Support `final/*=T*/ x;`
         type = _parseOptionalTypeNameComment();
       }
     } else if (keyword == Keyword.VAR) {
       keywordToken = getAndAdvance();
       // Support `var/*=T*/ x;`
       type = _parseOptionalTypeNameComment();
       if (type != null) {
         // Clear the keyword to prevent an error.
         keywordToken = null;
       }
     } else if (_isTypedIdentifier(_currentToken)) {
       type = parseReturnType(false);
     } else if (inFunctionType && _matchesIdentifier()) {
       type = parseTypeAnnotation(false);
     } else if (!optional) {
       _reportErrorForCurrentToken(
           ParserErrorCode.MISSING_CONST_FINAL_VAR_OR_TYPE);
     } else {
       // Support parameters such as `(/*=K*/ key, /*=V*/ value)`
       // This is not supported if the type is required.
       type = _parseOptionalTypeNameComment();
     }
     return new FinalConstVarOrType(keywordToken, type);
   }

   /**
    * Parse a formal parameter. At most one of `isOptional` and `isNamed` can be
    * `true`. The [kind] is the kind of parameter being expected based on the
    * presence or absence of group delimiters. Return the formal parameter that
    * was parsed.
    *
    *     defaultFormalParameter ::=
    *         normalFormalParameter ('=' expression)?
    *
    *     defaultNamedParameter ::=
    *         normalFormalParameter ('=' expression)?
    *         normalFormalParameter (':' expression)?
    */
   FormalParameter parseFormalParameter(ParameterKind kind,
       {bool inFunctionType: false}) {
     NormalFormalParameter parameter =
         parseNormalFormalParameter(inFunctionType: inFunctionType);
     TokenType type = _currentToken.type;
     if (type == TokenType.EQ) {
       if (inFunctionType) {
         _reportErrorForCurrentToken(
             ParserErrorCode.DEFAULT_VALUE_IN_FUNCTION_TYPE);
       }
       Token separator = getAndAdvance();
       Expression defaultValue = parseExpression2();
       if (kind == ParameterKind.REQUIRED) {
         _reportErrorForNode(
             ParserErrorCode.POSITIONAL_PARAMETER_OUTSIDE_GROUP, parameter);
         kind = ParameterKind.POSITIONAL;
       } else if (kind == ParameterKind.NAMED &&
           inFunctionType &&
           parameter.identifier == null) {
         _reportErrorForCurrentToken(
             ParserErrorCode.MISSING_NAME_FOR_NAMED_PARAMETER);
       }
       return astFactory.defaultFormalParameter(
           parameter, kind, separator, defaultValue);
     } else if (type == TokenType.COLON) {
       if (inFunctionType) {
         _reportErrorForCurrentToken(
             ParserErrorCode.DEFAULT_VALUE_IN_FUNCTION_TYPE);
       }
       Token separator = getAndAdvance();
       Expression defaultValue = parseExpression2();
       if (kind == ParameterKind.REQUIRED) {
         _reportErrorForNode(
             ParserErrorCode.NAMED_PARAMETER_OUTSIDE_GROUP, parameter);
         kind = ParameterKind.NAMED;
       } else if (kind == ParameterKind.POSITIONAL) {
         _reportErrorForToken(
             ParserErrorCode.WRONG_SEPARATOR_FOR_POSITIONAL_PARAMETER,
             separator);
       } else if (kind == ParameterKind.NAMED &&
           inFunctionType &&
           parameter.identifier == null) {
         _reportErrorForCurrentToken(
             ParserErrorCode.MISSING_NAME_FOR_NAMED_PARAMETER);
       }
       return astFactory.defaultFormalParameter(
           parameter, kind, separator, defaultValue);
     } else if (kind != ParameterKind.REQUIRED) {
       if (kind == ParameterKind.NAMED &&
           inFunctionType &&
           parameter.identifier == null) {
         _reportErrorForCurrentToken(
             ParserErrorCode.MISSING_NAME_FOR_NAMED_PARAMETER);
       }
       return astFactory.defaultFormalParameter(parameter, kind, null, null);
     }
     return parameter;
   }

   /**
    * Parse a list of formal parameters. Return the formal parameters that were
    * parsed.
    *
    *     formalParameterList ::=
    *         '(' ')'
    *       | '(' normalFormalParameters (',' optionalFormalParameters)? ')'
    *       | '(' optionalFormalParameters ')'
    *
    *     normalFormalParameters ::=
    *         normalFormalParameter (',' normalFormalParameter)*
    *
    *     optionalFormalParameters ::=
    *         optionalPositionalFormalParameters
    *       | namedFormalParameters
    *
    *     optionalPositionalFormalParameters ::=
    *         '[' defaultFormalParameter (',' defaultFormalParameter)* ']'
    *
    *     namedFormalParameters ::=
    *         '{' defaultNamedParameter (',' defaultNamedParameter)* '}'
    */
   FormalParameterList parseFormalParameterList({bool inFunctionType: false}) {
     if (_matches(TokenType.OPEN_PAREN)) {
       return _parseFormalParameterListUnchecked(inFunctionType: inFunctionType);
     }
     // TODO(brianwilkerson) Improve the error message.
     _reportErrorForCurrentToken(
         ParserErrorCode.EXPECTED_TOKEN, [TokenType.OPEN_PAREN.lexeme]);
     // Recovery: Check for an unmatched closing paren and parse parameters until
     // it is reached.
     return _parseFormalParameterListAfterParen(
         _createSyntheticToken(TokenType.OPEN_PAREN));
   }

   /**
    * Parse a for statement. Return the for statement that was parsed.
    *
    *     forStatement ::=
    *         'for' '(' forLoopParts ')' statement
    *
    *     forLoopParts ::=
    *         forInitializerStatement expression? ';' expressionList?
    *       | declaredIdentifier 'in' expression
    *       | identifier 'in' expression
    *
    *     forInitializerStatement ::=
    *         localVariableDeclaration ';'
    *       | expression? ';'
    */
   Statement parseForStatement() {
     bool wasInLoop = _inLoop;
     _inLoop = true;
     try {
       Token awaitKeyword = null;
       if (_matchesString(_AWAIT)) {
         awaitKeyword = getAndAdvance();
       }
       Token forKeyword = _expectKeyword(Keyword.FOR);
       Token leftParenthesis = _expect(TokenType.OPEN_PAREN);
       VariableDeclarationList variableList = null;
       Expression initialization = null;
       if (!_matches(TokenType.SEMICOLON)) {
         CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
         if (_matchesIdentifier() &&
             (_tokenMatchesKeyword(_peek(), Keyword.IN) ||
                 _tokenMatches(_peek(), TokenType.COLON))) {
           SimpleIdentifier variableName = _parseSimpleIdentifierUnchecked();
           variableList = astFactory.variableDeclarationList(
               commentAndMetadata.comment,
               commentAndMetadata.metadata,
               null,
               null, <VariableDeclaration>[
             astFactory.variableDeclaration(variableName, null, null)
           ]);
         } else if (isInitializedVariableDeclaration()) {
           variableList =
               parseVariableDeclarationListAfterMetadata(commentAndMetadata);
         } else {
           initialization = parseExpression2();
         }
         TokenType type = _currentToken.type;
         if (_matchesKeyword(Keyword.IN) || type == TokenType.COLON) {
           if (type == TokenType.COLON) {
             _reportErrorForCurrentToken(ParserErrorCode.COLON_IN_PLACE_OF_IN);
           }
           DeclaredIdentifier loopVariable = null;
           SimpleIdentifier identifier = null;
           if (variableList == null) {
             // We found: <expression> 'in'
             _reportErrorForCurrentToken(
                 ParserErrorCode.MISSING_VARIABLE_IN_FOR_EACH);
           } else {
             NodeList<VariableDeclaration> variables = variableList.variables;
             if (variables.length > 1) {
               _reportErrorForCurrentToken(
                   ParserErrorCode.MULTIPLE_VARIABLES_IN_FOR_EACH,
                   [variables.length.toString()]);
             }
             VariableDeclaration variable = variables[0];
             if (variable.initializer != null) {
               _reportErrorForCurrentToken(
                   ParserErrorCode.INITIALIZED_VARIABLE_IN_FOR_EACH);
             }
             Token keyword = variableList.keyword;
             TypeAnnotation type = variableList.type;
             if (keyword != null || type != null) {
               loopVariable = astFactory.declaredIdentifier(
                   commentAndMetadata.comment,
                   commentAndMetadata.metadata,
                   keyword,
                   type,
                   astFactory.simpleIdentifier(variable.name.token,
                       isDeclaration: true));
             } else {
               if (commentAndMetadata.hasMetadata) {
                 // TODO(jwren) metadata isn't allowed before the identifier in
                 // "identifier in expression", add warning if commentAndMetadata
                 // has content
               }
               identifier = variable.name;
             }
           }
           Token inKeyword = getAndAdvance();
           Expression iterator = parseExpression2();
           Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
           Statement body = parseStatement2();
           if (loopVariable == null) {
             return astFactory.forEachStatementWithReference(
                 awaitKeyword,
                 forKeyword,
                 leftParenthesis,
                 identifier,
                 inKeyword,
                 iterator,
                 rightParenthesis,
                 body);
           }
           return astFactory.forEachStatementWithDeclaration(
               awaitKeyword,
               forKeyword,
               leftParenthesis,
               loopVariable,
               inKeyword,
               iterator,
               rightParenthesis,
               body);
         }
       }
       if (awaitKeyword != null) {
         _reportErrorForToken(
             ParserErrorCode.INVALID_AWAIT_IN_FOR, awaitKeyword);
       }
       Token leftSeparator = _expect(TokenType.SEMICOLON);
       Expression condition = null;
       if (!_matches(TokenType.SEMICOLON)) {
         condition = parseExpression2();
       }
       Token rightSeparator = _expect(TokenType.SEMICOLON);
       List<Expression> updaters = null;
       if (!_matches(TokenType.CLOSE_PAREN)) {
         updaters = parseExpressionList();
       }
       Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
       Statement body = parseStatement2();
       return astFactory.forStatement(
           forKeyword,
           leftParenthesis,
           variableList,
           initialization,
           leftSeparator,
           condition,
           rightSeparator,
           updaters,
           rightParenthesis,
           body);
     } finally {
       _inLoop = wasInLoop;
     }
   }

   /**
    * Parse a function body. The [mayBeEmpty] is `true` if the function body is
    * allowed to be empty. The [emptyErrorCode] is the error code to report if
    * function body expected, but not found. The [inExpression] is `true` if the
    * function body is being parsed as part of an expression and therefore does
    * not have a terminating semicolon. Return the function body that was parsed.
    *
    *     functionBody ::=
    *         '=>' expression ';'
    *       | block
    *
    *     functionExpressionBody ::=
    *         '=>' expression
    *       | block
    */
   FunctionBody parseFunctionBody(
       bool mayBeEmpty, ParserErrorCode emptyErrorCode, bool inExpression) {
     bool wasInAsync = _inAsync;
     bool wasInGenerator = _inGenerator;
     bool wasInLoop = _inLoop;
     bool wasInSwitch = _inSwitch;
     _inAsync = false;
     _inGenerator = false;
     _inLoop = false;
     _inSwitch = false;
     try {
       TokenType type = _currentToken.type;
       if (type == TokenType.SEMICOLON) {
         if (!mayBeEmpty) {
           _reportErrorForCurrentToken(emptyErrorCode);
         }
         return astFactory.emptyFunctionBody(getAndAdvance());
       }
       Token keyword = null;
       Token star = null;
       bool foundAsync = false;
       bool foundSync = false;
       if (type == TokenType.IDENTIFIER) {
         String lexeme = _currentToken.lexeme;
         if (lexeme == ASYNC) {
           foundAsync = true;
           keyword = getAndAdvance();
           if (_matches(TokenType.STAR)) {
             star = getAndAdvance();
             _inGenerator = true;
           }
           type = _currentToken.type;
           _inAsync = true;
         } else if (lexeme == SYNC) {
           foundSync = true;
           keyword = getAndAdvance();
           if (_matches(TokenType.STAR)) {
             star = getAndAdvance();
             _inGenerator = true;
           }
           type = _currentToken.type;
         }
       }
       if (type == TokenType.FUNCTION) {
         if (keyword != null) {
           if (!foundAsync) {
             _reportErrorForToken(ParserErrorCode.INVALID_SYNC, keyword);
             keyword = null;
           } else if (star != null) {
             _reportErrorForToken(
                 ParserErrorCode.INVALID_STAR_AFTER_ASYNC, star);
           }
         }
         Token functionDefinition = getAndAdvance();
         if (_matchesKeyword(Keyword.RETURN)) {
           _reportErrorForToken(ParserErrorCode.UNEXPECTED_TOKEN, _currentToken,
               [_currentToken.lexeme]);
           _advance();
         }
         Expression expression = parseExpression2();
         Token semicolon = null;
         if (!inExpression) {
           semicolon = _expect(TokenType.SEMICOLON);
         }
         if (!_parseFunctionBodies) {
           return astFactory
               .emptyFunctionBody(_createSyntheticToken(TokenType.SEMICOLON));
         }
         return astFactory.expressionFunctionBody(
             keyword, functionDefinition, expression, semicolon);
       } else if (type == TokenType.OPEN_CURLY_BRACKET) {
         if (keyword != null) {
           if (foundSync && star == null) {
             _reportErrorForToken(
                 ParserErrorCode.MISSING_STAR_AFTER_SYNC, keyword);
           }
         }
         if (!_parseFunctionBodies) {
           _skipBlock();
           return astFactory
               .emptyFunctionBody(_createSyntheticToken(TokenType.SEMICOLON));
         }
         return astFactory.blockFunctionBody(keyword, star, parseBlock());
       } else if (_matchesString(_NATIVE)) {
         Token nativeToken = getAndAdvance();
         StringLiteral stringLiteral = null;
         if (_matches(TokenType.STRING)) {
           stringLiteral = _parseStringLiteralUnchecked();
         }
         return astFactory.nativeFunctionBody(
             nativeToken, stringLiteral, _expect(TokenType.SEMICOLON));
       } else {
         // Invalid function body
         _reportErrorForCurrentToken(emptyErrorCode);
         return astFactory
             .emptyFunctionBody(_createSyntheticToken(TokenType.SEMICOLON));
       }
     } finally {
       _inAsync = wasInAsync;
       _inGenerator = wasInGenerator;
       _inLoop = wasInLoop;
       _inSwitch = wasInSwitch;
     }
   }

   /**
    * Parse a function declaration. The [commentAndMetadata] is the documentation
    * comment and metadata to be associated with the declaration. The
    * [externalKeyword] is the 'external' keyword, or `null` if the function is
    * not external. The [returnType] is the return type, or `null` if there is no
    * return type. The [isStatement] is `true` if the function declaration is
    * being parsed as a statement. Return the function declaration that was
    * parsed.
    *
    *     functionDeclaration ::=
    *         functionSignature functionBody
    *       | returnType? getOrSet identifier formalParameterList functionBody
    */
   FunctionDeclaration parseFunctionDeclaration(
       CommentAndMetadata commentAndMetadata,
       Token externalKeyword,
       TypeAnnotation returnType) {
     Token keywordToken = null;
     bool isGetter = false;
     Keyword keyword = _currentToken.keyword;
     SimpleIdentifier name = null;
     if (keyword == Keyword.GET) {
       keywordToken = getAndAdvance();
       isGetter = true;
     } else if (keyword == Keyword.SET) {
       keywordToken = getAndAdvance();
     }
     if (keywordToken != null && _matches(TokenType.OPEN_PAREN)) {
       name = astFactory.simpleIdentifier(keywordToken, isDeclaration: true);
       keywordToken = null;
       isGetter = false;
     } else {
       name = parseSimpleIdentifier(isDeclaration: true);
     }
     TypeParameterList typeParameters = _parseGenericMethodTypeParameters();
     FormalParameterList parameters = null;
     if (!isGetter) {
       if (_matches(TokenType.OPEN_PAREN)) {
         parameters = _parseFormalParameterListUnchecked();
         _validateFormalParameterList(parameters);
       } else {
         _reportErrorForCurrentToken(
             ParserErrorCode.MISSING_FUNCTION_PARAMETERS);
         parameters = astFactory.formalParameterList(
             _createSyntheticToken(TokenType.OPEN_PAREN),
             null,
             null,
             null,
             _createSyntheticToken(TokenType.CLOSE_PAREN));
       }
     } else if (_matches(TokenType.OPEN_PAREN)) {
       _reportErrorForCurrentToken(ParserErrorCode.GETTER_WITH_PARAMETERS);
       _parseFormalParameterListUnchecked();
     }
     FunctionBody body;
     if (externalKeyword == null) {
       body = parseFunctionBody(
           false, ParserErrorCode.MISSING_FUNCTION_BODY, false);
     } else {
       body = astFactory.emptyFunctionBody(_expect(TokenType.SEMICOLON));
     }
 //        if (!isStatement && matches(TokenType.SEMICOLON)) {
 //          // TODO(brianwilkerson) Improve this error message.
 //          reportError(ParserErrorCode.UNEXPECTED_TOKEN, currentToken.getLexeme());
 //          advance();
 //        }
     return astFactory.functionDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         externalKeyword,
         returnType,
         keywordToken,
         name,
         astFactory.functionExpression(typeParameters, parameters, body));
   }

   /**
    * Parse a function declaration statement. Return the function declaration
    * statement that was parsed.
    *
    *     functionDeclarationStatement ::=
    *         functionSignature functionBody
    */
   Statement parseFunctionDeclarationStatement() {
     Modifiers modifiers = parseModifiers();
     _validateModifiersForFunctionDeclarationStatement(modifiers);
     return _parseFunctionDeclarationStatementAfterReturnType(
         parseCommentAndMetadata(), _parseOptionalReturnType());
   }

   /**
    * Parse a function expression. Return the function expression that was
    * parsed.
    *
    *     functionExpression ::=
    *         typeParameters? formalParameterList functionExpressionBody
    */
   FunctionExpression parseFunctionExpression() {
     TypeParameterList typeParameters = _parseGenericMethodTypeParameters();
     FormalParameterList parameters = parseFormalParameterList();
     _validateFormalParameterList(parameters);
     FunctionBody body =
         parseFunctionBody(false, ParserErrorCode.MISSING_FUNCTION_BODY, true);
     return astFactory.functionExpression(typeParameters, parameters, body);
   }

   /**
    * Parse the portion of a generic function type following the [returnType].
    *
    *     functionType ::=
    *         returnType? 'Function' typeParameters? parameterTypeList
    *     parameterTypeList ::=
    *         '(' ')' |
    *       | '(' normalParameterTypes ','? ')' |
    *       | '(' normalParameterTypes ',' optionalParameterTypes ')' |
    *       | '(' optionalParameterTypes ')'
    *     normalParameterTypes ::=
    *     normalParameterType (',' normalParameterType)*
    *     normalParameterType ::=
    *         type | typedIdentifier
    *     optionalParameterTypes ::=
    *         optionalPositionalParameterTypes | namedParameterTypes
    *     optionalPositionalParameterTypes ::=
    *         '[' normalParameterTypes ','? ']'
    *     namedParameterTypes ::=
    *         '{' typedIdentifier (',' typedIdentifier)* ','? '}'
    *     typedIdentifier ::=
    *         type identifier
    */
   GenericFunctionType parseGenericFunctionTypeAfterReturnType(
       TypeAnnotation returnType) {
     Token functionKeyword = null;
     if (_matchesString('Function')) {
       functionKeyword = getAndAdvance();
     } else if (_matchesIdentifier()) {
       _reportErrorForCurrentToken(ParserErrorCode.NAMED_FUNCTION_TYPE);
     } else {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_FUNCTION_KEYWORD);
     }
     TypeParameterList typeParameters = null;
     if (_matches(TokenType.LT)) {
       typeParameters = parseTypeParameterList();
     }
     FormalParameterList parameters =
         parseFormalParameterList(inFunctionType: true);
     return astFactory.genericFunctionType(
         returnType, functionKeyword, typeParameters, parameters);
   }

   /**
    * Parse a generic function type alias.
    *
    * This method assumes that the current token is an identifier.
    *
    *     genericTypeAlias ::=
    *         'typedef' identifier typeParameterList? '=' functionType ';'
    */
   GenericTypeAlias parseGenericTypeAlias(
       CommentAndMetadata commentAndMetadata, Token keyword) {
     Identifier name = _parseSimpleIdentifierUnchecked(isDeclaration: true);
     TypeParameterList typeParameters = null;
     if (_matches(TokenType.LT)) {
       typeParameters = parseTypeParameterList();
     }
     Token equals = _expect(TokenType.EQ);
     TypeAnnotation functionType = parseTypeAnnotation(false);
     Token semicolon = _expect(TokenType.SEMICOLON);
     if (functionType is! GenericFunctionType) {
       // TODO(brianwilkerson) Generate an error and recover (better than this).
       return astFactory.genericTypeAlias(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           keyword,
           name,
           typeParameters,
           equals,
           null,
           semicolon);
     }
     return astFactory.genericTypeAlias(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         keyword,
         name,
         typeParameters,
         equals,
         functionType,
         semicolon);
   }

   /**
    * Parse a getter. The [commentAndMetadata] is the documentation comment and
    * metadata to be associated with the declaration. The externalKeyword] is the
    * 'external' token. The staticKeyword] is the static keyword, or `null` if
    * the getter is not static. The [returnType] the return type that has already
    * been parsed, or `null` if there was no return type. Return the getter that
    * was parsed.
    *
    * This method assumes that the current token matches `Keyword.GET`.
    *
    *     getter ::=
    *         getterSignature functionBody?
    *
    *     getterSignature ::=
    *         'external'? 'static'? returnType? 'get' identifier
    */
   MethodDeclaration parseGetter(CommentAndMetadata commentAndMetadata,
       Token externalKeyword, Token staticKeyword, TypeAnnotation returnType) {
     Token propertyKeyword = getAndAdvance();
     SimpleIdentifier name = parseSimpleIdentifier(isDeclaration: true);
     if (_matches(TokenType.OPEN_PAREN) &&
         _tokenMatches(_peek(), TokenType.CLOSE_PAREN)) {
       _reportErrorForCurrentToken(ParserErrorCode.GETTER_WITH_PARAMETERS);
       _advance();
       _advance();
     }
     FunctionBody body = parseFunctionBody(
         externalKeyword != null || staticKeyword == null,
         ParserErrorCode.STATIC_GETTER_WITHOUT_BODY,
         false);
     if (externalKeyword != null && body is! EmptyFunctionBody) {
       _reportErrorForCurrentToken(ParserErrorCode.EXTERNAL_GETTER_WITH_BODY);
     }
     return astFactory.methodDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         externalKeyword,
         staticKeyword,
         returnType,
         propertyKeyword,
         null,
         name,
         null,
         null,
         body);
   }

   /**
    * Parse a list of identifiers. Return the list of identifiers that were
    * parsed.
    *
    *     identifierList ::=
    *         identifier (',' identifier)*
    */
   List<SimpleIdentifier> parseIdentifierList() {
     List<SimpleIdentifier> identifiers = <SimpleIdentifier>[
       parseSimpleIdentifier()
     ];
     while (_optional(TokenType.COMMA)) {
       identifiers.add(parseSimpleIdentifier());
     }
     return identifiers;
   }

   /**
    * Parse an if-null expression.  Return the if-null expression that was
    * parsed.
    *
    *     ifNullExpression ::= logicalOrExpression ('??' logicalOrExpression)*
    */
   Expression parseIfNullExpression() {
     Expression expression = parseLogicalOrExpression();
     while (_currentToken.type == TokenType.QUESTION_QUESTION) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseLogicalOrExpression());
     }
     return expression;
   }

   /**
    * Parse an if statement. Return the if statement that was parsed.
    *
    * This method assumes that the current token matches `Keyword.IF`.
    *
    *     ifStatement ::=
    *         'if' '(' expression ')' statement ('else' statement)?
    */
   Statement parseIfStatement() {
     Token ifKeyword = getAndAdvance();
     Token leftParenthesis = _expect(TokenType.OPEN_PAREN);
     Expression condition = parseExpression2();
     Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
     Statement thenStatement = parseStatement2();
     Token elseKeyword = null;
     Statement elseStatement = null;
     if (_matchesKeyword(Keyword.ELSE)) {
       elseKeyword = getAndAdvance();
       elseStatement = parseStatement2();
     }
     return astFactory.ifStatement(ifKeyword, leftParenthesis, condition,
         rightParenthesis, thenStatement, elseKeyword, elseStatement);
   }

