// Copyright (c) 2012, 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 _fe_analyzer_shared.parser.parser;

import 'package:_fe_analyzer_shared/src/parser/type_info_impl.dart';

import '../messages/codes.dart' as codes;

import '../scanner/scanner.dart' show ErrorToken, Token;

import '../scanner/token.dart'
    show
        ASSIGNMENT_PRECEDENCE,
        BeginToken,
        CASCADE_PRECEDENCE,
        EQUALITY_PRECEDENCE,
        Keyword,
        POSTFIX_PRECEDENCE,
        RELATIONAL_PRECEDENCE,
        SELECTOR_PRECEDENCE,
        SyntheticBeginToken,
        SyntheticKeywordToken,
        SyntheticStringToken,
        SyntheticToken,
        TokenType;

import '../scanner/token_constants.dart'
    show
        BANG_EQ_EQ_TOKEN,
        COMMA_TOKEN,
        DOUBLE_TOKEN,
        EOF_TOKEN,
        EQ_EQ_EQ_TOKEN,
        EQ_TOKEN,
        FUNCTION_TOKEN,
        HASH_TOKEN,
        HEXADECIMAL_TOKEN,
        IDENTIFIER_TOKEN,
        INT_TOKEN,
        KEYWORD_TOKEN,
        LT_TOKEN,
        OPEN_CURLY_BRACKET_TOKEN,
        OPEN_PAREN_TOKEN,
        OPEN_SQUARE_BRACKET_TOKEN,
        SEMICOLON_TOKEN,
        STRING_INTERPOLATION_IDENTIFIER_TOKEN,
        STRING_INTERPOLATION_TOKEN,
        STRING_TOKEN;

import 'assert.dart' show Assert;

import 'async_modifier.dart' show AsyncModifier;

import 'block_kind.dart';

import 'declaration_kind.dart' show DeclarationKind;

import 'directive_context.dart';

import 'formal_parameter_kind.dart'
    show
        FormalParameterKind,
        isMandatoryFormalParameterKind,
        isOptionalPositionalFormalParameterKind;

import 'forwarding_listener.dart' show ForwardingListener, NullListener;

import 'identifier_context.dart'
    show IdentifierContext, looksLikeExpressionStart;

import 'listener.dart' show Listener;

import 'literal_entry_info.dart'
    show
        LiteralEntryInfo,
        computeLiteralEntry,
        looksLikeLiteralEntry,
        simpleEntry;

import 'loop_state.dart' show LoopState;

import 'member_kind.dart' show MemberKind;

import 'modifier_context.dart' show ModifierRecoveryContext, isModifier;

import 'recovery_listeners.dart'
    show
        ClassHeaderRecoveryListener,
        ImportRecoveryListener,
        MixinHeaderRecoveryListener;

import 'token_stream_rewriter.dart'
    show
        TokenStreamRewriter,
        TokenStreamRewriterImpl,
        UndoableTokenStreamRewriter;

import 'type_info.dart'
    show
        TypeInfo,
        TypeParamOrArgInfo,
        computeMethodTypeArguments,
        computeType,
        computeTypeParamOrArg,
        isValidTypeReference,
        noType,
        noTypeParamOrArg;

import 'util.dart'
    show
        findNonZeroLengthToken,
        findPreviousNonZeroLengthToken,
        isLetter,
        isLetterOrDigit,
        isOneOf,
        isOneOfOrEof,
        isWhitespace,
        optional;

/// An event generating parser of Dart programs. This parser expects all tokens
/// in a linked list (aka a token stream).
///
/// The class [Scanner] is used to generate a token stream. See the file
/// [scanner.dart](../scanner.dart).
///
/// Subclasses of the class [Listener] are used to listen to events.
///
/// Most methods of this class belong in one of four major categories: parse
/// methods, peek methods, ensure methods, and skip methods.
///
/// Parse methods all have the prefix `parse`, generate events
/// (by calling methods on [listener]), and return the next token to parse.
/// Some exceptions to this last point are methods such as [parseFunctionBody]
/// and [parseClassOrMixinOrExtensionBody] which return the last token parsed
/// rather than the next token to be parsed.
/// Parse methods are generally named `parseGrammarProductionSuffix`.
/// The suffix can be one of `opt`, or `star`.
/// `opt` means zero or one matches, `star` means zero or more matches.
/// For example, [parseMetadataStar] corresponds to this grammar snippet:
/// `metadata*`, and [parseArgumentsOpt] corresponds to: `arguments?`.
///
/// Peek methods all have the prefix `peek`, do not generate events
/// (except for errors) and may return null.
///
/// Ensure methods all have the prefix `ensure` and may generate events.
/// They return the current token, or insert and return a synthetic token
/// if the current token does not match. For example,
/// [ensureSemicolon] returns the current token if the current token is a
/// semicolon, otherwise inserts a synthetic semicolon in the token stream
/// before the current token and then returns that new synthetic token.
///
/// Skip methods are like parse methods, but all have the prefix `skip`
/// and skip over some parts of the file being parsed.
/// Typically, skip methods generate an event for the structure being skipped,
/// but not for its substructures.
///
/// ## Current Token
///
/// The current token is always to be found in a formal parameter named
/// `token`. This parameter should be the first as this increases the chance
/// that a compiler will place it in a register.
///
/// ## Implementation Notes
///
/// The parser assumes that keywords, built-in identifiers, and other special
/// words (pseudo-keywords) are all canonicalized. To extend the parser to
/// recognize a new identifier, one should modify
/// [keyword.dart](../scanner/keyword.dart) and ensure the identifier is added
/// to the keyword table.
///
/// As a consequence of this, one should not use `==` to compare strings in the
/// parser. One should favor the methods [optional] and [expect] to recognize
/// keywords or identifiers. In some cases, it's possible to compare a token's
/// `stringValue` using [identical], but normally [optional] will suffice.
///
/// Historically, we over-used identical, and when identical is used on objects
/// other than strings, it can often be replaced by `==`.
///
/// ## Flexibility, Extensibility, and Specification
///
/// The parser is designed to be flexible and extensible. Its methods are
/// designed to be overridden in subclasses, so it can be extended to handle
/// unspecified language extension or experiments while everything in this file
/// attempts to follow the specification (unless when it interferes with error
/// recovery).
///
/// We achieve flexibility, extensible, and specification compliance by
/// following a few rules-of-thumb:
///
/// 1. All methods in the parser should be public.
///
/// 2. The methods follow the specified grammar, and do not implement custom
/// extensions, for example, `native`.
///
/// 3. The parser doesn't rewrite the token stream (when dealing with `>>`).
///
/// ### Implementing Extensions
///
/// For various reasons, some Dart language implementations have used
/// custom/unspecified extensions to the Dart grammar. Examples of this
/// includes diet parsing, patch files, `native` keyword, and generic
/// comments. This class isn't supposed to implement any of these
/// features. Instead it provides hooks for those extensions to be implemented
/// in subclasses or listeners. Let's examine how diet parsing and `native`
/// keyword is currently supported by Fasta.
///
/// #### Legacy Implementation of `native` Keyword
///
/// TODO(ahe,danrubel): Remove this section.
///
/// Both dart2js and the Dart VM have used the `native` keyword to mark methods
/// that couldn't be implemented in the Dart language and needed to be
/// implemented in JavaScript or C++, respectively. An example of the syntax
/// extension used by the Dart VM is:
///
///     nativeFunction() native "NativeFunction";
///
/// When attempting to parse this function, the parser eventually calls
/// [parseFunctionBody]. This method will report an unrecoverable error to the
/// listener with the code [fasta.messageExpectedFunctionBody]. The listener can
/// then look at the error code and the token and use the methods in
/// [native_support.dart](native_support.dart) to parse the native syntax.
///
/// #### Implementation of Diet Parsing
///
/// We call it _diet_ _parsing_ when the parser skips parts of a file. Both
/// dart2js and the Dart VM have been relying on this from early on as it allows
/// them to more quickly compile small programs that use small parts of big
/// libraries. It's also become an integrated part of how Fasta builds up
/// outlines before starting to parse method bodies.
///
/// When looking through this parser, you'll find a number of unused methods
/// starting with `skip`. These methods are only used by subclasses, such as
/// [ClassMemberParser](class_member_parser.dart) and
/// [TopLevelParser](top_level_parser.dart). These methods violate the
/// principle above about following the specified grammar, and originally lived
/// in subclasses. However, we realized that these methods were so widely used
/// and hard to maintain in subclasses, that it made sense to move them here.
///
/// ### Specification and Error Recovery
///
/// To improve error recovery, the parser will inform the listener of
/// recoverable errors and continue to parse.  An example of a recoverable
/// error is:
///
///     Error: Asynchronous for-loop can only be used in 'async' or 'async*'...
///     main() { await for (var x in []) {} }
///              ^^^^^
///
/// ### Legacy Error Recovery
///
/// What's described below will be phased out in preference of the parser
/// reporting and recovering from syntax errors. The motivation for this is
/// that we have multiple listeners that use the parser, and this will ensure
/// consistency.
///
/// For unrecoverable errors, the parser will ask the listener for help to
/// recover from the error. We haven't made much progress on these kinds of
/// errors, so in most cases, the parser aborts by skipping to the end of file.
///
/// Historically, this parser has been rather lax in what it allows, and
/// deferred the enforcement of some syntactical rules to subsequent phases. It
/// doesn't matter how we got there, only that we've identified that it's
/// easier if the parser reports as many errors it can, but informs the
/// listener if the error is recoverable or not.
class Parser {
  Listener listener;

  Uri get uri => listener.uri;

  bool mayParseFunctionExpressions = true;

  /// Represents parser state: what asynchronous syntax is allowed in the
  /// function being currently parsed. In rare situations, this can be set by
  /// external clients, for example, to parse an expression outside a function.
  AsyncModifier asyncState = AsyncModifier.Sync;

  // TODO(danrubel): The [loopState] and associated functionality in the
  // [Parser] duplicates work that the resolver needs to do when resolving
  // break/continue targets. Long term, this state and functionality will be
  // removed from the [Parser] class and the resolver will be responsible
  // for generating all break/continue error messages.

  /// Represents parser state: whether parsing outside a loop,
  /// inside a loop, or inside a switch. This is used to determine whether
  /// break and continue statements are allowed.
  LoopState loopState = LoopState.OutsideLoop;

  /// A rewriter for inserting synthetic tokens.
  /// Access using [rewriter] for lazy initialization.
  TokenStreamRewriter cachedRewriter;

  TokenStreamRewriter get rewriter {
    cachedRewriter ??= new TokenStreamRewriterImpl();
    return cachedRewriter;
  }

  Parser(this.listener);

  bool get inGenerator {
    return asyncState == AsyncModifier.AsyncStar ||
        asyncState == AsyncModifier.SyncStar;
  }

  bool get inAsync {
    return asyncState == AsyncModifier.Async ||
        asyncState == AsyncModifier.AsyncStar;
  }

  bool get inPlainSync => asyncState == AsyncModifier.Sync;

  bool get isBreakAllowed => loopState != LoopState.OutsideLoop;

  bool get isContinueAllowed => loopState == LoopState.InsideLoop;

  bool get isContinueWithLabelAllowed => loopState != LoopState.OutsideLoop;

  /// Parse a compilation unit.
  ///
  /// This method is only invoked from outside the parser. As a result, this
  /// method takes the next token to be consumed rather than the last consumed
  /// token and returns the token after the last consumed token rather than the
  /// last consumed token.
  ///
  /// ```
  /// libraryDefinition:
  ///   scriptTag?
  ///   libraryName?
  ///   importOrExport*
  ///   partDirective*
  ///   topLevelDefinition*
  /// ;
  ///
  /// partDeclaration:
  ///   partHeader topLevelDefinition*
  /// ;
  /// ```
  Token parseUnit(Token token) {
    // Skip over error tokens and report them at the end
    // so that the parser has the chance to adjust the error location.
    Token errorToken = token;
    token = skipErrorTokens(errorToken);

    listener.beginCompilationUnit(token);
    int count = 0;
    DirectiveContext directiveState = new DirectiveContext();
    token = syntheticPreviousToken(token);
    if (identical(token.next.type, TokenType.SCRIPT_TAG)) {
      directiveState?.checkScriptTag(this, token.next);
      token = parseScript(token);
    }
    while (!token.next.isEof) {
      final Token start = token.next;
      token = parseTopLevelDeclarationImpl(token, directiveState);
      listener.endTopLevelDeclaration(token.next);
      count++;
      if (start == token.next) {
        // Recovery:
        // If progress has not been made reaching the end of the token stream,
        // then report an error and skip the current token.
        token = token.next;
        listener.beginMetadataStar(token);
        listener.endMetadataStar(/* count = */ 0);
        reportRecoverableErrorWithToken(
            token, codes.templateExpectedDeclaration);
        listener.handleInvalidTopLevelDeclaration(token);
        listener.endTopLevelDeclaration(token.next);
        count++;
      }
    }
    token = token.next;
    reportAllErrorTokens(errorToken);
    listener.endCompilationUnit(count, token);
    // Clear fields that could lead to memory leak.
    cachedRewriter = null;
    return token;
  }

  /// This method exists for analyzer compatibility only
  /// and will be removed once analyzer/fasta integration is complete.
  ///
  /// Similar to [parseUnit], this method parses a compilation unit,
  /// but stops when it reaches the first declaration or EOF.
  ///
  /// This method is only invoked from outside the parser. As a result, this
  /// method takes the next token to be consumed rather than the last consumed
  /// token and returns the token after the last consumed token rather than the
  /// last consumed token.
  Token parseDirectives(Token token) {
    listener.beginCompilationUnit(token);
    int count = 0;
    DirectiveContext directiveState = new DirectiveContext();
    token = syntheticPreviousToken(token);
    while (!token.next.isEof) {
      final Token start = token.next;
      final String nextValue = start.next.stringValue;

      // If a built-in keyword is being used as function name, then stop.
      if (identical(nextValue, '.') ||
          identical(nextValue, '<') ||
          identical(nextValue, '(')) {
        break;
      }

      if (identical(token.next.type, TokenType.SCRIPT_TAG)) {
        directiveState?.checkScriptTag(this, token.next);
        token = parseScript(token);
      } else {
        token = parseMetadataStar(token);
        Token keyword = token.next;
        final String value = keyword.stringValue;
        if (identical(value, 'import')) {
          directiveState?.checkImport(this, keyword);
          token = parseImport(keyword);
        } else if (identical(value, 'export')) {
          directiveState?.checkExport(this, keyword);
          token = parseExport(keyword);
        } else if (identical(value, 'library')) {
          directiveState?.checkLibrary(this, keyword);
          token = parseLibraryName(keyword);
        } else if (identical(value, 'part')) {
          token = parsePartOrPartOf(keyword, directiveState);
        } else if (identical(value, ';')) {
          token = start;
          listener.handleDirectivesOnly();
        } else {
          listener.handleDirectivesOnly();
          break;
        }
      }
      listener.endTopLevelDeclaration(token.next);
    }
    token = token.next;
    listener.endCompilationUnit(count, token);
    // Clear fields that could lead to memory leak.
    cachedRewriter = null;
    return token;
  }

  /// Parse a top-level declaration.
  ///
  /// This method is only invoked from outside the parser. As a result, this
  /// method takes the next token to be consumed rather than the last consumed
  /// token and returns the token after the last consumed token rather than the
  /// last consumed token.
  Token parseTopLevelDeclaration(Token token) {
    token = parseTopLevelDeclarationImpl(
            syntheticPreviousToken(token), /* directiveState = */ null)
        .next;
    listener.endTopLevelDeclaration(token);
    return token;
  }

  /// ```
  /// topLevelDefinition:
  ///   classDefinition |
  ///   enumType |
  ///   typeAlias |
  ///   'external'? functionSignature ';' |
  ///   'external'? getterSignature ';' |
  ///   'external''? setterSignature ';' |
  ///   functionSignature functionBody |
  ///   returnType? 'get' identifier functionBody |
  ///   returnType? 'set' identifier formalParameterList functionBody |
  ///   ('final' | 'const') type? staticFinalDeclarationList ';' |
  ///   variableDeclaration ';'
  /// ;
  /// ```
  Token parseTopLevelDeclarationImpl(
      Token token, DirectiveContext directiveState) {
    token = parseMetadataStar(token);
    Token next = token.next;
    if (next.isTopLevelKeyword) {
      return parseTopLevelKeywordDeclaration(token, next, directiveState);
    }
    Token start = token;
    // Skip modifiers to find a top level keyword or identifier
    if (next.isModifier) {
      if (optional('var', next) ||
          optional('late', next) ||
          ((optional('const', next) || optional('final', next)) &&
              // Ignore `const class` and `final class` so that it is reported
              // below as an invalid modifier on a class.
              !optional('class', next.next))) {
        directiveState?.checkDeclaration();
        return parseTopLevelMemberImpl(token);
      }
      while (token.next.isModifier) {
        token = token.next;
      }
    }
    next = token.next;
    if (next.isTopLevelKeyword) {
      return parseTopLevelKeywordDeclaration(start, next, directiveState);
    } else if (next.isKeywordOrIdentifier) {
      // TODO(danrubel): improve parseTopLevelMember
      // so that we don't parse modifiers twice.
      directiveState?.checkDeclaration();
      return parseTopLevelMemberImpl(start);
    } else if (start.next != next) {
      directiveState?.checkDeclaration();
      // Handle the edge case where a modifier is being used as an identifier
      return parseTopLevelMemberImpl(start);
    }
    // Recovery
    if (next.isOperator && optional('(', next.next)) {
      // This appears to be a top level operator declaration, which is invalid.
      reportRecoverableError(next, codes.messageTopLevelOperator);
      // Insert a synthetic identifier
      // and continue parsing as a top level function.
      rewriter.insertSyntheticIdentifier(
          next, '#synthetic_function_${next.charOffset}');
      return parseTopLevelMemberImpl(next);
    }
    // Ignore any preceding modifiers and just report the unexpected token
    listener.beginTopLevelMember(next);
    return parseInvalidTopLevelDeclaration(token);
  }

  /// Parse the modifiers before the `class` keyword.
  /// Return the first `abstract` modifier or `null` if not found.
  Token parseClassDeclarationModifiers(Token start, Token keyword) {
    Token modifier = start.next;
    while (modifier != keyword) {
      if (optional('abstract', modifier)) {
        parseTopLevelKeywordModifiers(modifier, keyword);
        return modifier;
      } else {
        // Recovery
        reportTopLevelModifierError(modifier, keyword);
      }
      modifier = modifier.next;
    }
    return null;
  }

  /// Report errors on any modifiers before the specified keyword.
  void parseTopLevelKeywordModifiers(Token start, Token keyword) {
    Token modifier = start.next;
    while (modifier != keyword) {
      // Recovery
      reportTopLevelModifierError(modifier, keyword);
      modifier = modifier.next;
    }
  }

  // Report an error for the given modifier preceding a top level keyword
  // such as `import` or `class`.
  void reportTopLevelModifierError(Token modifier, Token afterModifiers) {
    if (optional('const', modifier) && optional('class', afterModifiers)) {
      reportRecoverableError(modifier, codes.messageConstClass);
    } else if (optional('external', modifier)) {
      if (optional('class', afterModifiers)) {
        reportRecoverableError(modifier, codes.messageExternalClass);
      } else if (optional('enum', afterModifiers)) {
        reportRecoverableError(modifier, codes.messageExternalEnum);
      } else if (optional('typedef', afterModifiers)) {
        reportRecoverableError(modifier, codes.messageExternalTypedef);
      } else {
        reportRecoverableErrorWithToken(
            modifier, codes.templateExtraneousModifier);
      }
    } else {
      reportRecoverableErrorWithToken(
          modifier, codes.templateExtraneousModifier);
    }
  }

  /// Parse any top-level declaration that begins with a keyword.
  /// [start] is the token before any modifiers preceding [keyword].
  Token parseTopLevelKeywordDeclaration(
      Token start, Token keyword, DirectiveContext directiveState) {
    assert(keyword.isTopLevelKeyword);
    final String value = keyword.stringValue;
    if (identical(value, 'class')) {
      directiveState?.checkDeclaration();
      Token abstractToken = parseClassDeclarationModifiers(start, keyword);
      return parseClassOrNamedMixinApplication(abstractToken, keyword);
    } else if (identical(value, 'enum')) {
      directiveState?.checkDeclaration();
      parseTopLevelKeywordModifiers(start, keyword);
      return parseEnum(keyword);
    } else {
      // The remaining top level keywords are built-in keywords
      // and can be used in a top level declaration
      // as an identifier such as "abstract<T>() => 0;"
      // or as a prefix such as "abstract.A b() => 0;".
      String nextValue = keyword.next.stringValue;
      if (identical(nextValue, '(') || identical(nextValue, '.')) {
        directiveState?.checkDeclaration();
        return parseTopLevelMemberImpl(start);
      } else if (identical(nextValue, '<')) {
        if (identical(value, 'extension')) {
          // The name in an extension declaration is optional:
          // `extension<T> on ...`
          Token endGroup = keyword.next.endGroup;
          if (endGroup != null && optional('on', endGroup.next)) {
            directiveState?.checkDeclaration();
            return parseExtension(keyword);
          }
        }
        directiveState?.checkDeclaration();
        return parseTopLevelMemberImpl(start);
      } else {
        parseTopLevelKeywordModifiers(start, keyword);
        if (identical(value, 'import')) {
          directiveState?.checkImport(this, keyword);
          return parseImport(keyword);
        } else if (identical(value, 'export')) {
          directiveState?.checkExport(this, keyword);
          return parseExport(keyword);
        } else if (identical(value, 'typedef')) {
          directiveState?.checkDeclaration();
          return parseTypedef(keyword);
        } else if (identical(value, 'mixin')) {
          directiveState?.checkDeclaration();
          return parseMixin(keyword);
        } else if (identical(value, 'extension')) {
          directiveState?.checkDeclaration();
          return parseExtension(keyword);
        } else if (identical(value, 'part')) {
          return parsePartOrPartOf(keyword, directiveState);
        } else if (identical(value, 'library')) {
          directiveState?.checkLibrary(this, keyword);
          return parseLibraryName(keyword);
        }
      }
    }

    throw "Internal error: Unhandled top level keyword '$value'.";
  }

  /// ```
  /// libraryDirective:
  ///   'library' qualified ';'
  /// ;
  /// ```
  Token parseLibraryName(Token libraryKeyword) {
    assert(optional('library', libraryKeyword));
    listener.beginUncategorizedTopLevelDeclaration(libraryKeyword);
    listener.beginLibraryName(libraryKeyword);
    Token token = parseQualified(libraryKeyword, IdentifierContext.libraryName,
        IdentifierContext.libraryNameContinuation);
    token = ensureSemicolon(token);
    listener.endLibraryName(libraryKeyword, token);
    return token;
  }

  /// ```
  /// importPrefix:
  ///   'deferred'? 'as' identifier
  /// ;
  /// ```
  Token parseImportPrefixOpt(Token token) {
    Token next = token.next;
    if (optional('deferred', next) && optional('as', next.next)) {
      Token deferredToken = next;
      Token asKeyword = next.next;
      token = ensureIdentifier(
          asKeyword, IdentifierContext.importPrefixDeclaration);
      listener.handleImportPrefix(deferredToken, asKeyword);
    } else if (optional('as', next)) {
      Token asKeyword = next;
      token = ensureIdentifier(next, IdentifierContext.importPrefixDeclaration);
      listener.handleImportPrefix(/* deferredKeyword = */ null, asKeyword);
    } else {
      listener.handleImportPrefix(
          /* deferredKeyword = */ null,
          /* asKeyword = */ null);
    }
    return token;
  }

  /// ```
  /// importDirective:
  ///   'import' uri ('if' '(' test ')' uri)* importPrefix? combinator* ';'
  /// ;
  /// ```
  Token parseImport(Token importKeyword) {
    assert(optional('import', importKeyword));
    listener.beginUncategorizedTopLevelDeclaration(importKeyword);
    listener.beginImport(importKeyword);
    Token token = ensureLiteralString(importKeyword);
    Token uri = token;
    token = parseConditionalUriStar(token);
    token = parseImportPrefixOpt(token);
    token = parseCombinatorStar(token).next;
    if (optional(';', token)) {
      listener.endImport(importKeyword, token);
      return token;
    } else {
      // Recovery
      listener.endImport(importKeyword, /* semicolon = */ null);
      return parseImportRecovery(uri);
    }
  }

  /// Recover given out-of-order clauses in an import directive where [token] is
  /// the import keyword.
  Token parseImportRecovery(Token token) {
    final Listener primaryListener = listener;
    final ImportRecoveryListener recoveryListener =
        new ImportRecoveryListener();

    // Reparse to determine which clauses have already been parsed
    // but intercept the events so they are not sent to the primary listener
    listener = recoveryListener;
    token = parseConditionalUriStar(token);
    token = parseImportPrefixOpt(token);
    token = parseCombinatorStar(token);

    Token firstDeferredKeyword = recoveryListener.deferredKeyword;
    bool hasPrefix = recoveryListener.asKeyword != null;
    bool hasCombinator = recoveryListener.hasCombinator;

    // Update the recovery listener to forward subsequent events
    // to the primary listener
    recoveryListener.listener = primaryListener;

    // Parse additional out-of-order clauses.
    Token semicolon;
    do {
      Token start = token.next;

      // Check for extraneous token in the middle of an import statement.
      token = skipUnexpectedTokenOpt(
          token, const <String>['if', 'deferred', 'as', 'hide', 'show', ';']);