   /**
    * Parse an implements clause. Return the implements clause that was parsed.
    *
    * This method assumes that the current token matches `Keyword.IMPLEMENTS`.
    *
    *     implementsClause ::=
    *         'implements' type (',' type)*
    */
   ImplementsClause parseImplementsClause() {
     Token keyword = getAndAdvance();
     List<TypeName> interfaces = <TypeName>[];
     do {
       TypeName typeName = parseTypeName(false);
       _mustNotBeNullable(typeName, ParserErrorCode.NULLABLE_TYPE_IN_IMPLEMENTS);
       interfaces.add(typeName);
     } while (_optional(TokenType.COMMA));
     return astFactory.implementsClause(keyword, interfaces);
   }

   /**
    * Parse an import directive. The [commentAndMetadata] is the metadata to be
    * associated with the directive. Return the import directive that was parsed.
    *
    * This method assumes that the current token matches `Keyword.IMPORT`.
    *
    *     importDirective ::=
    *         metadata 'import' stringLiteral configuration* (deferred)? ('as' identifier)? combinator*';'
    */
   ImportDirective parseImportDirective(CommentAndMetadata commentAndMetadata) {
     Token importKeyword = getAndAdvance();
     StringLiteral libraryUri = _parseUri();
     List<Configuration> configurations = _parseConfigurations();
     Token deferredToken = null;
     Token asToken = null;
     SimpleIdentifier prefix = null;
     if (_matchesKeyword(Keyword.DEFERRED)) {
       deferredToken = getAndAdvance();
     }
     if (_matchesKeyword(Keyword.AS)) {
       asToken = getAndAdvance();
       prefix = parseSimpleIdentifier(isDeclaration: true);
     } else if (deferredToken != null) {
       _reportErrorForCurrentToken(
           ParserErrorCode.MISSING_PREFIX_IN_DEFERRED_IMPORT);
     } else if (!_matches(TokenType.SEMICOLON) &&
         !_matchesString(_SHOW) &&
         !_matchesString(_HIDE)) {
       Token nextToken = _peek();
       if (_tokenMatchesKeyword(nextToken, Keyword.AS) ||
           _tokenMatchesString(nextToken, _SHOW) ||
           _tokenMatchesString(nextToken, _HIDE)) {
         _reportErrorForCurrentToken(
             ParserErrorCode.UNEXPECTED_TOKEN, [_currentToken]);
         _advance();
         if (_matchesKeyword(Keyword.AS)) {
           asToken = getAndAdvance();
           prefix = parseSimpleIdentifier(isDeclaration: true);
         }
       }
     }
     List<Combinator> combinators = parseCombinators();
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.importDirective(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         importKeyword,
         libraryUri,
         configurations,
         deferredToken,
         asToken,
         prefix,
         combinators,
         semicolon);
   }

   /**
    * Parse a list of initialized identifiers. The [commentAndMetadata] is the
    * documentation comment and metadata to be associated with the declaration.
    * The [staticKeyword] is the static keyword, or `null` if the getter is not
    * static. The [keyword] is the token representing the 'final', 'const' or
    * 'var' keyword, or `null` if there is no keyword. The [type] is the type
    * that has already been parsed, or `null` if 'var' was provided. Return the
    * getter that was parsed.
    *
    *     declaration ::=
    *         ('static' | 'covariant')? ('var' | type) initializedIdentifierList ';'
    *       | 'final' type? initializedIdentifierList ';'
    *
    *     initializedIdentifierList ::=
    *         initializedIdentifier (',' initializedIdentifier)*
    *
    *     initializedIdentifier ::=
    *         identifier ('=' expression)?
    */
   FieldDeclaration parseInitializedIdentifierList(
       CommentAndMetadata commentAndMetadata,
       Token staticKeyword,
       Token covariantKeyword,
       Token keyword,
       TypeAnnotation type) {
     VariableDeclarationList fieldList =
         parseVariableDeclarationListAfterType(null, keyword, type);
     FieldDeclarationImpl field = astFactory.fieldDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         staticKeyword,
         fieldList,
         _expect(TokenType.SEMICOLON));
     field.covariantKeyword = covariantKeyword;
     return field;
   }

   /**
    * Parse an instance creation expression. The [keyword] is the 'new' or
    * 'const' keyword that introduces the expression. Return the instance
    * creation expression that was parsed.
    *
    *     instanceCreationExpression ::=
    *         ('new' | 'const') type ('.' identifier)? argumentList
    */
   InstanceCreationExpression parseInstanceCreationExpression(Token keyword) {
     ConstructorName constructorName = parseConstructorName();
     ArgumentList argumentList = _parseArgumentListChecked();
     return astFactory.instanceCreationExpression(
         keyword, constructorName, argumentList);
   }

   /**
    * Parse a label. Return the label that was parsed.
    *
    * This method assumes that the current token matches an identifier and that
    * the following token matches `TokenType.COLON`.
    *
    *     label ::=
    *         identifier ':'
    */
   Label parseLabel({bool isDeclaration: false}) {
     SimpleIdentifier label =
         _parseSimpleIdentifierUnchecked(isDeclaration: isDeclaration);
     Token colon = getAndAdvance();
     return astFactory.label(label, colon);
   }

   /**
    * Parse a library directive. The [commentAndMetadata] is the metadata to be
    * associated with the directive. Return the library directive that was
    * parsed.
    *
    * This method assumes that the current token matches `Keyword.LIBRARY`.
    *
    *     libraryDirective ::=
    *         metadata 'library' identifier ';'
    */
   LibraryDirective parseLibraryDirective(
       CommentAndMetadata commentAndMetadata) {
     Token keyword = getAndAdvance();
     LibraryIdentifier libraryName = _parseLibraryName(
         ParserErrorCode.MISSING_NAME_IN_LIBRARY_DIRECTIVE, keyword);
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.libraryDirective(commentAndMetadata.comment,
         commentAndMetadata.metadata, keyword, libraryName, semicolon);
   }

   /**
    * Parse a library identifier. Return the library identifier that was parsed.
    *
    *     libraryIdentifier ::=
    *         identifier ('.' identifier)*
    */
   LibraryIdentifier parseLibraryIdentifier() {
     List<SimpleIdentifier> components = <SimpleIdentifier>[];
     components.add(parseSimpleIdentifier());
     while (_optional(TokenType.PERIOD)) {
       components.add(parseSimpleIdentifier());
     }
     return astFactory.libraryIdentifier(components);
   }

   /**
    * Parse a list literal. The [modifier] is the 'const' modifier appearing
    * before the literal, or `null` if there is no modifier. The [typeArguments]
    * is the type arguments appearing before the literal, or `null` if there are
    * no type arguments. Return the list literal that was parsed.
    *
    * This method assumes that the current token matches either
    * `TokenType.OPEN_SQUARE_BRACKET` or `TokenType.INDEX`.
    *
    *     listLiteral ::=
    *         'const'? typeArguments? '[' (expressionList ','?)? ']'
    */
   ListLiteral parseListLiteral(Token modifier, TypeArgumentList typeArguments) {
     if (_matches(TokenType.INDEX)) {
       _splitIndex();
       return astFactory.listLiteral(
           modifier, typeArguments, getAndAdvance(), null, getAndAdvance());
     }
     Token leftBracket = getAndAdvance();
     if (_matches(TokenType.CLOSE_SQUARE_BRACKET)) {
       return astFactory.listLiteral(
           modifier, typeArguments, leftBracket, null, getAndAdvance());
     }
     bool wasInInitializer = _inInitializer;
     _inInitializer = false;
     try {
       List<Expression> elements = <Expression>[parseExpression2()];
       while (_optional(TokenType.COMMA)) {
         if (_matches(TokenType.CLOSE_SQUARE_BRACKET)) {
           return astFactory.listLiteral(
               modifier, typeArguments, leftBracket, elements, getAndAdvance());
         }
         elements.add(parseExpression2());
       }
       Token rightBracket = _expect(TokenType.CLOSE_SQUARE_BRACKET);
       return astFactory.listLiteral(
           modifier, typeArguments, leftBracket, elements, rightBracket);
     } finally {
       _inInitializer = wasInInitializer;
     }
   }

   /**
    * Parse a list or map literal. The [modifier] is the 'const' modifier
    * appearing before the literal, or `null` if there is no modifier. Return the
    * list or map literal that was parsed.
    *
    *     listOrMapLiteral ::=
    *         listLiteral
    *       | mapLiteral
    */
   TypedLiteral parseListOrMapLiteral(Token modifier) {
     TypeArgumentList typeArguments = _parseOptionalTypeArguments();
     if (_matches(TokenType.OPEN_CURLY_BRACKET)) {
       return parseMapLiteral(modifier, typeArguments);
     } else if (_matches(TokenType.OPEN_SQUARE_BRACKET) ||
         _matches(TokenType.INDEX)) {
       return parseListLiteral(modifier, typeArguments);
     }
     _reportErrorForCurrentToken(ParserErrorCode.EXPECTED_LIST_OR_MAP_LITERAL);
     return astFactory.listLiteral(
         modifier,
         typeArguments,
         _createSyntheticToken(TokenType.OPEN_SQUARE_BRACKET),
         null,
         _createSyntheticToken(TokenType.CLOSE_SQUARE_BRACKET));
   }

   /**
    * Parse a logical and expression. Return the logical and expression that was
    * parsed.
    *
    *     logicalAndExpression ::=
    *         equalityExpression ('&&' equalityExpression)*
    */
   Expression parseLogicalAndExpression() {
     Expression expression = parseEqualityExpression();
     while (_currentToken.type == TokenType.AMPERSAND_AMPERSAND) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseEqualityExpression());
     }
     return expression;
   }

   /**
    * Parse a logical or expression. Return the logical or expression that was
    * parsed.
    *
    *     logicalOrExpression ::=
    *         logicalAndExpression ('||' logicalAndExpression)*
    */
   Expression parseLogicalOrExpression() {
     Expression expression = parseLogicalAndExpression();
     while (_currentToken.type == TokenType.BAR_BAR) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseLogicalAndExpression());
     }
     return expression;
   }

   /**
    * Parse a map literal. The [modifier] is the 'const' modifier appearing
    * before the literal, or `null` if there is no modifier. The [typeArguments]
    * is the type arguments that were declared, or `null` if there are no type
    * arguments. Return the map literal that was parsed.
    *
    * This method assumes that the current token matches
    * `TokenType.OPEN_CURLY_BRACKET`.
    *
    *     mapLiteral ::=
    *         'const'? typeArguments? '{' (mapLiteralEntry (',' mapLiteralEntry)* ','?)? '}'
    */
   MapLiteral parseMapLiteral(Token modifier, TypeArgumentList typeArguments) {
     Token leftBracket = getAndAdvance();
     if (_matches(TokenType.CLOSE_CURLY_BRACKET)) {
       return astFactory.mapLiteral(
           modifier, typeArguments, leftBracket, null, getAndAdvance());
     }
     bool wasInInitializer = _inInitializer;
     _inInitializer = false;
     try {
       List<MapLiteralEntry> entries = <MapLiteralEntry>[parseMapLiteralEntry()];
       while (_optional(TokenType.COMMA)) {
         if (_matches(TokenType.CLOSE_CURLY_BRACKET)) {
           return astFactory.mapLiteral(
               modifier, typeArguments, leftBracket, entries, getAndAdvance());
         }
         entries.add(parseMapLiteralEntry());
       }
       Token rightBracket = _expect(TokenType.CLOSE_CURLY_BRACKET);
       return astFactory.mapLiteral(
           modifier, typeArguments, leftBracket, entries, rightBracket);
     } finally {
       _inInitializer = wasInInitializer;
     }
   }

   /**
    * Parse a map literal entry. Return the map literal entry that was parsed.
    *
    *     mapLiteralEntry ::=
    *         expression ':' expression
    */
   MapLiteralEntry parseMapLiteralEntry() {
     Expression key = parseExpression2();
     Token separator = _expect(TokenType.COLON);
     Expression value = parseExpression2();
     return astFactory.mapLiteralEntry(key, separator, value);
   }

   /**
    * Parse the modifiers preceding a declaration. This method allows the
    * modifiers to appear in any order but does generate errors for duplicated
    * modifiers. Checks for other problems, such as having the modifiers appear
    * in the wrong order or specifying both 'const' and 'final', are reported in
    * one of the methods whose name is prefixed with `validateModifiersFor`.
    * Return the modifiers that were parsed.
    *
    *     modifiers ::=
    *         ('abstract' | 'const' | 'external' | 'factory' | 'final' | 'static' | 'var')*
    */
   Modifiers parseModifiers() {
     Modifiers modifiers = new Modifiers();
     bool progress = true;
     while (progress) {
       TokenType nextType = _peek().type;
       if (nextType == TokenType.PERIOD ||
           nextType == TokenType.LT ||
           nextType == TokenType.OPEN_PAREN) {
         return modifiers;
       }
       Keyword keyword = _currentToken.keyword;
       if (keyword == Keyword.ABSTRACT) {
         if (modifiers.abstractKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.abstractKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.CONST) {
         if (modifiers.constKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.constKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.COVARIANT) {
         if (modifiers.covariantKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.covariantKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.EXTERNAL) {
         if (modifiers.externalKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.externalKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.FACTORY) {
         if (modifiers.factoryKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.factoryKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.FINAL) {
         if (modifiers.finalKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.finalKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.STATIC) {
         if (modifiers.staticKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.staticKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.VAR) {
         if (modifiers.varKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
         } else {
           modifiers.varKeyword = getAndAdvance();
         }
       } else {
         progress = false;
       }
     }
     return modifiers;
   }

   /**
    * Parse a multiplicative expression. Return the multiplicative expression
    * that was parsed.
    *
    *     multiplicativeExpression ::=
    *         unaryExpression (multiplicativeOperator unaryExpression)*
    *       | 'super' (multiplicativeOperator unaryExpression)+
    */
   Expression parseMultiplicativeExpression() {
     Expression expression;
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type.isMultiplicativeOperator) {
       expression = astFactory.superExpression(getAndAdvance());
     } else {
       expression = parseUnaryExpression();
     }
     while (_currentToken.type.isMultiplicativeOperator) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseUnaryExpression());
     }
     return expression;
   }

   /**
    * Parse a new expression. Return the new expression that was parsed.
    *
    * This method assumes that the current token matches `Keyword.NEW`.
    *
    *     newExpression ::=
    *         instanceCreationExpression
    */
   InstanceCreationExpression parseNewExpression() =>
       parseInstanceCreationExpression(getAndAdvance());

   /**
    * Parse a non-labeled statement. Return the non-labeled statement that was
    * parsed.
    *
    *     nonLabeledStatement ::=
    *         block
    *       | assertStatement
    *       | breakStatement
    *       | continueStatement
    *       | doStatement
    *       | forStatement
    *       | ifStatement
    *       | returnStatement
    *       | switchStatement
    *       | tryStatement
    *       | whileStatement
    *       | variableDeclarationList ';'
    *       | expressionStatement
    *       | functionSignature functionBody
    */
   Statement parseNonLabeledStatement() {
     // TODO(brianwilkerson) Pass the comment and metadata on where appropriate.
     CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
     TokenType type = _currentToken.type;
     if (type == TokenType.OPEN_CURLY_BRACKET) {
       if (_tokenMatches(_peek(), TokenType.STRING)) {
         Token afterString = skipStringLiteral(_currentToken.next);
         if (afterString != null && afterString.type == TokenType.COLON) {
           return astFactory.expressionStatement(
               parseExpression2(), _expect(TokenType.SEMICOLON));
         }
       }
       return parseBlock();
     } else if (type == TokenType.KEYWORD &&
         !_currentToken.keyword.isPseudoKeyword) {
       Keyword keyword = _currentToken.keyword;
       // TODO(jwren) compute some metrics to figure out a better order for this
       // if-then sequence to optimize performance
       if (keyword == Keyword.ASSERT) {
         return parseAssertStatement();
       } else if (keyword == Keyword.BREAK) {
         return parseBreakStatement();
       } else if (keyword == Keyword.CONTINUE) {
         return parseContinueStatement();
       } else if (keyword == Keyword.DO) {
         return parseDoStatement();
       } else if (keyword == Keyword.FOR) {
         return parseForStatement();
       } else if (keyword == Keyword.IF) {
         return parseIfStatement();
       } else if (keyword == Keyword.RETHROW) {
         return astFactory.expressionStatement(
             parseRethrowExpression(), _expect(TokenType.SEMICOLON));
       } else if (keyword == Keyword.RETURN) {
         return parseReturnStatement();
       } else if (keyword == Keyword.SWITCH) {
         return parseSwitchStatement();
       } else if (keyword == Keyword.THROW) {
         return astFactory.expressionStatement(
             parseThrowExpression(), _expect(TokenType.SEMICOLON));
       } else if (keyword == Keyword.TRY) {
         return parseTryStatement();
       } else if (keyword == Keyword.WHILE) {
         return parseWhileStatement();
       } else if (keyword == Keyword.VAR || keyword == Keyword.FINAL) {
         return parseVariableDeclarationStatementAfterMetadata(
             commentAndMetadata);
       } else if (keyword == Keyword.VOID) {
         TypeName returnType = astFactory.typeName(
             astFactory.simpleIdentifier(getAndAdvance()), null);
         Token next = _currentToken.next;
         if (_matchesIdentifier() &&
             next.matchesAny(const <TokenType>[
               TokenType.OPEN_PAREN,
               TokenType.OPEN_CURLY_BRACKET,
               TokenType.FUNCTION,
               TokenType.LT
             ])) {
           return _parseFunctionDeclarationStatementAfterReturnType(
               commentAndMetadata, returnType);
         } else {
           //
           // We have found an error of some kind. Try to recover.
           //
           if (_matchesIdentifier()) {
             if (next.matchesAny(const <TokenType>[
               TokenType.EQ,
               TokenType.COMMA,
               TokenType.SEMICOLON
             ])) {
               //
               // We appear to have a variable declaration with a type of "void".
               //
               _reportErrorForNode(ParserErrorCode.VOID_VARIABLE, returnType);
               return parseVariableDeclarationStatementAfterMetadata(
                   commentAndMetadata);
             }
           } else if (_matches(TokenType.CLOSE_CURLY_BRACKET)) {
             //
             // We appear to have found an incomplete statement at the end of a
             // block. Parse it as a variable declaration.
             //
             return _parseVariableDeclarationStatementAfterType(
                 commentAndMetadata, null, returnType);
           }
           _reportErrorForCurrentToken(ParserErrorCode.MISSING_STATEMENT);
           // TODO(brianwilkerson) Recover from this error.
           return astFactory
               .emptyStatement(_createSyntheticToken(TokenType.SEMICOLON));
         }
       } else if (keyword == Keyword.CONST) {
         Token next = _currentToken.next;
         if (next.matchesAny(const <TokenType>[
           TokenType.LT,
           TokenType.OPEN_CURLY_BRACKET,
           TokenType.OPEN_SQUARE_BRACKET,
           TokenType.INDEX
         ])) {
           return astFactory.expressionStatement(
               parseExpression2(), _expect(TokenType.SEMICOLON));
         } else if (_tokenMatches(next, TokenType.IDENTIFIER)) {
           Token afterType = skipTypeName(next);
           if (afterType != null) {
             if (_tokenMatches(afterType, TokenType.OPEN_PAREN) ||
                 (_tokenMatches(afterType, TokenType.PERIOD) &&
                     _tokenMatches(afterType.next, TokenType.IDENTIFIER) &&
                     _tokenMatches(afterType.next.next, TokenType.OPEN_PAREN))) {
               return astFactory.expressionStatement(
                   parseExpression2(), _expect(TokenType.SEMICOLON));
             }
           }
         }
         return parseVariableDeclarationStatementAfterMetadata(
             commentAndMetadata);
       } else if (keyword == Keyword.NEW ||
           keyword == Keyword.TRUE ||
           keyword == Keyword.FALSE ||
           keyword == Keyword.NULL ||
           keyword == Keyword.SUPER ||
           keyword == Keyword.THIS) {
         return astFactory.expressionStatement(
             parseExpression2(), _expect(TokenType.SEMICOLON));
       } else {
         //
         // We have found an error of some kind. Try to recover.
         //
         _reportErrorForCurrentToken(ParserErrorCode.MISSING_STATEMENT);
         return astFactory
             .emptyStatement(_createSyntheticToken(TokenType.SEMICOLON));
       }
     } else if (_inGenerator && _matchesString(_YIELD)) {
       return parseYieldStatement();
     } else if (_inAsync && _matchesString(_AWAIT)) {
       if (_tokenMatchesKeyword(_peek(), Keyword.FOR)) {
         return parseForStatement();
       }
       return astFactory.expressionStatement(
           parseExpression2(), _expect(TokenType.SEMICOLON));
     } else if (_matchesString(_AWAIT) &&
         _tokenMatchesKeyword(_peek(), Keyword.FOR)) {
       Token awaitToken = _currentToken;
       Statement statement = parseForStatement();
       if (statement is! ForStatement) {
         _reportErrorForToken(
             CompileTimeErrorCode.ASYNC_FOR_IN_WRONG_CONTEXT, awaitToken);
       }
       return statement;
     } else if (type == TokenType.SEMICOLON) {
       return parseEmptyStatement();
     } else if (isInitializedVariableDeclaration()) {
       return parseVariableDeclarationStatementAfterMetadata(commentAndMetadata);
     } else if (isFunctionDeclaration()) {
       return parseFunctionDeclarationStatement();
     } else if (type == TokenType.CLOSE_CURLY_BRACKET) {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_STATEMENT);
       return astFactory
           .emptyStatement(_createSyntheticToken(TokenType.SEMICOLON));
     } else {
       return astFactory.expressionStatement(
           parseExpression2(), _expect(TokenType.SEMICOLON));
     }
   }

   /**
    * Parse a normal formal parameter. Return the normal formal parameter that
    * was parsed.
    *
    *     normalFormalParameter ::=
    *         functionSignature
    *       | fieldFormalParameter
    *       | simpleFormalParameter
    *
    *     functionSignature:
    *         metadata returnType? identifier typeParameters? formalParameterList
    *
    *     fieldFormalParameter ::=
    *         metadata finalConstVarOrType? 'this' '.' identifier
    *
    *     simpleFormalParameter ::=
    *         declaredIdentifier
    *       | metadata identifier
    */
   NormalFormalParameter parseNormalFormalParameter(
       {bool inFunctionType: false}) {
     Token covariantKeyword;
     CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
     if (_matchesKeyword(Keyword.COVARIANT)) {
       // Check to ensure that 'covariant' isn't being used as the parameter name.
       Token next = _peek();
       if (_tokenMatchesKeyword(next, Keyword.FINAL) ||
           _tokenMatchesKeyword(next, Keyword.CONST) ||
           _tokenMatchesKeyword(next, Keyword.VAR) ||
           _tokenMatchesKeyword(next, Keyword.THIS) ||
           _tokenMatchesIdentifier(next)) {
         covariantKeyword = getAndAdvance();
       }
     }
     FinalConstVarOrType holder = parseFinalConstVarOrType(!inFunctionType,
         inFunctionType: inFunctionType);
     Token thisKeyword = null;
     Token period = null;
     if (_matchesKeyword(Keyword.THIS)) {
       thisKeyword = getAndAdvance();
       period = _expect(TokenType.PERIOD);
     }
     if (!_matchesIdentifier() && inFunctionType) {
       SimpleFormalParameterImpl parameter = astFactory.simpleFormalParameter(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           holder.keyword,
           holder.type,
           null);
       parameter.covariantKeyword = covariantKeyword;
       return parameter;
     }
     SimpleIdentifier identifier = parseSimpleIdentifier();
     TypeParameterList typeParameters = _parseGenericMethodTypeParameters();
     if (_matches(TokenType.OPEN_PAREN)) {
       FormalParameterList parameters = _parseFormalParameterListUnchecked();
       if (thisKeyword == null) {
         if (holder.keyword != null) {
           _reportErrorForToken(
               ParserErrorCode.FUNCTION_TYPED_PARAMETER_VAR, holder.keyword);
         }
         Token question = null;
         if (enableNnbd && _matches(TokenType.QUESTION)) {
           question = getAndAdvance();
         }
         FunctionTypedFormalParameterImpl parameter =
             astFactory.functionTypedFormalParameter(
                 commentAndMetadata.comment,
                 commentAndMetadata.metadata,
                 holder.type,
                 astFactory.simpleIdentifier(identifier.token,
                     isDeclaration: true),
                 typeParameters,
                 parameters,
                 question: question);
         parameter.covariantKeyword = covariantKeyword;
         return parameter;
       } else {
         FieldFormalParameterImpl parameter = astFactory.fieldFormalParameter(
             commentAndMetadata.comment,
             commentAndMetadata.metadata,
             holder.keyword,
             holder.type,
             thisKeyword,
             period,
             identifier,
             typeParameters,
             parameters);
         parameter.covariantKeyword = covariantKeyword;
         return parameter;
       }
     } else if (typeParameters != null) {
       // TODO(brianwilkerson) Report an error. It looks like a function-typed
       // parameter with no parameter list.
       //_reportErrorForToken(ParserErrorCode.MISSING_PARAMETERS, typeParameters.endToken);
     }
     TypeAnnotation type = holder.type;
     if (type != null) {
       if (type is TypeName &&
           _tokenMatchesKeyword(type.name.beginToken, Keyword.VOID)) {
         _reportErrorForToken(
             ParserErrorCode.VOID_PARAMETER, type.name.beginToken);
       } else if (holder.keyword != null &&
           _tokenMatchesKeyword(holder.keyword, Keyword.VAR)) {
         _reportErrorForToken(ParserErrorCode.VAR_AND_TYPE, holder.keyword);
       }
     }
     if (thisKeyword != null) {
       // TODO(brianwilkerson) If there are type parameters but no parameters,
       // should we create a synthetic empty parameter list here so we can
       // capture the type parameters?
       FieldFormalParameterImpl parameter = astFactory.fieldFormalParameter(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           holder.keyword,
           type,
           thisKeyword,
           period,
           identifier,
           null,
           null);
       parameter.covariantKeyword = covariantKeyword;
       return parameter;
     }
     SimpleFormalParameterImpl parameter = astFactory.simpleFormalParameter(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         holder.keyword,
         type,
         astFactory.simpleIdentifier(identifier.token, isDeclaration: true));
     parameter.covariantKeyword = covariantKeyword;
     return parameter;
   }

   /**
    * Parse an operator declaration. The [commentAndMetadata] is the
    * documentation comment and metadata to be associated with the declaration.
    * The [externalKeyword] is the 'external' token. The [returnType] is the
    * return type that has already been parsed, or `null` if there was no return
    * type. Return the operator declaration that was parsed.
    *
    *     operatorDeclaration ::=
    *         operatorSignature (';' | functionBody)
    *
    *     operatorSignature ::=
    *         'external'? returnType? 'operator' operator formalParameterList
    */
   MethodDeclaration parseOperator(CommentAndMetadata commentAndMetadata,
       Token externalKeyword, TypeName returnType) {
     Token operatorKeyword;
     if (_matchesKeyword(Keyword.OPERATOR)) {
       operatorKeyword = getAndAdvance();
     } else {
       _reportErrorForToken(
           ParserErrorCode.MISSING_KEYWORD_OPERATOR, _currentToken);
       operatorKeyword = _createSyntheticKeyword(Keyword.OPERATOR);
     }
     return _parseOperatorAfterKeyword(
         commentAndMetadata, externalKeyword, returnType, operatorKeyword);
   }

   /**
    * Parse a part or part-of directive. The [commentAndMetadata] is the metadata
    * to be associated with the directive. Return the part or part-of directive
    * that was parsed.
    *
    * This method assumes that the current token matches `Keyword.PART`.
    *
    *     partDirective ::=
    *         metadata 'part' stringLiteral ';'
    *
    *     partOfDirective ::=
    *         metadata 'part' 'of' identifier ';'
    */
   Directive parsePartOrPartOfDirective(CommentAndMetadata commentAndMetadata) {
     if (_tokenMatchesString(_peek(), _OF)) {
       return _parsePartOfDirective(commentAndMetadata);
     }
     return _parsePartDirective(commentAndMetadata);
   }

   /**
    * Parse a postfix expression. Return the postfix expression that was parsed.
    *
    *     postfixExpression ::=
    *         assignableExpression postfixOperator
    *       | primary selector*
    *
    *     selector ::=
    *         assignableSelector
    *       | argumentList
    */
   Expression parsePostfixExpression() {
     Expression operand = parseAssignableExpression(true);
     TokenType type = _currentToken.type;
     if (type == TokenType.OPEN_SQUARE_BRACKET ||
         type == TokenType.PERIOD ||
         type == TokenType.QUESTION_PERIOD ||
         type == TokenType.OPEN_PAREN ||
         type == TokenType.LT ||
         type == TokenType.INDEX) {
       do {
         if (_isLikelyArgumentList()) {
           TypeArgumentList typeArguments = _parseOptionalTypeArguments();
           ArgumentList argumentList = parseArgumentList();
           Expression currentOperand = operand;
           if (currentOperand is PropertyAccess) {
             operand = astFactory.methodInvocation(
                 currentOperand.target,
                 currentOperand.operator,
                 currentOperand.propertyName,
                 typeArguments,
                 argumentList);
           } else {
             operand = astFactory.functionExpressionInvocation(
                 operand, typeArguments, argumentList);
           }
         } else {
           operand = parseAssignableSelector(operand, true);
         }
         type = _currentToken.type;
       } while (type == TokenType.OPEN_SQUARE_BRACKET ||
           type == TokenType.PERIOD ||
           type == TokenType.QUESTION_PERIOD ||
           type == TokenType.OPEN_PAREN ||
           type == TokenType.INDEX);
       return operand;
     }
     if (!_currentToken.type.isIncrementOperator) {
       return operand;
     }
     _ensureAssignable(operand);
     Token operator = getAndAdvance();
     return astFactory.postfixExpression(operand, operator);
   }

   /**
    * Parse a prefixed identifier. Return the prefixed identifier that was
    * parsed.
    *
    *     prefixedIdentifier ::=
    *         identifier ('.' identifier)?
    */
   Identifier parsePrefixedIdentifier() {
     return _parsePrefixedIdentifierAfterIdentifier(parseSimpleIdentifier());
   }

   /**
    * Parse a primary expression. Return the primary expression that was parsed.
    *
    *     primary ::=
    *         thisExpression
    *       | 'super' unconditionalAssignableSelector
    *       | functionExpression
    *       | literal
    *       | identifier
    *       | newExpression
    *       | constObjectExpression
    *       | '(' expression ')'
    *       | argumentDefinitionTest
    *
    *     literal ::=
    *         nullLiteral
    *       | booleanLiteral
    *       | numericLiteral
    *       | stringLiteral
    *       | symbolLiteral
    *       | mapLiteral
    *       | listLiteral
    */
   Expression parsePrimaryExpression() {
     if (_matchesIdentifier()) {
       // TODO(brianwilkerson) The code below was an attempt to recover from an
       // error case, but it needs to be applied as a recovery only after we
       // know that parsing it as an identifier doesn't work. Leaving the code as
       // a reminder of how to recover.
 //      if (isFunctionExpression(_peek())) {
 //        //
 //        // Function expressions were allowed to have names at one point, but this is now illegal.
 //        //
 //        reportError(ParserErrorCode.NAMED_FUNCTION_EXPRESSION, getAndAdvance());
 //        return parseFunctionExpression();
 //      }
       return _parsePrefixedIdentifierUnchecked();
     }
     TokenType type = _currentToken.type;
     if (type == TokenType.STRING) {
       return parseStringLiteral();
     } else if (type == TokenType.INT) {
       Token token = getAndAdvance();
       int value = null;
       try {
         value = int.parse(token.lexeme);
       } on FormatException {
         // The invalid format should have been reported by the scanner.
       }
       return astFactory.integerLiteral(token, value);
     }
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.NULL) {
       return astFactory.nullLiteral(getAndAdvance());
     } else if (keyword == Keyword.NEW) {
       return parseNewExpression();
     } else if (keyword == Keyword.THIS) {
       return astFactory.thisExpression(getAndAdvance());
     } else if (keyword == Keyword.SUPER) {
       // TODO(paulberry): verify with Gilad that "super" must be followed by
       // unconditionalAssignableSelector in this case.
       return parseAssignableSelector(
           astFactory.superExpression(getAndAdvance()), false,
           allowConditional: false);
     } else if (keyword == Keyword.FALSE) {
       return astFactory.booleanLiteral(getAndAdvance(), false);
     } else if (keyword == Keyword.TRUE) {
       return astFactory.booleanLiteral(getAndAdvance(), true);
     }
     if (type == TokenType.DOUBLE) {
       Token token = getAndAdvance();
       double value = 0.0;
       try {
         value = double.parse(token.lexeme);
       } on FormatException {
         // The invalid format should have been reported by the scanner.
       }
       return astFactory.doubleLiteral(token, value);
     } else if (type == TokenType.HEXADECIMAL) {
       Token token = getAndAdvance();
       int value = null;
       try {
         value = int.parse(token.lexeme.substring(2), radix: 16);
       } on FormatException {
         // The invalid format should have been reported by the scanner.
       }
       return astFactory.integerLiteral(token, value);
     } else if (keyword == Keyword.CONST) {
       return parseConstExpression();
     } else if (type == TokenType.OPEN_PAREN) {
       if (isFunctionExpression(_currentToken)) {
         return parseFunctionExpression();
       }
       Token leftParenthesis = getAndAdvance();
       bool wasInInitializer = _inInitializer;
       _inInitializer = false;
       try {
         Expression expression = parseExpression2();
         Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
         return astFactory.parenthesizedExpression(
             leftParenthesis, expression, rightParenthesis);
       } finally {
         _inInitializer = wasInInitializer;
       }
     } else if (type == TokenType.LT || _injectGenericCommentTypeList()) {
       if (isFunctionExpression(currentToken)) {
         return parseFunctionExpression();
       }
       return parseListOrMapLiteral(null);
     } else if (type == TokenType.OPEN_CURLY_BRACKET) {
       return parseMapLiteral(null, null);
     } else if (type == TokenType.OPEN_SQUARE_BRACKET ||
         type == TokenType.INDEX) {
       return parseListLiteral(null, null);
     } else if (type == TokenType.QUESTION &&
         _tokenMatches(_peek(), TokenType.IDENTIFIER)) {
       _reportErrorForCurrentToken(
           ParserErrorCode.UNEXPECTED_TOKEN, [_currentToken.lexeme]);
       _advance();
       return parsePrimaryExpression();
     } else if (keyword == Keyword.VOID) {
       //
       // Recover from having a return type of "void" where a return type is not
       // expected.
       //
       // TODO(brianwilkerson) Improve this error message.
       _reportErrorForCurrentToken(
           ParserErrorCode.UNEXPECTED_TOKEN, [_currentToken.lexeme]);
       _advance();
       return parsePrimaryExpression();
     } else if (type == TokenType.HASH) {
       return parseSymbolLiteral();
     } else {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
       return createSyntheticIdentifier();
     }
   }

   /**
    * Parse a redirecting constructor invocation. The flag [hasPeriod] should be
    * `true` if the `this` is followed by a period. Return the redirecting
    * constructor invocation that was parsed.
    *
    * This method assumes that the current token matches `Keyword.THIS`.
    *
    *     redirectingConstructorInvocation ::=
    *         'this' ('.' identifier)? arguments
    */
   RedirectingConstructorInvocation parseRedirectingConstructorInvocation(
       bool hasPeriod) {
     Token keyword = getAndAdvance();
     Token period = null;
     SimpleIdentifier constructorName = null;
     if (hasPeriod) {
       period = getAndAdvance();
       if (_matchesIdentifier()) {
         constructorName = _parseSimpleIdentifierUnchecked(isDeclaration: false);
       } else {
         _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
         constructorName = createSyntheticIdentifier(isDeclaration: false);
         _advance();
       }
     }
     ArgumentList argumentList = _parseArgumentListChecked();
     return astFactory.redirectingConstructorInvocation(
         keyword, period, constructorName, argumentList);
   }

   /**
    * Parse a relational expression. Return the relational expression that was
    * parsed.
    *
    *     relationalExpression ::=
    *         bitwiseOrExpression ('is' '!'? type | 'as' type | relationalOperator bitwiseOrExpression)?
    *       | 'super' relationalOperator bitwiseOrExpression
    */
   Expression parseRelationalExpression() {
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type.isRelationalOperator) {
       Expression expression = astFactory.superExpression(getAndAdvance());
       Token operator = getAndAdvance();
       return astFactory.binaryExpression(
           expression, operator, parseBitwiseOrExpression());
     }
     Expression expression = parseBitwiseOrExpression();
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.AS) {
       Token asOperator = getAndAdvance();
       return astFactory.asExpression(
           expression, asOperator, parseTypeAnnotation(true));
     } else if (keyword == Keyword.IS) {
       Token isOperator = getAndAdvance();
       Token notOperator = null;
       if (_matches(TokenType.BANG)) {
         notOperator = getAndAdvance();
       }
       TypeAnnotation type = parseTypeAnnotation(true);
       return astFactory.isExpression(expression, isOperator, notOperator, type);
     } else if (_currentToken.type.isRelationalOperator) {
       Token operator = getAndAdvance();
       return astFactory.binaryExpression(
           expression, operator, parseBitwiseOrExpression());
     }
     return expression;
   }

   /**
    * Parse a rethrow expression. Return the rethrow expression that was parsed.
    *
    * This method assumes that the current token matches `Keyword.RETHROW`.
    *
    *     rethrowExpression ::=
    *         'rethrow'
    */
   Expression parseRethrowExpression() =>
       astFactory.rethrowExpression(getAndAdvance());

   /**
    * Parse a return statement. Return the return statement that was parsed.
    *
    * This method assumes that the current token matches `Keyword.RETURN`.
    *
    *     returnStatement ::=
    *         'return' expression? ';'
    */
   Statement parseReturnStatement() {
     Token returnKeyword = getAndAdvance();
     if (_matches(TokenType.SEMICOLON)) {
       return astFactory.returnStatement(returnKeyword, null, getAndAdvance());
     }
     Expression expression = parseExpression2();
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.returnStatement(returnKeyword, expression, semicolon);
   }

   /**
    * Parse a return type. Return the return type that was parsed.
    *
    *     returnType ::=
    *         'void'
    *       | type
    */
   TypeAnnotation parseReturnType(bool inExpression) {
     if (_currentToken.keyword == Keyword.VOID) {
       return astFactory.typeName(
           astFactory.simpleIdentifier(getAndAdvance()), null);
     } else {
       return parseTypeAnnotation(inExpression);
     }
   }

   /**
    * Parse a setter. The [commentAndMetadata] is the documentation comment and
    * metadata to be associated with the declaration. The [externalKeyword] is
    * the 'external' token. The [staticKeyword] is the static keyword, or `null`
    * if the setter is not static. The [returnType] is the return type that has
    * already been parsed, or `null` if there was no return type. Return the
    * setter that was parsed.
    *
    * This method assumes that the current token matches `Keyword.SET`.
    *
    *     setter ::=
    *         setterSignature functionBody?
    *
    *     setterSignature ::=
    *         'external'? 'static'? returnType? 'set' identifier formalParameterList
    */
   MethodDeclaration parseSetter(CommentAndMetadata commentAndMetadata,
       Token externalKeyword, Token staticKeyword, TypeAnnotation returnType) {
     Token propertyKeyword = getAndAdvance();
     SimpleIdentifier name = parseSimpleIdentifier(isDeclaration: true);
     FormalParameterList parameters = parseFormalParameterList();
     _validateFormalParameterList(parameters);
     FunctionBody body = parseFunctionBody(
         externalKeyword != null || staticKeyword == null,
         ParserErrorCode.STATIC_SETTER_WITHOUT_BODY,
         false);
     if (externalKeyword != null && body is! EmptyFunctionBody) {
       _reportErrorForCurrentToken(ParserErrorCode.EXTERNAL_SETTER_WITH_BODY);
     }
     return astFactory.methodDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         externalKeyword,
         staticKeyword,
         returnType,
         propertyKeyword,
         null,
         name,
         null,
         parameters,
         body);
   }

   /**
    * Parse a shift expression. Return the shift expression that was parsed.
    *
    *     shiftExpression ::=
    *         additiveExpression (shiftOperator additiveExpression)*
    *       | 'super' (shiftOperator additiveExpression)+
    */
   Expression parseShiftExpression() {
     Expression expression;
     if (_currentToken.keyword == Keyword.SUPER &&
         _currentToken.next.type.isShiftOperator) {
       expression = astFactory.superExpression(getAndAdvance());
     } else {
       expression = parseAdditiveExpression();
     }
     while (_currentToken.type.isShiftOperator) {
       expression = astFactory.binaryExpression(
           expression, getAndAdvance(), parseAdditiveExpression());
     }
     return expression;
   }

   /**
    * Parse a simple identifier. Return the simple identifier that was parsed.
    *
    *     identifier ::=
    *         IDENTIFIER
    */
   SimpleIdentifier parseSimpleIdentifier({bool isDeclaration: false}) {
     if (_matchesIdentifier()) {
       return _parseSimpleIdentifierUnchecked(isDeclaration: isDeclaration);
     }
     _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
     return createSyntheticIdentifier(isDeclaration: isDeclaration);
   }

   /**
    * Parse a statement, starting with the given [token]. Return the statement
    * that was parsed, or `null` if the tokens do not represent a recognizable
    * statement.
    */
   Statement parseStatement(Token token) {
     _currentToken = token;
     return parseStatement2();
   }

   /**
    * Parse a statement. Return the statement that was parsed.
    *
    *     statement ::=
    *         label* nonLabeledStatement
    */
   Statement parseStatement2() {
     List<Label> labels = null;
     while (_matchesIdentifier() && _currentToken.next.type == TokenType.COLON) {
       Label label = parseLabel(isDeclaration: true);
       if (labels == null) {
         labels = <Label>[label];
       } else {
         labels.add(label);
       }
     }
     Statement statement = parseNonLabeledStatement();
     if (labels == null) {
       return statement;
     }
     return astFactory.labeledStatement(labels, statement);
   }

   /**
    * Parse a sequence of statements, starting with the given [token]. Return the
    * statements that were parsed, or `null` if the tokens do not represent a
    * recognizable sequence of statements.
    */
   List<Statement> parseStatements(Token token) {
     _currentToken = token;
     return _parseStatementList();
   }

   /**
    * Parse a string literal. Return the string literal that was parsed.
    *
    *     stringLiteral ::=
    *         MULTI_LINE_STRING+
    *       | SINGLE_LINE_STRING+
    */
   StringLiteral parseStringLiteral() {
     if (_matches(TokenType.STRING)) {
       return _parseStringLiteralUnchecked();
     }
     _reportErrorForCurrentToken(ParserErrorCode.EXPECTED_STRING_LITERAL);
     return createSyntheticStringLiteral();
   }

   /**
    * Parse a super constructor invocation. Return the super constructor
    * invocation that was parsed.
    *
    * This method assumes that the current token matches [Keyword.SUPER].
    *
    *     superConstructorInvocation ::=
    *         'super' ('.' identifier)? arguments
    */
   SuperConstructorInvocation parseSuperConstructorInvocation() {
     Token keyword = getAndAdvance();
     Token period = null;
     SimpleIdentifier constructorName = null;
     if (_matches(TokenType.PERIOD)) {
       period = getAndAdvance();
       constructorName = parseSimpleIdentifier();
     }
     ArgumentList argumentList = _parseArgumentListChecked();
     return astFactory.superConstructorInvocation(
         keyword, period, constructorName, argumentList);
   }

   /**
    * Parse a switch statement. Return the switch statement that was parsed.
    *
    *     switchStatement ::=
    *         'switch' '(' expression ')' '{' switchCase* defaultCase? '}'
    *
    *     switchCase ::=
    *         label* ('case' expression ':') statements
    *
    *     defaultCase ::=
    *         label* 'default' ':' statements
    */
   SwitchStatement parseSwitchStatement() {
     bool wasInSwitch = _inSwitch;
     _inSwitch = true;
     try {
       HashSet<String> definedLabels = new HashSet<String>();
       Token keyword = _expectKeyword(Keyword.SWITCH);
       Token leftParenthesis = _expect(TokenType.OPEN_PAREN);
       Expression expression = parseExpression2();
       Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
       Token leftBracket = _expect(TokenType.OPEN_CURLY_BRACKET);
       Token defaultKeyword = null;
       List<SwitchMember> members = <SwitchMember>[];
       TokenType type = _currentToken.type;
       while (type != TokenType.EOF && type != TokenType.CLOSE_CURLY_BRACKET) {
         List<Label> labels = <Label>[];
         while (
             _matchesIdentifier() && _tokenMatches(_peek(), TokenType.COLON)) {
           SimpleIdentifier identifier =
               _parseSimpleIdentifierUnchecked(isDeclaration: true);
           String label = identifier.token.lexeme;
           if (definedLabels.contains(label)) {
             _reportErrorForToken(
                 ParserErrorCode.DUPLICATE_LABEL_IN_SWITCH_STATEMENT,
                 identifier.token,
                 [label]);
           } else {
             definedLabels.add(label);
           }
           Token colon = getAndAdvance();
           labels.add(astFactory.label(identifier, colon));
         }
         Keyword keyword = _currentToken.keyword;
         if (keyword == Keyword.CASE) {
           Token caseKeyword = getAndAdvance();
           Expression caseExpression = parseExpression2();
           Token colon = _expect(TokenType.COLON);
           members.add(astFactory.switchCase(labels, caseKeyword, caseExpression,
               colon, _parseStatementList()));
           if (defaultKeyword != null) {
             _reportErrorForToken(
                 ParserErrorCode.SWITCH_HAS_CASE_AFTER_DEFAULT_CASE,
                 caseKeyword);
           }
         } else if (keyword == Keyword.DEFAULT) {
           if (defaultKeyword != null) {
             _reportErrorForToken(
                 ParserErrorCode.SWITCH_HAS_MULTIPLE_DEFAULT_CASES, _peek());
           }
           defaultKeyword = getAndAdvance();
           Token colon = _expect(TokenType.COLON);
           members.add(astFactory.switchDefault(
               labels, defaultKeyword, colon, _parseStatementList()));
         } else {
           // We need to advance, otherwise we could end up in an infinite loop,
           // but this could be a lot smarter about recovering from the error.
           _reportErrorForCurrentToken(ParserErrorCode.EXPECTED_CASE_OR_DEFAULT);
           bool atEndOrNextMember() {
             TokenType type = _currentToken.type;
             if (type == TokenType.EOF ||
                 type == TokenType.CLOSE_CURLY_BRACKET) {
               return true;
             }
             Keyword keyword = _currentToken.keyword;
             return keyword == Keyword.CASE || keyword == Keyword.DEFAULT;
           }

           while (!atEndOrNextMember()) {
             _advance();
           }
         }
         type = _currentToken.type;
       }
       Token rightBracket = _expect(TokenType.CLOSE_CURLY_BRACKET);
       return astFactory.switchStatement(keyword, leftParenthesis, expression,
           rightParenthesis, leftBracket, members, rightBracket);
     } finally {
       _inSwitch = wasInSwitch;
     }
   }

   /**
    * Parse a symbol literal. Return the symbol literal that was parsed.
    *
    * This method assumes that the current token matches [TokenType.HASH].
    *
    *     symbolLiteral ::=
    *         '#' identifier ('.' identifier)*
    */
   SymbolLiteral parseSymbolLiteral() {
     Token poundSign = getAndAdvance();
     List<Token> components = <Token>[];
     if (_matchesIdentifier()) {
       components.add(getAndAdvance());
       while (_optional(TokenType.PERIOD)) {
         if (_matchesIdentifier()) {
           components.add(getAndAdvance());
         } else {
           _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
           components.add(_createSyntheticToken(TokenType.IDENTIFIER));
           break;
         }
       }
     } else if (_currentToken.isOperator) {
       components.add(getAndAdvance());
     } else if (_matchesKeyword(Keyword.VOID)) {
       components.add(getAndAdvance());
     } else {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
       components.add(_createSyntheticToken(TokenType.IDENTIFIER));
     }
     return astFactory.symbolLiteral(poundSign, components);
   }

   /**
    * Parse a throw expression. Return the throw expression that was parsed.
    *
    * This method assumes that the current token matches [Keyword.THROW].
    *
    *     throwExpression ::=
    *         'throw' expression
    */
   Expression parseThrowExpression() {
     Token keyword = getAndAdvance();
     TokenType type = _currentToken.type;
     if (type == TokenType.SEMICOLON || type == TokenType.CLOSE_PAREN) {
       _reportErrorForToken(
           ParserErrorCode.MISSING_EXPRESSION_IN_THROW, _currentToken);
       return astFactory.throwExpression(keyword, createSyntheticIdentifier());
     }
     Expression expression = parseExpression2();
     return astFactory.throwExpression(keyword, expression);
   }