      // During recovery, clauses are parsed in the same order
      // and generate the same events as in the parseImport method above.
      recoveryListener.clear();
      token = parseConditionalUriStar(token);
      if (recoveryListener.ifKeyword != null) {
        if (firstDeferredKeyword != null) {
          // TODO(danrubel): report error indicating conditional should
          // be moved before deferred keyword
        } else if (hasPrefix) {
          // TODO(danrubel): report error indicating conditional should
          // be moved before prefix clause
        } else if (hasCombinator) {
          // TODO(danrubel): report error indicating conditional should
          // be moved before combinators
        }
      }

      if (optional('deferred', token.next) &&
          !optional('as', token.next.next)) {
        listener.handleImportPrefix(token.next, /* asKeyword = */ null);
        token = token.next;
      } else {
        token = parseImportPrefixOpt(token);
      }
      if (recoveryListener.deferredKeyword != null) {
        if (firstDeferredKeyword != null) {
          reportRecoverableError(
              recoveryListener.deferredKeyword, codes.messageDuplicateDeferred);
        } else {
          if (hasPrefix) {
            reportRecoverableError(recoveryListener.deferredKeyword,
                codes.messageDeferredAfterPrefix);
          }
          firstDeferredKeyword = recoveryListener.deferredKeyword;
        }
      }
      if (recoveryListener.asKeyword != null) {
        if (hasPrefix) {
          reportRecoverableError(
              recoveryListener.asKeyword, codes.messageDuplicatePrefix);
        } else {
          if (hasCombinator) {
            reportRecoverableError(
                recoveryListener.asKeyword, codes.messagePrefixAfterCombinator);
          }
          hasPrefix = true;
        }
      }

      token = parseCombinatorStar(token);
      hasCombinator = hasCombinator || recoveryListener.hasCombinator;

      if (optional(';', token.next)) {
        semicolon = token.next;
      } else if (identical(start, token.next)) {
        // If no forward progress was made, insert ';' so that we exit loop.
        semicolon = ensureSemicolon(token);
      }
      listener.handleRecoverImport(semicolon);
    } while (semicolon == null);

    if (firstDeferredKeyword != null && !hasPrefix) {
      reportRecoverableError(
          firstDeferredKeyword, codes.messageMissingPrefixInDeferredImport);
    }

    return semicolon;
  }

  /// ```
  /// conditionalUris:
  ///   conditionalUri*
  /// ;
  /// ```
  Token parseConditionalUriStar(Token token) {
    listener.beginConditionalUris(token.next);
    int count = 0;
    while (optional('if', token.next)) {
      count++;
      token = parseConditionalUri(token);
    }
    listener.endConditionalUris(count);
    return token;
  }

  /// ```
  /// conditionalUri:
  ///   'if' '(' dottedName ('==' literalString)? ')' uri
  /// ;
  /// ```
  Token parseConditionalUri(Token token) {
    Token ifKeyword = token = token.next;
    assert(optional('if', token));
    listener.beginConditionalUri(token);
    Token leftParen = token.next;
    if (!optional('(', leftParen)) {
      reportRecoverableError(
          leftParen, codes.templateExpectedButGot.withArguments('('));
      leftParen = rewriter.insertParens(token, /* includeIdentifier = */ true);
    }
    token = parseDottedName(leftParen);
    Token next = token.next;
    Token equalitySign;
    if (optional('==', next)) {
      equalitySign = next;
      token = ensureLiteralString(next);
      next = token.next;
    }
    if (next != leftParen.endGroup) {
      Token endGroup = leftParen.endGroup;
      if (endGroup.isSynthetic) {
        // The scanner did not place the synthetic ')' correctly, so move it.
        next = rewriter.moveSynthetic(token, endGroup);
      } else {
        reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
        next = endGroup;
      }
    }
    token = next;
    assert(optional(')', token));

    token = ensureLiteralString(token);
    listener.endConditionalUri(ifKeyword, leftParen, equalitySign);
    return token;
  }

  /// ```
  /// dottedName:
  ///   identifier ('.' identifier)*
  /// ;
  /// ```
  Token parseDottedName(Token token) {
    token = ensureIdentifier(token, IdentifierContext.dottedName);
    Token firstIdentifier = token;
    int count = 1;
    while (optional('.', token.next)) {
      token = ensureIdentifier(
          token.next, IdentifierContext.dottedNameContinuation);
      count++;
    }
    listener.handleDottedName(count, firstIdentifier);
    return token;
  }

  /// ```
  /// exportDirective:
  ///   'export' uri conditional-uris* combinator* ';'
  /// ;
  /// ```
  Token parseExport(Token exportKeyword) {
    assert(optional('export', exportKeyword));
    listener.beginUncategorizedTopLevelDeclaration(exportKeyword);
    listener.beginExport(exportKeyword);
    Token token = ensureLiteralString(exportKeyword);
    token = parseConditionalUriStar(token);
    token = parseCombinatorStar(token);
    token = ensureSemicolon(token);
    listener.endExport(exportKeyword, token);
    return token;
  }

  /// ```
  /// combinators:
  ///   (hideCombinator | showCombinator)*
  /// ;
  /// ```
  Token parseCombinatorStar(Token token) {
    Token next = token.next;
    listener.beginCombinators(next);
    int count = 0;
    while (true) {
      String value = next.stringValue;
      if (identical('hide', value)) {
        token = parseHide(token);
      } else if (identical('show', value)) {
        token = parseShow(token);
      } else {
        listener.endCombinators(count);
        break;
      }
      next = token.next;
      count++;
    }
    return token;
  }

  /// ```
  /// hideCombinator:
  ///   'hide' identifierList
  /// ;
  /// ```
  Token parseHide(Token token) {
    Token hideKeyword = token.next;
    assert(optional('hide', hideKeyword));
    listener.beginHide(hideKeyword);
    token = parseIdentifierList(hideKeyword);
    listener.endHide(hideKeyword);
    return token;
  }

  /// ```
  /// showCombinator:
  ///   'show' identifierList
  /// ;
  /// ```
  Token parseShow(Token token) {
    Token showKeyword = token.next;
    assert(optional('show', showKeyword));
    listener.beginShow(showKeyword);
    token = parseIdentifierList(showKeyword);
    listener.endShow(showKeyword);
    return token;
  }

  /// ```
  /// identifierList:
  ///   identifier (',' identifier)*
  /// ;
  /// ```
  Token parseIdentifierList(Token token) {
    token = ensureIdentifier(token, IdentifierContext.combinator);
    int count = 1;
    while (optional(',', token.next)) {
      token = ensureIdentifier(token.next, IdentifierContext.combinator);
      count++;
    }
    listener.handleIdentifierList(count);
    return token;
  }

  /// ```
  /// typeList:
  ///   type (',' type)*
  /// ;
  /// ```
  Token parseTypeList(Token token) {
    listener.beginTypeList(token.next);
    token =
        computeType(token, /* required = */ true).ensureTypeOrVoid(token, this);
    int count = 1;
    while (optional(',', token.next)) {
      token = computeType(token.next, /* required = */ true)
          .ensureTypeOrVoid(token.next, this);
      count++;
    }
    listener.endTypeList(count);
    return token;
  }

  Token parsePartOrPartOf(Token partKeyword, DirectiveContext directiveState) {
    assert(optional('part', partKeyword));
    listener.beginUncategorizedTopLevelDeclaration(partKeyword);
    if (optional('of', partKeyword.next)) {
      directiveState?.checkPartOf(this, partKeyword);
      return parsePartOf(partKeyword);
    } else {
      directiveState?.checkPart(this, partKeyword);
      return parsePart(partKeyword);
    }
  }

  /// ```
  /// partDirective:
  ///   'part' uri ';'
  /// ;
  /// ```
  Token parsePart(Token partKeyword) {
    assert(optional('part', partKeyword));
    listener.beginPart(partKeyword);
    Token token = ensureLiteralString(partKeyword);
    token = ensureSemicolon(token);
    listener.endPart(partKeyword, token);
    return token;
  }

  /// ```
  /// partOfDirective:
  ///   'part' 'of' (qualified | uri) ';'
  /// ;
  /// ```
  Token parsePartOf(Token partKeyword) {
    Token ofKeyword = partKeyword.next;
    assert(optional('part', partKeyword));
    assert(optional('of', ofKeyword));
    listener.beginPartOf(partKeyword);
    bool hasName = ofKeyword.next.isIdentifier;
    Token token;
    if (hasName) {
      token = parseQualified(ofKeyword, IdentifierContext.partName,
          IdentifierContext.partNameContinuation);
    } else {
      token = ensureLiteralString(ofKeyword);
    }
    token = ensureSemicolon(token);
    listener.endPartOf(partKeyword, ofKeyword, token, hasName);
    return token;
  }

  /// ```
  /// metadata:
  ///   annotation*
  /// ;
  /// ```
  Token parseMetadataStar(Token token) {
    listener.beginMetadataStar(token.next);
    int count = 0;
    while (optional('@', token.next)) {
      token = parseMetadata(token);
      count++;
    }
    listener.endMetadataStar(count);
    return token;
  }

  /// ```
  /// annotation:
  ///   '@' qualified ('.' identifier)? arguments?
  /// ;
  /// ```
  Token parseMetadata(Token token) {
    Token atToken = token.next;
    assert(optional('@', atToken));
    listener.beginMetadata(atToken);
    token = ensureIdentifier(atToken, IdentifierContext.metadataReference);
    token =
        parseQualifiedRestOpt(token, IdentifierContext.metadataContinuation);
    if (optional("<", token.next)) {
      reportRecoverableError(token.next, codes.messageMetadataTypeArguments);
    }
    token = computeTypeParamOrArg(token).parseArguments(token, this);
    Token period = null;
    if (optional('.', token.next)) {
      period = token.next;
      token = ensureIdentifier(
          period, IdentifierContext.metadataContinuationAfterTypeArguments);
    }
    token = parseArgumentsOpt(token);
    listener.endMetadata(atToken, period, token.next);
    return token;
  }

  /// ```
  /// scriptTag:
  ///   '#!' (˜NEWLINE)* NEWLINE
  /// ;
  /// ```
  Token parseScript(Token token) {
    token = token.next;
    assert(identical(token.type, TokenType.SCRIPT_TAG));
    listener.handleScript(token);
    return token;
  }

  /// ```
  /// typeAlias:
  ///   metadata 'typedef' typeAliasBody |
  ///   metadata 'typedef' identifier typeParameters? '=' functionType ';'
  /// ;
  ///
  /// functionType:
  ///   returnType? 'Function' typeParameters? parameterTypeList
  ///
  /// typeAliasBody:
  ///   functionTypeAlias
  /// ;
  ///
  /// functionTypeAlias:
  ///   functionPrefix typeParameters? formalParameterList ‘;’
  /// ;
  ///
  /// functionPrefix:
  ///   returnType? identifier
  /// ;
  /// ```
  Token parseTypedef(Token typedefKeyword) {
    assert(optional('typedef', typedefKeyword));
    listener.beginUncategorizedTopLevelDeclaration(typedefKeyword);
    listener.beginFunctionTypeAlias(typedefKeyword);
    TypeInfo typeInfo = computeType(typedefKeyword, /* required = */ false);
    Token token = typeInfo.skipType(typedefKeyword);
    Token next = token.next;
    Token equals;
    TypeParamOrArgInfo typeParam =
        computeTypeParamOrArg(next, /* inDeclaration = */ true);
    if (typeInfo == noType && optional('=', typeParam.skip(next).next)) {
      // New style typedef, e.g. typedef foo = void Function();".

      // Parse as recovered here to 'force' using it as an identifier as we've
      // already established that the next token is the equal sign we're looking
      // for.
      token = ensureIdentifierPotentiallyRecovered(token,
          IdentifierContext.typedefDeclaration, /* isRecovered = */ true);

      token = typeParam.parseVariables(token, this);
      next = token.next;
      // parseVariables rewrites so even though we checked in the if,
      // we might not have an equal here now.
      if (!optional('=', next) && optional('=', next.next)) {
        // Recovery after recovery: A token was inserted, but we'll skip it now
        // to get more in line with what we thought in the if before.
        next = next.next;
      }
      if (optional('=', next)) {
        equals = next;
        TypeInfo type = computeType(equals, /* required = */ true);
        if (!type.isFunctionType) {
          // Recovery: In certain cases insert missing 'Function' and missing
          // parens.
          Token skippedType = type.skipType(equals);
          if (optional('(', skippedType.next) &&
              skippedType.next.endGroup != null &&
              optional(';', skippedType.next.endGroup.next)) {
            // Turn "<return type>? '(' <whatever> ')';"
            // into "<return type>? Function '(' <whatever> ')';".
            // Assume the type is meant as the return type.
            Token functionToken =
                rewriter.insertSyntheticKeyword(skippedType, Keyword.FUNCTION);
            reportRecoverableError(functionToken,
                codes.templateExpectedButGot.withArguments('Function'));
            type = computeType(equals, /* required = */ true);
          } else if (type is NoType &&
              optional('<', skippedType.next) &&
              skippedType.next.endGroup != null) {
            // Recover these two:
            // "<whatever>;" => "Function<whatever>();"
            // "<whatever>(<whatever>);" => "Function<whatever>(<whatever>);"
            Token endGroup = skippedType.next.endGroup;
            bool recover = false;
            if (optional(';', endGroup.next)) {
              // Missing parenthesis. Insert them.
              // Turn "<whatever>;" in to "<whatever>();"
              // Insert missing 'Function' below.
              reportRecoverableError(endGroup,
                  missingParameterMessage(MemberKind.FunctionTypeAlias));
              rewriter.insertParens(endGroup, /*includeIdentifier =*/ false);
              recover = true;
            } else if (optional('(', endGroup.next) &&
                endGroup.next.endGroup != null &&
                optional(';', endGroup.next.endGroup.next)) {
              // "<whatever>(<whatever>);". Insert missing 'Function' below.
              recover = true;
            }

            if (recover) {
              // Assume the '<' indicates type arguments to the function.
              // Insert 'Function' before them.
              Token functionToken =
                  rewriter.insertSyntheticKeyword(equals, Keyword.FUNCTION);
              reportRecoverableError(functionToken,
                  codes.templateExpectedButGot.withArguments('Function'));
              type = computeType(equals, /* required = */ true);
            }
          } else {
            // E.g. "typedef j = foo;" -- don't attempt any recovery.
          }
        }
        token = type.ensureTypeOrVoid(equals, this);
      } else {
        // A rewrite caused the = to disappear
        token = parseFormalParametersRequiredOpt(
            next, MemberKind.FunctionTypeAlias);
      }
    } else {
      // Old style typedef, e.g. "typedef void foo();".
      token = typeInfo.parseType(typedefKeyword, this);
      next = token.next;
      bool isIdentifierRecovered = false;
      if (next.kind != IDENTIFIER_TOKEN &&
          optional('(', typeParam.skip(next).next)) {
        // Recovery: Not a valid identifier, but is used as such.
        isIdentifierRecovered = true;
      }
      token = ensureIdentifierPotentiallyRecovered(
          token, IdentifierContext.typedefDeclaration, isIdentifierRecovered);
      token = typeParam.parseVariables(token, this);
      token =
          parseFormalParametersRequiredOpt(token, MemberKind.FunctionTypeAlias);
    }
    token = ensureSemicolon(token);
    listener.endFunctionTypeAlias(typedefKeyword, equals, token);
    return token;
  }

  /// Parse a mixin application starting from `with`. Assumes that the first
  /// type has already been parsed.
  Token parseMixinApplicationRest(Token token) {
    Token withKeyword = token.next;
    if (!optional('with', withKeyword)) {
      // Recovery: Report an error and insert synthetic `with` clause.
      reportRecoverableError(
          withKeyword, codes.templateExpectedButGot.withArguments('with'));
      withKeyword = rewriter.insertSyntheticKeyword(token, Keyword.WITH);
      if (!isValidTypeReference(withKeyword.next)) {
        rewriter.insertSyntheticIdentifier(withKeyword);
      }
    }
    token = parseTypeList(withKeyword);
    listener.handleNamedMixinApplicationWithClause(withKeyword);
    return token;
  }

  Token parseWithClauseOpt(Token token) {
    // <mixins> ::= with <typeNotVoidList>
    Token withKeyword = token.next;
    if (optional('with', withKeyword)) {
      token = parseTypeList(withKeyword);
      listener.handleClassWithClause(withKeyword);
    } else {
      listener.handleClassNoWithClause();
    }
    return token;
  }

  /// Parse the formal parameters of a getter (which shouldn't have parameters)
  /// or function or method.
  Token parseGetterOrFormalParameters(
      Token token, Token name, bool isGetter, MemberKind kind) {
    Token next = token.next;
    if (optional("(", next)) {
      if (isGetter) {
        reportRecoverableError(next, codes.messageGetterWithFormals);
      }
      token = parseFormalParameters(token, kind);
    } else if (isGetter) {
      listener.handleNoFormalParameters(next, kind);
    } else {
      // Recovery
      if (optional('operator', name)) {
        Token next = name.next;
        if (next.isOperator) {
          name = next;
        } else if (isUnaryMinus(next)) {
          name = next.next;
        }
      }
      reportRecoverableError(name, missingParameterMessage(kind));
      token = rewriter.insertParens(token, /* includeIdentifier = */ false);
      token = parseFormalParametersRest(token, kind);
    }
    return token;
  }

  Token parseFormalParametersOpt(Token token, MemberKind kind) {
    Token next = token.next;
    if (optional('(', next)) {
      token = parseFormalParameters(token, kind);
    } else {
      listener.handleNoFormalParameters(next, kind);
    }
    return token;
  }

  Token skipFormalParameters(Token token, MemberKind kind) {
    return skipFormalParametersRest(token.next, kind);
  }

  Token skipFormalParametersRest(Token token, MemberKind kind) {
    assert(optional('(', token));
    // TODO(ahe): Shouldn't this be `beginFormalParameters`?
    listener.beginOptionalFormalParameters(token);
    Token closeBrace = token.endGroup;
    assert(optional(')', closeBrace));
    listener.endFormalParameters(/* count = */ 0, token, closeBrace, kind);
    return closeBrace;
  }

  /// Parses the formal parameter list of a function.
  ///
  /// If `kind == MemberKind.GeneralizedFunctionType`, then names may be
  /// omitted (except for named arguments). Otherwise, types may be omitted.
  Token parseFormalParametersRequiredOpt(Token token, MemberKind kind) {
    Token next = token.next;
    if (!optional('(', next)) {
      reportRecoverableError(next, missingParameterMessage(kind));
      next = rewriter.insertParens(token, /* includeIdentifier = */ false);
    }
    return parseFormalParametersRest(next, kind);
  }

  /// Parses the formal parameter list of a function given that the left
  /// parenthesis is known to exist.
  ///
  /// If `kind == MemberKind.GeneralizedFunctionType`, then names may be
  /// omitted (except for named arguments). Otherwise, types may be omitted.
  Token parseFormalParameters(Token token, MemberKind kind) {
    return parseFormalParametersRest(token.next, kind);
  }

  /// Parses the formal parameter list of a function given that the left
  /// parenthesis passed in as [token].
  ///
  /// If `kind == MemberKind.GeneralizedFunctionType`, then names may be
  /// omitted (except for named arguments). Otherwise, types may be omitted.
  Token parseFormalParametersRest(Token token, MemberKind kind) {
    Token begin = token;
    assert(optional('(', token));
    listener.beginFormalParameters(begin, kind);
    int parameterCount = 0;
    while (true) {
      Token next = token.next;
      if (optional(')', next)) {
        token = next;
        break;
      }
      ++parameterCount;
      String value = next.stringValue;
      if (identical(value, '[')) {
        token = parseOptionalPositionalParameters(token, kind);
        token = ensureCloseParen(token, begin);
        break;
      } else if (identical(value, '{')) {
        token = parseOptionalNamedParameters(token, kind);
        token = ensureCloseParen(token, begin);
        break;
      } else if (identical(value, '[]')) {
        // Recovery
        token = rewriteSquareBrackets(token);
        token = parseOptionalPositionalParameters(token, kind);
        token = ensureCloseParen(token, begin);
        break;
      }
      token = parseFormalParameter(token, FormalParameterKind.mandatory, kind);
      next = token.next;
      if (!optional(',', next)) {
        Token next = token.next;
        if (optional(')', next)) {
          token = next;
        } else {
          // Recovery
          if (begin.endGroup.isSynthetic) {
            // Scanner has already reported a missing `)` error,
            // but placed the `)` in the wrong location, so move it.
            token = rewriter.moveSynthetic(token, begin.endGroup);
          } else if (next.kind == IDENTIFIER_TOKEN &&
              next.next.kind == IDENTIFIER_TOKEN) {
            // Looks like a missing comma
            token = rewriteAndRecover(
                token,
                codes.templateExpectedButGot.withArguments(','),
                new SyntheticToken(TokenType.COMMA, next.charOffset));
            continue;
          } else {
            token = ensureCloseParen(token, begin);
          }
        }
        break;
      }
      token = next;
    }
    assert(optional(')', token));
    listener.endFormalParameters(parameterCount, begin, token, kind);
    return token;
  }

  /// Return the message that should be produced when the formal parameters are
  /// missing.
  codes.Message missingParameterMessage(MemberKind kind) {
    if (kind == MemberKind.FunctionTypeAlias) {
      return codes.messageMissingTypedefParameters;
    } else if (kind == MemberKind.NonStaticMethod ||
        kind == MemberKind.StaticMethod) {
      return codes.messageMissingMethodParameters;
    }
    return codes.messageMissingFunctionParameters;
  }

  /// ```
  /// normalFormalParameter:
  ///   functionFormalParameter |
  ///   fieldFormalParameter |
  ///   simpleFormalParameter
  /// ;
  ///
  /// functionFormalParameter:
  ///   metadata 'covariant'? returnType? identifier formalParameterList
  /// ;
  ///
  /// simpleFormalParameter:
  ///   metadata 'covariant'? finalConstVarOrType? identifier |
  /// ;
  ///
  /// fieldFormalParameter:
  ///   metadata finalConstVarOrType? 'this' '.' identifier formalParameterList?
  /// ;
  /// ```
  Token parseFormalParameter(
      Token token, FormalParameterKind parameterKind, MemberKind memberKind) {
    assert(parameterKind != null);
    token = parseMetadataStar(token);
    Token next = token.next;
    Token start = next;

    final bool inFunctionType =
        memberKind == MemberKind.GeneralizedFunctionType;

    Token requiredToken;
    Token covariantToken;
    Token varFinalOrConst;
    if (isModifier(next)) {
      if (optional('required', next)) {
        if (parameterKind == FormalParameterKind.optionalNamed) {
          requiredToken = token = next;
          next = token.next;
        }
      }

      if (isModifier(next)) {
        if (optional('covariant', next)) {
          if (memberKind != MemberKind.StaticMethod &&
              memberKind != MemberKind.TopLevelMethod &&
              memberKind != MemberKind.ExtensionNonStaticMethod &&
              memberKind != MemberKind.ExtensionStaticMethod) {
            covariantToken = token = next;
            next = token.next;
          }
        }

        if (isModifier(next)) {
          if (!inFunctionType) {
            if (optional('var', next)) {
              varFinalOrConst = token = next;
              next = token.next;
            } else if (optional('final', next)) {
              varFinalOrConst = token = next;
              next = token.next;
            }
          }

          if (isModifier(next)) {
            // Recovery
            ModifierRecoveryContext context = new ModifierRecoveryContext(this)
              ..covariantToken = covariantToken
              ..requiredToken = requiredToken
              ..varFinalOrConst = varFinalOrConst;

            token = context.parseFormalParameterModifiers(
                token, parameterKind, memberKind);
            next = token.next;

            covariantToken = context.covariantToken;
            requiredToken = context.requiredToken;
            varFinalOrConst = context.varFinalOrConst;

            context = null;
          }
        }
      }
    }

    listener.beginFormalParameter(
        start, memberKind, requiredToken, covariantToken, varFinalOrConst);

    // Type is required in a generalized function type, but optional otherwise.
    final Token beforeType = token;
    TypeInfo typeInfo = computeType(token, inFunctionType);
    token = typeInfo.skipType(token);
    next = token.next;
    if (typeInfo == noType &&
        (optional('.', next) ||
            (next.isIdentifier && optional('.', next.next)))) {
      // Recovery: Malformed type reference.
      typeInfo = computeType(beforeType, /* required = */ true);
      token = typeInfo.skipType(beforeType);
      next = token.next;
    }

    final bool isNamedParameter =
        parameterKind == FormalParameterKind.optionalNamed;

    Token thisKeyword;
    Token periodAfterThis;
    IdentifierContext nameContext =
        IdentifierContext.formalParameterDeclaration;

    if (!inFunctionType && optional('this', next)) {
      thisKeyword = token = next;
      next = token.next;
      if (!optional('.', next)) {
        // Recover from a missing period by inserting one.
        next = rewriteAndRecover(
            token,
            codes.templateExpectedButGot.withArguments('.'),
            new SyntheticToken(TokenType.PERIOD, next.charOffset));
      }
      periodAfterThis = token = next;
      next = token.next;
      nameContext = IdentifierContext.fieldInitializer;
    }

    if (next.isIdentifier) {
      token = next;
      next = token.next;
    }
    Token beforeInlineFunctionType;
    TypeParamOrArgInfo typeParam = noTypeParamOrArg;
    if (optional("<", next)) {
      typeParam = computeTypeParamOrArg(token);
      if (typeParam != noTypeParamOrArg) {
        Token closer = typeParam.skip(token);
        if (optional("(", closer.next)) {
          if (varFinalOrConst != null) {
            reportRecoverableError(
                varFinalOrConst, codes.messageFunctionTypedParameterVar);
          }
          beforeInlineFunctionType = token;
          token = closer.next.endGroup;
          next = token.next;
        }
      }
    } else if (optional("(", next)) {
      if (varFinalOrConst != null) {
        reportRecoverableError(
            varFinalOrConst, codes.messageFunctionTypedParameterVar);
      }
      beforeInlineFunctionType = token;
      token = next.endGroup;
      next = token.next;
    }
    if (typeInfo != noType &&
        varFinalOrConst != null &&
        optional('var', varFinalOrConst)) {
      reportRecoverableError(varFinalOrConst, codes.messageTypeAfterVar);
    }

    Token endInlineFunctionType;
    if (beforeInlineFunctionType != null) {
      endInlineFunctionType =
          typeParam.parseVariables(beforeInlineFunctionType, this);
      listener.beginFunctionTypedFormalParameter(beforeInlineFunctionType.next);
      token = typeInfo.parseType(beforeType, this);
      endInlineFunctionType = parseFormalParametersRequiredOpt(
          endInlineFunctionType, MemberKind.FunctionTypedParameter);
      Token question;
      if (optional('?', endInlineFunctionType.next)) {
        question = endInlineFunctionType = endInlineFunctionType.next;
      }
      listener.endFunctionTypedFormalParameter(
          beforeInlineFunctionType, question);

      // Generalized function types don't allow inline function types.
      // The following isn't allowed:
      //    int Function(int bar(String x)).
      if (inFunctionType) {
        reportRecoverableError(beforeInlineFunctionType.next,
            codes.messageInvalidInlineFunctionType);
      }
    } else if (inFunctionType) {
      token = typeInfo.ensureTypeOrVoid(beforeType, this);
    } else {
      token = typeInfo.parseType(beforeType, this);
    }

    Token nameToken;
    if (periodAfterThis != null) {
      token = periodAfterThis;
    }
    next = token.next;
    if (inFunctionType &&
        !isNamedParameter &&
        !next.isKeywordOrIdentifier &&
        beforeInlineFunctionType == null) {
      nameToken = token.next;
      listener.handleNoName(nameToken);
    } else {
      nameToken = token = ensureIdentifier(token, nameContext);
      if (isNamedParameter && nameToken.lexeme.startsWith("_")) {
        reportRecoverableError(nameToken, codes.messagePrivateNamedParameter);
      }
    }
    if (endInlineFunctionType != null) {
      token = endInlineFunctionType;
    }
    next = token.next;

    String value = next.stringValue;
    Token initializerStart, initializerEnd;
    if ((identical('=', value)) || (identical(':', value))) {
      Token equal = next;
      initializerStart = equal.next;
      listener.beginFormalParameterDefaultValueExpression();
      token = initializerEnd = parseExpression(equal);
      next = token.next;
      listener.endFormalParameterDefaultValueExpression();
      // TODO(danrubel): Consider removing the last parameter from the
      // handleValuedFormalParameter event... it appears to be unused.
      listener.handleValuedFormalParameter(equal, next);
      if (isMandatoryFormalParameterKind(parameterKind)) {
        reportRecoverableError(
            equal, codes.messageRequiredParameterWithDefault);
      } else if (isOptionalPositionalFormalParameterKind(parameterKind) &&
          identical(':', value)) {
        reportRecoverableError(
            equal, codes.messagePositionalParameterWithEquals);
      } else if (inFunctionType ||
          memberKind == MemberKind.FunctionTypeAlias ||
          memberKind == MemberKind.FunctionTypedParameter) {
        reportRecoverableError(equal, codes.messageFunctionTypeDefaultValue);
      }
    } else {
      listener.handleFormalParameterWithoutValue(next);
    }
    listener.endFormalParameter(thisKeyword, periodAfterThis, nameToken,
        initializerStart, initializerEnd, parameterKind, memberKind);
    return token;
  }

  /// ```
  /// defaultFormalParameter:
  ///   normalFormalParameter ('=' expression)?
  /// ;
  /// ```
  Token parseOptionalPositionalParameters(Token token, MemberKind kind) {
    Token begin = token = token.next;
    assert(optional('[', token));
    listener.beginOptionalFormalParameters(begin);
    int parameterCount = 0;
    while (true) {
      Token next = token.next;
      if (optional(']', next)) {
        break;
      }
      token = parseFormalParameter(
          token, FormalParameterKind.optionalPositional, kind);
      next = token.next;
      ++parameterCount;
      if (!optional(',', next)) {
        if (!optional(']', next)) {
          // Recovery
          reportRecoverableError(
              next, codes.templateExpectedButGot.withArguments(']'));
          // Scanner guarantees a closing bracket.
          next = begin.endGroup;
          while (token.next != next) {
            token = token.next;
          }
        }
        break;
      }
      token = next;
    }
    if (parameterCount == 0) {
      rewriteAndRecover(
          token,
          codes.messageEmptyOptionalParameterList,
          new SyntheticStringToken(TokenType.IDENTIFIER, '',
              token.next.charOffset, /* _length = */ 0));
      token = parseFormalParameter(
          token, FormalParameterKind.optionalPositional, kind);
      ++parameterCount;
    }
    token = token.next;
    assert(optional(']', token));
    listener.endOptionalFormalParameters(parameterCount, begin, token);
    return token;
  }

  /// ```
  /// defaultNamedParameter:
  ///   normalFormalParameter ('=' expression)? |
  ///   normalFormalParameter (':' expression)?
  /// ;
  /// ```
  Token parseOptionalNamedParameters(Token token, MemberKind kind) {
    Token begin = token = token.next;
    assert(optional('{', token));
    listener.beginOptionalFormalParameters(begin);
    int parameterCount = 0;
    while (true) {
      Token next = token.next;
      if (optional('}', next)) {
        break;
      }
      token =
          parseFormalParameter(token, FormalParameterKind.optionalNamed, kind);
      next = token.next;
      ++parameterCount;
      if (!optional(',', next)) {
        if (!optional('}', next)) {
          // Recovery
          reportRecoverableError(
              next, codes.templateExpectedButGot.withArguments('}'));
          // Scanner guarantees a closing bracket.
          next = begin.endGroup;
          while (token.next != next) {
            token = token.next;
          }
        }
        break;
      }
      token = next;
    }
    if (parameterCount == 0) {
      rewriteAndRecover(
          token,
          codes.messageEmptyNamedParameterList,
          new SyntheticStringToken(TokenType.IDENTIFIER, '',
              token.next.charOffset, /* _length = */ 0));
      token =
          parseFormalParameter(token, FormalParameterKind.optionalNamed, kind);
      ++parameterCount;
    }
    token = token.next;
    assert(optional('}', token));
    listener.endOptionalFormalParameters(parameterCount, begin, token);
    return token;
  }

  /// ```
  /// qualified:
  ///   identifier qualifiedRest*
  /// ;
  /// ```
  Token parseQualified(Token token, IdentifierContext context,
      IdentifierContext continuationContext) {
    token = ensureIdentifier(token, context);
    while (optional('.', token.next)) {
      token = parseQualifiedRest(token, continuationContext);
    }
    return token;
  }

  /// ```
  /// qualifiedRestOpt:
  ///   qualifiedRest?
  /// ;
  /// ```
  Token parseQualifiedRestOpt(
      Token token, IdentifierContext continuationContext) {
    if (optional('.', token.next)) {
      return parseQualifiedRest(token, continuationContext);
    } else {
      return token;
    }
  }

  /// ```
  /// qualifiedRest:
  ///   '.' identifier
  /// ;
  /// ```
  Token parseQualifiedRest(Token token, IdentifierContext context) {
    token = token.next;
    assert(optional('.', token));
    Token period = token;
    token = ensureIdentifier(token, context);
    listener.handleQualified(period);
    return token;
  }

  Token skipBlock(Token token) {
    // The scanner ensures that `{` always has a closing `}`.
    return ensureBlock(
            token, /* template = */ null, /* missingBlockName = */ null)
        .endGroup;
  }

  /// ```
  /// enumType:
  ///   metadata 'enum' id '{' metadata id [',' metadata id]* [','] '}'
  /// ;
  /// ```
  Token parseEnum(Token enumKeyword) {
    assert(optional('enum', enumKeyword));
    listener.beginUncategorizedTopLevelDeclaration(enumKeyword);
    listener.beginEnum(enumKeyword);
    Token token =
        ensureIdentifier(enumKeyword, IdentifierContext.enumDeclaration);
    Token leftBrace = token.next;
    int count = 0;
    if (optional('{', leftBrace)) {
      token = leftBrace;
      while (true) {
        Token next = token.next;
        if (optional('}', next)) {
          token = next;
          if (count == 0) {
            reportRecoverableError(token, codes.messageEnumDeclarationEmpty);
          }
          break;
        }
        token = parseMetadataStar(token);
        token = ensureIdentifier(token, IdentifierContext.enumValueDeclaration);
        next = token.next;
        count++;
        if (optional(',', next)) {
          token = next;
        } else if (optional('}', next)) {
          token = next;
          break;
        } else {
          // Recovery
          Token endGroup = leftBrace.endGroup;
          if (endGroup.isSynthetic) {
            // The scanner did not place the synthetic '}' correctly.
            token = rewriter.moveSynthetic(token, endGroup);
            break;
          } else if (next.isIdentifier) {
            // If the next token is an identifier, assume a missing comma.
            // TODO(danrubel): Consider improved recovery for missing `}`
            // both here and when the scanner inserts a synthetic `}`
            // for situations such as `enum Letter {a, b   Letter e;`.
            reportRecoverableError(
                next, codes.templateExpectedButGot.withArguments(','));
          } else {
            // Otherwise assume a missing `}` and exit the loop
            reportRecoverableError(
                next, codes.templateExpectedButGot.withArguments('}'));
            token = leftBrace.endGroup;
            break;
          }
        }
      }
    } else {
      // TODO(danrubel): merge this error message with missing class/mixin body
      leftBrace = ensureBlock(
          token, codes.templateExpectedEnumBody, /* missingBlockName = */ null);
      token = leftBrace.endGroup;
    }
    assert(optional('}', token));
    listener.endEnum(enumKeyword, leftBrace, count);
    return token;
  }

  Token parseClassOrNamedMixinApplication(
      Token abstractToken, Token classKeyword) {
    assert(optional('class', classKeyword));
    Token begin = abstractToken ?? classKeyword;
    listener.beginClassOrNamedMixinApplicationPrelude(begin);
    Token name = ensureIdentifier(
        classKeyword, IdentifierContext.classOrMixinOrExtensionDeclaration);
    Token token = computeTypeParamOrArg(
            name, /* inDeclaration = */ true, /* allowsVariance = */ true)
        .parseVariables(name, this);
    if (optional('=', token.next)) {
      listener.beginNamedMixinApplication(begin, abstractToken, name);
      return parseNamedMixinApplication(token, begin, classKeyword);
    } else {
      listener.beginClassDeclaration(begin, abstractToken, name);
      return parseClass(token, begin, classKeyword, name.lexeme);
    }
  }

  Token parseNamedMixinApplication(
      Token token, Token begin, Token classKeyword) {
    Token equals = token = token.next;
    assert(optional('=', equals));
    token = computeType(token, /* required = */ true)
        .ensureTypeNotVoid(token, this);
    token = parseMixinApplicationRest(token);
    Token implementsKeyword = null;
    if (optional('implements', token.next)) {
      implementsKeyword = token.next;
      token = parseTypeList(implementsKeyword);
    }
    token = ensureSemicolon(token);
    listener.endNamedMixinApplication(
        begin, classKeyword, equals, implementsKeyword, token);
    return token;
  }

  /// Parse the portion of a class declaration (not a mixin application) that
  /// follows the end of the type parameters.
  ///
  /// ```
  /// classDefinition:
  ///   metadata abstract? 'class' identifier typeParameters?
  ///       (superclass mixins?)? interfaces?
  ///       '{' (metadata classMemberDefinition)* '}' |
  ///   metadata abstract? 'class' mixinApplicationClass
  /// ;
  /// ```
  Token parseClass(
      Token token, Token begin, Token classKeyword, String className) {
    Token start = token;
    token = parseClassHeaderOpt(token, begin, classKeyword);
    if (!optional('{', token.next)) {
      // Recovery
      token = parseClassHeaderRecovery(start, begin, classKeyword);
      ensureBlock(token, /* template = */ null, 'class declaration');
    }
    token = parseClassOrMixinOrExtensionBody(
        token, DeclarationKind.Class, className);
    listener.endClassDeclaration(begin, token);
    return token;
  }

  Token parseClassHeaderOpt(Token token, Token begin, Token classKeyword) {
    token = parseClassExtendsOpt(token);
    token = parseWithClauseOpt(token);
    token = parseClassOrMixinImplementsOpt(token);
    Token nativeToken;
    if (optional('native', token.next)) {
      nativeToken = token.next;
      token = parseNativeClause(token);
    }
    listener.handleClassHeader(begin, classKeyword, nativeToken);
    return token;
  }

  /// Recover given out-of-order clauses in a class header.
  Token parseClassHeaderRecovery(Token token, Token begin, Token classKeyword) {
    final Listener primaryListener = listener;
    final ClassHeaderRecoveryListener recoveryListener =
        new ClassHeaderRecoveryListener();

    // Reparse to determine which clauses have already been parsed
    // but intercept the events so they are not sent to the primary listener.
    listener = recoveryListener;
    token = parseClassHeaderOpt(token, begin, classKeyword);
    bool hasExtends = recoveryListener.extendsKeyword != null;
    bool hasImplements = recoveryListener.implementsKeyword != null;
    bool hasWith = recoveryListener.withKeyword != null;

    // Update the recovery listener to forward subsequent events
    // to the primary listener.
    recoveryListener.listener = primaryListener;

    // Parse additional out-of-order clauses
    Token start;
    do {
      start = token;

      // Check for extraneous token in the middle of a class header.
      token = skipUnexpectedTokenOpt(
          token, const <String>['extends', 'with', 'implements', '{']);

      // During recovery, clauses are parsed in the same order
      // and generate the same events as in the parseClassHeader method above.
      recoveryListener.clear();

      if (token.next.isKeywordOrIdentifier &&
          const ['extend', 'on'].contains(token.next.lexeme)) {
        reportRecoverableError(
            token.next, codes.templateExpectedInstead.withArguments('extends'));
        token = parseClassExtendsSeenExtendsClause(token.next, token);
      } else {
        token = parseClassExtendsOpt(token);
      }

      if (recoveryListener.extendsKeyword != null) {
        if (hasExtends) {
          reportRecoverableError(
              recoveryListener.extendsKeyword, codes.messageMultipleExtends);
        } else {
          if (hasWith) {
            reportRecoverableError(recoveryListener.extendsKeyword,
                codes.messageWithBeforeExtends);
          } else if (hasImplements) {
            reportRecoverableError(recoveryListener.extendsKeyword,
                codes.messageImplementsBeforeExtends);
          }
          hasExtends = true;
        }
      }

      token = parseWithClauseOpt(token);

      if (recoveryListener.withKeyword != null) {
        if (hasWith) {
          reportRecoverableError(
              recoveryListener.withKeyword, codes.messageMultipleWith);
        } else {
          if (hasImplements) {
            reportRecoverableError(recoveryListener.withKeyword,
                codes.messageImplementsBeforeWith);
          }
          hasWith = true;
        }
      }

      token = parseClassOrMixinImplementsOpt(token);

      if (recoveryListener.implementsKeyword != null) {
        if (hasImplements) {
          reportRecoverableError(recoveryListener.implementsKeyword,
              codes.messageMultipleImplements);
        } else {
          hasImplements = true;
        }
      }

      listener.handleRecoverClassHeader();

      // Exit if a class body is detected, or if no progress has been made
    } while (!optional('{', token.next) && start != token);

    listener = primaryListener;
    return token;
  }

  Token parseClassExtendsOpt(Token token) {
    // extends <typeNotVoid>
    Token next = token.next;
    if (optional('extends', next)) {
      token = parseClassExtendsSeenExtendsClause(next, token);
    } else {
      listener.handleNoType(token);
      listener.handleClassExtends(
          /* extendsKeyword = */ null,
          /* typeCount = */ 1);
    }
    return token;
  }

  Token parseClassExtendsSeenExtendsClause(Token extendsKeyword, Token token) {
    Token next = extendsKeyword;
    token =
        computeType(next, /* required = */ true).ensureTypeNotVoid(next, this);
    int count = 1;

    // Error recovery: extends <typeNotVoid>, <typeNotVoid> [...]
    if (optional(',', token.next)) {
      reportRecoverableError(token.next, codes.messageMultipleExtends);

      while (optional(',', token.next)) {
        next = token.next;
        token = computeType(next, /* required = */ true)
            .ensureTypeNotVoid(next, this);
        count++;
      }
    }

    listener.handleClassExtends(extendsKeyword, count);
    return token;
  }

  /// ```
  /// implementsClause:
  ///   'implements' typeName (',' typeName)*
  /// ;
  /// ```
  Token parseClassOrMixinImplementsOpt(Token token) {
    Token implementsKeyword;
    int interfacesCount = 0;
    if (optional('implements', token.next)) {
      implementsKeyword = token.next;
      do {
        token = computeType(token.next, /* required = */ true)
            .ensureTypeNotVoid(token.next, this);
        ++interfacesCount;
      } while (optional(',', token.next));
    }
    listener.handleClassOrMixinImplements(implementsKeyword, interfacesCount);
    return token;
  }

  /// Parse a mixin declaration.
  ///
  /// ```
  /// mixinDeclaration:
  ///   metadata? 'mixin' [SimpleIdentifier] [TypeParameterList]?
  ///        [OnClause]? [ImplementsClause]? '{' [ClassMember]* '}'
  /// ;
  /// ```
  Token parseMixin(Token mixinKeyword) {
    assert(optional('mixin', mixinKeyword));
    listener.beginClassOrNamedMixinApplicationPrelude(mixinKeyword);
    Token name = ensureIdentifier(
        mixinKeyword, IdentifierContext.classOrMixinOrExtensionDeclaration);
    Token headerStart = computeTypeParamOrArg(
            name, /* inDeclaration = */ true, /* allowsVariance = */ true)
        .parseVariables(name, this);
    listener.beginMixinDeclaration(mixinKeyword, name);
    Token token = parseMixinHeaderOpt(headerStart, mixinKeyword);
    if (!optional('{', token.next)) {
      // Recovery
      token = parseMixinHeaderRecovery(token, mixinKeyword, headerStart);
      ensureBlock(token, /* template = */ null, 'mixin declaration');
    }
    token = parseClassOrMixinOrExtensionBody(
        token, DeclarationKind.Mixin, name.lexeme);
    listener.endMixinDeclaration(mixinKeyword, token);
    return token;
  }

  Token parseMixinHeaderOpt(Token token, Token mixinKeyword) {
    token = parseMixinOnOpt(token);
    token = parseClassOrMixinImplementsOpt(token);
    listener.handleMixinHeader(mixinKeyword);
    return token;
  }

  Token parseMixinHeaderRecovery(
      Token token, Token mixinKeyword, Token headerStart) {
    final Listener primaryListener = listener;
    final MixinHeaderRecoveryListener recoveryListener =
        new MixinHeaderRecoveryListener();

    // Reparse to determine which clauses have already been parsed
    // but intercept the events so they are not sent to the primary listener.
    listener = recoveryListener;
    token = parseMixinHeaderOpt(headerStart, mixinKeyword);
    bool hasOn = recoveryListener.onKeyword != null;
    bool hasImplements = recoveryListener.implementsKeyword != null;

    // Update the recovery listener to forward subsequent events
    // to the primary listener.
    recoveryListener.listener = primaryListener;

    // Parse additional out-of-order clauses
    Token start;
    do {
      start = token;

      // Check for extraneous token in the middle of a class header.
      token = skipUnexpectedTokenOpt(
          token, const <String>['on', 'implements', '{']);

      // During recovery, clauses are parsed in the same order and
      // generate the same events as in the parseMixinHeaderOpt method above.
      recoveryListener.clear();

      if (token.next.isKeywordOrIdentifier &&
          const ['extend', 'extends'].contains(token.next.lexeme)) {
        reportRecoverableError(
            token.next, codes.templateExpectedInstead.withArguments('on'));
        token = parseMixinOn(token);
      } else {
        token = parseMixinOnOpt(token);
      }

      if (recoveryListener.onKeyword != null) {
        if (hasOn) {
          reportRecoverableError(
              recoveryListener.onKeyword, codes.messageMultipleOnClauses);
        } else {
          if (hasImplements) {
            reportRecoverableError(
                recoveryListener.onKeyword, codes.messageImplementsBeforeOn);
          }
          hasOn = true;
        }
      }

      token = parseClassOrMixinImplementsOpt(token);

      if (recoveryListener.implementsKeyword != null) {
        if (hasImplements) {
          reportRecoverableError(recoveryListener.implementsKeyword,
              codes.messageMultipleImplements);
        } else {
          hasImplements = true;
        }
      }

      listener.handleRecoverMixinHeader();

      // Exit if a mixin body is detected, or if no progress has been made
    } while (!optional('{', token.next) && start != token);

    listener = primaryListener;
    return token;
  }

  /// ```
  /// onClause:
  ///   'on' typeName (',' typeName)*
  /// ;
  /// ```
  Token parseMixinOnOpt(Token token) {
    if (!optional('on', token.next)) {
      listener.handleMixinOn(/* onKeyword = */ null, /* typeCount = */ 0);
      return token;
    }
    return parseMixinOn(token);
  }

  Token parseMixinOn(Token token) {
    Token onKeyword = token.next;
    // During recovery, the [onKeyword] can be "extend" or "extends"
    assert(optional('on', onKeyword) ||
        optional('extends', onKeyword) ||
        onKeyword.lexeme == 'extend');
    int typeCount = 0;
    do {
      token = computeType(token.next, /* required = */ true)
          .ensureTypeNotVoid(token.next, this);
      ++typeCount;
    } while (optional(',', token.next));
    listener.handleMixinOn(onKeyword, typeCount);
    return token;
  }

  /// ```
  /// 'extension' <identifier>? <typeParameters>? 'on' <type> '?'?
  //   `{'
  //     <memberDeclaration>*
  //   `}'
  /// ```
  Token parseExtension(Token extensionKeyword) {
    assert(optional('extension', extensionKeyword));
    Token token = extensionKeyword;
    listener.beginExtensionDeclarationPrelude(extensionKeyword);
    Token name = token.next;
    if (name.isIdentifier && !optional('on', name)) {
      token = name;
      if (name.type.isBuiltIn) {
        reportRecoverableErrorWithToken(
            token, codes.templateBuiltInIdentifierInDeclaration);
      }
    } else {
      name = null;
    }
    token = computeTypeParamOrArg(token, /* inDeclaration = */ true)
        .parseVariables(token, this);
    listener.beginExtensionDeclaration(extensionKeyword, name);
    Token onKeyword = token.next;
    if (!optional('on', onKeyword)) {
      // Recovery
      if (optional('extends', onKeyword) ||
          optional('implements', onKeyword) ||
          optional('with', onKeyword)) {
        reportRecoverableError(
            onKeyword, codes.templateExpectedInstead.withArguments('on'));
      } else {
        reportRecoverableError(
            token, codes.templateExpectedAfterButGot.withArguments('on'));
        onKeyword = rewriter.insertSyntheticKeyword(token, Keyword.ON);
      }
    }
    TypeInfo typeInfo = computeType(onKeyword, /* required = */ true);
    token = typeInfo.ensureTypeOrVoid(onKeyword, this);
    if (!optional('{', token.next)) {
      // Recovery
      Token next = token.next;
      while (!next.isEof) {
        if (optional(',', next) ||
            optional('extends', next) ||
            optional('implements', next) ||
            optional('on', next) ||
            optional('with', next)) {
          // Report an error and skip `,` or specific keyword
          // optionally followed by an identifier
          reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
          token = next;
          next = token.next;
          if (next.isIdentifier) {
            token = next;
            next = token.next;
          }
        } else {
          break;
        }
      }
      ensureBlock(token, /* template = */ null, 'extension declaration');
    }
    token = parseClassOrMixinOrExtensionBody(
        token, DeclarationKind.Extension, name?.lexeme);
    listener.endExtensionDeclaration(extensionKeyword, onKeyword, token);
    return token;
  }

  Token parseStringPart(Token token) {
    Token next = token.next;
    if (next.kind != STRING_TOKEN) {
      reportRecoverableErrorWithToken(next, codes.templateExpectedString);
      next = rewriter.insertToken(token,
          new SyntheticStringToken(TokenType.STRING, '', next.charOffset));
    }
    listener.handleStringPart(next);
    return next;
  }

  /// Insert a synthetic identifier after the given [token] and create an error
  /// message based on the given [context]. Return the synthetic identifier that
  /// was inserted.
  Token insertSyntheticIdentifier(Token token, IdentifierContext context,
      {codes.Message message, Token messageOnToken}) {
    Token next = token.next;
    reportRecoverableError(messageOnToken ?? next,
        message ?? context.recoveryTemplate.withArguments(next));
    return rewriter.insertSyntheticIdentifier(token);
  }

  /// Parse a simple identifier at the given [token], and return the identifier
  /// that was parsed.
  ///
  /// If the token is not an identifier, or is not appropriate for use as an
  /// identifier in the given [context], create a synthetic identifier, report
  /// an error, and return the synthetic identifier.
  Token ensureIdentifier(Token token, IdentifierContext context) {
    assert(context != null);
    Token identifier = token.next;
    if (identifier.kind != IDENTIFIER_TOKEN) {
      identifier = context.ensureIdentifier(token, this);
      assert(identifier != null);
      assert(identifier.isKeywordOrIdentifier);
    }
    listener.handleIdentifier(identifier, context);
    return identifier;
  }