   /**
    * Parse a throw expression. Return the throw expression that was parsed.
    *
    * This method assumes that the current token matches [Keyword.THROW].
    *
    *     throwExpressionWithoutCascade ::=
    *         'throw' expressionWithoutCascade
    */
   Expression parseThrowExpressionWithoutCascade() {
     Token keyword = getAndAdvance();
     TokenType type = _currentToken.type;
     if (type == TokenType.SEMICOLON || type == TokenType.CLOSE_PAREN) {
       _reportErrorForToken(
           ParserErrorCode.MISSING_EXPRESSION_IN_THROW, _currentToken);
       return astFactory.throwExpression(keyword, createSyntheticIdentifier());
     }
     Expression expression = parseExpressionWithoutCascade();
     return astFactory.throwExpression(keyword, expression);
   }

   /**
    * Parse a try statement. Return the try statement that was parsed.
    *
    * This method assumes that the current token matches [Keyword.TRY].
    *
    *     tryStatement ::=
    *         'try' block (onPart+ finallyPart? | finallyPart)
    *
    *     onPart ::=
    *         catchPart block
    *       | 'on' type catchPart? block
    *
    *     catchPart ::=
    *         'catch' '(' identifier (',' identifier)? ')'
    *
    *     finallyPart ::=
    *         'finally' block
    */
   Statement parseTryStatement() {
     Token tryKeyword = getAndAdvance();
     Block body = _parseBlockChecked();
     List<CatchClause> catchClauses = <CatchClause>[];
     Block finallyClause = null;
     while (_matchesString(_ON) || _matchesKeyword(Keyword.CATCH)) {
       Token onKeyword = null;
       TypeName exceptionType = null;
       if (_matchesString(_ON)) {
         onKeyword = getAndAdvance();
         exceptionType = parseTypeAnnotation(false);
       }
       Token catchKeyword = null;
       Token leftParenthesis = null;
       SimpleIdentifier exceptionParameter = null;
       Token comma = null;
       SimpleIdentifier stackTraceParameter = null;
       Token rightParenthesis = null;
       if (_matchesKeyword(Keyword.CATCH)) {
         catchKeyword = getAndAdvance();
         leftParenthesis = _expect(TokenType.OPEN_PAREN);
         exceptionParameter = parseSimpleIdentifier(isDeclaration: true);
         if (_matches(TokenType.COMMA)) {
           comma = getAndAdvance();
           stackTraceParameter = parseSimpleIdentifier(isDeclaration: true);
         }
         rightParenthesis = _expect(TokenType.CLOSE_PAREN);
       }
       Block catchBody = _parseBlockChecked();
       catchClauses.add(astFactory.catchClause(
           onKeyword,
           exceptionType,
           catchKeyword,
           leftParenthesis,
           exceptionParameter,
           comma,
           stackTraceParameter,
           rightParenthesis,
           catchBody));
     }
     Token finallyKeyword = null;
     if (_matchesKeyword(Keyword.FINALLY)) {
       finallyKeyword = getAndAdvance();
       finallyClause = _parseBlockChecked();
     } else if (catchClauses.isEmpty) {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_CATCH_OR_FINALLY);
     }
     return astFactory.tryStatement(
         tryKeyword, body, catchClauses, finallyKeyword, finallyClause);
   }

   /**
    * Parse a type alias. The [commentAndMetadata] is the metadata to be
    * associated with the member. Return the type alias that was parsed.
    *
    * This method assumes that the current token matches [Keyword.TYPEDEF].
    *
    *     typeAlias ::=
    *         'typedef' typeAliasBody
    *       | genericTypeAlias
    *
    *     typeAliasBody ::=
    *         functionTypeAlias
    *
    *     functionTypeAlias ::=
    *         functionPrefix typeParameterList? formalParameterList ';'
    *
    *     functionPrefix ::=
    *         returnType? name
    */
   TypeAlias parseTypeAlias(CommentAndMetadata commentAndMetadata) {
     Token keyword = getAndAdvance();
     if (_matchesIdentifier()) {
       Token next = _peek();
       if (_tokenMatches(next, TokenType.LT)) {
         next = _skipTypeParameterList(next);
         if (next != null && _tokenMatches(next, TokenType.EQ)) {
           TypeAlias typeAlias =
               parseGenericTypeAlias(commentAndMetadata, keyword);
           return typeAlias;
         }
       } else if (_tokenMatches(next, TokenType.EQ)) {
         TypeAlias typeAlias =
             parseGenericTypeAlias(commentAndMetadata, keyword);
         return typeAlias;
       }
     }
     return _parseFunctionTypeAlias(commentAndMetadata, keyword);
   }

   /**
    * Parse a type.
    *
    *     type ::=
    *         typeWithoutFunction
    *       | functionType
    */
   TypeAnnotation parseTypeAnnotation(bool inExpression) {
     if (parseGenericFunctionTypes) {
       TypeAnnotation type = null;
       if (_atGenericFunctionTypeAfterReturnType(_currentToken)) {
         // Generic function type with no return type.
         type = parseGenericFunctionTypeAfterReturnType(null);
       } else if (_currentToken.keyword == Keyword.VOID &&
           _atGenericFunctionTypeAfterReturnType(_currentToken.next)) {
         type = astFactory.typeName(
             astFactory.simpleIdentifier(getAndAdvance()), null);
       } else {
         type = parseTypeName(inExpression);
       }
       while (_atGenericFunctionTypeAfterReturnType(_currentToken)) {
         type = parseGenericFunctionTypeAfterReturnType(type);
       }
       return type;
     }
     return parseTypeName(inExpression);
   }

   /**
    * Parse a list of type arguments. Return the type argument list that was
    * parsed.
    *
    * This method assumes that the current token matches `TokenType.LT`.
    *
    *     typeArguments ::=
    *         '<' typeList '>'
    *
    *     typeList ::=
    *         type (',' type)*
    */
   TypeArgumentList parseTypeArgumentList() {
     Token leftBracket = getAndAdvance();
     List<TypeAnnotation> arguments = <TypeAnnotation>[
       parseTypeAnnotation(false)
     ];
     while (_optional(TokenType.COMMA)) {
       arguments.add(parseTypeAnnotation(false));
     }
     Token rightBracket = _expectGt();
     return astFactory.typeArgumentList(leftBracket, arguments, rightBracket);
   }

   /**
    * Parse a type name. Return the type name that was parsed.
    *
    *     type ::=
    *         qualified typeArguments?
    */
   TypeName parseTypeName(bool inExpression) {
     TypeName realType = _parseTypeName(inExpression);
     // If this is followed by a generic method type comment, allow the comment
     // type to replace the real type name.
     // TODO(jmesserly): this feels like a big hammer. Can we restrict it to
     // only work inside generic methods?
     TypeName typeFromComment = _parseOptionalTypeNameComment();
     return typeFromComment ?? realType;
   }

   /**
    * Parse a type parameter. Return the type parameter that was parsed.
    *
    *     typeParameter ::=
    *         metadata name ('extends' bound)?
    */
   TypeParameter parseTypeParameter() {
     CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
     SimpleIdentifier name = parseSimpleIdentifier(isDeclaration: true);
     if (_matches(TokenType.QUESTION)) {
       _reportErrorForCurrentToken(ParserErrorCode.NULLABLE_TYPE_PARAMETER);
       _advance();
     }
     if (_matchesKeyword(Keyword.EXTENDS)) {
       Token keyword = getAndAdvance();
       TypeAnnotation bound = parseTypeAnnotation(false);
       return astFactory.typeParameter(commentAndMetadata.comment,
           commentAndMetadata.metadata, name, keyword, bound);
     }
     return astFactory.typeParameter(commentAndMetadata.comment,
         commentAndMetadata.metadata, name, null, null);
   }

   /**
    * Parse a list of type parameters. Return the list of type parameters that
    * were parsed.
    *
    * This method assumes that the current token matches `TokenType.LT`.
    *
    *     typeParameterList ::=
    *         '<' typeParameter (',' typeParameter)* '>'
    */
   TypeParameterList parseTypeParameterList() {
     Token leftBracket = getAndAdvance();
     List<TypeParameter> typeParameters = <TypeParameter>[parseTypeParameter()];
     while (_optional(TokenType.COMMA)) {
       typeParameters.add(parseTypeParameter());
     }
     Token rightBracket = _expectGt();
     return astFactory.typeParameterList(
         leftBracket, typeParameters, rightBracket);
   }

   /**
    * Parse a unary expression. Return the unary expression that was parsed.
    *
    *     unaryExpression ::=
    *         prefixOperator unaryExpression
    *       | awaitExpression
    *       | postfixExpression
    *       | unaryOperator 'super'
    *       | '-' 'super'
    *       | incrementOperator assignableExpression
    */
   Expression parseUnaryExpression() {
     TokenType type = _currentToken.type;
     if (type == TokenType.MINUS ||
         type == TokenType.BANG ||
         type == TokenType.TILDE) {
       Token operator = getAndAdvance();
       if (_matchesKeyword(Keyword.SUPER)) {
         TokenType nextType = _peek().type;
         if (nextType == TokenType.OPEN_SQUARE_BRACKET ||
             nextType == TokenType.PERIOD) {
           //     "prefixOperator unaryExpression"
           // --> "prefixOperator postfixExpression"
           // --> "prefixOperator primary                    selector*"
           // --> "prefixOperator 'super' assignableSelector selector*"
           return astFactory.prefixExpression(operator, parseUnaryExpression());
         }
         return astFactory.prefixExpression(
             operator, astFactory.superExpression(getAndAdvance()));
       }
       return astFactory.prefixExpression(operator, parseUnaryExpression());
     } else if (_currentToken.type.isIncrementOperator) {
       Token operator = getAndAdvance();
       if (_matchesKeyword(Keyword.SUPER)) {
         TokenType nextType = _peek().type;
         if (nextType == TokenType.OPEN_SQUARE_BRACKET ||
             nextType == TokenType.PERIOD) {
           // --> "prefixOperator 'super' assignableSelector selector*"
           return astFactory.prefixExpression(operator, parseUnaryExpression());
         }
         //
         // Even though it is not valid to use an incrementing operator
         // ('++' or '--') before 'super', we can (and therefore must) interpret
         // "--super" as semantically equivalent to "-(-super)". Unfortunately,
         // we cannot do the same for "++super" because "+super" is also not
         // valid.
         //
         if (type == TokenType.MINUS_MINUS) {
           Token firstOperator = _createToken(operator, TokenType.MINUS);
           Token secondOperator =
               new Token(TokenType.MINUS, operator.offset + 1);
           secondOperator.setNext(_currentToken);
           firstOperator.setNext(secondOperator);
           operator.previous.setNext(firstOperator);
           return astFactory.prefixExpression(
               firstOperator,
               astFactory.prefixExpression(
                   secondOperator, astFactory.superExpression(getAndAdvance())));
         }
         // Invalid operator before 'super'
         _reportErrorForCurrentToken(
             ParserErrorCode.INVALID_OPERATOR_FOR_SUPER, [operator.lexeme]);
         return astFactory.prefixExpression(
             operator, astFactory.superExpression(getAndAdvance()));
       }
       return astFactory.prefixExpression(
           operator, _parseAssignableExpressionNotStartingWithSuper(false));
     } else if (type == TokenType.PLUS) {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_IDENTIFIER);
       return createSyntheticIdentifier();
     } else if (_inAsync && _matchesString(_AWAIT)) {
       return parseAwaitExpression();
     }
     return parsePostfixExpression();
   }

   /**
    * Parse a variable declaration. Return the variable declaration that was
    * parsed.
    *
    *     variableDeclaration ::=
    *         identifier ('=' expression)?
    */
   VariableDeclaration parseVariableDeclaration() {
     // TODO(paulberry): prior to the fix for bug 23204, we permitted
     // annotations before variable declarations (e.g. "String @deprecated s;").
     // Although such constructions are prohibited by the spec, we may want to
     // consider handling them anyway to allow for better parser recovery in the
     // event that the user erroneously tries to use them.  However, as a
     // counterargument, this would likely degrade parser recovery in the event
     // of a construct like "class C { int @deprecated foo() {} }" (i.e. the
     // user is in the middle of inserting "int bar;" prior to
     // "@deprecated foo() {}").
     SimpleIdentifier name = parseSimpleIdentifier(isDeclaration: true);
     Token equals = null;
     Expression initializer = null;
     if (_matches(TokenType.EQ)) {
       equals = getAndAdvance();
       initializer = parseExpression2();
     }
     return astFactory.variableDeclaration(name, equals, initializer);
   }

   /**
    * Parse a variable declaration list. The [commentAndMetadata] is the metadata
    * to be associated with the variable declaration list. Return the variable
    * declaration list that was parsed.
    *
    *     variableDeclarationList ::=
    *         finalConstVarOrType variableDeclaration (',' variableDeclaration)*
    */
   VariableDeclarationList parseVariableDeclarationListAfterMetadata(
       CommentAndMetadata commentAndMetadata) {
     FinalConstVarOrType holder = parseFinalConstVarOrType(false);
     return parseVariableDeclarationListAfterType(
         commentAndMetadata, holder.keyword, holder.type);
   }

   /**
    * Parse a variable declaration list. The [commentAndMetadata] is the metadata
    * to be associated with the variable declaration list, or `null` if there is
    * no attempt at parsing the comment and metadata. The [keyword] is the token
    * representing the 'final', 'const' or 'var' keyword, or `null` if there is
    * no keyword. The [type] is the type of the variables in the list. Return the
    * variable declaration list that was parsed.
    *
    *     variableDeclarationList ::=
    *         finalConstVarOrType variableDeclaration (',' variableDeclaration)*
    */
   VariableDeclarationList parseVariableDeclarationListAfterType(
       CommentAndMetadata commentAndMetadata,
       Token keyword,
       TypeAnnotation type) {
     if (type != null &&
         keyword != null &&
         _tokenMatchesKeyword(keyword, Keyword.VAR)) {
       _reportErrorForToken(ParserErrorCode.VAR_AND_TYPE, keyword);
     }
     List<VariableDeclaration> variables = <VariableDeclaration>[
       parseVariableDeclaration()
     ];
     while (_optional(TokenType.COMMA)) {
       variables.add(parseVariableDeclaration());
     }
     return astFactory.variableDeclarationList(commentAndMetadata?.comment,
         commentAndMetadata?.metadata, keyword, type, variables);
   }

   /**
    * Parse a variable declaration statement. The [commentAndMetadata] is the
    * metadata to be associated with the variable declaration statement, or
    * `null` if there is no attempt at parsing the comment and metadata. Return
    * the variable declaration statement that was parsed.
    *
    *     variableDeclarationStatement ::=
    *         variableDeclarationList ';'
    */
   VariableDeclarationStatement parseVariableDeclarationStatementAfterMetadata(
       CommentAndMetadata commentAndMetadata) {
     //    Token startToken = currentToken;
     VariableDeclarationList variableList =
         parseVariableDeclarationListAfterMetadata(commentAndMetadata);
 //        if (!matches(TokenType.SEMICOLON)) {
 //          if (matches(startToken, Keyword.VAR) && isTypedIdentifier(startToken.getNext())) {
 //            // TODO(brianwilkerson) This appears to be of the form "var type variable". We should do
 //            // a better job of recovering in this case.
 //          }
 //        }
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.variableDeclarationStatement(variableList, semicolon);
   }

   /**
    * Parse a while statement. Return the while statement that was parsed.
    *
    * This method assumes that the current token matches [Keyword.WHILE].
    *
    *     whileStatement ::=
    *         'while' '(' expression ')' statement
    */
   Statement parseWhileStatement() {
     bool wasInLoop = _inLoop;
     _inLoop = true;
     try {
       Token keyword = getAndAdvance();
       Token leftParenthesis = _expect(TokenType.OPEN_PAREN);
       Expression condition = parseExpression2();
       Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
       Statement body = parseStatement2();
       return astFactory.whileStatement(
           keyword, leftParenthesis, condition, rightParenthesis, body);
     } finally {
       _inLoop = wasInLoop;
     }
   }

   /**
    * Parse a with clause. Return the with clause that was parsed.
    *
    * This method assumes that the current token matches `Keyword.WITH`.
    *
    *     withClause ::=
    *         'with' typeName (',' typeName)*
    */
   WithClause parseWithClause() {
     Token withKeyword = getAndAdvance();
     List<TypeName> types = <TypeName>[];
     do {
       TypeName typeName = parseTypeName(false);
       _mustNotBeNullable(typeName, ParserErrorCode.NULLABLE_TYPE_IN_WITH);
       types.add(typeName);
     } while (_optional(TokenType.COMMA));
     return astFactory.withClause(withKeyword, types);
   }

   /**
    * Parse a yield statement. Return the yield statement that was parsed.
    *
    * This method assumes that the current token matches [Keyword.YIELD].
    *
    *     yieldStatement ::=
    *         'yield' '*'? expression ';'
    */
   YieldStatement parseYieldStatement() {
     Token yieldToken = getAndAdvance();
     Token star = null;
     if (_matches(TokenType.STAR)) {
       star = getAndAdvance();
     }
     Expression expression = parseExpression2();
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.yieldStatement(yieldToken, star, expression, semicolon);
   }

   /**
    * Parse a formal parameter list, starting at the [startToken], without
    * actually creating a formal parameter list or changing the current token.
    * Return the token following the parameter list that was parsed, or `null`
    * if the given token is not the first token in a valid parameter list.
    *
    * This method must be kept in sync with [parseFormalParameterList].
    */
   Token skipFormalParameterList(Token startToken) {
     if (!_tokenMatches(startToken, TokenType.OPEN_PAREN)) {
       return null;
     }
     return (startToken as BeginToken).endToken;
   }

   /**
    * Parse the portion of a generic function type after the return type,
    * starting at the [startToken], without actually creating a generic function
    * type or changing the current token. Return the token following the generic
    * function type that was parsed, or `null` if the given token is not the
    * first token in a valid generic function type.
    *
    * This method must be kept in sync with
    * [parseGenericFunctionTypeAfterReturnType].
    */
   Token skipGenericFunctionTypeAfterReturnType(Token startToken) {
     Token next = startToken.next; // Skip 'Function'
     if (_tokenMatches(next, TokenType.LT)) {
       next = skipTypeParameterList(next);
     }
     return skipFormalParameterList(next);
   }

   /**
    * Parse a prefixed identifier, starting at the [startToken], without actually
    * creating a prefixed identifier or changing the current token. Return the
    * token following the prefixed identifier that was parsed, or `null` if the
    * given token is not the first token in a valid prefixed identifier.
    *
    * This method must be kept in sync with [parsePrefixedIdentifier].
    *
    *     prefixedIdentifier ::=
    *         identifier ('.' identifier)?
    */
   Token skipPrefixedIdentifier(Token startToken) {
     Token token = skipSimpleIdentifier(startToken);
     if (token == null) {
       return null;
     } else if (!_tokenMatches(token, TokenType.PERIOD)) {
       return token;
     }
     token = token.next;
     Token nextToken = skipSimpleIdentifier(token);
     if (nextToken != null) {
       return nextToken;
     } else if (_tokenMatches(token, TokenType.CLOSE_PAREN) ||
         _tokenMatches(token, TokenType.COMMA)) {
       // If the `id.` is followed by something that cannot produce a valid
       // structure then assume this is a prefixed identifier but missing the
       // trailing identifier
       return token;
     }
     return null;
   }

   /**
    * Parse a return type, starting at the [startToken], without actually
    * creating a return type or changing the current token. Return the token
    * following the return type that was parsed, or `null` if the given token is
    * not the first token in a valid return type.
    *
    * This method must be kept in sync with [parseReturnType].
    *
    *     returnType ::=
    *         'void'
    *       | type
    */
   Token skipReturnType(Token startToken) {
     if (_tokenMatchesKeyword(startToken, Keyword.VOID)) {
       return startToken.next;
     } else {
       return skipTypeAnnotation(startToken);
     }
   }

   /**
    * Parse a simple identifier, starting at the [startToken], without actually
    * creating a simple identifier or changing the current token. Return the
    * token following the simple identifier that was parsed, or `null` if the
    * given token is not the first token in a valid simple identifier.
    *
    * This method must be kept in sync with [parseSimpleIdentifier].
    *
    *     identifier ::=
    *         IDENTIFIER
    */
   Token skipSimpleIdentifier(Token startToken) {
     if (_tokenMatches(startToken, TokenType.IDENTIFIER) ||
         _tokenMatchesPseudoKeyword(startToken)) {
       return startToken.next;
     }
     return null;
   }

   /**
    * Parse a string literal, starting at the [startToken], without actually
    * creating a string literal or changing the current token. Return the token
    * following the string literal that was parsed, or `null` if the given token
    * is not the first token in a valid string literal.
    *
    * This method must be kept in sync with [parseStringLiteral].
    *
    *     stringLiteral ::=
    *         MULTI_LINE_STRING+
    *       | SINGLE_LINE_STRING+
    */
   Token skipStringLiteral(Token startToken) {
     Token token = startToken;
     while (token != null && _tokenMatches(token, TokenType.STRING)) {
       token = token.next;
       TokenType type = token.type;
       if (type == TokenType.STRING_INTERPOLATION_EXPRESSION ||
           type == TokenType.STRING_INTERPOLATION_IDENTIFIER) {
         token = _skipStringInterpolation(token);
       }
     }
     if (identical(token, startToken)) {
       return null;
     }
     return token;
   }

   /**
    * Parse a type annotation, starting at the [startToken], without actually
    * creating a type annotation or changing the current token. Return the token
    * following the type annotation that was parsed, or `null` if the given token
    * is not the first token in a valid type annotation.
    *
    * This method must be kept in sync with [parseTypeAnnotation].
    */
   Token skipTypeAnnotation(Token startToken) {
     if (parseGenericFunctionTypes) {
       Token next = null;
       if (_atGenericFunctionTypeAfterReturnType(startToken)) {
         next = skipGenericFunctionTypeAfterReturnType(startToken);
       } else if (_currentToken.keyword == Keyword.VOID &&
           _atGenericFunctionTypeAfterReturnType(_currentToken.next)) {
         next = next.next;
       } else {
         next = skipTypeName(startToken);
       }
       while (next != null && _tokenMatchesString(next, 'Function')) {
         next = skipGenericFunctionTypeAfterReturnType(next);
       }
       return next;
     }
     return skipTypeName(startToken);
   }

   /**
    * Parse a list of type arguments, starting at the [startToken], without
    * actually creating a type argument list or changing the current token.
    * Return the token following the type argument list that was parsed, or
    * `null` if the given token is not the first token in a valid type argument
    * list.
    *
    * This method must be kept in sync with [parseTypeArgumentList].
    *
    *     typeArguments ::=
    *         '<' typeList '>'
    *
    *     typeList ::=
    *         type (',' type)*
    */
   Token skipTypeArgumentList(Token startToken) {
     Token token = startToken;
     if (!_tokenMatches(token, TokenType.LT) &&
         !_injectGenericCommentTypeList()) {
       return null;
     }
     token = skipTypeName(token.next);
     if (token == null) {
       // If the start token '<' is followed by '>'
       // then assume this should be type argument list but is missing a type
       token = startToken.next;
       if (_tokenMatches(token, TokenType.GT)) {
         return token.next;
       }
       return null;
     }
     while (_tokenMatches(token, TokenType.COMMA)) {
       token = skipTypeName(token.next);
       if (token == null) {
         return null;
       }
     }
     if (token.type == TokenType.GT) {
       return token.next;
     } else if (token.type == TokenType.GT_GT) {
       Token second = new Token(TokenType.GT, token.offset + 1);
       second.setNextWithoutSettingPrevious(token.next);
       return second;
     }
     return null;
   }

   /**
    * Parse a type name, starting at the [startToken], without actually creating
    * a type name or changing the current token. Return the token following the
    * type name that was parsed, or `null` if the given token is not the first
    * token in a valid type name.
    *
    * This method must be kept in sync with [parseTypeName].
    *
    *     type ::=
    *         qualified typeArguments?
    */
   Token skipTypeName(Token startToken) {
     Token token = skipPrefixedIdentifier(startToken);
     if (token == null) {
       return null;
     }
     if (_tokenMatches(token, TokenType.LT)) {
       token = skipTypeArgumentList(token);
     }
     return token;
   }

   /**
    * Parse a type parameter list, starting at the [startToken], without actually
    * creating a type parameter list or changing the current token. Return the
    * token following the type parameter list that was parsed, or `null` if the
    * given token is not the first token in a valid type parameter list.
    *
    * This method must be kept in sync with [parseTypeParameterList].
    */
   Token skipTypeParameterList(Token startToken) {
     if (!_tokenMatches(startToken, TokenType.LT)) {
       return null;
     }
     int depth = 1;
     Token previous = startToken;
     Token next = startToken.next;
     while (next != previous) {
       if (_tokenMatches(startToken, TokenType.LT)) {
         depth++;
       } else if (_tokenMatches(next, TokenType.GT)) {
         depth--;
         if (depth == 0) {
           return next;
         }
       }
       previous = next;
       next = next.next;
     }
     return null;
   }