  /// Parse a simple identifier at the given [token], and return the identifier
  /// that was parsed.
  ///
  /// If the token is not an identifier, or is not appropriate for use as an
  /// identifier in the given [context], create a synthetic identifier, report
  /// an error, and return the synthetic identifier.
  /// [isRecovered] is passed to [context] which - if true - allows implementers
  /// to use the token as an identifier, even if it isn't a valid identifier.
  Token ensureIdentifierPotentiallyRecovered(
      Token token, IdentifierContext context, bool isRecovered) {
    assert(context != null);
    Token identifier = token.next;
    if (identifier.kind != IDENTIFIER_TOKEN) {
      identifier = context.ensureIdentifierPotentiallyRecovered(
          token, this, isRecovered);
      assert(identifier != null);
      assert(identifier.isKeywordOrIdentifier);
    }
    listener.handleIdentifier(identifier, context);
    return identifier;
  }

  bool notEofOrValue(String value, Token token) {
    return !identical(token.kind, EOF_TOKEN) &&
        !identical(value, token.stringValue);
  }

  Token parseTypeVariablesOpt(Token token) {
    return computeTypeParamOrArg(token, /* inDeclaration = */ true)
        .parseVariables(token, this);
  }

  /// Parse a top level field or function.
  ///
  /// This method is only invoked from outside the parser. As a result, this
  /// method takes the next token to be consumed rather than the last consumed
  /// token and returns the token after the last consumed token rather than the
  /// last consumed token.
  Token parseTopLevelMember(Token token) {
    token = parseMetadataStar(syntheticPreviousToken(token));
    return parseTopLevelMemberImpl(token).next;
  }

  Token parseTopLevelMemberImpl(Token token) {
    Token beforeStart = token;
    Token next = token.next;
    listener.beginTopLevelMember(next);

    Token externalToken;
    Token lateToken;
    Token varFinalOrConst;

    if (isModifier(next)) {
      if (optional('external', next)) {
        externalToken = token = next;
        next = token.next;
      }
      if (isModifier(next)) {
        if (optional('final', next)) {
          varFinalOrConst = token = next;
          next = token.next;
        } else if (optional('var', next)) {
          varFinalOrConst = token = next;
          next = token.next;
        } else if (optional('const', next)) {
          varFinalOrConst = token = next;
          next = token.next;
        } else if (optional('late', next)) {
          lateToken = token = next;
          next = token.next;
          if (isModifier(next) && optional('final', next)) {
            varFinalOrConst = token = next;
            next = token.next;
          }
        }
        if (isModifier(next)) {
          // Recovery
          if (varFinalOrConst != null &&
              (optional('final', next) ||
                  optional('var', next) ||
                  optional('const', next))) {
            // If another `var`, `final`, or `const` then fall through
            // to parse that as part of the next top level declaration.
          } else {
            ModifierRecoveryContext context = new ModifierRecoveryContext(this)
              ..externalToken = externalToken
              ..lateToken = lateToken
              ..varFinalOrConst = varFinalOrConst;

            token = context.parseTopLevelModifiers(token);
            next = token.next;

            externalToken = context.externalToken;
            lateToken = context.lateToken;
            varFinalOrConst = context.varFinalOrConst;

            context = null;
          }
        }
      }
    }

    Token beforeType = token;
    TypeInfo typeInfo =
        computeType(token, /* required = */ false, /* inDeclaration = */ true);
    token = typeInfo.skipType(token);
    next = token.next;

    Token getOrSet;
    String value = next.stringValue;
    if (identical(value, 'get') || identical(value, 'set')) {
      if (next.next.isIdentifier) {
        getOrSet = token = next;
        next = token.next;
      }
    }

    bool nameIsRecovered = false;

    // Recovery: If the code is
    // <return type>? <reserved word> <token indicating method or field>
    // take the reserved keyword as the name.
    if (typeInfo == noType &&
        varFinalOrConst == null &&
        isReservedKeyword(next.next) &&
        indicatesMethodOrField(next.next.next)) {
      // Recovery: Use the reserved keyword despite that not being legal.
      typeInfo = computeType(
          token,
          /*required = */ true,
          /* inDeclaration = */ true);
      token = typeInfo.skipType(token);
      next = token.next;
      nameIsRecovered = true;
    }

    if (next.type != TokenType.IDENTIFIER) {
      value = next.stringValue;
      if (identical(value, 'factory') || identical(value, 'operator')) {
        // `factory` and `operator` can be used as an identifier.
        value = next.next.stringValue;
        if (getOrSet == null &&
            !identical(value, '(') &&
            !identical(value, '{') &&
            !identical(value, '<') &&
            !identical(value, '=>') &&
            !identical(value, '=') &&
            !identical(value, ';') &&
            !identical(value, ',')) {
          // Recovery
          value = next.stringValue;
          if (identical(value, 'factory')) {
            reportRecoverableError(
                next, codes.messageFactoryTopLevelDeclaration);
          } else {
            reportRecoverableError(next, codes.messageTopLevelOperator);
            if (next.next.isOperator) {
              token = next;
              next = token.next;
              if (optional('(', next.next)) {
                rewriter.insertSyntheticIdentifier(
                    next, '#synthetic_identifier_${next.charOffset}');
              }
            }
          }
          listener.handleInvalidTopLevelDeclaration(next);
          return next;
        }
        // Fall through and continue parsing
      } else if (!next.isIdentifier) {
        // Recovery
        if (next.isKeyword) {
          // Fall through to parse the keyword as the identifier.
          // ensureIdentifier will report the error.
        } else if (token == beforeStart) {
          // Ensure we make progress.
          return parseInvalidTopLevelDeclaration(token);
        } else {
          // Looks like a declaration missing an identifier.
          // Insert synthetic identifier and fall through.
          insertSyntheticIdentifier(token, IdentifierContext.methodDeclaration);
          next = token.next;
        }
      }
    }
    // At this point, `token` is beforeName.

    // Recovery: Inserted ! after method name.
    if (optional('!', next.next)) {
      next = next.next;
    }

    next = next.next;
    value = next.stringValue;
    if (getOrSet != null ||
        identical(value, '(') ||
        identical(value, '{') ||
        identical(value, '<') ||
        identical(value, '.') ||
        identical(value, '=>')) {
      if (varFinalOrConst != null) {
        if (optional('var', varFinalOrConst)) {
          reportRecoverableError(varFinalOrConst, codes.messageVarReturnType);
        } else {
          reportRecoverableErrorWithToken(
              varFinalOrConst, codes.templateExtraneousModifier);
        }
      } else if (lateToken != null) {
        reportRecoverableErrorWithToken(
            lateToken, codes.templateExtraneousModifier);
      }
      return parseTopLevelMethod(beforeStart, externalToken, beforeType,
          typeInfo, getOrSet, token.next, nameIsRecovered);
    }

    if (getOrSet != null) {
      reportRecoverableErrorWithToken(
          getOrSet, codes.templateExtraneousModifier);
    }
    return parseFields(
        beforeStart,
        /* abstractToken = */ null,
        externalToken,
        /* staticToken = */ null,
        /* covariantToken = */ null,
        lateToken,
        varFinalOrConst,
        beforeType,
        typeInfo,
        token.next,
        DeclarationKind.TopLevel,
        /* enclosingDeclarationName = */ null,
        nameIsRecovered);
  }

  Token parseFields(
      Token beforeStart,
      Token abstractToken,
      Token externalToken,
      Token staticToken,
      Token covariantToken,
      Token lateToken,
      Token varFinalOrConst,
      Token beforeType,
      TypeInfo typeInfo,
      Token name,
      DeclarationKind kind,
      String enclosingDeclarationName,
      bool nameIsRecovered) {
    listener.beginFields(beforeStart);

    // Covariant affects only the setter and final fields do not have a setter,
    // unless it's a late field (dartbug.com/40805).
    // Field that are covariant late final with initializers are checked further
    // down.
    if (covariantToken != null && lateToken == null) {
      if (varFinalOrConst != null && optional('final', varFinalOrConst)) {
        reportRecoverableError(covariantToken, codes.messageFinalAndCovariant);
        covariantToken = null;
      }
    }
    if (typeInfo == noType) {
      if (varFinalOrConst == null) {
        reportRecoverableError(name, codes.messageMissingConstFinalVarOrType);
      }
    } else {
      if (varFinalOrConst != null && optional('var', varFinalOrConst)) {
        reportRecoverableError(varFinalOrConst, codes.messageTypeAfterVar);
      }
    }
    if (abstractToken != null && externalToken != null) {
      reportRecoverableError(abstractToken, codes.messageAbstractExternalField);
    }

    Token token = typeInfo.parseType(beforeType, this);
    assert(token.next == name || token.next.isEof);

    IdentifierContext context = kind == DeclarationKind.TopLevel
        ? IdentifierContext.topLevelVariableDeclaration
        : IdentifierContext.fieldDeclaration;
    Token firstName = name = ensureIdentifierPotentiallyRecovered(
        token, context, /* isRecovered = */ nameIsRecovered);

    // Check for covariant late final with initializer.
    if (covariantToken != null && lateToken != null) {
      if (varFinalOrConst != null && optional('final', varFinalOrConst)) {
        Token next = name.next;
        if (optional('=', next)) {
          reportRecoverableError(covariantToken,
              codes.messageFinalAndCovariantLateWithInitializer);
          covariantToken = null;
        }
      }
    }

    int fieldCount = 1;
    token = parseFieldInitializerOpt(name, name, lateToken, abstractToken,
        externalToken, varFinalOrConst, kind, enclosingDeclarationName);
    while (optional(',', token.next)) {
      name = ensureIdentifier(token.next, context);
      token = parseFieldInitializerOpt(name, name, lateToken, abstractToken,
          externalToken, varFinalOrConst, kind, enclosingDeclarationName);
      ++fieldCount;
    }
    Token semicolon = token.next;
    if (optional(';', semicolon)) {
      token = semicolon;
    } else {
      // Recovery
      if (kind == DeclarationKind.TopLevel &&
          beforeType.next.isIdentifier &&
          beforeType.next.lexeme == 'extension') {
        // Looks like an extension method
        // TODO(danrubel): Remove when extension methods are enabled by default
        // because then 'extension' will be interpreted as a built-in
        // and this code will never be executed
        reportRecoverableError(
            beforeType.next,
            codes.templateExperimentNotEnabled
                .withArguments('extension-methods', '2.6'));
        token = rewriter.insertSyntheticToken(token, TokenType.SEMICOLON);
      } else {
        token = ensureSemicolon(token);
      }
    }
    switch (kind) {
      case DeclarationKind.TopLevel:
        assert(abstractToken == null);
        listener.endTopLevelFields(externalToken, staticToken, covariantToken,
            lateToken, varFinalOrConst, fieldCount, beforeStart.next, token);
        break;
      case DeclarationKind.Class:
        listener.endClassFields(
            abstractToken,
            externalToken,
            staticToken,
            covariantToken,
            lateToken,
            varFinalOrConst,
            fieldCount,
            beforeStart.next,
            token);
        break;
      case DeclarationKind.Mixin:
        listener.endMixinFields(
            abstractToken,
            externalToken,
            staticToken,
            covariantToken,
            lateToken,
            varFinalOrConst,
            fieldCount,
            beforeStart.next,
            token);
        break;
      case DeclarationKind.Extension:
        if (abstractToken != null) {
          reportRecoverableError(
              firstName, codes.messageAbstractExtensionField);
        }
        if (staticToken == null && externalToken == null) {
          reportRecoverableError(
              firstName, codes.messageExtensionDeclaresInstanceField);
        }
        listener.endExtensionFields(
            abstractToken,
            externalToken,
            staticToken,
            covariantToken,
            lateToken,
            varFinalOrConst,
            fieldCount,
            beforeStart.next,
            token);
        break;
    }
    return token;
  }

  Token parseTopLevelMethod(
      Token beforeStart,
      Token externalToken,
      Token beforeType,
      TypeInfo typeInfo,
      Token getOrSet,
      Token name,
      bool nameIsRecovered) {
    listener.beginTopLevelMethod(beforeStart, externalToken);

    Token token = typeInfo.parseType(beforeType, this);
    assert(token.next == (getOrSet ?? name) || token.next.isEof);
    name = ensureIdentifierPotentiallyRecovered(
        getOrSet ?? token,
        IdentifierContext.topLevelFunctionDeclaration,
        /* isRecovered = */ nameIsRecovered);

    bool isGetter = false;
    if (getOrSet == null) {
      token = parseMethodTypeVar(name);
    } else {
      isGetter = optional("get", getOrSet);
      token = name;
      listener.handleNoTypeVariables(token.next);
    }
    token = parseGetterOrFormalParameters(
        token, name, isGetter, MemberKind.TopLevelMethod);
    AsyncModifier savedAsyncModifier = asyncState;
    Token asyncToken = token.next;
    token = parseAsyncModifierOpt(token);
    if (getOrSet != null && !inPlainSync && optional("set", getOrSet)) {
      reportRecoverableError(asyncToken, codes.messageSetterNotSync);
    }
    bool isExternal = externalToken != null;
    if (isExternal && !optional(';', token.next)) {
      reportRecoverableError(
          externalToken, codes.messageExternalMethodWithBody);
    }
    token = parseFunctionBody(
        token, /* ofFunctionExpression = */ false, isExternal);
    asyncState = savedAsyncModifier;
    listener.endTopLevelMethod(beforeStart.next, getOrSet, token);
    return token;
  }

  Token parseMethodTypeVar(Token name) {
    if (optional('!', name.next)) {
      // Recovery
      name = name.next;
      reportRecoverableErrorWithToken(name, codes.templateUnexpectedToken);
    }
    if (!optional('<', name.next)) {
      return noTypeParamOrArg.parseVariables(name, this);
    }
    TypeParamOrArgInfo typeVar =
        computeTypeParamOrArg(name, /* inDeclaration = */ true);
    Token token = typeVar.parseVariables(name, this);
    if (optional('=', token.next)) {
      // Recovery
      token = token.next;
      reportRecoverableErrorWithToken(token, codes.templateUnexpectedToken);
    }
    return token;
  }

  Token parseFieldInitializerOpt(
      Token token,
      Token name,
      Token lateToken,
      Token abstractToken,
      Token externalToken,
      Token varFinalOrConst,
      DeclarationKind kind,
      String enclosingDeclarationName) {
    if (name.lexeme == enclosingDeclarationName) {
      reportRecoverableError(name, codes.messageMemberWithSameNameAsClass);
    }
    Token next = token.next;
    if (optional('=', next)) {
      Token assignment = next;
      listener.beginFieldInitializer(next);
      token = parseExpression(next);
      listener.endFieldInitializer(assignment, token.next);
    } else {
      if (varFinalOrConst != null && !name.isSynthetic) {
        if (optional("const", varFinalOrConst)) {
          reportRecoverableError(
              name,
              codes.templateConstFieldWithoutInitializer
                  .withArguments(name.lexeme));
        } else if (kind == DeclarationKind.TopLevel &&
            optional("final", varFinalOrConst) &&
            lateToken == null &&
            abstractToken == null &&
            externalToken == null) {
          reportRecoverableError(
              name,
              codes.templateFinalFieldWithoutInitializer
                  .withArguments(name.lexeme));
        }
      }
      listener.handleNoFieldInitializer(token.next);
    }
    return token;
  }

  Token parseVariableInitializerOpt(Token token) {
    if (optional('=', token.next)) {
      Token assignment = token.next;
      listener.beginVariableInitializer(assignment);
      token = parseExpression(assignment);
      listener.endVariableInitializer(assignment);
    } else {
      listener.handleNoVariableInitializer(token);
    }
    return token;
  }

  Token parseInitializersOpt(Token token) {
    if (optional(':', token.next)) {
      return parseInitializers(token.next);
    } else {
      listener.handleNoInitializers();
      return token;
    }
  }

  /// ```
  /// initializers:
  ///   ':' initializerListEntry (',' initializerListEntry)*
  /// ;
  /// ```
  Token parseInitializers(Token token) {
    Token begin = token;
    assert(optional(':', begin));
    listener.beginInitializers(begin);
    int count = 0;
    bool old = mayParseFunctionExpressions;
    mayParseFunctionExpressions = false;
    Token next = begin;
    while (true) {
      token = parseInitializer(next);
      ++count;
      next = token.next;
      if (!optional(',', next)) {
        // Recovery: Found an identifier which could be
        // 1) missing preceding `,` thus it's another initializer, or
        // 2) missing preceding `;` thus it's a class member, or
        // 3) missing preceding '{' thus it's a statement
        if (optional('assert', next)) {
          next = next.next;
          if (!optional('(', next)) {
            break;
          }
          // Looks like assert expression ... fall through to insert comma
        } else if (!next.isIdentifier && !optional('this', next)) {
          // An identifier that wasn't an initializer. Break.
          break;
        } else {
          if (optional('this', next)) {
            next = next.next;
            if (!optional('.', next)) {
              break;
            }
            next = next.next;
            if (!next.isIdentifier && !optional('assert', next)) {
              break;
            }
          }
          next = next.next;
          if (!optional('=', next)) {
            break;
          }
          // Looks like field assignment... fall through to insert comma
        }
        // TODO(danrubel): Consider enhancing this to indicate that we are
        // expecting one of `,` or `;` or `{`
        reportRecoverableError(
            token, codes.templateExpectedAfterButGot.withArguments(','));
        next = rewriter.insertSyntheticToken(token, TokenType.COMMA);
      }
    }
    mayParseFunctionExpressions = old;
    listener.endInitializers(count, begin, token.next);
    return token;
  }

  /// ```
  /// initializerListEntry:
  ///   'super' ('.' identifier)? arguments |
  ///   fieldInitializer |
  ///   assertion
  /// ;
  ///
  /// fieldInitializer:
  ///   ('this' '.')? identifier '=' conditionalExpression cascadeSection*
  /// ;
  /// ```
  Token parseInitializer(Token token) {
    Token next = token.next;
    listener.beginInitializer(next);
    Token beforeExpression = token;
    if (optional('assert', next)) {
      token = parseAssert(token, Assert.Initializer);
      listener.endInitializer(token.next);
      return token;
    } else if (optional('super', next)) {
      return parseSuperInitializerExpression(token);
    } else if (optional('this', next)) {
      token = next;
      next = token.next;
      if (optional('.', next)) {
        token = next;
        next = token.next;
        if (next.isIdentifier) {
          token = next;
        } else {
          // Recovery
          token = insertSyntheticIdentifier(
              token, IdentifierContext.fieldInitializer);
        }
        next = token.next;
        if (optional('=', next)) {
          return parseInitializerExpressionRest(beforeExpression);
        }
      }
      if (optional('(', next)) {
        token = parseInitializerExpressionRest(beforeExpression);
        next = token.next;
        if (optional('{', next) || optional('=>', next)) {
          reportRecoverableError(
              next, codes.messageRedirectingConstructorWithBody);
        }
        return token;
      }
      // Recovery
      if (optional('this', token)) {
        // TODO(danrubel): Consider a better error message indicating that
        // `this.<fieldname>=` is expected.
        reportRecoverableError(
            next, codes.templateExpectedButGot.withArguments('.'));
        rewriter.insertSyntheticToken(token, TokenType.PERIOD);
        token = rewriter.insertSyntheticIdentifier(token.next);
        next = token.next;
      }
      // Fall through to recovery
    } else if (next.isIdentifier) {
      Token next2 = next.next;
      if (optional('=', next2)) {
        return parseInitializerExpressionRest(token);
      }
      // Recovery: If this looks like an expression,
      // then fall through to insert the LHS and `=` of the assignment,
      // otherwise insert an `=` and synthetic identifier.
      if (!next2.isOperator && !optional('.', next2)) {
        token = rewriter.insertSyntheticToken(next, TokenType.EQ);
        token = insertSyntheticIdentifier(token, IdentifierContext.expression,
            message: codes.messageMissingAssignmentInInitializer,
            messageOnToken: next);
        return parseInitializerExpressionRest(beforeExpression);
      }
    } else {
      // Recovery: Insert a synthetic assignment.
      token = insertSyntheticIdentifier(
          token, IdentifierContext.fieldInitializer,
          message: codes.messageExpectedAnInitializer, messageOnToken: token);
      token = rewriter.insertSyntheticToken(token, TokenType.EQ);
      token = rewriter.insertSyntheticIdentifier(token);
      return parseInitializerExpressionRest(beforeExpression);
    }
    // Recovery:
    // Insert a synthetic identifier and assignment operator
    // to ensure that the expression is indeed an assignment.
    // Failing to do so causes this test to fail:
    // pkg/front_end/testcases/regress/issue_31192.dart
    // TODO(danrubel): Investigate better recovery.
    token = insertSyntheticIdentifier(
        beforeExpression, IdentifierContext.fieldInitializer,
        message: codes.messageMissingAssignmentInInitializer);
    rewriter.insertSyntheticToken(token, TokenType.EQ);
    return parseInitializerExpressionRest(beforeExpression);
  }

  /// Parse the `super` initializer:
  /// ```
  ///   'super' ('.' identifier)? arguments ;
  /// ```
  Token parseSuperInitializerExpression(final Token start) {
    Token token = start.next;
    assert(optional('super', token));
    Token next = token.next;
    if (optional('.', next)) {
      token = next;
      next = token.next;
      if (next.kind != IDENTIFIER_TOKEN) {
        next = IdentifierContext.expressionContinuation
            .ensureIdentifier(token, this);
      }
      token = next;
      next = token.next;
    }
    if (!optional('(', next)) {
      // Recovery
      if (optional('?.', next)) {
        // An error for `super?.` is reported in parseSuperExpression.
        token = next;
        next = token.next;
        if (!next.isIdentifier) {
          // Insert a synthetic identifier but don't report another error.
          next = rewriter.insertSyntheticIdentifier(token);
        }
        token = next;
        next = token.next;
      }
      if (optional('=', next)) {
        if (optional('super', token)) {
          // parseExpression will report error on assignment to super
        } else {
          reportRecoverableError(
              token, codes.messageFieldInitializedOutsideDeclaringClass);
        }
      } else if (!optional('(', next)) {
        reportRecoverableError(
            next, codes.templateExpectedAfterButGot.withArguments('('));
        rewriter.insertParens(token, /* includeIdentifier = */ false);
      }
    }
    return parseInitializerExpressionRest(start);
  }

  Token parseInitializerExpressionRest(Token token) {
    token = parseExpression(token);
    listener.endInitializer(token.next);
    return token;
  }

  /// If the next token is an opening curly brace, return it. Otherwise, use the
  /// given [template] or [missingBlockName] to report an error, insert an
  /// opening and a closing curly brace, and return the newly inserted opening
  /// curly brace. If  [template] and [missingBlockName] are `null`, then use
  /// a default error message instead.
  Token ensureBlock(
      Token token,
      codes.Template<codes.Message Function(Token token)> template,
      String missingBlockName) {
    Token next = token.next;
    if (optional('{', next)) return next;
    if (template == null) {
      if (missingBlockName == null) {
        // TODO(danrubel): rename ExpectedButGot to ExpectedBefore
        reportRecoverableError(
            next, codes.templateExpectedButGot.withArguments('{'));
      } else {
        // TODO(danrubel): rename ExpectedClassOrMixinBody
        //  to ExpectedDeclarationOrClauseBody
        reportRecoverableError(
            token,
            codes.templateExpectedClassOrMixinBody
                .withArguments(missingBlockName));
      }
    } else {
      reportRecoverableError(next, template.withArguments(next));
    }
    return insertBlock(token);
  }

  Token insertBlock(Token token) {
    Token next = token.next;
    BeginToken beginGroup = rewriter.insertToken(token,
        new SyntheticBeginToken(TokenType.OPEN_CURLY_BRACKET, next.offset));
    Token endGroup = rewriter.insertToken(beginGroup,
        new SyntheticToken(TokenType.CLOSE_CURLY_BRACKET, next.offset));
    beginGroup.endGroup = endGroup;
    return beginGroup;
  }

  /// If the next token is a closing parenthesis, return it.
  /// Otherwise, report an error and return the closing parenthesis
  /// associated with the specified open parenthesis.
  Token ensureCloseParen(Token token, Token openParen) {
    Token next = token.next;
    if (optional(')', next)) {
      return next;
    }
    if (openParen.endGroup.isSynthetic) {
      // Scanner has already reported a missing `)` error,
      // but placed the `)` in the wrong location, so move it.
      return rewriter.moveSynthetic(token, openParen.endGroup);
    }

    // TODO(danrubel): Pass in context for better error message.
    reportRecoverableError(
        next, codes.templateExpectedButGot.withArguments(')'));

    // Scanner guarantees a closing parenthesis
    // TODO(danrubel): Improve recovery by having callers parse tokens
    // between `token` and `openParen.endGroup`.
    return openParen.endGroup;
  }

  /// If the next token is a colon, return it. Otherwise, report an
  /// error, insert a synthetic colon, and return the inserted colon.
  Token ensureColon(Token token) {
    Token next = token.next;
    if (optional(':', next)) return next;
    codes.Message message = codes.templateExpectedButGot.withArguments(':');
    Token newToken = new SyntheticToken(TokenType.COLON, next.charOffset);
    return rewriteAndRecover(token, message, newToken);
  }

  /// If the token after [token] is a not literal string,
  /// then insert a synthetic literal string.
  /// Call `parseLiteralString` and return the result.
  Token ensureLiteralString(Token token) {
    Token next = token.next;
    if (!identical(next.kind, STRING_TOKEN)) {
      codes.Message message = codes.templateExpectedString.withArguments(next);
      Token newToken = new SyntheticStringToken(
          TokenType.STRING, '""', next.charOffset, /* _length = */ 0);
      rewriteAndRecover(token, message, newToken);
    }
    return parseLiteralString(token);
  }

  /// If the token after [token] is a semi-colon, return it.
  /// Otherwise, report an error, insert a synthetic semi-colon,
  /// and return the inserted semi-colon.
  Token ensureSemicolon(Token token) {
    // TODO(danrubel): Once all expect(';'...) call sites have been converted
    // to use this method, remove similar semicolon recovery code
    // from the handleError method in element_listener.dart.
    Token next = token.next;
    if (optional(';', next)) return next;