   /**
    * Advance to the next token in the token stream.
    */
   void _advance() {
     _currentToken = _currentToken.next;
   }

   /**
    * Append the character equivalent of the given [codePoint] to the given
    * [builder]. Use the [startIndex] and [endIndex] to report an error, and
    * don't append anything to the builder, if the code point is invalid. The
    * [escapeSequence] is the escape sequence that was parsed to produce the
    * code point (used for error reporting).
    */
   void _appendCodePoint(StringBuffer buffer, String source, int codePoint,
       int startIndex, int endIndex) {
     if (codePoint < 0 || codePoint > Character.MAX_CODE_POINT) {
       String escapeSequence = source.substring(startIndex, endIndex + 1);
       _reportErrorForCurrentToken(
           ParserErrorCode.INVALID_CODE_POINT, [escapeSequence]);
       return;
     }
     if (codePoint < Character.MAX_VALUE) {
       buffer.writeCharCode(codePoint);
     } else {
       buffer.write(Character.toChars(codePoint));
     }
   }

   /**
    * Return `true` if we are positioned at the keyword 'Function' in a generic
    * function type alias.
    */
   bool _atGenericFunctionTypeAfterReturnType(Token startToken) {
     if (_tokenMatchesString(startToken, 'Function')) {
       Token next = startToken.next;
       if (next != null &&
           (_tokenMatches(next, TokenType.OPEN_PAREN) ||
               _tokenMatches(next, TokenType.LT))) {
         return true;
       }
     }
     return false;
   }

   /**
    * Clone all token starting from the given [token] up to the end of the token
    * stream, and return the first token in the new token stream.
    */
   Token _cloneTokens(Token token) {
     if (token == null) {
       return null;
     }
     token = token is CommentToken ? token.parent : token;
     Token head = new Token(TokenType.EOF, -1);
     head.setNext(head);
     Token current = head;
     while (token.type != TokenType.EOF) {
       Token clone = token.copy();
       current.setNext(clone);
       current = clone;
       token = token.next;
     }
     Token tail = new Token(TokenType.EOF, 0);
     tail.setNext(tail);
     current.setNext(tail);
     return head.next;
   }

   /**
    * Convert the given [method] declaration into the nearest valid top-level
    * function declaration (that is, the function declaration that most closely
    * captures the components of the given method declaration).
    */
   FunctionDeclaration _convertToFunctionDeclaration(MethodDeclaration method) =>
       astFactory.functionDeclaration(
           method.documentationComment,
           method.metadata,
           method.externalKeyword,
           method.returnType,
           method.propertyKeyword,
           method.name,
           astFactory.functionExpression(
               method.typeParameters, method.parameters, method.body));

   /**
    * Return `true` if the current token could be the start of a compilation unit
    * member. This method is used for recovery purposes to decide when to stop
    * skipping tokens after finding an error while parsing a compilation unit
    * member.
    */
   bool _couldBeStartOfCompilationUnitMember() {
     Keyword keyword = _currentToken.keyword;
     Token next = _currentToken.next;
     TokenType nextType = next.type;
     if ((keyword == Keyword.IMPORT ||
             keyword == Keyword.EXPORT ||
             keyword == Keyword.LIBRARY ||
             keyword == Keyword.PART) &&
         nextType != TokenType.PERIOD &&
         nextType != TokenType.LT) {
       // This looks like the start of a directive
       return true;
     } else if (keyword == Keyword.CLASS) {
       // This looks like the start of a class definition
       return true;
     } else if (keyword == Keyword.TYPEDEF &&
         nextType != TokenType.PERIOD &&
         nextType != TokenType.LT) {
       // This looks like the start of a typedef
       return true;
     } else if (keyword == Keyword.VOID ||
         ((keyword == Keyword.GET || keyword == Keyword.SET) &&
             _tokenMatchesIdentifier(next)) ||
         (keyword == Keyword.OPERATOR && _isOperator(next))) {
       // This looks like the start of a function
       return true;
     } else if (_matchesIdentifier()) {
       if (nextType == TokenType.OPEN_PAREN) {
         // This looks like the start of a function
         return true;
       }
       Token token = skipReturnType(_currentToken);
       if (token == null) {
         return false;
       }
       // TODO(brianwilkerson) This looks wrong; should we be checking 'token'?
       if (keyword == Keyword.GET ||
           keyword == Keyword.SET ||
           (keyword == Keyword.OPERATOR && _isOperator(next)) ||
           _matchesIdentifier()) {
         return true;
       }
     }
     return false;
   }

   /**
    * Return a synthetic token representing the given [keyword].
    */
   Token _createSyntheticKeyword(Keyword keyword) => _injectToken(
       new Parser_SyntheticKeywordToken(keyword, _currentToken.offset));

   /**
    * Return a synthetic token with the given [type].
    */
   Token _createSyntheticToken(TokenType type) =>
       _injectToken(new StringToken(type, "", _currentToken.offset));

   /**
    * Create and return a new token with the given [type]. The token will replace
    * the first portion of the given [token], so it will have the same offset and
    * will have any comments that might have preceeded the token.
    */
   Token _createToken(Token token, TokenType type, {bool isBegin: false}) {
     CommentToken comments = token.precedingComments;
     if (comments == null) {
       if (isBegin) {
         return new BeginToken(type, token.offset);
       }
       return new Token(type, token.offset);
     } else if (isBegin) {
       return new BeginTokenWithComment(type, token.offset, comments);
     }
     return new TokenWithComment(type, token.offset, comments);
   }

   /**
    * Check that the given [expression] is assignable and report an error if it
    * isn't.
    *
    *     assignableExpression ::=
    *         primary (arguments* assignableSelector)+
    *       | 'super' unconditionalAssignableSelector
    *       | identifier
    *
    *     unconditionalAssignableSelector ::=
    *         '[' expression ']'
    *       | '.' identifier
    *
    *     assignableSelector ::=
    *         unconditionalAssignableSelector
    *       | '?.' identifier
    */
   void _ensureAssignable(Expression expression) {
     if (expression != null && !expression.isAssignable) {
       _reportErrorForCurrentToken(
           ParserErrorCode.ILLEGAL_ASSIGNMENT_TO_NON_ASSIGNABLE);
     }
   }

   /**
    * If the current token has the expected type, return it after advancing to
    * the next token. Otherwise report an error and return the current token
    * without advancing.
    *
    * Note that the method [_expectGt] should be used if the argument to this
    * method would be [TokenType.GT].
    *
    * The [type] is the type of token that is expected.
    */
   Token _expect(TokenType type) {
     if (_matches(type)) {
       return getAndAdvance();
     }
     // Remove uses of this method in favor of matches?
     // Pass in the error code to use to report the error?
     if (type == TokenType.SEMICOLON) {
       if (_tokenMatches(_currentToken.next, TokenType.SEMICOLON)) {
         _reportErrorForCurrentToken(
             ParserErrorCode.UNEXPECTED_TOKEN, [_currentToken.lexeme]);
         _advance();
         return getAndAdvance();
       }
       _reportErrorForToken(ParserErrorCode.EXPECTED_TOKEN,
           _currentToken.previous, [type.lexeme]);
       return _createSyntheticToken(TokenType.SEMICOLON);
     }
     _reportErrorForCurrentToken(ParserErrorCode.EXPECTED_TOKEN, [type.lexeme]);
     return _createSyntheticToken(type);
   }

   /**
    * If the current token has the type [TokenType.GT], return it after advancing
    * to the next token. Otherwise report an error and create a synthetic token.
    */
   Token _expectGt() {
     if (_matchesGt()) {
       return getAndAdvance();
     }
     _reportErrorForCurrentToken(
         ParserErrorCode.EXPECTED_TOKEN, [TokenType.GT.lexeme]);
     return _createSyntheticToken(TokenType.GT);
   }

   /**
    * If the current token is a keyword matching the given [keyword], return it
    * after advancing to the next token. Otherwise report an error and return the
    * current token without advancing.
    */
   Token _expectKeyword(Keyword keyword) {
     if (_matchesKeyword(keyword)) {
       return getAndAdvance();
     }
     // Remove uses of this method in favor of matches?
     // Pass in the error code to use to report the error?
     _reportErrorForCurrentToken(
         ParserErrorCode.EXPECTED_TOKEN, [keyword.syntax]);
     return _currentToken;
   }

   /**
    * Search the given list of [ranges] for a range that contains the given
    * [index]. Return the range that was found, or `null` if none of the ranges
    * contain the index.
    */
   List<int> _findRange(List<List<int>> ranges, int index) {
     int rangeCount = ranges.length;
     for (int i = 0; i < rangeCount; i++) {
       List<int> range = ranges[i];
       if (range[0] <= index && index <= range[1]) {
         return range;
       } else if (index < range[0]) {
         return null;
       }
     }
     return null;
   }

   /**
    * Return a list of the ranges of characters in the given [comment] that
    * should be treated as code blocks.
    */
   List<List<int>> _getCodeBlockRanges(String comment) {
     List<List<int>> ranges = <List<int>>[];
     int length = comment.length;
     if (length < 3) {
       return ranges;
     }
     int index = 0;
     int firstChar = comment.codeUnitAt(0);
     if (firstChar == 0x2F) {
       int secondChar = comment.codeUnitAt(1);
       int thirdChar = comment.codeUnitAt(2);
       if ((secondChar == 0x2A && thirdChar == 0x2A) ||
           (secondChar == 0x2F && thirdChar == 0x2F)) {
         index = 3;
       }
     }
     if (StringUtilities.startsWith4(comment, index, 0x20, 0x20, 0x20, 0x20)) {
       int end = index + 4;
       while (end < length &&
           comment.codeUnitAt(end) != 0xD &&
           comment.codeUnitAt(end) != 0xA) {
         end = end + 1;
       }
       ranges.add(<int>[index, end]);
       index = end;
     }
     while (index < length) {
       int currentChar = comment.codeUnitAt(index);
       if (currentChar == 0xD || currentChar == 0xA) {
         index = index + 1;
         while (index < length &&
             Character.isWhitespace(comment.codeUnitAt(index))) {
           index = index + 1;
         }
         if (StringUtilities.startsWith6(
             comment, index, 0x2A, 0x20, 0x20, 0x20, 0x20, 0x20)) {
           int end = index + 6;
           while (end < length &&
               comment.codeUnitAt(end) != 0xD &&
               comment.codeUnitAt(end) != 0xA) {
             end = end + 1;
           }
           ranges.add(<int>[index, end]);
           index = end;
         }
       } else if (index + 1 < length &&
           currentChar == 0x5B &&
           comment.codeUnitAt(index + 1) == 0x3A) {
         int end = StringUtilities.indexOf2(comment, index + 2, 0x3A, 0x5D);
         if (end < 0) {
           end = length;
         }
         ranges.add(<int>[index, end]);
         index = end + 1;
       } else {
         index = index + 1;
       }
     }
     return ranges;
   }

   /**
    * Return the end token associated with the given [beginToken], or `null` if
    * either the given token is not a begin token or it does not have an end
    * token associated with it.
    */
   Token _getEndToken(Token beginToken) {
     if (beginToken is BeginToken) {
       return beginToken.endToken;
     }
     return null;
   }

   bool _injectGenericComment(TokenType type, int prefixLen) {
     if (parseGenericMethodComments) {
       CommentToken t = _currentToken.precedingComments;
       for (; t != null; t = t.next) {
         if (t.type == type) {
           String comment = t.lexeme.substring(prefixLen, t.lexeme.length - 2);
           Token list = _scanGenericMethodComment(comment, t.offset + prefixLen);
           if (list != null) {
             // Remove the token from the comment stream.
             t.remove();
             // Insert the tokens into the stream.
             _injectTokenList(list);
             return true;
           }
         }
       }
     }
     return false;
   }

   /**
    * Matches a generic comment type substitution and injects it into the token
    * stream. Returns true if a match was injected, otherwise false.
    *
    * These comments are of the form `/*=T*/`, in other words, a [TypeName]
    * inside a slash-star comment, preceded by equals sign.
    */
   bool _injectGenericCommentTypeAssign() {
     return _injectGenericComment(TokenType.GENERIC_METHOD_TYPE_ASSIGN, 3);
   }

   /**
    * Matches a generic comment type parameters and injects them into the token
    * stream. Returns true if a match was injected, otherwise false.
    *
    * These comments are of the form `/*<K, V>*/`, in other words, a
    * [TypeParameterList] or [TypeArgumentList] inside a slash-star comment.
    */
   bool _injectGenericCommentTypeList() {
     return _injectGenericComment(TokenType.GENERIC_METHOD_TYPE_LIST, 2);
   }

   /**
    * Inject the given [token] into the token stream immediately before the
    * current token.
    */
   Token _injectToken(Token token) {
     Token previous = _currentToken.previous;
     token.setNext(_currentToken);
     previous.setNext(token);
     return token;
   }

   void _injectTokenList(Token firstToken) {
     // Scanner creates a cyclic EOF token.
     Token lastToken = firstToken;
     while (lastToken.next.type != TokenType.EOF) {
       lastToken = lastToken.next;
     }
     // Inject these new tokens into the stream.
     Token previous = _currentToken.previous;
     lastToken.setNext(_currentToken);
     previous.setNext(firstToken);
     _currentToken = firstToken;
   }

   /**
    * Return `true` if the current token could be the question mark in a
    * condition expression. The current token is assumed to be a question mark.
    */
   bool _isConditionalOperator() {
     void parseOperation(Parser parser) {
       parser.parseExpressionWithoutCascade();
     }

     Token token = _skip(_currentToken.next, parseOperation);
     if (token == null || !_tokenMatches(token, TokenType.COLON)) {
       return false;
     }
     token = _skip(token.next, parseOperation);
     return token != null;
   }

   /**
    * Return `true` if the given [character] is a valid hexadecimal digit.
    */
   bool _isHexDigit(int character) =>
       (0x30 <= character && character <= 0x39) ||
       (0x41 <= character && character <= 0x46) ||
       (0x61 <= character && character <= 0x66);

   bool _isLikelyArgumentList() {
     // Try to reduce the amount of lookahead required here before enabling
     // generic methods.
     if (_matches(TokenType.OPEN_PAREN)) {
       return true;
     }
     Token token = skipTypeArgumentList(_currentToken);
     return token != null && _tokenMatches(token, TokenType.OPEN_PAREN);
   }

   /**
    * Given that we have just found bracketed text within the given [comment],
    * look to see whether that text is (a) followed by a parenthesized link
    * address, (b) followed by a colon, or (c) followed by optional whitespace
    * and another square bracket. The [rightIndex] is the index of the right
    * bracket. Return `true` if the bracketed text is followed by a link address.
    *
    * This method uses the syntax described by the
    * <a href="http://daringfireball.net/projects/markdown/syntax">markdown</a>
    * project.
    */
   bool _isLinkText(String comment, int rightIndex) {
     int length = comment.length;
     int index = rightIndex + 1;
     if (index >= length) {
       return false;
     }
     int nextChar = comment.codeUnitAt(index);
     if (nextChar == 0x28 || nextChar == 0x3A) {
       return true;
     }
     while (Character.isWhitespace(nextChar)) {
       index = index + 1;
       if (index >= length) {
         return false;
       }
       nextChar = comment.codeUnitAt(index);
     }
     return nextChar == 0x5B;
   }

   /**
    * Return `true` if the given [startToken] appears to be the beginning of an
    * operator declaration.
    */
   bool _isOperator(Token startToken) {
     // Accept any operator here, even if it is not user definable.
     if (!startToken.isOperator) {
       return false;
     }
     // Token "=" means that it is actually a field initializer.
     if (startToken.type == TokenType.EQ) {
       return false;
     }
     // Consume all operator tokens.
     Token token = startToken.next;
     while (token.isOperator) {
       token = token.next;
     }
     // Formal parameter list is expect now.
     return _tokenMatches(token, TokenType.OPEN_PAREN);
   }

   bool _isPeekGenericTypeParametersAndOpenParen() {
     Token token = _skipTypeParameterList(_peek());
     return token != null && _tokenMatches(token, TokenType.OPEN_PAREN);
   }

   /**
    * Return `true` if the [startToken] appears to be the first token of a type
    * name that is followed by a variable or field formal parameter.
    */
   bool _isTypedIdentifier(Token startToken) {
     Token token = skipReturnType(startToken);
     if (token == null) {
       return false;
     } else if (_tokenMatchesIdentifier(token)) {
       return true;
     } else if (_tokenMatchesKeyword(token, Keyword.THIS) &&
         _tokenMatches(token.next, TokenType.PERIOD) &&
         _tokenMatchesIdentifier(token.next.next)) {
       return true;
     } else if (_tokenMatchesKeyword(startToken, Keyword.VOID)) {
       // The keyword 'void' isn't a valid identifier, so it should be assumed to
       // be a type name.
       return true;
     } else if (startToken.next != token &&
         !_tokenMatches(token, TokenType.OPEN_PAREN)) {
       // The type is more than a simple identifier, so it should be assumed to
       // be a type name.
       return true;
     }
     return false;
   }

   /**
    * Increments the error reporting lock level. If level is more than `0`, then
    * [reportError] wont report any error.
    */
   void _lockErrorListener() {
     _errorListenerLock++;
   }

   /**
    * Return `true` if the current token has the given [type]. Note that the
    * method [_matchesGt] should be used if the argument to this method would be
    * [TokenType.GT].
    */
   bool _matches(TokenType type) => _currentToken.type == type;

   /**
    * Return `true` if the current token has a type of [TokenType.GT]. Note that
    * this method, unlike other variants, will modify the token stream if
    * possible to match desired type. In particular, if the next token is either
    * a '>>' or '>>>', the token stream will be re-written and `true` will be
    * returned.
    */
   bool _matchesGt() {
     TokenType currentType = _currentToken.type;
     if (currentType == TokenType.GT) {
       return true;
     } else if (currentType == TokenType.GT_GT) {
       Token first = _createToken(_currentToken, TokenType.GT);
       Token second = new Token(TokenType.GT, _currentToken.offset + 1);
       second.setNext(_currentToken.next);
       first.setNext(second);
       _currentToken.previous.setNext(first);
       _currentToken = first;
       return true;
     } else if (currentType == TokenType.GT_EQ) {
       Token first = _createToken(_currentToken, TokenType.GT);
       Token second = new Token(TokenType.EQ, _currentToken.offset + 1);
       second.setNext(_currentToken.next);
       first.setNext(second);
       _currentToken.previous.setNext(first);
       _currentToken = first;
       return true;
     } else if (currentType == TokenType.GT_GT_EQ) {
       int offset = _currentToken.offset;
       Token first = _createToken(_currentToken, TokenType.GT);
       Token second = new Token(TokenType.GT, offset + 1);
       Token third = new Token(TokenType.EQ, offset + 2);
       third.setNext(_currentToken.next);
       second.setNext(third);
       first.setNext(second);
       _currentToken.previous.setNext(first);
       _currentToken = first;
       return true;
     }
     return false;
   }

   /**
    * Return `true` if the current token is a valid identifier. Valid identifiers
    * include built-in identifiers (pseudo-keywords).
    */
   bool _matchesIdentifier() => _tokenMatchesIdentifier(_currentToken);

   /**
    * Return `true` if the current token matches the given [keyword].
    */
   bool _matchesKeyword(Keyword keyword) =>
       _tokenMatchesKeyword(_currentToken, keyword);

   /**
    * Return `true` if the current token matches the given [identifier].
    */
   bool _matchesString(String identifier) =>
       _currentToken.type == TokenType.IDENTIFIER &&
       _currentToken.lexeme == identifier;

   /**
    * Report an error with the given [errorCode] if the given [typeName] has been
    * marked as nullable.
    */
   void _mustNotBeNullable(TypeName typeName, ParserErrorCode errorCode) {
     if (typeName.question != null) {
       _reportErrorForToken(errorCode, typeName.question);
     }
   }

   /**
    * If the current token has the given [type], then advance to the next token
    * and return `true`. Otherwise, return `false` without advancing. This method
    * should not be invoked with an argument value of [TokenType.GT].
    */
   bool _optional(TokenType type) {
     if (_currentToken.type == type) {
       _advance();
       return true;
     }
     return false;
   }

   /**
    * Parse an argument list when we need to check for an open paren and recover
    * when there isn't one. Return the argument list that was parsed.
    */
   ArgumentList _parseArgumentListChecked() {
     if (_matches(TokenType.OPEN_PAREN)) {
       return parseArgumentList();
     }
     _reportErrorForCurrentToken(
         ParserErrorCode.EXPECTED_TOKEN, [TokenType.OPEN_PAREN.lexeme]);
     // Recovery: Look to see whether there is a close paren that isn't matched
     // to an open paren and if so parse the list of arguments as normal.
     return astFactory.argumentList(_createSyntheticToken(TokenType.OPEN_PAREN),
         null, _createSyntheticToken(TokenType.CLOSE_PAREN));
   }

   /**
    * Parse an assert within a constructor's initializer list. Return the assert.
    *
    * This method assumes that the current token matches `Keyword.ASSERT`.
    *
    *     assertInitializer ::=
    *         'assert' '(' expression [',' expression] ')'
    */
   AssertInitializer _parseAssertInitializer() {
     Token keyword = getAndAdvance();
     Token leftParen = _expect(TokenType.OPEN_PAREN);
     Expression expression = parseExpression2();
     Token comma;
     Expression message;
     if (_matches(TokenType.COMMA)) {
       comma = getAndAdvance();
       message = parseExpression2();
     }
     Token rightParen = _expect(TokenType.CLOSE_PAREN);
     return astFactory.assertInitializer(
         keyword, leftParen, expression, comma, message, rightParen);
   }

   /**
    * Parse an assignable expression given that the current token is not 'super'.
    * The [primaryAllowed] is `true` if the expression is allowed to be a primary
    * without any assignable selector. Return the assignable expression that was
    * parsed.
    */
   Expression _parseAssignableExpressionNotStartingWithSuper(
       bool primaryAllowed) {
     //
     // A primary expression can start with an identifier. We resolve the
     // ambiguity by determining whether the primary consists of anything other
     // than an identifier and/or is followed by an assignableSelector.
     //
     Expression expression = parsePrimaryExpression();
     bool isOptional = primaryAllowed || expression is SimpleIdentifier;
     while (true) {
       while (_isLikelyArgumentList()) {
         TypeArgumentList typeArguments = _parseOptionalTypeArguments();
         ArgumentList argumentList = parseArgumentList();
         Expression currentExpression = expression;
         if (currentExpression is SimpleIdentifier) {
           expression = astFactory.methodInvocation(
               null, null, currentExpression, typeArguments, argumentList);
         } else if (currentExpression is PrefixedIdentifier) {
           expression = astFactory.methodInvocation(
               currentExpression.prefix,
               currentExpression.period,
               currentExpression.identifier,
               typeArguments,
               argumentList);
         } else if (currentExpression is PropertyAccess) {
           expression = astFactory.methodInvocation(
               currentExpression.target,
               currentExpression.operator,
               currentExpression.propertyName,
               typeArguments,
               argumentList);
         } else {
           expression = astFactory.functionExpressionInvocation(
               expression, typeArguments, argumentList);
         }
         if (!primaryAllowed) {
           isOptional = false;
         }
       }
       Expression selectorExpression = parseAssignableSelector(
           expression, isOptional || (expression is PrefixedIdentifier));
       if (identical(selectorExpression, expression)) {
         if (!isOptional && (expression is PrefixedIdentifier)) {
           PrefixedIdentifier identifier = expression as PrefixedIdentifier;
           expression = astFactory.propertyAccess(
               identifier.prefix, identifier.period, identifier.identifier);
         }
         return expression;
       }
       expression = selectorExpression;
       isOptional = true;
     }
   }

   /**
    * Parse a block when we need to check for an open curly brace and recover
    * when there isn't one. Return the block that was parsed.
    *
    *     block ::=
    *         '{' statements '}'
    */
   Block _parseBlockChecked() {
     if (_matches(TokenType.OPEN_CURLY_BRACKET)) {
       return parseBlock();
     }
     // TODO(brianwilkerson) Improve the error message.
     _reportErrorForCurrentToken(
         ParserErrorCode.EXPECTED_TOKEN, [TokenType.OPEN_CURLY_BRACKET.lexeme]);
     // Recovery: Check for an unmatched closing curly bracket and parse
     // statements until it is reached.
     return astFactory.block(_createSyntheticToken(TokenType.OPEN_CURLY_BRACKET),
         null, _createSyntheticToken(TokenType.CLOSE_CURLY_BRACKET));
   }

   /**
    * Parse a list of class members. The [className] is the name of the class
    * whose members are being parsed. The [closingBracket] is the closing bracket
    * for the class, or `null` if the closing bracket is missing. Return the list
    * of class members that were parsed.
    *
    *     classMembers ::=
    *         (metadata memberDefinition)*
    */
   List<ClassMember> _parseClassMembers(String className, Token closingBracket) {
     List<ClassMember> members = <ClassMember>[];
     Token memberStart = _currentToken;
     TokenType type = _currentToken.type;
     Keyword keyword = _currentToken.keyword;
     while (type != TokenType.EOF &&
         type != TokenType.CLOSE_CURLY_BRACKET &&
         (closingBracket != null ||
             (keyword != Keyword.CLASS && keyword != Keyword.TYPEDEF))) {
       if (type == TokenType.SEMICOLON) {
         _reportErrorForToken(ParserErrorCode.UNEXPECTED_TOKEN, _currentToken,
             [_currentToken.lexeme]);
         _advance();
       } else {
         ClassMember member = parseClassMember(className);
         if (member != null) {
           members.add(member);
         }
       }
       if (identical(_currentToken, memberStart)) {
         _reportErrorForToken(ParserErrorCode.UNEXPECTED_TOKEN, _currentToken,
             [_currentToken.lexeme]);
         _advance();
       }
       memberStart = _currentToken;
       type = _currentToken.type;
       keyword = _currentToken.keyword;
     }
     return members;
   }

   /**
    * Parse a class type alias. The [commentAndMetadata] is the metadata to be
    * associated with the member. The [abstractKeyword] is the token representing
    * the 'abstract' keyword. The [classKeyword] is the token representing the
    * 'class' keyword. The [className] is the name of the alias, and the
    * [typeParameters] are the type parameters following the name. Return the
    * class type alias that was parsed.
    *
    *     classTypeAlias ::=
    *         identifier typeParameters? '=' 'abstract'? mixinApplication
    *
    *     mixinApplication ::=
    *         type withClause implementsClause? ';'
    */
   ClassTypeAlias _parseClassTypeAliasAfterName(
       CommentAndMetadata commentAndMetadata,
       Token abstractKeyword,
       Token classKeyword,
       SimpleIdentifier className,
       TypeParameterList typeParameters) {
     Token equals = _expect(TokenType.EQ);
     TypeName superclass = parseTypeName(false);
     WithClause withClause = null;
     if (_matchesKeyword(Keyword.WITH)) {
       withClause = parseWithClause();
     } else {
       _reportErrorForCurrentToken(
           ParserErrorCode.EXPECTED_TOKEN, [Keyword.WITH.syntax]);
     }
     ImplementsClause implementsClause = null;
     if (_matchesKeyword(Keyword.IMPLEMENTS)) {
       implementsClause = parseImplementsClause();
     }
     Token semicolon;
     if (_matches(TokenType.SEMICOLON)) {
       semicolon = getAndAdvance();
     } else {
       if (_matches(TokenType.OPEN_CURLY_BRACKET)) {
         _reportErrorForCurrentToken(
             ParserErrorCode.EXPECTED_TOKEN, [TokenType.SEMICOLON.lexeme]);
         Token leftBracket = getAndAdvance();
         _parseClassMembers(className.name, _getEndToken(leftBracket));
         _expect(TokenType.CLOSE_CURLY_BRACKET);
       } else {
         _reportErrorForToken(ParserErrorCode.EXPECTED_TOKEN,
             _currentToken.previous, [TokenType.SEMICOLON.lexeme]);
       }
       semicolon = _createSyntheticToken(TokenType.SEMICOLON);
     }
     return astFactory.classTypeAlias(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         classKeyword,
         className,
         typeParameters,
         equals,
         abstractKeyword,
         superclass,
         withClause,
         implementsClause,
         semicolon);
   }

   /**
    * Parse a list of configurations. Return the configurations that were parsed,
    * or `null` if there are no configurations.
    */
   List<Configuration> _parseConfigurations() {
     List<Configuration> configurations = null;
     while (_matchesKeyword(Keyword.IF)) {
       configurations ??= <Configuration>[];
       configurations.add(parseConfiguration());
     }
     return configurations;
   }

   ConstructorDeclaration _parseConstructor(
       CommentAndMetadata commentAndMetadata,
       Token externalKeyword,
       Token constKeyword,
       Token factoryKeyword,
       SimpleIdentifier returnType,
       Token period,
       SimpleIdentifier name,
       FormalParameterList parameters) {
     bool bodyAllowed = externalKeyword == null;
     Token separator = null;
     List<ConstructorInitializer> initializers = null;
     if (_matches(TokenType.COLON)) {
       separator = getAndAdvance();
       initializers = <ConstructorInitializer>[];
       do {
         Keyword keyword = _currentToken.keyword;
         if (keyword == Keyword.THIS) {
           TokenType nextType = _peek().type;
           if (nextType == TokenType.OPEN_PAREN) {
             bodyAllowed = false;
             initializers.add(parseRedirectingConstructorInvocation(false));
           } else if (nextType == TokenType.PERIOD &&
               _tokenMatches(_peekAt(3), TokenType.OPEN_PAREN)) {
             bodyAllowed = false;
             initializers.add(parseRedirectingConstructorInvocation(true));
           } else {
             initializers.add(parseConstructorFieldInitializer(true));
           }
         } else if (keyword == Keyword.SUPER) {
           initializers.add(parseSuperConstructorInvocation());
         } else if (_matches(TokenType.OPEN_CURLY_BRACKET) ||
             _matches(TokenType.FUNCTION)) {
           _reportErrorForCurrentToken(ParserErrorCode.MISSING_INITIALIZER);
         } else if (_enableAssertInitializer &&
             _matchesKeyword(Keyword.ASSERT)) {
           initializers.add(_parseAssertInitializer());
         } else {
           initializers.add(parseConstructorFieldInitializer(false));
         }
       } while (_optional(TokenType.COMMA));
       if (factoryKeyword != null) {
         _reportErrorForToken(
             ParserErrorCode.FACTORY_WITH_INITIALIZERS, factoryKeyword);
       }
     }
     ConstructorName redirectedConstructor = null;
     FunctionBody body;
     if (_matches(TokenType.EQ)) {
       separator = getAndAdvance();
       redirectedConstructor = parseConstructorName();
       body = astFactory.emptyFunctionBody(_expect(TokenType.SEMICOLON));
       if (factoryKeyword == null) {
         _reportErrorForNode(
             ParserErrorCode.REDIRECTION_IN_NON_FACTORY_CONSTRUCTOR,
             redirectedConstructor);
       }
     } else {
       body =
           parseFunctionBody(true, ParserErrorCode.MISSING_FUNCTION_BODY, false);
       if (constKeyword != null &&
           factoryKeyword != null &&
           externalKeyword == null &&
           body is! NativeFunctionBody) {
         _reportErrorForToken(ParserErrorCode.CONST_FACTORY, factoryKeyword);
       } else if (body is EmptyFunctionBody) {
         if (factoryKeyword != null &&
             externalKeyword == null &&
             _parseFunctionBodies) {
           _reportErrorForToken(
               ParserErrorCode.FACTORY_WITHOUT_BODY, factoryKeyword);
         }
       } else {
         if (constKeyword != null && body is! NativeFunctionBody) {
           _reportErrorForNode(
               ParserErrorCode.CONST_CONSTRUCTOR_WITH_BODY, body);
         } else if (externalKeyword != null) {
           _reportErrorForNode(
               ParserErrorCode.EXTERNAL_CONSTRUCTOR_WITH_BODY, body);
         } else if (!bodyAllowed) {
           _reportErrorForNode(
               ParserErrorCode.REDIRECTING_CONSTRUCTOR_WITH_BODY, body);
         }
       }
     }
     return astFactory.constructorDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         externalKeyword,
         constKeyword,
         factoryKeyword,
         returnType,
         period,
         name,
         parameters,
         separator,
         initializers,
         redirectedConstructor,
         body);
   }

   /**
    * Parse an enum constant declaration. Return the enum constant declaration
    * that was parsed.
    *
    * Specified:
    *
    *     enumConstant ::=
    *         id
    *
    * Actual:
    *
    *     enumConstant ::=
    *         metadata id
    */
   EnumConstantDeclaration _parseEnumConstantDeclaration() {
     CommentAndMetadata commentAndMetadata = parseCommentAndMetadata();
     SimpleIdentifier name;
     if (_matchesIdentifier()) {
       name = _parseSimpleIdentifierUnchecked(isDeclaration: true);
     } else {
       name = createSyntheticIdentifier();
     }
     if (commentAndMetadata.hasMetadata) {
       _reportErrorForNode(ParserErrorCode.ANNOTATION_ON_ENUM_CONSTANT,
           commentAndMetadata.metadata[0]);
     }
     return astFactory.enumConstantDeclaration(
         commentAndMetadata.comment, commentAndMetadata.metadata, name);
   }

   /**
    * Parse a list of formal parameters given that the list starts with the given
    * [leftParenthesis]. Return the formal parameters that were parsed.
    */
   FormalParameterList _parseFormalParameterListAfterParen(Token leftParenthesis,
       {bool inFunctionType: false}) {
     if (_matches(TokenType.CLOSE_PAREN)) {
       return astFactory.formalParameterList(
           leftParenthesis, null, null, null, getAndAdvance());
     }
     //
     // Even though it is invalid to have default parameters outside of brackets,
     // required parameters inside of brackets, or multiple groups of default and
     // named parameters, we allow all of these cases so that we can recover
     // better.
     //
     List<FormalParameter> parameters = <FormalParameter>[];
     Token leftSquareBracket = null;
     Token rightSquareBracket = null;
     Token leftCurlyBracket = null;
     Token rightCurlyBracket = null;
     ParameterKind kind = ParameterKind.REQUIRED;
     bool firstParameter = true;
     bool reportedMultiplePositionalGroups = false;
     bool reportedMultipleNamedGroups = false;
     bool reportedMixedGroups = false;
     bool wasOptionalParameter = false;
     Token initialToken = null;
     do {
       if (firstParameter) {
         firstParameter = false;
       } else if (!_optional(TokenType.COMMA)) {
         // TODO(brianwilkerson) The token is wrong, we need to recover from this
         // case.
         if (_getEndToken(leftParenthesis) != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.EXPECTED_TOKEN, [TokenType.COMMA.lexeme]);
         } else {
           _reportErrorForToken(ParserErrorCode.MISSING_CLOSING_PARENTHESIS,
               _currentToken.previous);
           break;
         }
       }
       initialToken = _currentToken;
       //
       // Handle the beginning of parameter groups.
       //
       TokenType type = _currentToken.type;
       if (type == TokenType.OPEN_SQUARE_BRACKET) {
         wasOptionalParameter = true;
         if (leftSquareBracket != null && !reportedMultiplePositionalGroups) {
           _reportErrorForCurrentToken(
               ParserErrorCode.MULTIPLE_POSITIONAL_PARAMETER_GROUPS);
           reportedMultiplePositionalGroups = true;
         }
         if (leftCurlyBracket != null && !reportedMixedGroups) {
           _reportErrorForCurrentToken(ParserErrorCode.MIXED_PARAMETER_GROUPS);
           reportedMixedGroups = true;
         }
         leftSquareBracket = getAndAdvance();
         kind = ParameterKind.POSITIONAL;
       } else if (type == TokenType.OPEN_CURLY_BRACKET) {
         wasOptionalParameter = true;
         if (leftCurlyBracket != null && !reportedMultipleNamedGroups) {
           _reportErrorForCurrentToken(
               ParserErrorCode.MULTIPLE_NAMED_PARAMETER_GROUPS);
           reportedMultipleNamedGroups = true;
         }
         if (leftSquareBracket != null && !reportedMixedGroups) {
           _reportErrorForCurrentToken(ParserErrorCode.MIXED_PARAMETER_GROUPS);
           reportedMixedGroups = true;
         }
         leftCurlyBracket = getAndAdvance();
         kind = ParameterKind.NAMED;
       }
       //
       // Parse and record the parameter.
       //
       FormalParameter parameter =
           parseFormalParameter(kind, inFunctionType: inFunctionType);
       parameters.add(parameter);
       if (kind == ParameterKind.REQUIRED && wasOptionalParameter) {
         _reportErrorForNode(
             ParserErrorCode.NORMAL_BEFORE_OPTIONAL_PARAMETERS, parameter);
       }
       //
       // Handle the end of parameter groups.
       //
       // TODO(brianwilkerson) Improve the detection and reporting of missing and
       // mismatched delimiters.
       type = _currentToken.type;

       // Advance past trailing commas as appropriate.
       if (type == TokenType.COMMA) {
         // Only parse commas trailing normal (non-positional/named) params.
         if (rightSquareBracket == null && rightCurlyBracket == null) {
           Token next = _peek();
           if (next.type == TokenType.CLOSE_PAREN ||
               next.type == TokenType.CLOSE_CURLY_BRACKET ||
               next.type == TokenType.CLOSE_SQUARE_BRACKET) {
             _advance();
             type = _currentToken.type;
           }
         }
       }

       if (type == TokenType.CLOSE_SQUARE_BRACKET) {
         rightSquareBracket = getAndAdvance();
         if (leftSquareBracket == null) {
           if (leftCurlyBracket != null) {
             _reportErrorForCurrentToken(
                 ParserErrorCode.WRONG_TERMINATOR_FOR_PARAMETER_GROUP,
                 ['}', ']']);
             rightCurlyBracket = rightSquareBracket;
             rightSquareBracket = null;
           } else {
             _reportErrorForCurrentToken(
                 ParserErrorCode.UNEXPECTED_TERMINATOR_FOR_PARAMETER_GROUP,
                 ["["]);
           }
         }
         kind = ParameterKind.REQUIRED;
       } else if (type == TokenType.CLOSE_CURLY_BRACKET) {
         rightCurlyBracket = getAndAdvance();
         if (leftCurlyBracket == null) {
           if (leftSquareBracket != null) {
             _reportErrorForCurrentToken(
                 ParserErrorCode.WRONG_TERMINATOR_FOR_PARAMETER_GROUP,
                 [']', '}']);
             rightSquareBracket = rightCurlyBracket;
             rightCurlyBracket = null;
           } else {
             _reportErrorForCurrentToken(
                 ParserErrorCode.UNEXPECTED_TERMINATOR_FOR_PARAMETER_GROUP,
                 ["{"]);
           }
         }
         kind = ParameterKind.REQUIRED;
       }
     } while (!_matches(TokenType.CLOSE_PAREN) &&
         !identical(initialToken, _currentToken));
     Token rightParenthesis = _expect(TokenType.CLOSE_PAREN);
     //
     // Check that the groups were closed correctly.
     //
     if (leftSquareBracket != null && rightSquareBracket == null) {
       _reportErrorForCurrentToken(
           ParserErrorCode.MISSING_TERMINATOR_FOR_PARAMETER_GROUP, ["]"]);
     }
     if (leftCurlyBracket != null && rightCurlyBracket == null) {
       _reportErrorForCurrentToken(
           ParserErrorCode.MISSING_TERMINATOR_FOR_PARAMETER_GROUP, ["}"]);
     }
     //
     // Build the parameter list.
     //
     leftSquareBracket ??= leftCurlyBracket;
     rightSquareBracket ??= rightCurlyBracket;
     return astFactory.formalParameterList(leftParenthesis, parameters,
         leftSquareBracket, rightSquareBracket, rightParenthesis);
   }

   /**
    * Parse a list of formal parameters. Return the formal parameters that were
    * parsed.
    *
    * This method assumes that the current token matches `TokenType.OPEN_PAREN`.
    */
   FormalParameterList _parseFormalParameterListUnchecked(
       {bool inFunctionType: false}) {
     return _parseFormalParameterListAfterParen(getAndAdvance(),
         inFunctionType: inFunctionType);
   }

   /**
    * Parse a function declaration statement. The [commentAndMetadata] is the
    * documentation comment and metadata to be associated with the declaration.
    * The [returnType] is the return type, or `null` if there is no return type.
    * Return the function declaration statement that was parsed.
    *
    *     functionDeclarationStatement ::=
    *         functionSignature functionBody
    */
   Statement _parseFunctionDeclarationStatementAfterReturnType(
       CommentAndMetadata commentAndMetadata, TypeAnnotation returnType) {
     FunctionDeclaration declaration =
         parseFunctionDeclaration(commentAndMetadata, null, returnType);
     Token propertyKeyword = declaration.propertyKeyword;
     if (propertyKeyword != null) {
       if (propertyKeyword.keyword == Keyword.GET) {
         _reportErrorForToken(
             ParserErrorCode.GETTER_IN_FUNCTION, propertyKeyword);
       } else {
         _reportErrorForToken(
             ParserErrorCode.SETTER_IN_FUNCTION, propertyKeyword);
       }
     }
     return astFactory.functionDeclarationStatement(declaration);
   }

   /**
    * Parse a function type alias. The [commentAndMetadata] is the metadata to be
    * associated with the member. The [keyword] is the token representing the
    * 'typedef' keyword. Return the function type alias that was parsed.
    *
    *     functionTypeAlias ::=
    *         functionPrefix typeParameterList? formalParameterList ';'
    *
    *     functionPrefix ::=
    *         returnType? name
    */
   FunctionTypeAlias _parseFunctionTypeAlias(
       CommentAndMetadata commentAndMetadata, Token keyword) {
     TypeAnnotation returnType = null;
     if (hasReturnTypeInTypeAlias) {
       returnType = parseReturnType(false);
     }
     SimpleIdentifier name = parseSimpleIdentifier(isDeclaration: true);
     TypeParameterList typeParameters = null;
     if (_matches(TokenType.LT)) {
       typeParameters = parseTypeParameterList();
     }
     TokenType type = _currentToken.type;
     if (type == TokenType.SEMICOLON || type == TokenType.EOF) {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_TYPEDEF_PARAMETERS);
       FormalParameterList parameters = astFactory.formalParameterList(
           _createSyntheticToken(TokenType.OPEN_PAREN),
           null,
           null,
           null,
           _createSyntheticToken(TokenType.CLOSE_PAREN));
       Token semicolon = _expect(TokenType.SEMICOLON);
       return astFactory.functionTypeAlias(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           keyword,
           returnType,
           name,
           typeParameters,
           parameters,
           semicolon);
     } else if (type == TokenType.OPEN_PAREN) {
       FormalParameterList parameters = _parseFormalParameterListUnchecked();
       _validateFormalParameterList(parameters);
       Token semicolon = _expect(TokenType.SEMICOLON);
       return astFactory.functionTypeAlias(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           keyword,
           returnType,
           name,
           typeParameters,
           parameters,
           semicolon);
     } else {
       _reportErrorForCurrentToken(ParserErrorCode.MISSING_TYPEDEF_PARAMETERS);
       // Recovery: At the very least we should skip to the start of the next
       // valid compilation unit member, allowing for the possibility of finding
       // the typedef parameters before that point.
       return astFactory.functionTypeAlias(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           keyword,
           returnType,
           name,
           typeParameters,
           astFactory.formalParameterList(
               _createSyntheticToken(TokenType.OPEN_PAREN),
               null,
               null,
               null,
               _createSyntheticToken(TokenType.CLOSE_PAREN)),
           _createSyntheticToken(TokenType.SEMICOLON));
     }
   }

   /**
    * Parses generic type parameters from a comment.
    *
    * Normally this is handled by [_parseGenericMethodTypeParameters], but if the
    * code already handles the normal generic type parameters, the comment
    * matcher can be called directly. For example, we may have already tried
    * matching `<` (less than sign) in a method declaration, and be currently
    * on the `(` (open paren) because we didn't find it. In that case, this
    * function will parse the preceding comment such as `/*<T, R>*/`.
    */
   TypeParameterList _parseGenericCommentTypeParameters() {
     if (_injectGenericCommentTypeList()) {
       return parseTypeParameterList();
     }
     return null;
   }

   /**
    * Parse the generic method or function's type parameters.
    *
    * For backwards compatibility this can optionally use comments.
    * See [parseGenericMethodComments].
    */
   TypeParameterList _parseGenericMethodTypeParameters() {
     if (_matches(TokenType.LT) || _injectGenericCommentTypeList()) {
       return parseTypeParameterList();
     }
     return null;
   }

   /**
    * Parse a library name. The [missingNameError] is the error code to be used
    * if the library name is missing. The [missingNameToken] is the token
    * associated with the error produced if the library name is missing. Return
    * the library name that was parsed.
    *
    *     libraryName ::=
    *         libraryIdentifier
    */
   LibraryIdentifier _parseLibraryName(
       ParserErrorCode missingNameError, Token missingNameToken) {
     if (_matchesIdentifier()) {
       return parseLibraryIdentifier();
     } else if (_matches(TokenType.STRING)) {
       // Recovery: This should be extended to handle arbitrary tokens until we
       // can find a token that can start a compilation unit member.
       StringLiteral string = parseStringLiteral();
       _reportErrorForNode(ParserErrorCode.NON_IDENTIFIER_LIBRARY_NAME, string);
     } else {
       _reportErrorForToken(missingNameError, missingNameToken);
     }
     return astFactory
         .libraryIdentifier(<SimpleIdentifier>[createSyntheticIdentifier()]);
   }

   /**
    * Parse a method declaration. The [commentAndMetadata] is the documentation
    * comment and metadata to be associated with the declaration. The
    * [externalKeyword] is the 'external' token. The [staticKeyword] is the
    * static keyword, or `null` if the getter is not static. The [returnType] is
    * the return type of the method. The [name] is the name of the method. The
    * [parameters] is the parameters to the method. Return the method declaration
    * that was parsed.
    *
    *     functionDeclaration ::=
    *         ('external' 'static'?)? functionSignature functionBody
    *       | 'external'? functionSignature ';'
    */
   MethodDeclaration _parseMethodDeclarationAfterParameters(
       CommentAndMetadata commentAndMetadata,
       Token externalKeyword,
       Token staticKeyword,
       TypeAnnotation returnType,
       SimpleIdentifier name,
       TypeParameterList typeParameters,
       FormalParameterList parameters) {
     FunctionBody body = parseFunctionBody(
         externalKeyword != null || staticKeyword == null,
         ParserErrorCode.MISSING_FUNCTION_BODY,
         false);
     if (externalKeyword != null) {
       if (body is! EmptyFunctionBody) {
         _reportErrorForNode(ParserErrorCode.EXTERNAL_METHOD_WITH_BODY, body);
       }
     } else if (staticKeyword != null) {
       if (body is EmptyFunctionBody && _parseFunctionBodies) {
         _reportErrorForNode(ParserErrorCode.ABSTRACT_STATIC_METHOD, body);
       }
     }
     return astFactory.methodDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         externalKeyword,
         staticKeyword,
         returnType,
         null,
         null,
         name,
         typeParameters,
         parameters,
         body);
   }

   /**
    * Parse a method declaration. The [commentAndMetadata] is the documentation
    * comment and metadata to be associated with the declaration. The
    * [externalKeyword] is the 'external' token. The [staticKeyword] is the
    * static keyword, or `null` if the getter is not static. The [returnType] is
    * the return type of the method. Return the method declaration that was
    * parsed.
    *
    *     functionDeclaration ::=
    *         'external'? 'static'? functionSignature functionBody
    *       | 'external'? functionSignature ';'
    */
   MethodDeclaration _parseMethodDeclarationAfterReturnType(
       CommentAndMetadata commentAndMetadata,
       Token externalKeyword,
       Token staticKeyword,
       TypeAnnotation returnType) {
     SimpleIdentifier methodName = parseSimpleIdentifier(isDeclaration: true);
     TypeParameterList typeParameters = _parseGenericMethodTypeParameters();
     FormalParameterList parameters;
     TokenType type = _currentToken.type;
     // TODO(brianwilkerson) Figure out why we care what the current token is if
     // it isn't a paren.
     if (type != TokenType.OPEN_PAREN &&
         (type == TokenType.OPEN_CURLY_BRACKET || type == TokenType.FUNCTION)) {
       _reportErrorForToken(
           ParserErrorCode.MISSING_METHOD_PARAMETERS, _currentToken.previous);
       parameters = astFactory.formalParameterList(
           _createSyntheticToken(TokenType.OPEN_PAREN),
           null,
           null,
           null,
           _createSyntheticToken(TokenType.CLOSE_PAREN));
     } else {
       parameters = parseFormalParameterList();
     }
     _validateFormalParameterList(parameters);
     return _parseMethodDeclarationAfterParameters(
         commentAndMetadata,
         externalKeyword,
         staticKeyword,
         returnType,
         methodName,
         typeParameters,
         parameters);
   }