    // Find a token on the same line as where the ';' should be inserted.
    // Reporting the error on this token makes it easier
    // for users to understand and fix the error.
    reportRecoverableError(findPreviousNonZeroLengthToken(token),
        codes.templateExpectedAfterButGot.withArguments(';'));
    return rewriter.insertSyntheticToken(token, TokenType.SEMICOLON);
  }

  /// Report an error at the token after [token] that has the given [message].
  /// Insert the [newToken] after [token] and return [newToken].
  Token rewriteAndRecover(Token token, codes.Message message, Token newToken) {
    reportRecoverableError(token.next, message);
    return rewriter.insertToken(token, newToken);
  }

  /// Replace the token after [token] with `[` followed by `]`
  /// and return [token].
  Token rewriteSquareBrackets(Token token) {
    Token next = token.next;
    assert(optional('[]', next));
    Token replacement;
    if (next.isSynthetic) {
      replacement = link(
          new SyntheticBeginToken(TokenType.OPEN_SQUARE_BRACKET, next.offset,
              next.precedingComments),
          new SyntheticToken(TokenType.CLOSE_SQUARE_BRACKET, next.offset));
    } else {
      replacement = link(
          new BeginToken(TokenType.OPEN_SQUARE_BRACKET, next.offset,
              next.precedingComments),
          new Token(TokenType.CLOSE_SQUARE_BRACKET, next.offset + 1));
    }
    rewriter.replaceTokenFollowing(token, replacement);
    return token;
  }

  /// Report the given token as unexpected and return the next token if the next
  /// token is one of the [expectedNext], otherwise just return the given token.
  Token skipUnexpectedTokenOpt(Token token, List<String> expectedNext) {
    Token next = token.next;
    if (next.keyword == null) {
      final String nextValue = next.next.stringValue;
      for (String expectedValue in expectedNext) {
        if (identical(nextValue, expectedValue)) {
          reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
          return next;
        }
      }
    }
    return token;
  }

  Token parseNativeClause(Token token) {
    Token nativeToken = token = token.next;
    assert(optional('native', nativeToken));
    bool hasName = false;
    if (token.next.kind == STRING_TOKEN) {
      hasName = true;
      token = parseLiteralString(token);
    }
    listener.handleNativeClause(nativeToken, hasName);
    reportRecoverableError(
        nativeToken, codes.messageNativeClauseShouldBeAnnotation);
    return token;
  }

  Token skipClassOrMixinOrExtensionBody(Token token) {
    // The scanner ensures that `{` always has a closing `}`.
    return ensureBlock(
        token, /* template = */ null, /* missingBlockName = */ null);
  }

  /// ```
  /// classBody:
  ///   '{' classMember* '}'
  /// ;
  /// ```
  Token parseClassOrMixinOrExtensionBody(
      Token token, DeclarationKind kind, String enclosingDeclarationName) {
    Token begin = token = token.next;
    assert(optional('{', token));
    listener.beginClassOrMixinBody(kind, token);
    int count = 0;
    while (notEofOrValue('}', token.next)) {
      token = parseClassOrMixinOrExtensionMemberImpl(
          token, kind, enclosingDeclarationName);
      ++count;
    }
    token = token.next;
    assert(token.isEof || optional('}', token));
    listener.endClassOrMixinBody(kind, count, begin, token);
    return token;
  }

  bool isUnaryMinus(Token token) =>
      token.kind == IDENTIFIER_TOKEN &&
      token.lexeme == 'unary' &&
      optional('-', token.next);

  /// Parse a class member.
  ///
  /// This method is only invoked from outside the parser. As a result, this
  /// method takes the next token to be consumed rather than the last consumed
  /// token and returns the token after the last consumed token rather than the
  /// last consumed token.
  Token parseClassMember(Token token, String className) {
    return parseClassOrMixinOrExtensionMemberImpl(
            syntheticPreviousToken(token), DeclarationKind.Class, className)
        .next;
  }

  /// Parse a mixin member.
  ///
  /// This method is only invoked from outside the parser. As a result, this
  /// method takes the next token to be consumed rather than the last consumed
  /// token and returns the token after the last consumed token rather than the
  /// last consumed token.
  Token parseMixinMember(Token token, String mixinName) {
    return parseClassOrMixinOrExtensionMemberImpl(
            syntheticPreviousToken(token), DeclarationKind.Mixin, mixinName)
        .next;
  }

  /// Parse an extension member.
  ///
  /// This method is only invoked from outside the parser. As a result, this
  /// method takes the next token to be consumed rather than the last consumed
  /// token and returns the token after the last consumed token rather than the
  /// last consumed token.
  Token parseExtensionMember(Token token, String extensionName) {
    return parseClassOrMixinOrExtensionMemberImpl(syntheticPreviousToken(token),
            DeclarationKind.Extension, extensionName)
        .next;
  }

  bool isReservedKeyword(Token token) {
    if (!token.isKeyword) return false;
    return token.type.isReservedWord;
  }

  bool indicatesMethodOrField(Token token) {
    String value = token.stringValue;
    if (identical(value, ';') ||
        identical(value, '=') ||
        identical(value, '(') ||
        identical(value, '{') ||
        identical(value, '=>') ||
        identical(value, '<')) {
      return true;
    }
    return false;
  }

  /// ```
  /// classMember:
  ///   fieldDeclaration |
  ///   constructorDeclaration |
  ///   methodDeclaration
  /// ;
  ///
  /// mixinMember:
  ///   fieldDeclaration |
  ///   methodDeclaration
  /// ;
  ///
  /// extensionMember:
  ///   staticFieldDeclaration |
  ///   methodDeclaration
  /// ;
  /// ```
  Token parseClassOrMixinOrExtensionMemberImpl(
      Token token, DeclarationKind kind, String enclosingDeclarationName) {
    Token beforeStart = token = parseMetadataStar(token);

    Token covariantToken;
    Token abstractToken;
    Token externalToken;
    Token lateToken;
    Token staticToken;
    Token varFinalOrConst;

    Token next = token.next;
    if (isModifier(next)) {
      if (optional('external', next)) {
        externalToken = token = next;
        next = token.next;
      } else if (optional('abstract', next)) {
        abstractToken = token = next;
        next = token.next;
      }
      if (isModifier(next)) {
        if (optional('static', next)) {
          staticToken = token = next;
          next = token.next;
        } else if (optional('covariant', next)) {
          covariantToken = token = next;
          next = token.next;
        }
        if (isModifier(next)) {
          if (optional('final', next)) {
            varFinalOrConst = token = next;
            next = token.next;
          } else if (optional('var', next)) {
            varFinalOrConst = token = next;
            next = token.next;
          } else if (optional('const', next) && covariantToken == null) {
            varFinalOrConst = token = next;
            next = token.next;
          } else if (optional('late', next)) {
            lateToken = token = next;
            next = token.next;
            if (isModifier(next) && optional('final', next)) {
              varFinalOrConst = token = next;
              next = token.next;
            }
          }
          if (isModifier(next)) {
            ModifierRecoveryContext context = new ModifierRecoveryContext(this)
              ..covariantToken = covariantToken
              ..externalToken = externalToken
              ..lateToken = lateToken
              ..staticToken = staticToken
              ..varFinalOrConst = varFinalOrConst
              ..abstractToken = abstractToken;

            token = context.parseClassMemberModifiers(token);
            next = token.next;

            covariantToken = context.covariantToken;
            externalToken = context.externalToken;
            lateToken = context.lateToken;
            staticToken = context.staticToken;
            varFinalOrConst = context.varFinalOrConst;
            abstractToken = context.abstractToken;

            context = null;
          }
        }
      }
    }

    listener.beginMember();

    Token beforeType = token;
    TypeInfo typeInfo = computeType(
        token,
        /*required = */ false,
        /* inDeclaration = */ true);
    token = typeInfo.skipType(token);
    next = token.next;

    Token getOrSet;
    bool nameIsRecovered = false;
    if (next.type != TokenType.IDENTIFIER) {
      String value = next.stringValue;
      if (identical(value, 'get') || identical(value, 'set')) {
        if (next.next.isIdentifier) {
          getOrSet = token = next;
          next = token.next;
        } else if (isReservedKeyword(next.next) &&
            indicatesMethodOrField(next.next.next)) {
          // Recovery: Getter or setter followed by a reserved word (name).
          getOrSet = token = next;
          next = token.next;
          nameIsRecovered = true;
        }
        // Fall through to continue parsing `get` or `set` as an identifier.
      } else if (identical(value, 'factory')) {
        Token next2 = next.next;
        if (next2.isIdentifier || next2.isModifier) {
          if (beforeType != token) {
            reportRecoverableError(token, codes.messageTypeBeforeFactory);
          }
          if (abstractToken != null) {
            reportRecoverableError(
                abstractToken, codes.messageAbstractClassMember);
          }
          token = parseFactoryMethod(token, kind, beforeStart, externalToken,
              staticToken ?? covariantToken, varFinalOrConst);
          listener.endMember();
          return token;
        }
        // Fall through to continue parsing `factory` as an identifier.
      } else if (identical(value, 'operator')) {
        Token next2 = next.next;
        TypeParamOrArgInfo typeParam = computeTypeParamOrArg(next);
        // `operator` can be used as an identifier as in
        // `int operator<T>()` or `int operator = 2`
        if (next2.isUserDefinableOperator && typeParam == noTypeParamOrArg) {
          token = parseMethod(
              beforeStart,
              abstractToken,
              externalToken,
              staticToken,
              covariantToken,
              lateToken,
              varFinalOrConst,
              beforeType,
              typeInfo,
              getOrSet,
              token.next,
              kind,
              enclosingDeclarationName,
              nameIsRecovered);
          listener.endMember();
          return token;
        } else if (optional('===', next2) ||
            optional('!==', next2) ||
            (next2.isOperator &&
                !optional('=', next2) &&
                !optional('<', next2))) {
          // Recovery: Invalid operator
          return parseInvalidOperatorDeclaration(
              beforeStart,
              abstractToken,
              externalToken,
              staticToken,
              covariantToken,
              lateToken,
              varFinalOrConst,
              beforeType,
              kind,
              enclosingDeclarationName);
        } else if (isUnaryMinus(next2)) {
          // Recovery
          token = parseMethod(
              beforeStart,
              abstractToken,
              externalToken,
              staticToken,
              covariantToken,
              lateToken,
              varFinalOrConst,
              beforeType,
              typeInfo,
              getOrSet,
              token.next,
              kind,
              enclosingDeclarationName,
              nameIsRecovered);
          listener.endMember();
          return token;
        }
        // Fall through to continue parsing `operator` as an identifier.
      } else if (!next.isIdentifier ||
          (identical(value, 'typedef') &&
              token == beforeStart &&
              next.next.isIdentifier)) {
        if (abstractToken != null) {
          reportRecoverableError(
              abstractToken, codes.messageAbstractClassMember);
        }
        // Recovery
        return recoverFromInvalidMember(
            token,
            beforeStart,
            abstractToken,
            externalToken,
            staticToken,
            covariantToken,
            lateToken,
            varFinalOrConst,
            beforeType,
            typeInfo,
            getOrSet,
            kind,
            enclosingDeclarationName);
      }
    } else if (typeInfo == noType && varFinalOrConst == null) {
      Token next2 = next.next;
      if (next2.isUserDefinableOperator && next2.endGroup == null) {
        String value = next2.next.stringValue;
        if (identical(value, '(') ||
            identical(value, '{') ||
            identical(value, '=>')) {
          // Recovery: Missing `operator` keyword
          return parseInvalidOperatorDeclaration(
              beforeStart,
              abstractToken,
              externalToken,
              staticToken,
              covariantToken,
              lateToken,
              varFinalOrConst,
              beforeType,
              kind,
              enclosingDeclarationName);
        }
      } else if (isReservedKeyword(next2) &&
          indicatesMethodOrField(next2.next)) {
        // Recovery: Use the reserved keyword despite that not being legal.
        typeInfo = computeType(
            token,
            /*required = */ true,
            /* inDeclaration = */ true);
        token = typeInfo.skipType(token);
        next = token.next;
        nameIsRecovered = true;
      }
    }

    // At this point, token is before the name, and next is the name
    next = next.next;
    String value = next.stringValue;
    if (getOrSet != null ||
        identical(value, '(') ||
        identical(value, '{') ||
        identical(value, '<') ||
        identical(value, '.') ||
        identical(value, '=>')) {
      token = parseMethod(
          beforeStart,
          abstractToken,
          externalToken,
          staticToken,
          covariantToken,
          lateToken,
          varFinalOrConst,
          beforeType,
          typeInfo,
          getOrSet,
          token.next,
          kind,
          enclosingDeclarationName,
          nameIsRecovered);
    } else {
      if (getOrSet != null) {
        reportRecoverableErrorWithToken(
            getOrSet, codes.templateExtraneousModifier);
      }
      token = parseFields(
          beforeStart,
          abstractToken,
          externalToken,
          staticToken,
          covariantToken,
          lateToken,
          varFinalOrConst,
          beforeType,
          typeInfo,
          token.next,
          kind,
          enclosingDeclarationName,
          nameIsRecovered);
    }
    listener.endMember();
    return token;
  }

  Token parseMethod(
      Token beforeStart,
      Token abstractToken,
      Token externalToken,
      Token staticToken,
      Token covariantToken,
      Token lateToken,
      Token varFinalOrConst,
      Token beforeType,
      TypeInfo typeInfo,
      Token getOrSet,
      Token name,
      DeclarationKind kind,
      String enclosingDeclarationName,
      bool nameIsRecovered) {
    if (abstractToken != null) {
      reportRecoverableError(abstractToken, codes.messageAbstractClassMember);
    }
    if (lateToken != null) {
      reportRecoverableErrorWithToken(
          lateToken, codes.templateExtraneousModifier);
    }
    bool isOperator = false;
    if (getOrSet == null && optional('operator', name)) {
      Token operator = name.next;
      if (operator.isOperator ||
          identical(operator.kind, EQ_EQ_EQ_TOKEN) ||
          identical(operator.kind, BANG_EQ_EQ_TOKEN) ||
          isUnaryMinus(operator)) {
        isOperator = true;
      }
    }

    if (staticToken != null) {
      if (isOperator) {
        reportRecoverableError(staticToken, codes.messageStaticOperator);
        staticToken = null;
      }
    } else if (covariantToken != null) {
      if (getOrSet == null || optional('get', getOrSet)) {
        reportRecoverableError(covariantToken, codes.messageCovariantMember);
        covariantToken = null;
      }
    }
    if (varFinalOrConst != null) {
      if (optional('const', varFinalOrConst)) {
        if (getOrSet != null) {
          reportRecoverableErrorWithToken(
              varFinalOrConst, codes.templateExtraneousModifier);
          varFinalOrConst = null;
        }
      } else if (optional('var', varFinalOrConst)) {
        reportRecoverableError(varFinalOrConst, codes.messageVarReturnType);
        varFinalOrConst = null;
      } else {
        assert(optional('final', varFinalOrConst));
        reportRecoverableErrorWithToken(
            varFinalOrConst, codes.templateExtraneousModifier);
        varFinalOrConst = null;
      }
    }

    // TODO(danrubel): Consider parsing the name before calling beginMethod
    // rather than passing the name token into beginMethod.
    listener.beginMethod(externalToken, staticToken, covariantToken,
        varFinalOrConst, getOrSet, name);

    Token token = typeInfo.parseType(beforeType, this);
    assert(token.next == (getOrSet ?? name));
    token = getOrSet ?? token;

    bool hasQualifiedName = false;

    if (isOperator) {
      token = parseOperatorName(token);
    } else {
      token = ensureIdentifierPotentiallyRecovered(
          token,
          IdentifierContext.methodDeclaration,
          /* isRecovered = */ nameIsRecovered);
      // Possible recovery: This call only does something if the next token is
      // a '.' --- that's not legal for get or set, but an error is reported
      // later, and it will recover better if we allow it.
      Token qualified = parseQualifiedRestOpt(
          token, IdentifierContext.methodDeclarationContinuation);
      if (token != qualified) {
        hasQualifiedName = true;
      }
      token = qualified;
    }

    bool isConsideredGetter = false;
    if (getOrSet == null) {
      token = parseMethodTypeVar(token);
    } else {
      isConsideredGetter = optional("get", getOrSet);
      listener.handleNoTypeVariables(token.next);

      // If it becomes considered a constructor below, don't consider it a
      // getter now (this also enforces parenthesis (and thus parameters)).
      if (hasQualifiedName) {
        isConsideredGetter = false;
      } else if (isConsideredGetter && optional(':', token.next)) {
        isConsideredGetter = false;
      } else if (isConsideredGetter &&
          name.lexeme == enclosingDeclarationName) {
        // This is a simple case of an badly named getter so we don't consider
        // that a constructor. We issue an error about the name below.
      }
    }

    Token beforeParam = token;
    Token beforeInitializers = parseGetterOrFormalParameters(
        token,
        name,
        isConsideredGetter,
        kind == DeclarationKind.Extension
            ? staticToken != null
                ? MemberKind.ExtensionStaticMethod
                : MemberKind.ExtensionNonStaticMethod
            : staticToken != null
                ? MemberKind.StaticMethod
                : MemberKind.NonStaticMethod);
    token = parseInitializersOpt(beforeInitializers);
    if (token == beforeInitializers) beforeInitializers = null;

    AsyncModifier savedAsyncModifier = asyncState;
    Token asyncToken = token.next;
    token = parseAsyncModifierOpt(token);
    if (getOrSet != null && !inPlainSync && optional("set", getOrSet)) {
      reportRecoverableError(asyncToken, codes.messageSetterNotSync);
    }
    final Token bodyStart = token.next;
    if (externalToken != null) {
      if (!optional(';', bodyStart)) {
        reportRecoverableError(bodyStart, codes.messageExternalMethodWithBody);
      }
    }
    if (optional('=', bodyStart)) {
      reportRecoverableError(bodyStart, codes.messageRedirectionInNonFactory);
      token = parseRedirectingFactoryBody(token);
    } else {
      token = parseFunctionBody(token, /* ofFunctionExpression = */ false,
          (staticToken == null || externalToken != null) && inPlainSync);
    }
    asyncState = savedAsyncModifier;

    bool isConstructor = false;
    if (optional('.', name.next) || beforeInitializers != null) {
      // This is only legal for constructors.
      isConstructor = true;
    } else if (name.lexeme == enclosingDeclarationName) {
      if (getOrSet != null) {
        // Recovery: The (simple) get/set member name is invalid.
        // Report an error and continue with invalid name
        // (keeping it as a getter/setter).
        reportRecoverableError(name, codes.messageMemberWithSameNameAsClass);
      } else {
        isConstructor = true;
      }
    }

    if (isConstructor) {
      //
      // constructor
      //
      if (name.lexeme != enclosingDeclarationName) {
        reportRecoverableError(name, codes.messageConstructorWithWrongName);
      }
      if (staticToken != null) {
        reportRecoverableError(staticToken, codes.messageStaticConstructor);
      }
      if (getOrSet != null) {
        if (optional("get", getOrSet)) {
          reportRecoverableError(getOrSet, codes.messageGetterConstructor);
        } else {
          reportRecoverableError(getOrSet, codes.messageSetterConstructor);
        }
      }
      if (typeInfo != noType) {
        reportRecoverableError(
            beforeType.next, codes.messageConstructorWithReturnType);
      }
      if (beforeInitializers != null && externalToken != null) {
        reportRecoverableError(beforeInitializers.next,
            codes.messageExternalConstructorWithInitializer);
      }

      switch (kind) {
        case DeclarationKind.Class:
          // TODO(danrubel): Remove getOrSet from constructor events
          listener.endClassConstructor(getOrSet, beforeStart.next,
              beforeParam.next, beforeInitializers?.next, token);
          break;
        case DeclarationKind.Mixin:
          reportRecoverableError(name, codes.messageMixinDeclaresConstructor);
          listener.endMixinConstructor(getOrSet, beforeStart.next,
              beforeParam.next, beforeInitializers?.next, token);
          break;
        case DeclarationKind.Extension:
          reportRecoverableError(
              name, codes.messageExtensionDeclaresConstructor);
          listener.endExtensionConstructor(getOrSet, beforeStart.next,
              beforeParam.next, beforeInitializers?.next, token);
          break;
        case DeclarationKind.TopLevel:
          throw "Internal error: TopLevel constructor.";
          break;
      }
    } else {
      //
      // method
      //
      if (varFinalOrConst != null) {
        assert(optional('const', varFinalOrConst));
        reportRecoverableError(varFinalOrConst, codes.messageConstMethod);
      }
      switch (kind) {
        case DeclarationKind.Class:
          // TODO(danrubel): Remove beginInitializers token from method events
          listener.endClassMethod(getOrSet, beforeStart.next, beforeParam.next,
              beforeInitializers?.next, token);
          break;
        case DeclarationKind.Mixin:
          listener.endMixinMethod(getOrSet, beforeStart.next, beforeParam.next,
              beforeInitializers?.next, token);
          break;
        case DeclarationKind.Extension:
          if (optional(';', bodyStart) && externalToken == null) {
            reportRecoverableError(isOperator ? name.next : name,
                codes.messageExtensionDeclaresAbstractMember);
          }
          listener.endExtensionMethod(getOrSet, beforeStart.next,
              beforeParam.next, beforeInitializers?.next, token);
          break;
        case DeclarationKind.TopLevel:
          throw "Internal error: TopLevel method.";
          break;
      }
    }
    return token;
  }

  Token parseFactoryMethod(Token token, DeclarationKind kind, Token beforeStart,
      Token externalToken, Token staticOrCovariant, Token varFinalOrConst) {
    Token factoryKeyword = token = token.next;
    assert(optional('factory', factoryKeyword));

    if (!isValidTypeReference(token.next)) {
      // Recovery
      ModifierRecoveryContext context = new ModifierRecoveryContext(this)
        ..externalToken = externalToken
        ..staticOrCovariant = staticOrCovariant
        ..varFinalOrConst = varFinalOrConst;

      token = context.parseModifiersAfterFactory(token);

      externalToken = context.externalToken;
      staticOrCovariant = context.staticToken ?? context.covariantToken;
      varFinalOrConst = context.varFinalOrConst;

      context = null;
    }

    if (staticOrCovariant != null) {
      reportRecoverableErrorWithToken(
          staticOrCovariant, codes.templateExtraneousModifier);
    }
    if (varFinalOrConst != null && !optional('const', varFinalOrConst)) {
      reportRecoverableErrorWithToken(
          varFinalOrConst, codes.templateExtraneousModifier);
      varFinalOrConst = null;
    }

    listener.beginFactoryMethod(beforeStart, externalToken, varFinalOrConst);
    token = ensureIdentifier(token, IdentifierContext.methodDeclaration);
    token = parseQualifiedRestOpt(
        token, IdentifierContext.methodDeclarationContinuation);
    token = parseMethodTypeVar(token);
    token = parseFormalParametersRequiredOpt(token, MemberKind.Factory);
    Token asyncToken = token.next;
    token = parseAsyncModifierOpt(token);
    Token next = token.next;
    if (!inPlainSync) {
      reportRecoverableError(asyncToken, codes.messageFactoryNotSync);
    }
    if (optional('=', next)) {
      if (externalToken != null) {
        reportRecoverableError(next, codes.messageExternalFactoryRedirection);
      }
      token = parseRedirectingFactoryBody(token);
    } else if (externalToken != null) {
      if (!optional(';', next)) {
        reportRecoverableError(next, codes.messageExternalFactoryWithBody);
      }
      token = parseFunctionBody(
          token,
          /* ofFunctionExpression = */ false,
          /* allowAbstract = */ true);
    } else {
      if (varFinalOrConst != null && !optional('native', next)) {
        if (optional('const', varFinalOrConst)) {
          reportRecoverableError(varFinalOrConst, codes.messageConstFactory);
        }
      }
      token = parseFunctionBody(
          token,
          /* ofFunctionExpression = */ false,
          /* allowAbstract = */ false);
    }
    switch (kind) {
      case DeclarationKind.Class:
        listener.endClassFactoryMethod(beforeStart.next, factoryKeyword, token);
        break;
      case DeclarationKind.Mixin:
        reportRecoverableError(
            factoryKeyword, codes.messageMixinDeclaresConstructor);
        listener.endMixinFactoryMethod(beforeStart.next, factoryKeyword, token);
        break;
      case DeclarationKind.Extension:
        reportRecoverableError(
            factoryKeyword, codes.messageExtensionDeclaresConstructor);
        listener.endExtensionFactoryMethod(
            beforeStart.next, factoryKeyword, token);
        break;
      case DeclarationKind.TopLevel:
        throw "Internal error: TopLevel factory.";
        break;
    }
    return token;
  }

  Token parseOperatorName(Token token) {
    Token beforeToken = token;
    token = token.next;
    assert(optional('operator', token));
    Token next = token.next;
    if (next.isUserDefinableOperator) {
      if (computeTypeParamOrArg(token) != noTypeParamOrArg) {
        // `operator` is being used as an identifier.
        // For example: `int operator<T>(foo) => 0;`
        listener.handleIdentifier(token, IdentifierContext.methodDeclaration);
        return token;
      } else {
        listener.handleOperatorName(token, next);
        return next;
      }
    } else if (optional('(', next)) {
      return ensureIdentifier(beforeToken, IdentifierContext.operatorName);
    } else if (isUnaryMinus(next)) {
      // Recovery
      reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
      next = next.next;
      listener.handleOperatorName(token, next);
      return next;
    } else {
      // Recovery
      // Scanner reports an error for `===` and `!==`.
      if (next.type != TokenType.EQ_EQ_EQ &&
          next.type != TokenType.BANG_EQ_EQ) {
        // The user has specified an invalid operator name.
        // Report the error, accept the invalid operator name, and move on.
        reportRecoverableErrorWithToken(next, codes.templateInvalidOperator);
      }
      listener.handleInvalidOperatorName(token, next);
      return next;
    }
  }