   /**
    * Parse a class native clause. Return the native clause that was parsed.
    *
    * This method assumes that the current token matches `_NATIVE`.
    *
    *     classNativeClause ::=
    *         'native' name
    */
   NativeClause _parseNativeClause() {
     Token keyword = getAndAdvance();
     StringLiteral name = parseStringLiteral();
     return astFactory.nativeClause(keyword, name);
   }

   /**
    * Parse an operator declaration starting after the 'operator' keyword. The
    * [commentAndMetadata] is the documentation comment and metadata to be
    * associated with the declaration. The [externalKeyword] is the 'external'
    * token. The [returnType] is the return type that has already been parsed, or
    * `null` if there was no return type. The [operatorKeyword] is the 'operator'
    * keyword. Return the operator declaration that was parsed.
    *
    *     operatorDeclaration ::=
    *         operatorSignature (';' | functionBody)
    *
    *     operatorSignature ::=
    *         'external'? returnType? 'operator' operator formalParameterList
    */
   MethodDeclaration _parseOperatorAfterKeyword(
       CommentAndMetadata commentAndMetadata,
       Token externalKeyword,
       TypeAnnotation returnType,
       Token operatorKeyword) {
     if (!_currentToken.isUserDefinableOperator) {
       _reportErrorForCurrentToken(
           ParserErrorCode.NON_USER_DEFINABLE_OPERATOR, [_currentToken.lexeme]);
     }
     SimpleIdentifier name =
         astFactory.simpleIdentifier(getAndAdvance(), isDeclaration: true);
     if (_matches(TokenType.EQ)) {
       Token previous = _currentToken.previous;
       if ((_tokenMatches(previous, TokenType.EQ_EQ) ||
               _tokenMatches(previous, TokenType.BANG_EQ)) &&
           _currentToken.offset == previous.offset + 2) {
         _reportErrorForCurrentToken(ParserErrorCode.INVALID_OPERATOR,
             ["${previous.lexeme}${_currentToken.lexeme}"]);
         _advance();
       }
     }
     FormalParameterList parameters = parseFormalParameterList();
     _validateFormalParameterList(parameters);
     FunctionBody body =
         parseFunctionBody(true, ParserErrorCode.MISSING_FUNCTION_BODY, false);
     if (externalKeyword != null && body is! EmptyFunctionBody) {
       _reportErrorForCurrentToken(ParserErrorCode.EXTERNAL_OPERATOR_WITH_BODY);
     }
     return astFactory.methodDeclaration(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         externalKeyword,
         null,
         returnType,
         null,
         operatorKeyword,
         name,
         null,
         parameters,
         body);
   }

   /**
    * Parse a return type if one is given, otherwise return `null` without
    * advancing. Return the return type that was parsed.
    */
   TypeAnnotation _parseOptionalReturnType() {
     TypeName typeComment = _parseOptionalTypeNameComment();
     if (typeComment != null) {
       return typeComment;
     }
     Keyword keyword = _currentToken.keyword;
     if (keyword == Keyword.VOID) {
       return astFactory.typeName(
           astFactory.simpleIdentifier(getAndAdvance()), null);
     } else if (_matchesIdentifier()) {
       Token next = _peek();
       if (keyword != Keyword.GET &&
           keyword != Keyword.SET &&
           keyword != Keyword.OPERATOR &&
           (_tokenMatchesIdentifier(next) ||
               _tokenMatches(next, TokenType.LT))) {
         Token afterTypeParameters = _skipTypeParameterList(next);
         if (afterTypeParameters != null &&
             _tokenMatches(afterTypeParameters, TokenType.OPEN_PAREN)) {
           // If the identifier is followed by type parameters and a parenthesis,
           // then the identifier is the name of a generic method, not a return
           // type.
           return null;
         }
         return parseReturnType(false);
       }
       Token next2 = next.next;
       Token next3 = next2.next;
       if (_tokenMatches(next, TokenType.PERIOD) &&
           _tokenMatchesIdentifier(next2) &&
           (_tokenMatchesIdentifier(next3) ||
               _tokenMatches(next3, TokenType.LT))) {
         return parseReturnType(false);
       }
     }
     return null;
   }

   /**
    * Parse a [TypeArgumentList] if present, otherwise return null.
    * This also supports the comment form, if enabled: `/*<T>*/`
    */
   TypeArgumentList _parseOptionalTypeArguments() {
     if (_matches(TokenType.LT) || _injectGenericCommentTypeList()) {
       return parseTypeArgumentList();
     }
     return null;
   }

   TypeName _parseOptionalTypeNameComment() {
     if (_injectGenericCommentTypeAssign()) {
       return _parseTypeName(false);
     }
     return null;
   }

   /**
    * Parse a part directive. The [commentAndMetadata] is the metadata to be
    * associated with the directive. Return the part or part-of directive that
    * was parsed.
    *
    * This method assumes that the current token matches `Keyword.PART`.
    *
    *     partDirective ::=
    *         metadata 'part' stringLiteral ';'
    */
   Directive _parsePartDirective(CommentAndMetadata commentAndMetadata) {
     Token partKeyword = getAndAdvance();
     StringLiteral partUri = _parseUri();
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.partDirective(commentAndMetadata.comment,
         commentAndMetadata.metadata, partKeyword, partUri, semicolon);
   }

   /**
    * Parse a part-of directive. The [commentAndMetadata] is the metadata to be
    * associated with the directive. Return the part or part-of directive that
    * was parsed.
    *
    * This method assumes that the current token matches [Keyword.PART] and that
    * the following token matches the identifier 'of'.
    *
    *     partOfDirective ::=
    *         metadata 'part' 'of' identifier ';'
    */
   Directive _parsePartOfDirective(CommentAndMetadata commentAndMetadata) {
     Token partKeyword = getAndAdvance();
     Token ofKeyword = getAndAdvance();
     if (enableUriInPartOf && _matches(TokenType.STRING)) {
       StringLiteral libraryUri = _parseUri();
       Token semicolon = _expect(TokenType.SEMICOLON);
       return astFactory.partOfDirective(
           commentAndMetadata.comment,
           commentAndMetadata.metadata,
           partKeyword,
           ofKeyword,
           libraryUri,
           null,
           semicolon);
     }
     LibraryIdentifier libraryName = _parseLibraryName(
         ParserErrorCode.MISSING_NAME_IN_PART_OF_DIRECTIVE, ofKeyword);
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.partOfDirective(
         commentAndMetadata.comment,
         commentAndMetadata.metadata,
         partKeyword,
         ofKeyword,
         null,
         libraryName,
         semicolon);
   }

   /**
    * Parse a prefixed identifier given that the given [qualifier] was already
    * parsed. Return the prefixed identifier that was parsed.
    *
    *     prefixedIdentifier ::=
    *         identifier ('.' identifier)?
    */
   Identifier _parsePrefixedIdentifierAfterIdentifier(
       SimpleIdentifier qualifier) {
     if (!_matches(TokenType.PERIOD) || _injectGenericCommentTypeList()) {
       return qualifier;
     }
     Token period = getAndAdvance();
     SimpleIdentifier qualified = parseSimpleIdentifier();
     return astFactory.prefixedIdentifier(qualifier, period, qualified);
   }

   /**
    * Parse a prefixed identifier. Return the prefixed identifier that was
    * parsed.
    *
    * This method assumes that the current token matches an identifier.
    *
    *     prefixedIdentifier ::=
    *         identifier ('.' identifier)?
    */
   Identifier _parsePrefixedIdentifierUnchecked() {
     return _parsePrefixedIdentifierAfterIdentifier(
         _parseSimpleIdentifierUnchecked());
   }

   /**
    * Parse a simple identifier. Return the simple identifier that was parsed.
    *
    * This method assumes that the current token matches an identifier.
    *
    *     identifier ::=
    *         IDENTIFIER
    */
   SimpleIdentifier _parseSimpleIdentifierUnchecked(
       {bool isDeclaration: false}) {
     String lexeme = _currentToken.lexeme;
     if ((_inAsync || _inGenerator) &&
         (lexeme == ASYNC || lexeme == _AWAIT || lexeme == _YIELD)) {
       _reportErrorForCurrentToken(
           ParserErrorCode.ASYNC_KEYWORD_USED_AS_IDENTIFIER);
     }
     return astFactory.simpleIdentifier(getAndAdvance(),
         isDeclaration: isDeclaration);
   }

   /**
    * Parse a list of statements within a switch statement. Return the statements
    * that were parsed.
    *
    *     statements ::=
    *         statement*
    */
   List<Statement> _parseStatementList() {
     List<Statement> statements = <Statement>[];
     Token statementStart = _currentToken;
     TokenType type = _currentToken.type;
     while (type != TokenType.EOF &&
         type != TokenType.CLOSE_CURLY_BRACKET &&
         !isSwitchMember()) {
       statements.add(parseStatement2());
       if (identical(_currentToken, statementStart)) {
         _reportErrorForToken(ParserErrorCode.UNEXPECTED_TOKEN, _currentToken,
             [_currentToken.lexeme]);
         _advance();
       }
       statementStart = _currentToken;
       type = _currentToken.type;
     }
     return statements;
   }

   /**
    * Parse a string literal that contains interpolations. Return the string
    * literal that was parsed.
    *
    * This method assumes that the current token matches either
    * [TokenType.STRING_INTERPOLATION_EXPRESSION] or
    * [TokenType.STRING_INTERPOLATION_IDENTIFIER].
    */
   StringInterpolation _parseStringInterpolation(Token string) {
     List<InterpolationElement> elements = <InterpolationElement>[
       astFactory.interpolationString(
           string, computeStringValue(string.lexeme, true, false))
     ];
     bool hasMore = true;
     bool isExpression = _matches(TokenType.STRING_INTERPOLATION_EXPRESSION);
     while (hasMore) {
       if (isExpression) {
         Token openToken = getAndAdvance();
         bool wasInInitializer = _inInitializer;
         _inInitializer = false;
         try {
           Expression expression = parseExpression2();
           Token rightBracket = _expect(TokenType.CLOSE_CURLY_BRACKET);
           elements.add(astFactory.interpolationExpression(
               openToken, expression, rightBracket));
         } finally {
           _inInitializer = wasInInitializer;
         }
       } else {
         Token openToken = getAndAdvance();
         Expression expression = null;
         if (_matchesKeyword(Keyword.THIS)) {
           expression = astFactory.thisExpression(getAndAdvance());
         } else {
           expression = parseSimpleIdentifier();
         }
         elements.add(
             astFactory.interpolationExpression(openToken, expression, null));
       }
       if (_matches(TokenType.STRING)) {
         string = getAndAdvance();
         isExpression = _matches(TokenType.STRING_INTERPOLATION_EXPRESSION);
         hasMore =
             isExpression || _matches(TokenType.STRING_INTERPOLATION_IDENTIFIER);
         elements.add(astFactory.interpolationString(
             string, computeStringValue(string.lexeme, false, !hasMore)));
       } else {
         hasMore = false;
       }
     }
     return astFactory.stringInterpolation(elements);
   }

   /**
    * Parse a string literal. Return the string literal that was parsed.
    *
    * This method assumes that the current token matches `TokenType.STRING`.
    *
    *     stringLiteral ::=
    *         MULTI_LINE_STRING+
    *       | SINGLE_LINE_STRING+
    */
   StringLiteral _parseStringLiteralUnchecked() {
     List<StringLiteral> strings = <StringLiteral>[];
     do {
       Token string = getAndAdvance();
       if (_matches(TokenType.STRING_INTERPOLATION_EXPRESSION) ||
           _matches(TokenType.STRING_INTERPOLATION_IDENTIFIER)) {
         strings.add(_parseStringInterpolation(string));
       } else {
         strings.add(astFactory.simpleStringLiteral(
             string, computeStringValue(string.lexeme, true, true)));
       }
     } while (_matches(TokenType.STRING));
     return strings.length == 1
         ? strings[0]
         : astFactory.adjacentStrings(strings);
   }

   /**
    * Parse a type annotation, possibly superseded by a type name in a comment.
    * Return the type name that was parsed.
    *
    * This method assumes that the current token is an identifier.
    *
    *     type ::=
    *         qualified typeArguments?
    */
   TypeAnnotation _parseTypeAnnotationAfterIdentifier() {
     TypeAnnotation type = parseTypeAnnotation(false);
     // If this is followed by a generic method type comment, allow the comment
     // type to replace the real type name.
     TypeName typeFromComment = _parseOptionalTypeNameComment();
     return typeFromComment ?? type;
   }

   TypeName _parseTypeName(bool inExpression) {
     Identifier typeName;
     if (_matchesIdentifier()) {
       typeName = _parsePrefixedIdentifierUnchecked();
     } else if (_matchesKeyword(Keyword.VAR)) {
       _reportErrorForCurrentToken(ParserErrorCode.VAR_AS_TYPE_NAME);
       typeName = astFactory.simpleIdentifier(getAndAdvance());
     } else {
       typeName = createSyntheticIdentifier();
       _reportErrorForCurrentToken(ParserErrorCode.EXPECTED_TYPE_NAME);
     }
     TypeArgumentList typeArguments = _parseOptionalTypeArguments();
     Token question = null;
     if (enableNnbd && _matches(TokenType.QUESTION)) {
       if (!inExpression || !_isConditionalOperator()) {
         question = getAndAdvance();
       }
     }
     return astFactory.typeName(typeName, typeArguments, question: question);
   }

   /**
    * Parse a string literal representing a URI. Return the string literal that
    * was parsed.
    */
   StringLiteral _parseUri() {
     // TODO(brianwilkerson) Should this function also return true for valid
     // top-level keywords?
     bool isKeywordAfterUri(Token token) =>
         token.lexeme == Keyword.AS.syntax ||
         token.lexeme == _HIDE ||
         token.lexeme == _SHOW;
     TokenType type = _currentToken.type;
     if (type != TokenType.STRING &&
         type != TokenType.SEMICOLON &&
         !isKeywordAfterUri(_currentToken)) {
       // Attempt to recover in the case where the URI was not enclosed in
       // quotes.
       Token token = _currentToken;
       bool isValidInUri(Token token) {
         TokenType type = token.type;
         return type == TokenType.COLON ||
             type == TokenType.SLASH ||
             type == TokenType.PERIOD ||
             type == TokenType.PERIOD_PERIOD ||
             type == TokenType.PERIOD_PERIOD_PERIOD ||
             type == TokenType.INT ||
             type == TokenType.DOUBLE;
       }

       while ((_tokenMatchesIdentifier(token) && !isKeywordAfterUri(token)) ||
           isValidInUri(token)) {
         token = token.next;
       }
       if (_tokenMatches(token, TokenType.SEMICOLON) ||
           isKeywordAfterUri(token)) {
         Token endToken = token.previous;
         token = _currentToken;
         int endOffset = token.end;
         StringBuffer buffer = new StringBuffer();
         buffer.write(token.lexeme);
         while (token != endToken) {
           token = token.next;
           if (token.offset != endOffset || token.precedingComments != null) {
             return parseStringLiteral();
           }
           buffer.write(token.lexeme);
           endOffset = token.end;
         }
         String value = buffer.toString();
         Token newToken =
             new StringToken(TokenType.STRING, "'$value'", _currentToken.offset);
         _reportErrorForToken(
             ParserErrorCode.NON_STRING_LITERAL_AS_URI, newToken);
         _currentToken = endToken.next;
         return astFactory.simpleStringLiteral(newToken, value);
       }
     }
     return parseStringLiteral();
   }

   /**
    * Parse a variable declaration statement. The [commentAndMetadata] is the
    * metadata to be associated with the variable declaration statement, or
    * `null` if there is no attempt at parsing the comment and metadata. The
    * [keyword] is the token representing the 'final', 'const' or 'var' keyword,
    * or `null` if there is no keyword. The [type] is the type of the variables
    * in the list. Return the variable declaration statement that was parsed.
    *
    *     variableDeclarationStatement ::=
    *         variableDeclarationList ';'
    */
   VariableDeclarationStatement _parseVariableDeclarationStatementAfterType(
       CommentAndMetadata commentAndMetadata, Token keyword, TypeName type) {
     VariableDeclarationList variableList =
         parseVariableDeclarationListAfterType(
             commentAndMetadata, keyword, type);
     Token semicolon = _expect(TokenType.SEMICOLON);
     return astFactory.variableDeclarationStatement(variableList, semicolon);
   }

   /**
    * Return the token that is immediately after the current token. This is
    * equivalent to [_peekAt](1).
    */
   Token _peek() => _currentToken.next;

   /**
    * Return the token that is the given [distance] after the current token,
    * where the distance is the number of tokens to look ahead. A distance of `0`
    * is the current token, `1` is the next token, etc.
    */
   Token _peekAt(int distance) {
     Token token = _currentToken;
     for (int i = 0; i < distance; i++) {
       token = token.next;
     }
     return token;
   }

   String _removeGitHubInlineCode(String comment) {
     int index = 0;
     while (true) {
       int beginIndex = comment.indexOf('`', index);
       if (beginIndex == -1) {
         break;
       }
       int endIndex = comment.indexOf('`', beginIndex + 1);
       if (endIndex == -1) {
         break;
       }
       comment = comment.substring(0, beginIndex + 1) +
           ' ' * (endIndex - beginIndex - 1) +
           comment.substring(endIndex);
       index = endIndex + 1;
     }
     return comment;
   }

   /**
    * Report the given [error].
    */
   void _reportError(AnalysisError error) {
     if (_errorListenerLock != 0) {
       return;
     }
     _errorListener.onError(error);
   }

   /**
    * Report an error with the given [errorCode] and [arguments] associated with
    * the current token.
    */
   void _reportErrorForCurrentToken(ParserErrorCode errorCode,
       [List<Object> arguments]) {
     _reportErrorForToken(errorCode, _currentToken, arguments);
   }

   /**
    * Report an error with the given [errorCode] and [arguments] associated with
    * the given [node].
    */
   void _reportErrorForNode(ParserErrorCode errorCode, AstNode node,
       [List<Object> arguments]) {
     _reportError(new AnalysisError(
         _source, node.offset, node.length, errorCode, arguments));
   }

   /**
    * Report an error with the given [errorCode] and [arguments] associated with
    * the given [token].
    */
   void _reportErrorForToken(ErrorCode errorCode, Token token,
       [List<Object> arguments]) {
     if (token.type == TokenType.EOF) {
       token = token.previous;
     }
     _reportError(new AnalysisError(_source, token.offset,
         math.max(token.length, 1), errorCode, arguments));
   }

   /**
    * Scans the generic method comment, and returns the tokens, otherwise
    * returns null.
    */
   Token _scanGenericMethodComment(String code, int offset) {
     BooleanErrorListener listener = new BooleanErrorListener();
     Scanner scanner =
         new Scanner(null, new SubSequenceReader(code, offset), listener);
     scanner.setSourceStart(1, 1);
     Token firstToken = scanner.tokenize();
     if (listener.errorReported) {
       return null;
     }
     return firstToken;
   }

   /**
    * Execute the given [parseOperation] in a temporary parser whose current
    * token has been set to the given [startToken]. If the parse does not
    * generate any errors or exceptions, then return the token following the
    * matching portion of the token stream. Otherwise, return `null`.
    *
    * Note: This is an extremely inefficient way of testing whether the tokens in
    * the token stream match a given production. It should not be used for
    * production code.
    */
   Token _skip(Token startToken, parseOperation(Parser parser)) {
     BooleanErrorListener listener = new BooleanErrorListener();
     Parser parser = new Parser(_source, listener);
     parser._currentToken = _cloneTokens(startToken);
     parser._enableAssertInitializer = _enableAssertInitializer;
     parser._enableNnbd = _enableNnbd;
     parser._inAsync = _inAsync;
     parser._inGenerator = _inGenerator;
     parser._inInitializer = _inInitializer;
     parser._inLoop = _inLoop;
     parser._inSwitch = _inSwitch;
     parser._parseFunctionBodies = _parseFunctionBodies;
     try {
       parseOperation(parser);
     } catch (exception) {
       return null;
     }
     if (listener.errorReported) {
       return null;
     }
     return parser._currentToken;
   }

   /**
    * Skips a block with all containing blocks.
    */
   void _skipBlock() {
     Token endToken = (_currentToken as BeginToken).endToken;
     if (endToken == null) {
       endToken = _currentToken.next;
       while (!identical(endToken, _currentToken)) {
         _currentToken = endToken;
         endToken = _currentToken.next;
       }
       _reportErrorForToken(
           ParserErrorCode.EXPECTED_TOKEN, _currentToken.previous, ["}"]);
     } else {
       _currentToken = endToken.next;
     }
   }

   /**
    * Parse the 'final', 'const', 'var' or type preceding a variable declaration,
    * starting at the given token, without actually creating a type or changing
    * the current token. Return the token following the type that was parsed, or
    * `null` if the given token is not the first token in a valid type. The
    * [startToken] is the token at which parsing is to begin. Return the token
    * following the type that was parsed.
    *
    * finalConstVarOrType ::=
    *   | 'final' type?
    *   | 'const' type?
    *   | 'var'
    *   | type
    */
   Token _skipFinalConstVarOrType(Token startToken) {
     Keyword keyword = startToken.keyword;
     if (keyword == Keyword.FINAL || keyword == Keyword.CONST) {
       Token next = startToken.next;
       if (_tokenMatchesIdentifier(next)) {
         Token next2 = next.next;
         // "Type parameter" or "Type<" or "prefix.Type"
         if (_tokenMatchesIdentifier(next2) ||
             _tokenMatches(next2, TokenType.LT) ||
             _tokenMatches(next2, TokenType.PERIOD)) {
           return skipTypeName(next);
         }
         // "parameter"
         return next;
       }
     } else if (keyword == Keyword.VAR) {
       return startToken.next;
     } else if (_tokenMatchesIdentifier(startToken)) {
       Token next = startToken.next;
       if (_tokenMatchesIdentifier(next) ||
           _tokenMatches(next, TokenType.LT) ||
           _tokenMatchesKeyword(next, Keyword.THIS) ||
           (_tokenMatches(next, TokenType.PERIOD) &&
               _tokenMatchesIdentifier(next.next) &&
               (_tokenMatchesIdentifier(next.next.next) ||
                   _tokenMatches(next.next.next, TokenType.LT) ||
                   _tokenMatchesKeyword(next.next.next, Keyword.THIS)))) {
         return skipReturnType(startToken);
       }
     }
     return null;
   }

   /**
    * Parse a list of formal parameters, starting at the [startToken], without
    * actually creating a formal parameter list or changing the current token.
    * Return the token following the formal parameter list that was parsed, or
    * `null` if the given token is not the first token in a valid list of formal
    * parameter.
    *
    * Note that unlike other skip methods, this method uses a heuristic. In the
    * worst case, the parameters could be prefixed by metadata, which would
    * require us to be able to skip arbitrary expressions. Rather than duplicate
    * the logic of most of the parse methods we simply look for something that is
    * likely to be a list of parameters and then skip to returning the token
    * after the closing parenthesis.
    *
    * This method must be kept in sync with [parseFormalParameterList].
    *
    *     formalParameterList ::=
    *         '(' ')'
    *       | '(' normalFormalParameters (',' optionalFormalParameters)? ')'
    *       | '(' optionalFormalParameters ')'
    *
    *     normalFormalParameters ::=
    *         normalFormalParameter (',' normalFormalParameter)*
    *
    *     optionalFormalParameters ::=
    *         optionalPositionalFormalParameters
    *       | namedFormalParameters
    *
    *     optionalPositionalFormalParameters ::=
    *         '[' defaultFormalParameter (',' defaultFormalParameter)* ']'
    *
    *     namedFormalParameters ::=
    *         '{' defaultNamedParameter (',' defaultNamedParameter)* '}'
    */
   Token _skipFormalParameterList(Token startToken) {
     if (!_tokenMatches(startToken, TokenType.OPEN_PAREN)) {
       return null;
     }
     Token next = startToken.next;
     if (_tokenMatches(next, TokenType.CLOSE_PAREN)) {
       return next.next;
     }
     //
     // Look to see whether the token after the open parenthesis is something
     // that should only occur at the beginning of a parameter list.
     //
     if (next.matchesAny(const <TokenType>[
           TokenType.AT,
           TokenType.OPEN_SQUARE_BRACKET,
           TokenType.OPEN_CURLY_BRACKET
         ]) ||
         _tokenMatchesKeyword(next, Keyword.VOID) ||
         (_tokenMatchesIdentifier(next) &&
             (next.next.matchesAny(
                 const <TokenType>[TokenType.COMMA, TokenType.CLOSE_PAREN])))) {
       return _skipPastMatchingToken(startToken);
     }
     //
     // Look to see whether the first parameter is a function typed parameter
     // without a return type.
     //
     if (_tokenMatchesIdentifier(next) &&
         _tokenMatches(next.next, TokenType.OPEN_PAREN)) {
       Token afterParameters = _skipFormalParameterList(next.next);
       if (afterParameters != null &&
           afterParameters.matchesAny(
               const <TokenType>[TokenType.COMMA, TokenType.CLOSE_PAREN])) {
         return _skipPastMatchingToken(startToken);
       }
     }
     //
     // Look to see whether the first parameter has a type or is a function typed
     // parameter with a return type.
     //
     Token afterType = _skipFinalConstVarOrType(next);
     if (afterType == null) {
       return null;
     }
     if (skipSimpleIdentifier(afterType) == null) {
       return null;
     }
     return _skipPastMatchingToken(startToken);
   }

   /**
    * If the [startToken] is a begin token with an associated end token, then
    * return the token following the end token. Otherwise, return `null`.
    */
   Token _skipPastMatchingToken(Token startToken) {
     if (startToken is! BeginToken) {
       return null;
     }
     Token closeParen = (startToken as BeginToken).endToken;
     if (closeParen == null) {
       return null;
     }
     return closeParen.next;
   }

   /**
    * Parse a string literal that contains interpolations, starting at the
    * [startToken], without actually creating a string literal or changing the
    * current token. Return the token following the string literal that was
    * parsed, or `null` if the given token is not the first token in a valid
    * string literal.
    *
    * This method must be kept in sync with [parseStringInterpolation].
    */
   Token _skipStringInterpolation(Token startToken) {
     Token token = startToken;
     TokenType type = token.type;
     while (type == TokenType.STRING_INTERPOLATION_EXPRESSION ||
         type == TokenType.STRING_INTERPOLATION_IDENTIFIER) {
       if (type == TokenType.STRING_INTERPOLATION_EXPRESSION) {
         token = token.next;
         type = token.type;
         //
         // Rather than verify that the following tokens represent a valid
         // expression, we simply skip tokens until we reach the end of the
         // interpolation, being careful to handle nested string literals.
         //
         int bracketNestingLevel = 1;
         while (bracketNestingLevel > 0) {
           if (type == TokenType.EOF) {
             return null;
           } else if (type == TokenType.OPEN_CURLY_BRACKET) {
             bracketNestingLevel++;
             token = token.next;
           } else if (type == TokenType.CLOSE_CURLY_BRACKET) {
             bracketNestingLevel--;
             token = token.next;
           } else if (type == TokenType.STRING) {
             token = skipStringLiteral(token);
             if (token == null) {
               return null;
             }
           } else {
             token = token.next;
           }
           type = token.type;
         }
         token = token.next;
         type = token.type;
       } else {
         token = token.next;
         if (token.type != TokenType.IDENTIFIER) {
           return null;
         }
         token = token.next;
       }
       type = token.type;
       if (type == TokenType.STRING) {
         token = token.next;
         type = token.type;
       }
     }
     return token;
   }

   /**
    * Parse a list of type parameters, starting at the [startToken], without
    * actually creating a type parameter list or changing the current token.
    * Return the token following the type parameter list that was parsed, or
    * `null` if the given token is not the first token in a valid type parameter
    * list.
    *
    * This method must be kept in sync with [parseTypeParameterList].
    *
    *     typeParameterList ::=
    *         '<' typeParameter (',' typeParameter)* '>'
    */
   Token _skipTypeParameterList(Token startToken) {
     if (!_tokenMatches(startToken, TokenType.LT)) {
       return null;
     }
     //
     // We can't skip a type parameter because it can be preceeded by metadata,
     // so we just assume that everything before the matching end token is valid.
     //
     int depth = 1;
     Token next = startToken.next;
     while (depth > 0) {
       if (_tokenMatches(next, TokenType.EOF)) {
         return null;
       } else if (_tokenMatches(next, TokenType.LT)) {
         depth++;
       } else if (_tokenMatches(next, TokenType.GT)) {
         depth--;
       } else if (_tokenMatches(next, TokenType.GT_EQ)) {
         if (depth == 1) {
           Token fakeEquals = new Token(TokenType.EQ, next.offset + 2);
           fakeEquals.setNextWithoutSettingPrevious(next.next);
           return fakeEquals;
         }
         depth--;
       } else if (_tokenMatches(next, TokenType.GT_GT)) {
         depth -= 2;
       } else if (_tokenMatches(next, TokenType.GT_GT_EQ)) {
         if (depth < 2) {
           return null;
         } else if (depth == 2) {
           Token fakeEquals = new Token(TokenType.EQ, next.offset + 2);
           fakeEquals.setNextWithoutSettingPrevious(next.next);
           return fakeEquals;
         }
         depth -= 2;
       }
       next = next.next;
     }
     return next;
   }

   /**
    * Assuming that the current token is an index token ('[]'), split it into two
    * tokens ('[' and ']'), leaving the left bracket as the current token.
    */
   void _splitIndex() {
     // Split the token into two separate tokens.
     BeginToken leftBracket = _createToken(
         _currentToken, TokenType.OPEN_SQUARE_BRACKET,
         isBegin: true);
     Token rightBracket =
         new Token(TokenType.CLOSE_SQUARE_BRACKET, _currentToken.offset + 1);
     leftBracket.endToken = rightBracket;
     rightBracket.setNext(_currentToken.next);
     leftBracket.setNext(rightBracket);
     _currentToken.previous.setNext(leftBracket);
     _currentToken = leftBracket;
   }

   /**
    * Return `true` if the given [token] has the given [type].
    */
   bool _tokenMatches(Token token, TokenType type) => token.type == type;

   /**
    * Return `true` if the given [token] is a valid identifier. Valid identifiers
    * include built-in identifiers (pseudo-keywords).
    */
   bool _tokenMatchesIdentifier(Token token) =>
       _tokenMatches(token, TokenType.IDENTIFIER) ||
       _tokenMatchesPseudoKeyword(token);

   /**
    * Return `true` if the given [token] matches the given [keyword].
    */
   bool _tokenMatchesKeyword(Token token, Keyword keyword) =>
       token.keyword == keyword;

   /**
    * Return `true` if the given [token] matches a pseudo keyword.
    */
   bool _tokenMatchesPseudoKeyword(Token token) =>
       token.keyword?.isPseudoKeyword ?? false;

   /**
    * Return `true` if the given [token] matches the given [identifier].
    */
   bool _tokenMatchesString(Token token, String identifier) =>
       token.type == TokenType.IDENTIFIER && token.lexeme == identifier;

   /**
    * Translate the characters at the given [index] in the given [lexeme],
    * appending the translated character to the given [buffer]. The index is
    * assumed to be valid.
    */
   int _translateCharacter(StringBuffer buffer, String lexeme, int index) {
     int currentChar = lexeme.codeUnitAt(index);
     if (currentChar != 0x5C) {
       buffer.writeCharCode(currentChar);
       return index + 1;
     }
     //
     // We have found an escape sequence, so we parse the string to determine
     // what kind of escape sequence and what character to add to the builder.
     //
     int length = lexeme.length;
     int currentIndex = index + 1;
     if (currentIndex >= length) {
       // Illegal escape sequence: no char after escape.
       // This cannot actually happen because it would require the escape
       // character to be the last character in the string, but if it were it
       // would escape the closing quote, leaving the string unclosed.
       // reportError(ParserErrorCode.MISSING_CHAR_IN_ESCAPE_SEQUENCE);
       return length;
     }
     currentChar = lexeme.codeUnitAt(currentIndex);
     if (currentChar == 0x6E) {
       buffer.writeCharCode(0xA);
       // newline
     } else if (currentChar == 0x72) {
       buffer.writeCharCode(0xD);
       // carriage return
     } else if (currentChar == 0x66) {
       buffer.writeCharCode(0xC);
       // form feed
     } else if (currentChar == 0x62) {
       buffer.writeCharCode(0x8);
       // backspace
     } else if (currentChar == 0x74) {
       buffer.writeCharCode(0x9);
       // tab
     } else if (currentChar == 0x76) {
       buffer.writeCharCode(0xB);
       // vertical tab
     } else if (currentChar == 0x78) {
       if (currentIndex + 2 >= length) {
         // Illegal escape sequence: not enough hex digits
         _reportErrorForCurrentToken(ParserErrorCode.INVALID_HEX_ESCAPE);
         return length;
       }
       int firstDigit = lexeme.codeUnitAt(currentIndex + 1);
       int secondDigit = lexeme.codeUnitAt(currentIndex + 2);
       if (!_isHexDigit(firstDigit) || !_isHexDigit(secondDigit)) {
         // Illegal escape sequence: invalid hex digit
         _reportErrorForCurrentToken(ParserErrorCode.INVALID_HEX_ESCAPE);
       } else {
         int charCode = (Character.digit(firstDigit, 16) << 4) +
             Character.digit(secondDigit, 16);
         buffer.writeCharCode(charCode);
       }
       return currentIndex + 3;
     } else if (currentChar == 0x75) {
       currentIndex++;
       if (currentIndex >= length) {
         // Illegal escape sequence: not enough hex digits
         _reportErrorForCurrentToken(ParserErrorCode.INVALID_UNICODE_ESCAPE);
         return length;
       }
       currentChar = lexeme.codeUnitAt(currentIndex);
       if (currentChar == 0x7B) {
         currentIndex++;
         if (currentIndex >= length) {
           // Illegal escape sequence: incomplete escape
           _reportErrorForCurrentToken(ParserErrorCode.INVALID_UNICODE_ESCAPE);
           return length;
         }
         currentChar = lexeme.codeUnitAt(currentIndex);
         int digitCount = 0;
         int value = 0;
         while (currentChar != 0x7D) {
           if (!_isHexDigit(currentChar)) {
             // Illegal escape sequence: invalid hex digit
             _reportErrorForCurrentToken(ParserErrorCode.INVALID_UNICODE_ESCAPE);
             currentIndex++;
             while (currentIndex < length &&
                 lexeme.codeUnitAt(currentIndex) != 0x7D) {
               currentIndex++;
             }
             return currentIndex + 1;
           }
           digitCount++;
           value = (value << 4) + Character.digit(currentChar, 16);
           currentIndex++;
           if (currentIndex >= length) {
             // Illegal escape sequence: incomplete escape
             _reportErrorForCurrentToken(ParserErrorCode.INVALID_UNICODE_ESCAPE);
             return length;
           }
           currentChar = lexeme.codeUnitAt(currentIndex);
         }
         if (digitCount < 1 || digitCount > 6) {
           // Illegal escape sequence: not enough or too many hex digits
           _reportErrorForCurrentToken(ParserErrorCode.INVALID_UNICODE_ESCAPE);
         }
         _appendCodePoint(buffer, lexeme, value, index, currentIndex);
         return currentIndex + 1;
       } else {
         if (currentIndex + 3 >= length) {
           // Illegal escape sequence: not enough hex digits
           _reportErrorForCurrentToken(ParserErrorCode.INVALID_UNICODE_ESCAPE);
           return length;
         }
         int firstDigit = currentChar;
         int secondDigit = lexeme.codeUnitAt(currentIndex + 1);
         int thirdDigit = lexeme.codeUnitAt(currentIndex + 2);
         int fourthDigit = lexeme.codeUnitAt(currentIndex + 3);
         if (!_isHexDigit(firstDigit) ||
             !_isHexDigit(secondDigit) ||
             !_isHexDigit(thirdDigit) ||
             !_isHexDigit(fourthDigit)) {
           // Illegal escape sequence: invalid hex digits
           _reportErrorForCurrentToken(ParserErrorCode.INVALID_UNICODE_ESCAPE);
         } else {
           _appendCodePoint(
               buffer,
               lexeme,
               (((((Character.digit(firstDigit, 16) << 4) +
                                   Character.digit(secondDigit, 16)) <<
                               4) +
                           Character.digit(thirdDigit, 16)) <<
                       4) +
                   Character.digit(fourthDigit, 16),
               index,
               currentIndex + 3);
         }
         return currentIndex + 4;
       }
     } else {
       buffer.writeCharCode(currentChar);
     }
     return currentIndex + 1;
   }

   /**
    * Decrements the error reporting lock level. If level is more than `0`, then
    * [reportError] wont report any error.
    */
   void _unlockErrorListener() {
     if (_errorListenerLock == 0) {
       throw new StateError("Attempt to unlock not locked error listener.");
     }
     _errorListenerLock--;
   }

   /**
    * Validate that the given [parameterList] does not contain any field
    * initializers.
    */
   void _validateFormalParameterList(FormalParameterList parameterList) {
     for (FormalParameter parameter in parameterList.parameters) {
       if (parameter is FieldFormalParameter) {
         _reportErrorForNode(
             ParserErrorCode.FIELD_INITIALIZER_OUTSIDE_CONSTRUCTOR,
             parameter.identifier);
       }
     }
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a class and
    * return the 'abstract' keyword if there is one.
    */
   Token _validateModifiersForClass(Modifiers modifiers) {
     _validateModifiersForTopLevelDeclaration(modifiers);
     if (modifiers.constKeyword != null) {
       _reportErrorForToken(ParserErrorCode.CONST_CLASS, modifiers.constKeyword);
     }
     if (modifiers.externalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_CLASS, modifiers.externalKeyword);
     }
     if (modifiers.finalKeyword != null) {
       _reportErrorForToken(ParserErrorCode.FINAL_CLASS, modifiers.finalKeyword);
     }
     if (modifiers.varKeyword != null) {
       _reportErrorForToken(ParserErrorCode.VAR_CLASS, modifiers.varKeyword);
     }
     return modifiers.abstractKeyword;
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a constructor
    * and return the 'const' keyword if there is one.
    */
   Token _validateModifiersForConstructor(Modifiers modifiers) {
     if (modifiers.abstractKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.ABSTRACT_CLASS_MEMBER, modifiers.abstractKeyword);
     }
     if (modifiers.covariantKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.COVARIANT_CONSTRUCTOR, modifiers.covariantKeyword);
     }
     if (modifiers.finalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.FINAL_CONSTRUCTOR, modifiers.finalKeyword);
     }
     if (modifiers.staticKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.STATIC_CONSTRUCTOR, modifiers.staticKeyword);
     }
     if (modifiers.varKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.CONSTRUCTOR_WITH_RETURN_TYPE, modifiers.varKeyword);
     }
     Token externalKeyword = modifiers.externalKeyword;
     Token constKeyword = modifiers.constKeyword;
     Token factoryKeyword = modifiers.factoryKeyword;
     if (externalKeyword != null &&
         constKeyword != null &&
         constKeyword.offset < externalKeyword.offset) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_AFTER_CONST, externalKeyword);
     }
     if (externalKeyword != null &&
         factoryKeyword != null &&
         factoryKeyword.offset < externalKeyword.offset) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_AFTER_FACTORY, externalKeyword);
     }
     return constKeyword;
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for an enum and
    * return the 'abstract' keyword if there is one.
    */
   void _validateModifiersForEnum(Modifiers modifiers) {
     _validateModifiersForTopLevelDeclaration(modifiers);
     if (modifiers.abstractKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.ABSTRACT_ENUM, modifiers.abstractKeyword);
     }
     if (modifiers.constKeyword != null) {
       _reportErrorForToken(ParserErrorCode.CONST_ENUM, modifiers.constKeyword);
     }
     if (modifiers.externalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_ENUM, modifiers.externalKeyword);
     }
     if (modifiers.finalKeyword != null) {
       _reportErrorForToken(ParserErrorCode.FINAL_ENUM, modifiers.finalKeyword);
     }
     if (modifiers.varKeyword != null) {
       _reportErrorForToken(ParserErrorCode.VAR_ENUM, modifiers.varKeyword);
     }
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a field and
    * return the 'final', 'const' or 'var' keyword if there is one.
    */
   Token _validateModifiersForField(Modifiers modifiers) {
     if (modifiers.abstractKeyword != null) {
       _reportErrorForCurrentToken(ParserErrorCode.ABSTRACT_CLASS_MEMBER);
     }
     if (modifiers.externalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_FIELD, modifiers.externalKeyword);
     }
     if (modifiers.factoryKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.NON_CONSTRUCTOR_FACTORY, modifiers.factoryKeyword);
     }
     Token staticKeyword = modifiers.staticKeyword;
     Token covariantKeyword = modifiers.covariantKeyword;
     Token constKeyword = modifiers.constKeyword;
     Token finalKeyword = modifiers.finalKeyword;
     Token varKeyword = modifiers.varKeyword;
     if (constKeyword != null) {
       if (covariantKeyword != null) {
         _reportErrorForToken(
             ParserErrorCode.CONST_AND_COVARIANT, covariantKeyword);
       }
       if (finalKeyword != null) {
         _reportErrorForToken(ParserErrorCode.CONST_AND_FINAL, finalKeyword);
       }
       if (varKeyword != null) {
         _reportErrorForToken(ParserErrorCode.CONST_AND_VAR, varKeyword);
       }
       if (staticKeyword != null && constKeyword.offset < staticKeyword.offset) {
         _reportErrorForToken(ParserErrorCode.STATIC_AFTER_CONST, staticKeyword);
       }
     } else if (finalKeyword != null) {
       if (covariantKeyword != null) {
         _reportErrorForToken(
             ParserErrorCode.FINAL_AND_COVARIANT, covariantKeyword);
       }
       if (varKeyword != null) {
         _reportErrorForToken(ParserErrorCode.FINAL_AND_VAR, varKeyword);
       }
       if (staticKeyword != null && finalKeyword.offset < staticKeyword.offset) {
         _reportErrorForToken(ParserErrorCode.STATIC_AFTER_FINAL, staticKeyword);
       }
     } else if (varKeyword != null) {
       if (staticKeyword != null && varKeyword.offset < staticKeyword.offset) {
         _reportErrorForToken(ParserErrorCode.STATIC_AFTER_VAR, staticKeyword);
       }
       if (covariantKeyword != null &&
           varKeyword.offset < covariantKeyword.offset) {
         _reportErrorForToken(
             ParserErrorCode.COVARIANT_AFTER_VAR, covariantKeyword);
       }
     }
     if (covariantKeyword != null && staticKeyword != null) {
       _reportErrorForToken(ParserErrorCode.COVARIANT_AND_STATIC, staticKeyword);
     }
     return Token.lexicallyFirst([constKeyword, finalKeyword, varKeyword]);
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a local
    * function.
    */
   void _validateModifiersForFunctionDeclarationStatement(Modifiers modifiers) {
     if (modifiers.abstractKeyword != null ||
         modifiers.constKeyword != null ||
         modifiers.externalKeyword != null ||
         modifiers.factoryKeyword != null ||
         modifiers.finalKeyword != null ||
         modifiers.staticKeyword != null ||
         modifiers.varKeyword != null) {
       _reportErrorForCurrentToken(
           ParserErrorCode.LOCAL_FUNCTION_DECLARATION_MODIFIER);
     }
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a getter,
    * setter, or method.
    */
   void _validateModifiersForGetterOrSetterOrMethod(Modifiers modifiers) {
     if (modifiers.abstractKeyword != null) {
       _reportErrorForCurrentToken(ParserErrorCode.ABSTRACT_CLASS_MEMBER);
     }
     if (modifiers.constKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.CONST_METHOD, modifiers.constKeyword);
     }
     if (modifiers.covariantKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.COVARIANT_MEMBER, modifiers.covariantKeyword);
     }
     if (modifiers.factoryKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.NON_CONSTRUCTOR_FACTORY, modifiers.factoryKeyword);
     }
     if (modifiers.finalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.FINAL_METHOD, modifiers.finalKeyword);
     }
     if (modifiers.varKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.VAR_RETURN_TYPE, modifiers.varKeyword);
     }
     Token externalKeyword = modifiers.externalKeyword;
     Token staticKeyword = modifiers.staticKeyword;
     if (externalKeyword != null &&
         staticKeyword != null &&
         staticKeyword.offset < externalKeyword.offset) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_AFTER_STATIC, externalKeyword);
     }
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a getter,
    * setter, or method.
    */
   void _validateModifiersForOperator(Modifiers modifiers) {
     if (modifiers.abstractKeyword != null) {
       _reportErrorForCurrentToken(ParserErrorCode.ABSTRACT_CLASS_MEMBER);
     }
     if (modifiers.constKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.CONST_METHOD, modifiers.constKeyword);
     }
     if (modifiers.factoryKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.NON_CONSTRUCTOR_FACTORY, modifiers.factoryKeyword);
     }
     if (modifiers.finalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.FINAL_METHOD, modifiers.finalKeyword);
     }
     if (modifiers.staticKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.STATIC_OPERATOR, modifiers.staticKeyword);
     }
     if (modifiers.varKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.VAR_RETURN_TYPE, modifiers.varKeyword);
     }
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a top-level
    * declaration.
    */
   void _validateModifiersForTopLevelDeclaration(Modifiers modifiers) {
     if (modifiers.covariantKeyword != null) {
       _reportErrorForToken(ParserErrorCode.COVARIANT_TOP_LEVEL_DECLARATION,
           modifiers.covariantKeyword);
     }
     if (modifiers.factoryKeyword != null) {
       _reportErrorForToken(ParserErrorCode.FACTORY_TOP_LEVEL_DECLARATION,
           modifiers.factoryKeyword);
     }
     if (modifiers.staticKeyword != null) {
       _reportErrorForToken(ParserErrorCode.STATIC_TOP_LEVEL_DECLARATION,
           modifiers.staticKeyword);
     }
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a top-level
    * function.
    */
   void _validateModifiersForTopLevelFunction(Modifiers modifiers) {
     _validateModifiersForTopLevelDeclaration(modifiers);
     if (modifiers.abstractKeyword != null) {
       _reportErrorForCurrentToken(ParserErrorCode.ABSTRACT_TOP_LEVEL_FUNCTION);
     }
     if (modifiers.constKeyword != null) {
       _reportErrorForToken(ParserErrorCode.CONST_CLASS, modifiers.constKeyword);
     }
     if (modifiers.finalKeyword != null) {
       _reportErrorForToken(ParserErrorCode.FINAL_CLASS, modifiers.finalKeyword);
     }
     if (modifiers.varKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.VAR_RETURN_TYPE, modifiers.varKeyword);
     }
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a field and
    * return the 'final', 'const' or 'var' keyword if there is one.
    */
   Token _validateModifiersForTopLevelVariable(Modifiers modifiers) {
     _validateModifiersForTopLevelDeclaration(modifiers);
     if (modifiers.abstractKeyword != null) {
       _reportErrorForCurrentToken(ParserErrorCode.ABSTRACT_TOP_LEVEL_VARIABLE);
     }
     if (modifiers.externalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_FIELD, modifiers.externalKeyword);
     }
     Token constKeyword = modifiers.constKeyword;
     Token finalKeyword = modifiers.finalKeyword;
     Token varKeyword = modifiers.varKeyword;
     if (constKeyword != null) {
       if (finalKeyword != null) {
         _reportErrorForToken(ParserErrorCode.CONST_AND_FINAL, finalKeyword);
       }
       if (varKeyword != null) {
         _reportErrorForToken(ParserErrorCode.CONST_AND_VAR, varKeyword);
       }
     } else if (finalKeyword != null) {
       if (varKeyword != null) {
         _reportErrorForToken(ParserErrorCode.FINAL_AND_VAR, varKeyword);
       }
     }
     return Token.lexicallyFirst([constKeyword, finalKeyword, varKeyword]);
   }

   /**
    * Validate that the given set of [modifiers] is appropriate for a class and
    * return the 'abstract' keyword if there is one.
    */
   void _validateModifiersForTypedef(Modifiers modifiers) {
     _validateModifiersForTopLevelDeclaration(modifiers);
     if (modifiers.abstractKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.ABSTRACT_TYPEDEF, modifiers.abstractKeyword);
     }
     if (modifiers.constKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.CONST_TYPEDEF, modifiers.constKeyword);
     }
     if (modifiers.externalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.EXTERNAL_TYPEDEF, modifiers.externalKeyword);
     }
     if (modifiers.finalKeyword != null) {
       _reportErrorForToken(
           ParserErrorCode.FINAL_TYPEDEF, modifiers.finalKeyword);
     }
     if (modifiers.varKeyword != null) {
       _reportErrorForToken(ParserErrorCode.VAR_TYPEDEF, modifiers.varKeyword);
     }
   }
 }

 /**
  * A synthetic keyword token.
  */
 class Parser_SyntheticKeywordToken extends KeywordToken {
   /**
    * Initialize a newly created token to represent the given [keyword] at the
    * given [offset].
    */
   Parser_SyntheticKeywordToken(Keyword keyword, int offset)
       : super(keyword, offset);

   @override
   int get length => 0;

   @override
   Token copy() => new Parser_SyntheticKeywordToken(keyword, offset);
 }