  Token parseFunctionExpression(Token token) {
    Token beginToken = token.next;
    listener.beginFunctionExpression(beginToken);
    token = parseFormalParametersRequiredOpt(token, MemberKind.Local);
    token = parseAsyncOptBody(
        token, /* ofFunctionExpression = */ true, /* allowAbstract = */ false);
    listener.endFunctionExpression(beginToken, token.next);
    return token;
  }

  Token parseFunctionLiteral(
      Token start,
      Token beforeName,
      Token name,
      TypeInfo typeInfo,
      TypeParamOrArgInfo typeParam,
      IdentifierContext context) {
    Token formals = typeParam.parseVariables(name, this);
    listener.beginNamedFunctionExpression(start.next);
    typeInfo.parseType(start, this);
    return parseNamedFunctionRest(
        beforeName, start.next, formals, /* isFunctionExpression = */ true);
  }

  /// Parses the rest of a named function declaration starting from its [name]
  /// but then skips any type parameters and continue parsing from [formals]
  /// (the formal parameters).
  ///
  /// If [isFunctionExpression] is true, this method parses the rest of named
  /// function expression which isn't legal syntax in Dart.  Useful for
  /// recovering from Javascript code being pasted into a Dart program, as it
  /// will interpret `function foo() {}` as a named function expression with
  /// return type `function` and name `foo`.
  ///
  /// Precondition: the parser has previously generated these events:
  ///
  /// - Type variables.
  /// - `beginLocalFunctionDeclaration` if [isFunctionExpression] is false,
  ///   otherwise `beginNamedFunctionExpression`.
  /// - Return type.
  Token parseNamedFunctionRest(
      Token beforeName, Token begin, Token formals, bool isFunctionExpression) {
    Token token = beforeName.next;
    listener.beginFunctionName(token);
    token =
        ensureIdentifier(beforeName, IdentifierContext.localFunctionDeclaration)
            .next;
    if (isFunctionExpression) {
      reportRecoverableError(
          beforeName.next, codes.messageNamedFunctionExpression);
    }
    listener.endFunctionName(begin, token);
    token = parseFormalParametersRequiredOpt(formals, MemberKind.Local);
    token = parseInitializersOpt(token);
    token = parseAsyncOptBody(
        token, isFunctionExpression, /* allowAbstract = */ false);
    if (isFunctionExpression) {
      listener.endNamedFunctionExpression(token);
    } else {
      listener.endLocalFunctionDeclaration(token);
    }
    return token;
  }

  /// Parses a function body optionally preceded by an async modifier (see
  /// [parseAsyncModifierOpt]).  This method is used in both expression context
  /// (when [ofFunctionExpression] is true) and statement context. In statement
  /// context (when [ofFunctionExpression] is false), and if the function body
  /// is on the form `=> expression`, a trailing semicolon is required.
  ///
  /// It's an error if there's no function body unless [allowAbstract] is true.
  Token parseAsyncOptBody(
      Token token, bool ofFunctionExpression, bool allowAbstract) {
    AsyncModifier savedAsyncModifier = asyncState;
    token = parseAsyncModifierOpt(token);
    token = parseFunctionBody(token, ofFunctionExpression, allowAbstract);
    asyncState = savedAsyncModifier;
    return token;
  }

  Token parseConstructorReference(Token token, [TypeParamOrArgInfo typeArg]) {
    Token start =
        ensureIdentifier(token, IdentifierContext.constructorReference);
    listener.beginConstructorReference(start);
    token = parseQualifiedRestOpt(
        start, IdentifierContext.constructorReferenceContinuation);
    typeArg ??= computeTypeParamOrArg(token);
    token = typeArg.parseArguments(token, this);
    Token period = null;
    if (optional('.', token.next)) {
      period = token.next;
      token = ensureIdentifier(period,
          IdentifierContext.constructorReferenceContinuationAfterTypeArguments);
    } else {
      listener.handleNoConstructorReferenceContinuationAfterTypeArguments(
          token.next);
    }
    listener.endConstructorReference(start, period, token.next);
    return token;
  }

  Token parseRedirectingFactoryBody(Token token) {
    token = token.next;
    assert(optional('=', token));
    listener.beginRedirectingFactoryBody(token);
    Token equals = token;
    token = parseConstructorReference(token);
    token = ensureSemicolon(token);
    listener.endRedirectingFactoryBody(equals, token);
    return token;
  }

  Token skipFunctionBody(Token token, bool isExpression, bool allowAbstract) {
    assert(!isExpression);
    token = skipAsyncModifier(token);
    Token next = token.next;
    if (optional('native', next)) {
      Token nativeToken = next;
      // TODO(danrubel): skip the native clause rather than parsing it
      // or remove this code completely when we remove support
      // for the `native` clause.
      token = parseNativeClause(token);
      next = token.next;
      if (optional(';', next)) {
        listener.handleNativeFunctionBodySkipped(nativeToken, next);
        return token.next;
      }
      listener.handleNativeFunctionBodyIgnored(nativeToken, next);
      // Fall through to recover and skip function body
    }
    String value = next.stringValue;
    if (identical(value, ';')) {
      token = next;
      if (!allowAbstract) {
        reportRecoverableError(token, codes.messageExpectedBody);
      }
      listener.handleNoFunctionBody(token);
    } else if (identical(value, '=>')) {
      token = parseExpression(next);
      // There ought to be a semicolon following the expression, but we check
      // before advancing in order to be consistent with the way the method
      // [parseFunctionBody] recovers when the semicolon is missing.
      if (optional(';', token.next)) {
        token = token.next;
      }
      listener.handleFunctionBodySkipped(token, /* isExpressionBody = */ true);
    } else if (identical(value, '=')) {
      token = next;
      reportRecoverableError(token, codes.messageExpectedBody);
      token = parseExpression(token);
      // There ought to be a semicolon following the expression, but we check
      // before advancing in order to be consistent with the way the method
      // [parseFunctionBody] recovers when the semicolon is missing.
      if (optional(';', token.next)) {
        token = token.next;
      }
      listener.handleFunctionBodySkipped(token, /* isExpressionBody = */ true);
    } else {
      token = skipBlock(token);
      listener.handleFunctionBodySkipped(token, /* isExpressionBody = */ false);
    }
    return token;
  }

  /// Parses a function body.  This method is used in both expression context
  /// (when [ofFunctionExpression] is true) and statement context. In statement
  /// context (when [ofFunctionExpression] is false), and if the function body
  /// is on the form `=> expression`, a trailing semicolon is required.
  ///
  /// It's an error if there's no function body unless [allowAbstract] is true.
  Token parseFunctionBody(
      Token token, bool ofFunctionExpression, bool allowAbstract) {
    Token next = token.next;
    if (optional('native', next)) {
      Token nativeToken = next;
      token = parseNativeClause(token);
      next = token.next;
      if (optional(';', next)) {
        listener.handleNativeFunctionBody(nativeToken, next);
        return next;
      }
      reportRecoverableError(next, codes.messageExternalMethodWithBody);
      listener.handleNativeFunctionBodyIgnored(nativeToken, next);
      // Ignore the native keyword and fall through to parse the body
    }
    if (optional(';', next)) {
      if (!allowAbstract) {
        reportRecoverableError(next, codes.messageExpectedBody);
      }
      listener.handleEmptyFunctionBody(next);
      return next;
    } else if (optional('=>', next)) {
      return parseExpressionFunctionBody(next, ofFunctionExpression);
    } else if (optional('=', next)) {
      // Recover from a bad factory method.
      reportRecoverableError(next, codes.messageExpectedBody);
      next = rewriter.insertToken(
          next, new SyntheticToken(TokenType.FUNCTION, next.next.charOffset));
      Token begin = next;
      token = parseExpression(next);
      if (!ofFunctionExpression) {
        token = ensureSemicolon(token);
        listener.handleExpressionFunctionBody(begin, token);
      } else {
        listener.handleExpressionFunctionBody(begin, /* endToken = */ null);
      }
      return token;
    }
    Token begin = next;
    int statementCount = 0;
    if (!optional('{', next)) {
      // Recovery
      // If `return` used instead of `=>`, then report an error and continue
      if (optional('return', next)) {
        reportRecoverableError(next, codes.messageExpectedBody);
        next = rewriter.insertToken(
            next, new SyntheticToken(TokenType.FUNCTION, next.next.charOffset));
        return parseExpressionFunctionBody(next, ofFunctionExpression);
      }
      // If there is a stray simple identifier in the function expression
      // because the user is typing (e.g. `() asy => null;`)
      // then report an error, skip the token, and continue parsing.
      if (next.isKeywordOrIdentifier && optional('=>', next.next)) {
        reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
        return parseExpressionFunctionBody(next.next, ofFunctionExpression);
      }
      if (next.isKeywordOrIdentifier && optional('{', next.next)) {
        reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
        token = next;
        begin = next = token.next;
        // Fall through to parse the block.
      } else {
        token = ensureBlock(
            token,
            codes.templateExpectedFunctionBody,
            /* missingBlockName = */ null);
        listener.handleInvalidFunctionBody(token);
        return token.endGroup;
      }
    }

    LoopState savedLoopState = loopState;
    loopState = LoopState.OutsideLoop;
    listener.beginBlockFunctionBody(begin);
    token = next;
    while (notEofOrValue('}', token.next)) {
      Token startToken = token.next;
      token = parseStatement(token);
      if (identical(token.next, startToken)) {
        // No progress was made, so we report the current token as being invalid
        // and move forward.
        reportRecoverableError(
            token, codes.templateUnexpectedToken.withArguments(token));
        token = token.next;
      }
      ++statementCount;
    }
    token = token.next;
    assert(token.isEof || optional('}', token));
    listener.endBlockFunctionBody(statementCount, begin, token);
    loopState = savedLoopState;
    return token;
  }

  Token parseExpressionFunctionBody(Token token, bool ofFunctionExpression) {
    assert(optional('=>', token));
    Token begin = token;
    token = parseExpression(token);
    if (!ofFunctionExpression) {
      token = ensureSemicolon(token);
      listener.handleExpressionFunctionBody(begin, token);
    } else {
      listener.handleExpressionFunctionBody(begin, /* endToken = */ null);
    }
    if (inGenerator) {
      listener.handleInvalidStatement(
          begin, codes.messageGeneratorReturnsValue);
    }
    return token;
  }

  Token skipAsyncModifier(Token token) {
    String value = token.next.stringValue;
    if (identical(value, 'async')) {
      token = token.next;
      value = token.next.stringValue;

      if (identical(value, '*')) {
        token = token.next;
      }
    } else if (identical(value, 'sync')) {
      token = token.next;
      value = token.next.stringValue;

      if (identical(value, '*')) {
        token = token.next;
      }
    }
    return token;
  }

  Token parseAsyncModifierOpt(Token token) {
    Token async;
    Token star;
    asyncState = AsyncModifier.Sync;
    Token next = token.next;
    if (optional('async', next)) {
      async = token = next;
      next = token.next;
      if (optional('*', next)) {
        asyncState = AsyncModifier.AsyncStar;
        star = next;
        token = next;
      } else {
        asyncState = AsyncModifier.Async;
      }
    } else if (optional('sync', next)) {
      async = token = next;
      next = token.next;
      if (optional('*', next)) {
        asyncState = AsyncModifier.SyncStar;
        star = next;
        token = next;
      } else {
        reportRecoverableError(async, codes.messageInvalidSyncModifier);
      }
    }
    listener.handleAsyncModifier(async, star);
    if (!inPlainSync && optional(';', token.next)) {
      reportRecoverableError(token.next, codes.messageAbstractNotSync);
    }
    return token;
  }

  int statementDepth = 0;
  Token parseStatement(Token token) {
    if (statementDepth++ > 500) {
      // This happens for degenerate programs, for example, a lot of nested
      // if-statements. The language test deep_nesting2_negative_test, for
      // example, provokes this.
      return recoverFromStackOverflow(token);
    }
    Token result = parseStatementX(token);
    statementDepth--;
    return result;
  }

  Token parseStatementX(Token token) {
    if (identical(token.next.kind, IDENTIFIER_TOKEN)) {
      if (optional(':', token.next.next)) {
        return parseLabeledStatement(token);
      }
      return parseExpressionStatementOrDeclarationAfterModifiers(
          token,
          token,
          /* lateToken = */ null,
          /* varFinalOrConst = */ null,
          /* typeInfo = */ null,
          /* onlyParseVariableDeclarationStart = */ false);
    }
    final String value = token.next.stringValue;
    if (identical(value, '{')) {
      // The scanner ensures that `{` always has a closing `}`.
      return parseBlock(token, BlockKind.statement);
    } else if (identical(value, 'return')) {
      return parseReturnStatement(token);
    } else if (identical(value, 'var') || identical(value, 'final')) {
      Token varOrFinal = token.next;
      if (!isModifier(varOrFinal.next)) {
        return parseExpressionStatementOrDeclarationAfterModifiers(
            varOrFinal,
            token,
            /* lateToken = */ null,
            varOrFinal,
            /* typeInfo = */ null,
            /* onlyParseVariableDeclarationStart = */ false);
      }
      return parseExpressionStatementOrDeclaration(token);
    } else if (identical(value, 'if')) {
      return parseIfStatement(token);
    } else if (identical(value, 'await') && optional('for', token.next.next)) {
      return parseForStatement(token.next, token.next);
    } else if (identical(value, 'for')) {
      return parseForStatement(token, /* awaitToken = */ null);
    } else if (identical(value, 'rethrow')) {
      return parseRethrowStatement(token);
    } else if (identical(value, 'while')) {
      return parseWhileStatement(token);
    } else if (identical(value, 'do')) {
      return parseDoWhileStatement(token);
    } else if (identical(value, 'try')) {
      return parseTryStatement(token);
    } else if (identical(value, 'switch')) {
      return parseSwitchStatement(token);
    } else if (identical(value, 'break')) {
      return parseBreakStatement(token);
    } else if (identical(value, 'continue')) {
      return parseContinueStatement(token);
    } else if (identical(value, 'assert')) {
      return parseAssertStatement(token);
    } else if (identical(value, ';')) {
      return parseEmptyStatement(token);
    } else if (identical(value, 'yield')) {
      switch (asyncState) {
        case AsyncModifier.Sync:
          if (optional(':', token.next.next)) {
            return parseLabeledStatement(token);
          }
          if (looksLikeYieldStatement(token)) {
            // Recovery: looks like an expression preceded by `yield` but not
            // inside an Async or AsyncStar context. parseYieldStatement will
            // report the error.
            return parseYieldStatement(token);
          }
          return parseExpressionStatementOrDeclaration(token);

        case AsyncModifier.SyncStar:
        case AsyncModifier.AsyncStar:
          return parseYieldStatement(token);

        case AsyncModifier.Async:
          reportRecoverableError(token.next, codes.messageYieldNotGenerator);
          return parseYieldStatement(token);
      }
      throw "Internal error: Unknown asyncState: '$asyncState'.";
    } else if (identical(value, 'const')) {
      return parseExpressionStatementOrConstDeclaration(token);
    } else if (identical(value, 'await')) {
      if (inPlainSync) {
        if (!looksLikeAwaitExpression(token)) {
          return parseExpressionStatementOrDeclaration(token);
        }
        // Recovery: looks like an expression preceded by `await`
        // but not inside an async context.
        // Fall through to parseExpressionStatement
        // and parseAwaitExpression will report the error.
      }
      return parseExpressionStatement(token);
    } else if (identical(value, 'set') && token.next.next.isIdentifier) {
      // Recovery: invalid use of `set`
      reportRecoverableErrorWithToken(
          token.next, codes.templateUnexpectedToken);
      return parseStatementX(token.next);
    } else if (token.next.isIdentifier) {
      if (optional(':', token.next.next)) {
        return parseLabeledStatement(token);
      }
      return parseExpressionStatementOrDeclaration(token);
    } else {
      return parseExpressionStatementOrDeclaration(token);
    }
  }

  /// ```
  /// yieldStatement:
  ///   'yield' expression? ';'
  /// ;
  /// ```
  Token parseYieldStatement(Token token) {
    Token begin = token = token.next;
    assert(optional('yield', token));
    listener.beginYieldStatement(begin);
    Token starToken;
    if (optional('*', token.next)) {
      starToken = token = token.next;
    }
    token = parseExpression(token);
    token = ensureSemicolon(token);
    if (inPlainSync) {
      // `yield` is only allowed in generators; A recoverable error is already
      // reported in the "async" case in `parseStatementX`. Only the "sync" case
      // needs to be handled here.
      codes.MessageCode errorCode = codes.messageYieldNotGenerator;
      reportRecoverableError(begin, errorCode);
      // TODO(srawlins): Add tests in analyzer to ensure the AstBuilder
      //  correctly handles invalid yields, and that the error message is
      //  correctly plumbed through.
      listener.endInvalidYieldStatement(begin, starToken, token, errorCode);
    } else {
      listener.endYieldStatement(begin, starToken, token);
    }
    return token;
  }

  /// ```
  /// returnStatement:
  ///   'return' expression? ';'
  /// ;
  /// ```
  Token parseReturnStatement(Token token) {
    Token begin = token = token.next;
    assert(optional('return', token));
    listener.beginReturnStatement(begin);
    Token next = token.next;
    if (optional(';', next)) {
      listener.endReturnStatement(/* hasExpression = */ false, begin, next);
      return next;
    }
    token = parseExpression(token);
    token = ensureSemicolon(token);
    listener.endReturnStatement(/* hasExpression = */ true, begin, token);
    if (inGenerator) {
      listener.handleInvalidStatement(
          begin, codes.messageGeneratorReturnsValue);
    }
    return token;
  }

  /// ```
  /// label:
  ///   identifier ':'
  /// ;
  /// ```
  Token parseLabel(Token token) {
    assert(token.next.isIdentifier);
    token = ensureIdentifier(token, IdentifierContext.labelDeclaration).next;
    assert(optional(':', token));
    listener.handleLabel(token);
    return token;
  }

  /// ```
  /// statement:
  ///   label* nonLabelledStatement
  /// ;
  /// ```
  Token parseLabeledStatement(Token token) {
    Token next = token.next;
    assert(next.isIdentifier);
    assert(optional(':', next.next));
    int labelCount = 0;
    do {
      token = parseLabel(token);
      next = token.next;
      labelCount++;
    } while (next.isIdentifier && optional(':', next.next));
    listener.beginLabeledStatement(next, labelCount);
    token = parseStatement(token);
    listener.endLabeledStatement(labelCount);
    return token;
  }

  /// ```
  /// expressionStatement:
  ///   expression? ';'
  /// ;
  /// ```
  ///
  /// Note: This method can fail to make progress. If there is neither an
  /// expression nor a semi-colon, then a synthetic identifier and synthetic
  /// semicolon will be inserted before [token] and the semicolon will be
  /// returned.
  Token parseExpressionStatement(Token token) {
    // TODO(brianwilkerson): If the next token is not the start of a valid
    // expression, then this method shouldn't report that we have an expression
    // statement.
    token = parseExpression(token);
    token = ensureSemicolon(token);
    listener.handleExpressionStatement(token);
    return token;
  }

  int expressionDepth = 0;
  Token parseExpression(Token token) {
    if (expressionDepth++ > 500) {
      // This happens in degenerate programs, for example, with a lot of nested
      // list literals. This is provoked by, for example, the language test
      // deep_nesting1_negative_test.
      Token next = token.next;
      reportRecoverableError(next, codes.messageStackOverflow);

      // Recovery
      Token endGroup = next.endGroup;
      if (endGroup != null) {
        while (!next.isEof && !identical(next, endGroup)) {
          token = next;
          next = token.next;
        }
      } else {
        while (!isOneOf(next, const [')', ']', '}', ';'])) {
          token = next;
          next = token.next;
        }
      }
      if (!token.isEof) {
        token = rewriter.insertSyntheticIdentifier(token);
        listener.handleIdentifier(token, IdentifierContext.expression);
      }
    } else {
      token = optional('throw', token.next)
          ? parseThrowExpression(token, /* allowCascades = */ true)
          : parsePrecedenceExpression(
              token, ASSIGNMENT_PRECEDENCE, /* allowCascades = */ true);
    }
    expressionDepth--;
    return token;
  }

  Token parseExpressionWithoutCascade(Token token) {
    return optional('throw', token.next)
        ? parseThrowExpression(token, /* allowCascades = */ false)
        : parsePrecedenceExpression(
            token, ASSIGNMENT_PRECEDENCE, /* allowCascades = */ false);
  }

  bool canParseAsConditional(Token question) {
    // We want to check if we can parse, not send events and permanently change
    // the token stream. Set it up so we can do that.
    Listener originalListener = listener;
    TokenStreamRewriter originalRewriter = cachedRewriter;
    NullListener nullListener = listener = new NullListener();
    UndoableTokenStreamRewriter undoableTokenStreamRewriter =
        new UndoableTokenStreamRewriter();
    cachedRewriter = undoableTokenStreamRewriter;

    bool isConditional = false;

    Token afterExpression1 = parseExpressionWithoutCascade(question);
    if (!nullListener.hasErrors && optional(':', afterExpression1.next)) {
      parseExpressionWithoutCascade(afterExpression1.next);
      if (!nullListener.hasErrors) {
        // Now we know it's a conditional expression.
        isConditional = true;
      }
    }

    // Undo all changes and reset.
    undoableTokenStreamRewriter.undo();
    listener = originalListener;
    cachedRewriter = originalRewriter;

    return isConditional;
  }

  Token parseConditionalExpressionRest(Token token) {
    Token question = token = token.next;
    assert(optional('?', question));
    listener.beginConditionalExpression(token);
    token = parseExpressionWithoutCascade(token);
    Token colon = ensureColon(token);
    listener.handleConditionalExpressionColon();
    token = parseExpressionWithoutCascade(colon);
    listener.endConditionalExpression(question, colon);
    return token;
  }

  Token parsePrecedenceExpression(
      Token token, int precedence, bool allowCascades) {
    assert(precedence >= 1);
    assert(precedence <= SELECTOR_PRECEDENCE);
    token = parseUnaryExpression(token, allowCascades);
    Token bangToken = token;
    if (optional('!', token.next)) {
      bangToken = token.next;
    }
    TypeParamOrArgInfo typeArg = computeMethodTypeArguments(bangToken);
    if (typeArg != noTypeParamOrArg) {
      // For example a(b)<T>(c), where token is before '<'.
      if (optional('!', bangToken)) {
        listener.handleNonNullAssertExpression(bangToken);
      }
      token = typeArg.parseArguments(bangToken, this);
      assert(optional('(', token.next));
    }
    Token next = token.next;
    TokenType type = next.type;
    int tokenLevel = _computePrecedence(next);
    for (int level = tokenLevel; level >= precedence; --level) {
      int lastBinaryExpressionLevel = -1;
      Token lastCascade;
      while (identical(tokenLevel, level)) {
        Token operator = next;
        if (identical(tokenLevel, CASCADE_PRECEDENCE)) {
          if (!allowCascades) {
            return token;
          } else if (lastCascade != null && optional('?..', next)) {
            reportRecoverableError(
                next, codes.messageNullAwareCascadeOutOfOrder);
          }
          lastCascade = next;
          token = parseCascadeExpression(token);
        } else if (identical(tokenLevel, ASSIGNMENT_PRECEDENCE)) {
          // Right associative, so we recurse at the same precedence
          // level.
          Token next = token.next;
          token = optional('throw', next.next)
              ? parseThrowExpression(next, /* allowCascades = */ false)
              : parsePrecedenceExpression(next, level, allowCascades);
          listener.handleAssignmentExpression(operator);
        } else if (identical(tokenLevel, POSTFIX_PRECEDENCE)) {
          if ((identical(type, TokenType.PLUS_PLUS)) ||
              (identical(type, TokenType.MINUS_MINUS))) {
            listener.handleUnaryPostfixAssignmentExpression(token.next);
            token = next;
          } else if (identical(type, TokenType.BANG)) {
            listener.handleNonNullAssertExpression(next);
            token = next;
          }
        } else if (identical(tokenLevel, SELECTOR_PRECEDENCE)) {
          if (identical(type, TokenType.PERIOD) ||
              identical(type, TokenType.QUESTION_PERIOD)) {
            // Left associative, so we recurse at the next higher precedence
            // level. However, SELECTOR_PRECEDENCE is the highest level, so we
            // should just call [parseUnaryExpression] directly. However, a
            // unary expression isn't legal after a period, so we call
            // [parsePrimary] instead.
            token = parsePrimary(
                token.next, IdentifierContext.expressionContinuation);
            listener.handleEndingBinaryExpression(operator);

            Token bangToken = token;
            if (optional('!', token.next)) {
              bangToken = token.next;
            }
            typeArg = computeMethodTypeArguments(bangToken);
            if (typeArg != noTypeParamOrArg) {
              // For example e.f<T>(c), where token is before '<'.
              if (optional('!', bangToken)) {
                listener.handleNonNullAssertExpression(bangToken);
              }
              token = typeArg.parseArguments(bangToken, this);
              assert(optional('(', token.next));
            }
          } else if (identical(type, TokenType.OPEN_PAREN) ||
              identical(type, TokenType.OPEN_SQUARE_BRACKET)) {
            token = parseArgumentOrIndexStar(
                token, typeArg, /* checkedNullAware = */ false);
          } else if (identical(type, TokenType.QUESTION)) {
            // We have determined selector precedence so this is a null-aware
            // bracket operator.
            token = parseArgumentOrIndexStar(
                token, typeArg, /* checkedNullAware = */ true);
          } else if (identical(type, TokenType.INDEX)) {
            rewriteSquareBrackets(token);
            token = parseArgumentOrIndexStar(
                token, noTypeParamOrArg, /* checkedNullAware = */ false);
          } else if (identical(type, TokenType.BANG)) {
            listener.handleNonNullAssertExpression(token.next);
            token = next;
          } else {
            // Recovery
            reportRecoverableErrorWithToken(
                token.next, codes.templateUnexpectedToken);
            token = next;
          }
        } else if (identical(type, TokenType.IS)) {
          token = parseIsOperatorRest(token);
        } else if (identical(type, TokenType.AS)) {
          token = parseAsOperatorRest(token);
        } else if (identical(type, TokenType.QUESTION)) {
          token = parseConditionalExpressionRest(token);
        } else {
          if (level == EQUALITY_PRECEDENCE || level == RELATIONAL_PRECEDENCE) {
            // We don't allow (a == b == c) or (a < b < c).
            if (lastBinaryExpressionLevel == level) {
              // Report an error, then continue parsing as if it is legal.
              reportRecoverableError(
                  next, codes.messageEqualityCannotBeEqualityOperand);
            } else {
              // Set a flag to catch subsequent binary expressions of this type.
              lastBinaryExpressionLevel = level;
            }
          }
          listener.beginBinaryExpression(next);
          // Left associative, so we recurse at the next higher
          // precedence level.
          token =
              parsePrecedenceExpression(token.next, level + 1, allowCascades);
          listener.endBinaryExpression(operator);
        }
        next = token.next;
        type = next.type;
        tokenLevel = _computePrecedence(next);
      }
    }
    return token;
  }

  int _computePrecedence(Token token) {
    TokenType type = token.type;
    if (identical(type, TokenType.BANG)) {
      // The '!' has prefix precedence but here it's being used as a
      // postfix operator to assert the expression has a non-null value.
      TokenType nextType = token.next.type;
      if (identical(nextType, TokenType.PERIOD) ||
          identical(nextType, TokenType.QUESTION) ||
          identical(nextType, TokenType.OPEN_PAREN) ||
          identical(nextType, TokenType.OPEN_SQUARE_BRACKET) ||
          identical(nextType, TokenType.QUESTION_PERIOD)) {
        return SELECTOR_PRECEDENCE;
      }
      return POSTFIX_PRECEDENCE;
    } else if (identical(type, TokenType.QUESTION) &&
        optional('[', token.next)) {
      // "?[" can be a null-aware bracket or a conditional. If it's a
      // null-aware bracket it has selector precedence.
      bool isConditional = canParseAsConditional(token);
      if (!isConditional) {
        return SELECTOR_PRECEDENCE;
      }
    }
    return type.precedence;
  }

  Token parseCascadeExpression(Token token) {
    Token cascadeOperator = token = token.next;
    assert(optional('..', cascadeOperator) || optional('?..', cascadeOperator));
    listener.beginCascade(cascadeOperator);
    if (optional('[', token.next)) {
      token = parseArgumentOrIndexStar(
          token, noTypeParamOrArg, /* checkedNullAware = */ false);
    } else {
      token = parseSend(token, IdentifierContext.expressionContinuation);
      listener.handleEndingBinaryExpression(cascadeOperator);
    }
    Token next = token.next;
    Token mark;
    do {
      mark = token;
      if (optional('.', next) || optional('?.', next)) {
        Token period = next;
        token = parseSend(next, IdentifierContext.expressionContinuation);
        next = token.next;
        listener.handleEndingBinaryExpression(period);
      } else if (optional('!', next)) {
        listener.handleNonNullAssertExpression(next);
        token = next;
        next = token.next;
      }
      TypeParamOrArgInfo typeArg = computeMethodTypeArguments(token);
      if (typeArg != noTypeParamOrArg) {
        // For example a(b)..<T>(c), where token is '<'.
        token = typeArg.parseArguments(token, this);
        next = token.next;
        assert(optional('(', next));
      }
      TokenType nextType = next.type;
      if (identical(nextType, TokenType.INDEX)) {
        // If we don't split the '[]' here we will stop parsing it as a cascade
        // and either split it later (parsing it wrong) or inserting ; before it
        // (also wrong).
        // See also https://github.com/dart-lang/sdk/issues/42267.
        rewriteSquareBrackets(token);
      }
      token = parseArgumentOrIndexStar(
          token, typeArg, /* checkedNullAware = */ false);
      next = token.next;
    } while (!identical(mark, token));

    if (identical(next.type.precedence, ASSIGNMENT_PRECEDENCE)) {
      Token assignment = next;
      token = parseExpressionWithoutCascade(next);
      listener.handleAssignmentExpression(assignment);
    }
    listener.endCascade();
    return token;
  }

  Token parseUnaryExpression(Token token, bool allowCascades) {
    String value = token.next.stringValue;
    // Prefix:
    if (identical(value, 'await')) {
      if (inPlainSync) {
        if (!looksLikeAwaitExpression(token)) {
          return parsePrimary(token, IdentifierContext.expression);
        }
        // Recovery: Looks like an expression preceded by `await`.
        // Fall through and let parseAwaitExpression report the error.
      }
      return parseAwaitExpression(token, allowCascades);
    } else if (identical(value, '+')) {
      // Dart no longer allows prefix-plus.
      rewriteAndRecover(
          token,
          // TODO(danrubel): Consider reporting "missing identifier" instead.
          codes.messageUnsupportedPrefixPlus,
          new SyntheticStringToken(
              TokenType.IDENTIFIER, '', token.next.offset));
      return parsePrimary(token, IdentifierContext.expression);
    } else if ((identical(value, '!')) ||
        (identical(value, '-')) ||
        (identical(value, '~'))) {
      Token operator = token.next;
      // Right associative, so we recurse at the same precedence
      // level.
      token = parsePrecedenceExpression(
          token.next, POSTFIX_PRECEDENCE, allowCascades);
      listener.handleUnaryPrefixExpression(operator);
      return token;
    } else if ((identical(value, '++')) || identical(value, '--')) {
      // TODO(ahe): Validate this is used correctly.
      Token operator = token.next;
      // Right associative, so we recurse at the same precedence
      // level.
      token = parsePrecedenceExpression(
          token.next, POSTFIX_PRECEDENCE, allowCascades);
      listener.handleUnaryPrefixAssignmentExpression(operator);
      return token;
    } else if (token.next.isIdentifier) {
      Token identifier = token.next;
      if (optional(".", identifier.next)) {
        identifier = identifier.next.next;
      }
      if (identifier.isIdentifier) {
        // Looking at `identifier ('.' identifier)?`.
        if (optional("<", identifier.next)) {
          TypeParamOrArgInfo typeArg = computeTypeParamOrArg(identifier);
          if (typeArg != noTypeParamOrArg) {
            Token endTypeArguments = typeArg.skip(identifier);
            if (optional(".", endTypeArguments.next)) {
              return parseImplicitCreationExpression(token, typeArg);
            }
          }
        }
      }
    }
    return parsePrimary(token, IdentifierContext.expression);
  }

  Token parseArgumentOrIndexStar(
      Token token, TypeParamOrArgInfo typeArg, bool checkedNullAware) {
    Token next = token.next;
    final Token beginToken = next;
    while (true) {
      bool potentialNullAware =
          (optional('?', next) && optional('[', next.next));
      if (potentialNullAware && !checkedNullAware) {
        // While it's a potential null aware index it hasn't been checked.
        // It might be a conditional expression.
        assert(optional('?', next));
        bool isConditional = canParseAsConditional(next);
        if (isConditional) potentialNullAware = false;
      }

      if (optional('[', next) || potentialNullAware) {
        assert(typeArg == noTypeParamOrArg);
        Token openSquareBracket = next;
        Token question;
        if (optional('?', next)) {
          question = next;
          next = next.next;
          openSquareBracket = next;
          assert(optional('[', openSquareBracket));
        }
        bool old = mayParseFunctionExpressions;
        mayParseFunctionExpressions = true;
        token = parseExpression(next);
        next = token.next;
        mayParseFunctionExpressions = old;
        if (!optional(']', next)) {
          // Recovery
          reportRecoverableError(
              next, codes.templateExpectedButGot.withArguments(']'));
          // Scanner ensures a closing ']'
          Token endGroup = openSquareBracket.endGroup;
          if (endGroup.isSynthetic) {
            // Scanner inserted closing ']' in the wrong place, so move it.
            next = rewriter.moveSynthetic(token, endGroup);
          } else {
            // Skip over unexpected tokens to where the user placed the `]`.
            next = endGroup;
          }
        }
        listener.handleIndexedExpression(question, openSquareBracket, next);
        token = next;
        Token bangToken = token;
        if (optional('!', token.next)) {
          bangToken = token.next;
        }
        typeArg = computeMethodTypeArguments(bangToken);
        if (typeArg != noTypeParamOrArg) {
          // For example a[b]<T>(c), where token is before '<'.
          if (optional('!', bangToken)) {
            listener.handleNonNullAssertExpression(bangToken);
          }
          token = typeArg.parseArguments(bangToken, this);
          assert(optional('(', token.next));
        }
        next = token.next;
      } else if (optional('(', next)) {
        if (typeArg == noTypeParamOrArg) {
          listener.handleNoTypeArguments(next);
        }
        token = parseArguments(token);
        listener.handleSend(beginToken, token);
        Token bangToken = token;
        if (optional('!', token.next)) {
          bangToken = token.next;
        }
        typeArg = computeMethodTypeArguments(bangToken);
        if (typeArg != noTypeParamOrArg) {
          // For example a(b)<T>(c), where token is before '<'.
          if (optional('!', bangToken)) {
            listener.handleNonNullAssertExpression(bangToken);
          }
          token = typeArg.parseArguments(bangToken, this);
          assert(optional('(', token.next));
        }
        next = token.next;
      } else {
        break;
      }
    }
    return token;
  }

  Token parsePrimary(Token token, IdentifierContext context) {
    final int kind = token.next.kind;
    if (kind == IDENTIFIER_TOKEN) {
      return parseSendOrFunctionLiteral(token, context);
    } else if (kind == INT_TOKEN || kind == HEXADECIMAL_TOKEN) {
      return parseLiteralInt(token);
    } else if (kind == DOUBLE_TOKEN) {
      return parseLiteralDouble(token);
    } else if (kind == STRING_TOKEN) {
      return parseLiteralString(token);
    } else if (kind == HASH_TOKEN) {
      return parseLiteralSymbol(token);
    } else if (kind == KEYWORD_TOKEN) {
      final String value = token.next.stringValue;
      if (identical(value, "true") || identical(value, "false")) {
        return parseLiteralBool(token);
      } else if (identical(value, "null")) {
        return parseLiteralNull(token);
      } else if (identical(value, "this")) {
        return parseThisExpression(token, context);
      } else if (identical(value, "super")) {
        return parseSuperExpression(token, context);
      } else if (identical(value, "new")) {
        return parseNewExpression(token);
      } else if (identical(value, "const")) {
        return parseConstExpression(token);
      } else if (identical(value, "void")) {
        return parseSendOrFunctionLiteral(token, context);
      } else if (!inPlainSync &&
          (identical(value, "yield") || identical(value, "async"))) {
        // Fall through to the recovery code.
      } else if (identical(value, "assert")) {
        return parseAssert(token, Assert.Expression);
      } else if (token.next.isIdentifier) {
        return parseSendOrFunctionLiteral(token, context);
      } else if (identical(value, "return")) {
        // Recovery
        token = token.next;
        reportRecoverableErrorWithToken(token, codes.templateUnexpectedToken);
        return parsePrimary(token, context);
      } else {
        // Fall through to the recovery code.
      }
    } else if (kind == OPEN_PAREN_TOKEN) {
      return parseParenthesizedExpressionOrFunctionLiteral(token);
    } else if (kind == OPEN_SQUARE_BRACKET_TOKEN ||
        optional('[]', token.next)) {
      listener.handleNoTypeArguments(token.next);
      return parseLiteralListSuffix(token, /* constKeyword = */ null);
    } else if (kind == OPEN_CURLY_BRACKET_TOKEN) {
      listener.handleNoTypeArguments(token.next);
      return parseLiteralSetOrMapSuffix(token, /* constKeyword = */ null);
    } else if (kind == LT_TOKEN) {
      return parseLiteralListSetMapOrFunction(token, /* constKeyword = */ null);
    } else {
      // Fall through to the recovery code.
    }
    //
    // Recovery code.
    //
    return parseSend(token, context);
  }

  Token parseParenthesizedExpressionOrFunctionLiteral(Token token) {
    Token next = token.next;
    assert(optional('(', next));
    Token nextToken = next.endGroup.next;
    int kind = nextToken.kind;
    if (mayParseFunctionExpressions) {
      if ((identical(kind, FUNCTION_TOKEN) ||
          identical(kind, OPEN_CURLY_BRACKET_TOKEN))) {
        listener.handleNoTypeVariables(next);
        return parseFunctionExpression(token);
      } else if (identical(kind, KEYWORD_TOKEN) ||
          identical(kind, IDENTIFIER_TOKEN)) {
        if (optional('async', nextToken) || optional('sync', nextToken)) {
          listener.handleNoTypeVariables(next);
          return parseFunctionExpression(token);
        }
        // Recovery
        // If there is a stray simple identifier in the function expression
        // because the user is typing (e.g. `() asy {}`) then continue parsing
        // and allow parseFunctionExpression to report an unexpected token.
        kind = nextToken.next.kind;
        if ((identical(kind, FUNCTION_TOKEN) ||
            identical(kind, OPEN_CURLY_BRACKET_TOKEN))) {
          listener.handleNoTypeVariables(next);
          return parseFunctionExpression(token);
        }
      }
    }
    bool old = mayParseFunctionExpressions;
    mayParseFunctionExpressions = true;
    token = parseParenthesizedExpression(token);
    mayParseFunctionExpressions = old;
    return token;
  }

  Token ensureParenthesizedCondition(Token token) {
    Token openParen = token.next;
    if (!optional('(', openParen)) {
      // Recover
      reportRecoverableError(
          openParen, codes.templateExpectedToken.withArguments('('));
      openParen = rewriter.insertParens(token, /* includeIdentifier = */ false);
    }
    token = parseExpressionInParenthesisRest(openParen);
    listener.handleParenthesizedCondition(openParen);
    return token;
  }

  Token parseParenthesizedExpression(Token token) {
    Token begin = token.next;
    token = parseExpressionInParenthesis(token);
    listener.handleParenthesizedExpression(begin);
    return token;
  }

  Token parseExpressionInParenthesis(Token token) {
    return parseExpressionInParenthesisRest(token.next);
  }

  Token parseExpressionInParenthesisRest(Token token) {
    assert(optional('(', token));
    BeginToken begin = token;
    token = parseExpression(token);
    token = ensureCloseParen(token, begin);
    assert(optional(')', token));
    return token;
  }

  Token parseThisExpression(Token token, IdentifierContext context) {
    Token thisToken = token = token.next;
    assert(optional('this', thisToken));
    listener.handleThisExpression(thisToken, context);
    Token next = token.next;
    if (optional('(', next)) {
      // Constructor forwarding.
      listener.handleNoTypeArguments(next);
      token = parseArguments(token);
      listener.handleSend(thisToken, token.next);
    }
    return token;
  }

  Token parseSuperExpression(Token token, IdentifierContext context) {
    Token superToken = token = token.next;
    assert(optional('super', token));
    listener.handleSuperExpression(superToken, context);
    Token next = token.next;
    if (optional('(', next)) {
      // Super constructor.
      listener.handleNoTypeArguments(next);
      token = parseArguments(token);
      listener.handleSend(superToken, token.next);
    } else if (optional("?.", next)) {
      reportRecoverableError(next, codes.messageSuperNullAware);
    }
    return token;
  }

  /// This method parses the portion of a list literal starting with the left
  /// square bracket.
  ///
  /// ```
  /// listLiteral:
  ///   'const'? typeArguments? '[' (expressionList ','?)? ']'
  /// ;
  /// ```
  ///
  /// Provide a [constKeyword] if the literal is preceded by 'const', or `null`
  /// if not. This is a suffix parser because it is assumed that type arguments
  /// have been parsed, or `listener.handleNoTypeArguments` has been executed.
  Token parseLiteralListSuffix(Token token, Token constKeyword) {
    Token beforeToken = token;
    Token beginToken = token = token.next;
    assert(optional('[', token) || optional('[]', token));
    int count = 0;
    if (optional('[]', token)) {
      token = rewriteSquareBrackets(beforeToken).next;
      listener.handleLiteralList(
          /* count = */ 0,
          token,
          constKeyword,
          token.next);
      return token.next;
    }
    bool old = mayParseFunctionExpressions;
    mayParseFunctionExpressions = true;
    while (true) {
      Token next = token.next;
      if (optional(']', next)) {
        token = next;
        break;
      }
      int ifCount = 0;
      LiteralEntryInfo info = computeLiteralEntry(token);
      while (info != null) {
        if (info.hasEntry) {
          token = parseExpression(token);
        } else {
          token = info.parse(token, this);
        }
        ifCount += info.ifConditionDelta;
        info = info.computeNext(token);
      }
      next = token.next;
      ++count;
      if (!optional(',', next)) {
        if (optional(']', next)) {
          token = next;
          break;
        }

        // Recovery
        if (!looksLikeLiteralEntry(next)) {
          if (beginToken.endGroup.isSynthetic) {
            // The scanner has already reported an error,
            // but inserted `]` in the wrong place.
            token = rewriter.moveSynthetic(token, beginToken.endGroup);
          } else {
            // Report an error and jump to the end of the list.
            reportRecoverableError(
                next, codes.templateExpectedButGot.withArguments(']'));
            token = beginToken.endGroup;
          }
          break;
        }
        // This looks like the start of an expression.
        // Report an error, insert the comma, and continue parsing.
        SyntheticToken comma = new SyntheticToken(TokenType.COMMA, next.offset);
        codes.Message message = ifCount > 0
            ? codes.messageExpectedElseOrComma
            : codes.templateExpectedButGot.withArguments(',');
        next = rewriteAndRecover(token, message, comma);
      }
      token = next;
    }
    mayParseFunctionExpressions = old;
    listener.handleLiteralList(count, beginToken, constKeyword, token);
    return token;
  }

  /// This method parses the portion of a set or map literal that starts with
  /// the left curly brace when there are no leading type arguments.
  Token parseLiteralSetOrMapSuffix(Token token, Token constKeyword) {
    Token leftBrace = token = token.next;
    assert(optional('{', leftBrace));
    Token next = token.next;
    if (optional('}', next)) {
      listener.handleLiteralSetOrMap(/* count = */ 0, leftBrace, constKeyword,
          next, /* hasSetEntry = */ false);
      return next;
    }

    final bool old = mayParseFunctionExpressions;
    mayParseFunctionExpressions = true;
    int count = 0;
    // TODO(danrubel): hasSetEntry parameter exists for replicating existing
    // behavior and will be removed once unified collection has been enabled
    bool hasSetEntry;

    while (true) {
      int ifCount = 0;
      LiteralEntryInfo info = computeLiteralEntry(token);
      if (info == simpleEntry) {
        // TODO(danrubel): Remove this section and use the while loop below
        // once hasSetEntry is no longer needed.
        token = parseExpression(token);
        bool isMapEntry = optional(':', token.next);
        hasSetEntry ??= !isMapEntry;
        if (isMapEntry) {
          Token colon = token.next;
          token = parseExpression(colon);
          listener.handleLiteralMapEntry(colon, token.next);
        }
      } else {
        while (info != null) {
          if (info.hasEntry) {
            token = parseExpression(token);
            if (optional(':', token.next)) {
              Token colon = token.next;
              token = parseExpression(colon);
              listener.handleLiteralMapEntry(colon, token.next);
            }
          } else {
            token = info.parse(token, this);
          }
          ifCount += info.ifConditionDelta;
          info = info.computeNext(token);
        }
      }
      ++count;
      next = token.next;

      Token comma;
      if (optional(',', next)) {
        comma = token = next;
        next = token.next;
      }
      if (optional('}', next)) {
        listener.handleLiteralSetOrMap(
            count, leftBrace, constKeyword, next, hasSetEntry ?? false);
        mayParseFunctionExpressions = old;
        return next;
      }

      if (comma == null) {
        // Recovery
        if (looksLikeLiteralEntry(next)) {
          // If this looks like the start of an expression,
          // then report an error, insert the comma, and continue parsing.
          // TODO(danrubel): Consider better error message
          SyntheticToken comma =
              new SyntheticToken(TokenType.COMMA, next.offset);
          codes.Message message = ifCount > 0
              ? codes.messageExpectedElseOrComma
              : codes.templateExpectedButGot.withArguments(',');
          token = rewriteAndRecover(token, message, comma);
        } else {
          reportRecoverableError(
              next, codes.templateExpectedButGot.withArguments('}'));
          // Scanner guarantees a closing curly bracket
          next = leftBrace.endGroup;
          listener.handleLiteralSetOrMap(
              count, leftBrace, constKeyword, next, hasSetEntry ?? false);
          mayParseFunctionExpressions = old;
          return next;
        }
      }
    }
  }

  /// formalParameterList functionBody.
  ///
  /// This is a suffix parser because it is assumed that type arguments have
  /// been parsed, or `listener.handleNoTypeArguments(..)` has been executed.
  Token parseLiteralFunctionSuffix(Token token) {
    assert(optional('(', token.next));
    // Scanner ensures `(` has matching `)`.
    Token next = token.next.endGroup.next;
    int kind = next.kind;
    if (!identical(kind, FUNCTION_TOKEN) &&
        !identical(kind, OPEN_CURLY_BRACKET_TOKEN) &&
        (!identical(kind, KEYWORD_TOKEN) ||
            !optional('async', next) && !optional('sync', next))) {
      reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
    }
    return parseFunctionExpression(token);
  }

  /// genericListLiteral | genericMapLiteral | genericFunctionLiteral.
  ///
  /// Where
  ///   genericListLiteral ::= typeArguments '[' (expressionList ','?)? ']'
  ///   genericMapLiteral ::=
  ///       typeArguments '{' (mapLiteralEntry (',' mapLiteralEntry)* ','?)? '}'
  ///   genericFunctionLiteral ::=
  ///       typeParameters formalParameterList functionBody
  /// Provide token for [constKeyword] if preceded by 'const', null if not.
  Token parseLiteralListSetMapOrFunction(
      final Token start, Token constKeyword) {
    assert(optional('<', start.next));
    TypeParamOrArgInfo typeParamOrArg =
        computeTypeParamOrArg(start, /* inDeclaration = */ true);
    Token token = typeParamOrArg.skip(start);
    if (optional('(', token.next)) {
      if (constKeyword != null) {
        reportRecoverableErrorWithToken(
            constKeyword, codes.templateUnexpectedToken);
      }
      token = typeParamOrArg.parseVariables(start, this);
      return parseLiteralFunctionSuffix(token);
    }
    // Note that parseArguments can rewrite the token stream!
    token = typeParamOrArg.parseArguments(start, this);
    Token next = token.next;
    if (optional('{', next)) {
      if (typeParamOrArg.typeArgumentCount > 2) {
        reportRecoverableErrorWithEnd(start.next, token,
            codes.messageSetOrMapLiteralTooManyTypeArguments);
      }
      return parseLiteralSetOrMapSuffix(token, constKeyword);
    }
    if (!optional('[', next) && !optional('[]', next)) {
      // TODO(danrubel): Improve this error message.
      reportRecoverableError(
          next, codes.templateExpectedButGot.withArguments('['));
      rewriter.insertSyntheticToken(token, TokenType.INDEX);
    }
    return parseLiteralListSuffix(token, constKeyword);
  }

  /// ```
  /// mapLiteralEntry:
  ///   expression ':' expression |
  ///   'if' '(' expression ')' mapLiteralEntry ( 'else' mapLiteralEntry )? |
  ///   'await'? 'for' '(' forLoopParts ')' mapLiteralEntry |
  ///   ( '...' | '...?' ) expression
  /// ;
  /// ```
  Token parseMapLiteralEntry(Token token) {
    // Assume the listener rejects non-string keys.
    // TODO(brianwilkerson): Change the assumption above by moving error
    // checking into the parser, making it possible to recover.
    LiteralEntryInfo info = computeLiteralEntry(token);
    while (info != null) {
      if (info.hasEntry) {
        token = parseExpression(token);
        Token colon = ensureColon(token);
        token = parseExpression(colon);
        // TODO remove unused 2nd parameter
        listener.handleLiteralMapEntry(colon, token.next);
      } else {
        token = info.parse(token, this);
      }
      info = info.computeNext(token);
    }
    return token;
  }

  Token parseSendOrFunctionLiteral(Token token, IdentifierContext context) {
    if (!mayParseFunctionExpressions) {
      return parseSend(token, context);
    }
    TypeInfo typeInfo = computeType(token, /* required = */ false);
    Token beforeName = typeInfo.skipType(token);
    Token name = beforeName.next;
    if (name.isIdentifier) {
      TypeParamOrArgInfo typeParam = computeTypeParamOrArg(name);
      Token next = typeParam.skip(name).next;
      if (optional('(', next)) {
        if (looksLikeFunctionBody(next.endGroup.next)) {
          return parseFunctionLiteral(
              token, beforeName, name, typeInfo, typeParam, context);
        }
      }
    }
    return parseSend(token, context);
  }

  Token ensureArguments(Token token) {
    Token next = token.next;
    if (!optional('(', next)) {
      reportRecoverableError(
          token, codes.templateExpectedAfterButGot.withArguments('('));
      next = rewriter.insertParens(token, /* includeIdentifier = */ false);
    }
    return parseArgumentsRest(next);
  }

  Token parseConstructorInvocationArguments(Token token) {
    Token next = token.next;
    if (!optional('(', next)) {
      // Recovery: Check for invalid type parameters
      TypeParamOrArgInfo typeArg = computeTypeParamOrArg(token);
      if (typeArg == noTypeParamOrArg) {
        reportRecoverableError(
            token, codes.templateExpectedAfterButGot.withArguments('('));
      } else {
        reportRecoverableError(
            token, codes.messageConstructorWithTypeArguments);
        token = typeArg.parseArguments(token, this);
        listener.handleInvalidTypeArguments(token);
        next = token.next;
      }
      if (!optional('(', next)) {
        next = rewriter.insertParens(token, /* includeIdentifier = */ false);
      }
    }
    return parseArgumentsRest(next);
  }

  /// ```
  /// newExpression:
  ///   'new' type ('.' identifier)? arguments
  /// ;
  /// ```
  Token parseNewExpression(Token token) {
    Token newKeyword = token.next;
    assert(optional('new', newKeyword));
    listener.beginNewExpression(newKeyword);
    token = parseConstructorReference(newKeyword);
    token = parseConstructorInvocationArguments(token);
    listener.endNewExpression(newKeyword);
    return token;
  }

  Token parseImplicitCreationExpression(
      Token token, TypeParamOrArgInfo typeArg) {
    Token begin = token;
    listener.beginImplicitCreationExpression(token);
    token = parseConstructorReference(token, typeArg);
    token = parseConstructorInvocationArguments(token);
    listener.endImplicitCreationExpression(begin);
    return token;
  }

  /// This method parses a list or map literal that is known to start with the
  /// keyword 'const'.
  ///
  /// ```
  /// listLiteral:
  ///   'const'? typeArguments? '[' (expressionList ','?)? ']'
  /// ;
  ///
  /// mapLiteral:
  ///   'const'? typeArguments?
  ///     '{' (mapLiteralEntry (',' mapLiteralEntry)* ','?)? '}'
  /// ;
  ///
  /// mapLiteralEntry:
  ///   expression ':' expression
  /// ;
  /// ```
  Token parseConstExpression(Token token) {
    Token constKeyword = token = token.next;
    assert(optional('const', constKeyword));
    Token next = token.next;
    final String value = next.stringValue;
    if ((identical(value, '[')) || (identical(value, '[]'))) {
      listener.beginConstLiteral(next);
      listener.handleNoTypeArguments(next);
      token = parseLiteralListSuffix(token, constKeyword);
      listener.endConstLiteral(token.next);
      return token;
    }
    if (identical(value, '{')) {
      listener.beginConstLiteral(next);
      listener.handleNoTypeArguments(next);
      token = parseLiteralSetOrMapSuffix(token, constKeyword);
      listener.endConstLiteral(token.next);
      return token;
    }
    if (identical(value, '<')) {
      listener.beginConstLiteral(next);
      token = parseLiteralListSetMapOrFunction(token, constKeyword);
      listener.endConstLiteral(token.next);
      return token;
    }
    listener.beginConstExpression(constKeyword);
    token = parseConstructorReference(token);
    token = parseConstructorInvocationArguments(token);
    listener.endConstExpression(constKeyword);
    return token;
  }

  /// ```
  /// intLiteral:
  ///   integer
  /// ;
  /// ```
  Token parseLiteralInt(Token token) {
    token = token.next;
    assert(identical(token.kind, INT_TOKEN) ||
        identical(token.kind, HEXADECIMAL_TOKEN));
    listener.handleLiteralInt(token);
    return token;
  }

  /// ```
  /// doubleLiteral:
  ///   double
  /// ;
  /// ```
  Token parseLiteralDouble(Token token) {
    token = token.next;
    assert(identical(token.kind, DOUBLE_TOKEN));
    listener.handleLiteralDouble(token);
    return token;
  }

  /// ```
  /// stringLiteral:
  ///   (multilineString | singleLineString)+
  /// ;
  /// ```
  Token parseLiteralString(Token token) {
    Token startToken = token;
    assert(identical(token.next.kind, STRING_TOKEN));
    bool old = mayParseFunctionExpressions;
    mayParseFunctionExpressions = true;
    token = parseSingleLiteralString(token);
    int count = 1;
    while (identical(token.next.kind, STRING_TOKEN)) {
      token = parseSingleLiteralString(token);
      count++;
    }
    if (count > 1) {
      listener.handleStringJuxtaposition(startToken, count);
    }
    mayParseFunctionExpressions = old;
    return token;
  }

  /// ```
  /// symbolLiteral:
  ///   '#' (operator | (identifier ('.' identifier)*))
  /// ;
  /// ```
  Token parseLiteralSymbol(Token token) {
    Token hashToken = token = token.next;
    assert(optional('#', hashToken));
    listener.beginLiteralSymbol(hashToken);
    Token next = token.next;
    if (next.isUserDefinableOperator) {
      listener.handleOperator(next);
      listener.endLiteralSymbol(hashToken, /* identifierCount = */ 1);
      return next;
    } else if (optional('void', next)) {
      listener.handleSymbolVoid(next);
      listener.endLiteralSymbol(hashToken, /* identifierCount = */ 1);
      return next;
    } else {
      int count = 1;
      token = ensureIdentifier(token, IdentifierContext.literalSymbol);
      while (optional('.', token.next)) {
        count++;
        token = ensureIdentifier(
            token.next, IdentifierContext.literalSymbolContinuation);
      }
      listener.endLiteralSymbol(hashToken, count);
      return token;
    }
  }

  Token parseSingleLiteralString(Token token) {
    token = token.next;
    assert(identical(token.kind, STRING_TOKEN));
    listener.beginLiteralString(token);
    // Parsing the prefix, for instance 'x of 'x${id}y${id}z'
    int interpolationCount = 0;
    Token next = token.next;
    int kind = next.kind;
    while (kind != EOF_TOKEN) {
      if (identical(kind, STRING_INTERPOLATION_TOKEN)) {
        // Parsing ${expression}.
        token = parseExpression(next).next;
        if (!optional('}', token)) {
          reportRecoverableError(
              token, codes.templateExpectedButGot.withArguments('}'));
          token = next.endGroup;
        }
        listener.handleInterpolationExpression(next, token);
      } else if (identical(kind, STRING_INTERPOLATION_IDENTIFIER_TOKEN)) {
        // Parsing $identifier.
        token = parseIdentifierExpression(next);
        listener.handleInterpolationExpression(next, /* rightBracket = */ null);
      } else {
        break;
      }
      ++interpolationCount;
      // Parsing the infix/suffix, for instance y and z' of 'x${id}y${id}z'
      token = parseStringPart(token);
      next = token.next;
      kind = next.kind;
    }
    listener.endLiteralString(interpolationCount, next);
    return token;
  }

  Token parseIdentifierExpression(Token token) {
    Token next = token.next;
    if (next.kind == KEYWORD_TOKEN && identical(next.stringValue, "this")) {
      listener.handleThisExpression(next, IdentifierContext.expression);
      return next;
    } else {
      return parseSend(token, IdentifierContext.expression);
    }
  }

  /// ```
  /// booleanLiteral:
  ///   'true' |
  ///   'false'
  /// ;
  /// ```
  Token parseLiteralBool(Token token) {
    token = token.next;
    assert(optional('false', token) || optional('true', token));
    listener.handleLiteralBool(token);
    return token;
  }

  /// ```
  /// nullLiteral:
  ///   'null'
  /// ;
  /// ```
  Token parseLiteralNull(Token token) {
    token = token.next;
    assert(optional('null', token));
    listener.handleLiteralNull(token);
    return token;
  }

  Token parseSend(Token token, IdentifierContext context) {
    Token beginToken = token = ensureIdentifier(token, context);
    // Notice that we don't parse the bang (!) here as we do in many other
    // instances where we call computeMethodTypeArguments.
    // The reason is, that on a method call like "e.f!<int>()" we need the
    // "e.f" to become a "single unit" before processing the bang (!),
    // the type arguments and the arguments.
    // By not handling bang here we don't parse any of it, and the parser will
    // parse it correctly in a different recursion step.
    TypeParamOrArgInfo typeArg = computeMethodTypeArguments(token);
    if (typeArg != noTypeParamOrArg) {
      token = typeArg.parseArguments(token, this);
    } else {
      listener.handleNoTypeArguments(token.next);
    }
    token = parseArgumentsOpt(token);
    listener.handleSend(beginToken, token.next);
    return token;
  }

  Token skipArgumentsOpt(Token token) {
    Token next = token.next;
    listener.handleNoArguments(next);
    if (optional('(', next)) {
      return next.endGroup;
    } else {
      return token;
    }
  }

  Token parseArgumentsOpt(Token token) {
    Token next = token.next;
    if (!optional('(', next)) {
      listener.handleNoArguments(next);
      return token;
    } else {
      return parseArguments(token);
    }
  }

  /// ```
  /// arguments:
  ///   '(' (argumentList ','?)? ')'
  /// ;
  ///
  /// argumentList:
  ///   namedArgument (',' namedArgument)* |
  ///   expressionList (',' namedArgument)*
  /// ;
  ///
  /// namedArgument:
  ///   label expression
  /// ;
  /// ```
  Token parseArguments(Token token) {
    return parseArgumentsRest(token.next);
  }

  Token parseArgumentsRest(Token token) {
    Token begin = token;
    assert(optional('(', begin));
    listener.beginArguments(begin);
    int argumentCount = 0;
    bool hasSeenNamedArgument = false;
    bool old = mayParseFunctionExpressions;
    mayParseFunctionExpressions = true;
    while (true) {
      Token next = token.next;
      if (optional(')', next)) {
        token = next;
        break;
      }
      Token colon = null;
      if (optional(':', next.next)) {
        token =
            ensureIdentifier(token, IdentifierContext.namedArgumentReference)
                .next;
        colon = token;
        hasSeenNamedArgument = true;
      } else if (hasSeenNamedArgument) {
        // Positional argument after named argument.
        reportRecoverableError(next, codes.messagePositionalAfterNamedArgument);
      }
      token = parseExpression(token);
      next = token.next;
      if (colon != null) listener.handleNamedArgument(colon);
      ++argumentCount;
      if (!optional(',', next)) {
        if (optional(')', next)) {
          token = next;
          break;
        }
        // Recovery
        if (looksLikeExpressionStart(next)) {
          // If this looks like the start of an expression,
          // then report an error, insert the comma, and continue parsing.
          next = rewriteAndRecover(
              token,
              codes.templateExpectedButGot.withArguments(','),
              new SyntheticToken(TokenType.COMMA, next.offset));
        } else {
          token = ensureCloseParen(token, begin);
          break;
        }
      }
      token = next;
    }
    assert(optional(')', token));
    mayParseFunctionExpressions = old;
    listener.endArguments(argumentCount, begin, token);
    return token;
  }

  /// ```
  /// typeTest::
  ///   'is' '!'? type
  /// ;
  /// ```
  Token parseIsOperatorRest(Token token) {
    Token operator = token = token.next;
    assert(optional('is', operator));
    Token not = null;
    if (optional('!', token.next)) {
      not = token = token.next;
    }
    listener.beginIsOperatorType(operator);
    TypeInfo typeInfo = computeTypeAfterIsOrAs(token);
    token = typeInfo.ensureTypeNotVoid(token, this);
    listener.endIsOperatorType(operator);
    listener.handleIsOperator(operator, not);
    return skipChainedAsIsOperators(token);
  }

  TypeInfo computeTypeAfterIsOrAs(Token token) {
    TypeInfo typeInfo = computeType(token, /* required = */ true);
    if (typeInfo.isNullable) {
      Token next = typeInfo.skipType(token).next;
      if (!isOneOfOrEof(
          next, const [')', '?', '??', ',', ';', ':', 'is', 'as', '..'])) {
        // TODO(danrubel): investigate other situations
        // where `?` should be considered part of the type info
        // rather than the start of a conditional expression.
        typeInfo = typeInfo.asNonNullable;
      }
    }
    return typeInfo;
  }

  /// ```
  /// typeCast:
  ///   'as' type
  /// ;
  /// ```
  Token parseAsOperatorRest(Token token) {
    Token operator = token = token.next;
    assert(optional('as', operator));
    listener.beginAsOperatorType(operator);
    TypeInfo typeInfo = computeTypeAfterIsOrAs(token);
    token = typeInfo.ensureTypeNotVoid(token, this);
    listener.endAsOperatorType(operator);
    listener.handleAsOperator(operator);
    return skipChainedAsIsOperators(token);
  }

  Token skipChainedAsIsOperators(Token token) {
    while (true) {
      Token next = token.next;
      String value = next.stringValue;
      if (!identical(value, 'is') && !identical(value, 'as')) {
        return token;
      }
      // The is- and as-operators cannot be chained.
      // TODO(danrubel): Consider a better error message.
      reportRecoverableErrorWithToken(next, codes.templateUnexpectedToken);
      if (optional('!', next.next)) {
        next = next.next;
      }
      TypeInfo typeInfo = computeTypeAfterIsOrAs(next);
      token = typeInfo.skipType(next);
      next = token.next;
      value = next.stringValue;
    }
  }

  /// Returns true if [token] could be the start of a function declaration
  /// without a return type.
  bool looksLikeLocalFunction(Token token) {
    if (token.isIdentifier) {
      if (optional('<', token.next)) {
        TypeParamOrArgInfo typeParam = computeTypeParamOrArg(token);
        if (typeParam == noTypeParamOrArg) {
          return false;
        }
        token = typeParam.skip(token);
      }
      token = token.next;
      if (optional('(', token)) {
        token = token.endGroup.next;
        return optional('{', token) ||
            optional('=>', token) ||
            optional('async', token) ||
            optional('sync', token);
      } else if (optional('=>', token)) {
        // Recovery: Looks like a local function that is missing parenthesis.
        return true;
      }
    }
    return false;
  }

  /// Returns true if [token] could be the start of a function body.
  bool looksLikeFunctionBody(Token token) {
    return optional('{', token) ||
        optional('=>', token) ||
        optional('async', token) ||
        optional('sync', token);
  }

  Token parseExpressionStatementOrConstDeclaration(final Token start) {
    Token constToken = start.next;
    assert(optional('const', constToken));
    if (!isModifier(constToken.next)) {
      TypeInfo typeInfo = computeType(constToken, /* required = */ false);
      if (typeInfo == noType) {
        Token next = constToken.next;
        if (!next.isIdentifier) {
          return parseExpressionStatement(start);
        }
        next = next.next;
        if (!(optional('=', next) ||
            // Recovery
            next.isKeywordOrIdentifier ||
            optional(';', next) ||
            optional(',', next) ||
            optional('{', next))) {
          return parseExpressionStatement(start);
        }
      }
      return parseExpressionStatementOrDeclarationAfterModifiers(
          constToken,
          start,
          /* lateToken = */ null,
          constToken,
          typeInfo,
          /* onlyParseVariableDeclarationStart = */ false);
    }
    return parseExpressionStatementOrDeclaration(start);
  }

  /// This method has two modes based upon [onlyParseVariableDeclarationStart].
  ///
  /// If [onlyParseVariableDeclarationStart] is `false` (the default) then this
  /// method will parse a local variable declaration, a local function,
  /// or an expression statement, and then return the last consumed token.
  ///
  /// If [onlyParseVariableDeclarationStart] is `true` then this method
  /// will only parse the metadata, modifiers, and type of a local variable
  /// declaration if it exists. It is the responsibility of the caller to
  /// call [parseVariablesDeclarationRest] to finish parsing the local variable
  /// declaration. If a local variable declaration is not found then this
  /// method will return [start].
  Token parseExpressionStatementOrDeclaration(final Token start,
      [bool onlyParseVariableDeclarationStart = false]) {
    Token token = start;
    Token next = token.next;
    if (optional('@', next)) {
      token = parseMetadataStar(token);
      next = token.next;
    }

    Token lateToken;
    Token varFinalOrConst;

    if (isModifier(next)) {
      if (optional('var', next) ||
          optional('final', next) ||
          optional('const', next)) {
        varFinalOrConst = token = token.next;
        next = token.next;
      } else if (optional('late', next)) {
        lateToken = token = next;
        next = token.next;
        if (isModifier(next) &&
            (optional('var', next) || optional('final', next))) {
          varFinalOrConst = token = next;
          next = token.next;
        }
      }

      if (isModifier(next)) {
        // Recovery
        ModifierRecoveryContext context = new ModifierRecoveryContext(this)
          ..lateToken = lateToken
          ..varFinalOrConst = varFinalOrConst;

        token = context.parseVariableDeclarationModifiers(token);
        next = token.next;

        lateToken = context.lateToken;
        varFinalOrConst = context.varFinalOrConst;

        context = null;
      }
    }

    return parseExpressionStatementOrDeclarationAfterModifiers(
        token,
        start,
        lateToken,
        varFinalOrConst,
        /* typeInfo = */ null,
        onlyParseVariableDeclarationStart);
  }

  /// See [parseExpressionStatementOrDeclaration]
  Token parseExpressionStatementOrDeclarationAfterModifiers(
      final Token beforeType,
      final Token start,
      final Token lateToken,
      Token varFinalOrConst,
      TypeInfo typeInfo,
      bool onlyParseVariableDeclarationStart) {
    typeInfo ??= computeType(beforeType, /* required = */ false);

    Token token = typeInfo.skipType(beforeType);
    Token next = token.next;

    if (onlyParseVariableDeclarationStart) {
      if (lateToken != null) {
        reportRecoverableErrorWithToken(
            lateToken, codes.templateExtraneousModifier);
      }
    } else {
      if (looksLikeLocalFunction(next)) {
        // Parse a local function declaration.
        if (varFinalOrConst != null) {
          reportRecoverableErrorWithToken(
              varFinalOrConst, codes.templateExtraneousModifier);
        } else if (lateToken != null) {
          reportRecoverableErrorWithToken(
              lateToken, codes.templateExtraneousModifier);
        }
        if (!optional('@', start.next)) {
          listener.beginMetadataStar(start.next);
          listener.endMetadataStar(/* count = */ 0);
        }
        Token beforeFormals =
            computeTypeParamOrArg(next).parseVariables(next, this);
        listener.beginLocalFunctionDeclaration(start.next);
        token = typeInfo.parseType(beforeType, this);
        return parseNamedFunctionRest(
            token,
            start.next,
            beforeFormals,
            /* isFunctionExpression = */ false);
      }
    }

    if (beforeType == start &&
        typeInfo.isNullable &&
        typeInfo.couldBeExpression) {
      assert(optional('?', token));
      assert(next.isKeywordOrIdentifier);
      if (!next.isIdentifier) {
        reportRecoverableError(
            next, codes.templateExpectedIdentifier.withArguments(next));
        next = rewriter.insertSyntheticIdentifier(next);
      }
      Token afterIdentifier = next.next;
      //
      // found <typeref> `?` <identifier>
      // with no annotations or modifiers preceeding it
      //
      if (optional('=', afterIdentifier)) {
        //
        // look past the next expression
        // to determine if this is part of a conditional expression
        //
        Listener originalListener = listener;
        listener = new ForwardingListener();
        // TODO(danrubel): consider using TokenStreamGhostWriter here
        Token afterExpression =
            parseExpressionWithoutCascade(afterIdentifier).next;
        listener = originalListener;

        if (optional(':', afterExpression)) {
          // Looks like part of a conditional expression.
          // Drop the type information and reset the last consumed token.
          typeInfo = noType;
          token = start;
          next = token.next;
        }
      } else if (!afterIdentifier.isKeyword &&
          !isOneOfOrEof(afterIdentifier, const [';', ',', ')'])) {
        // Looks like part of a conditional expression.
        // Drop the type information and reset the last consumed token.
        typeInfo = noType;
        token = start;
        next = token.next;
      }
    }

    if (token == start) {
      // If no annotation, modifier, or type, and this is not a local function
      // then this must be an expression statement.
      if (onlyParseVariableDeclarationStart) {
        return start;
      } else {
        return parseExpressionStatement(start);
      }
    }

    if (next.type.isBuiltIn &&
        beforeType == start &&
        typeInfo.couldBeExpression) {
      // Detect expressions such as identifier `as` identifier
      // and treat those as expressions.
      if (optional('as', next) || optional('is', next)) {
        int kind = next.next.kind;
        if (EQ_TOKEN != kind &&
            SEMICOLON_TOKEN != kind &&
            COMMA_TOKEN != kind) {
          if (onlyParseVariableDeclarationStart) {
            if (!optional('in', next.next)) {
              return start;
            }
          } else {
            return parseExpressionStatement(start);
          }
        }
      }
    }

    if (next.isIdentifier) {
      // Only report these errors if there is an identifier. If there is not an
      // identifier, then allow ensureIdentifier to report an error
      // and don't report errors here.
      if (varFinalOrConst == null) {
        if (typeInfo == noType && lateToken == null) {
          reportRecoverableError(next, codes.messageMissingConstFinalVarOrType);
        }
      } else if (optional('var', varFinalOrConst)) {
        if (typeInfo != noType) {
          reportRecoverableError(varFinalOrConst, codes.messageTypeAfterVar);
        }
      }
    }

    if (!optional('@', start.next)) {
      listener.beginMetadataStar(start.next);
      listener.endMetadataStar(/* count = */ 0);
    }
    token = typeInfo.parseType(beforeType, this);
    next = token.next;
    listener.beginVariablesDeclaration(next, lateToken, varFinalOrConst);
    if (!onlyParseVariableDeclarationStart) {
      token =
          parseVariablesDeclarationRest(token, /* endWithSemicolon = */ true);
    }
    return token;
  }

  Token parseVariablesDeclarationRest(Token token, bool endWithSemicolon) {
    int count = 1;
    token = parseOptionallyInitializedIdentifier(token);
    while (optional(',', token.next)) {
      token = parseOptionallyInitializedIdentifier(token.next);
      ++count;
    }
    if (endWithSemicolon) {
      Token semicolon = ensureSemicolon(token);
      listener.endVariablesDeclaration(count, semicolon);
      return semicolon;
    } else {
      listener.endVariablesDeclaration(count, /* endToken = */ null);
      return token;
    }
  }

  Token parseOptionallyInitializedIdentifier(Token token) {
    Token nameToken =
        ensureIdentifier(token, IdentifierContext.localVariableDeclaration);
    listener.beginInitializedIdentifier(nameToken);
    token = parseVariableInitializerOpt(nameToken);
    listener.endInitializedIdentifier(nameToken);
    return token;
  }

  /// ```
  /// ifStatement:
  ///   'if' '(' expression ')' statement ('else' statement)?
  /// ;
  /// ```
  Token parseIfStatement(Token token) {
    Token ifToken = token.next;
    assert(optional('if', ifToken));
    listener.beginIfStatement(ifToken);
    token = ensureParenthesizedCondition(ifToken);
    listener.beginThenStatement(token.next);
    token = parseStatement(token);
    listener.endThenStatement(token);
    Token elseToken = null;
    if (optional('else', token.next)) {
      elseToken = token.next;
      listener.beginElseStatement(elseToken);
      token = parseStatement(elseToken);
      listener.endElseStatement(elseToken);
    }
    listener.endIfStatement(ifToken, elseToken);
    return token;
  }

  /// ```
  /// forStatement:
  ///   'await'? 'for' '(' forLoopParts ')' statement
  /// ;
  ///
  ///  forLoopParts:
  ///      localVariableDeclaration ';' expression? ';' expressionList?
  ///    | expression? ';' expression? ';' expressionList?
  ///    | localVariableDeclaration 'in' expression
  ///    | identifier 'in' expression
  /// ;
  ///
  /// forInitializerStatement:
  ///   localVariableDeclaration |
  ///   expression? ';'
  /// ;
  /// ```
  Token parseForStatement(Token token, Token awaitToken) {
    Token forToken = token = token.next;
    assert(awaitToken == null || optional('await', awaitToken));
    assert(optional('for', token));
    listener.beginForStatement(forToken);

    token = parseForLoopPartsStart(awaitToken, forToken);
    Token identifier = token.next;
    token = parseForLoopPartsMid(token, awaitToken, forToken);
    if (optional('in', token.next) || optional(':', token.next)) {
      // Process `for ( ... in ... )`
      return parseForInRest(token, awaitToken, forToken, identifier);
    } else {
      // Process `for ( ... ; ... ; ... )`
      return parseForRest(awaitToken, token, forToken);
    }
  }

  /// Parse the start of a for loop control structure
  /// from the open parenthesis up to but not including the identifier.
  Token parseForLoopPartsStart(Token awaitToken, Token forToken) {
    Token leftParenthesis = forToken.next;
    if (!optional('(', leftParenthesis)) {
      // Recovery
      reportRecoverableError(
          leftParenthesis, codes.templateExpectedButGot.withArguments('('));

      BeginToken openParen = rewriter.insertToken(
          forToken,
          new SyntheticBeginToken(
              TokenType.OPEN_PAREN, leftParenthesis.offset));

      Token token;
      if (awaitToken != null) {
        token = rewriter.insertSyntheticIdentifier(openParen);
        token = rewriter.insertSyntheticKeyword(token, Keyword.IN);
        token = rewriter.insertSyntheticIdentifier(token);
      } else {
        token = rewriter.insertSyntheticToken(openParen, TokenType.SEMICOLON);
        token = rewriter.insertSyntheticToken(token, TokenType.SEMICOLON);
      }

      openParen.endGroup = token = rewriter.insertToken(token,
          new SyntheticToken(TokenType.CLOSE_PAREN, leftParenthesis.offset));

      token = rewriter.insertSyntheticIdentifier(token);
      rewriter.insertSyntheticToken(token, TokenType.SEMICOLON);

      leftParenthesis = openParen;
    }

    // Pass `true` so that the [parseExpressionStatementOrDeclaration] only
    // parses the metadata, modifiers, and type of a local variable
    // declaration if it exists. This enables capturing [beforeIdentifier]
    // for later error reporting.
    return parseExpressionStatementOrDeclaration(
        leftParenthesis, /* onlyParseVariableDeclarationStart = */ true);
  }

  /// Parse the remainder of the local variable declaration
  /// or an expression if no local variable declaration was found.
  Token parseForLoopPartsMid(Token token, Token awaitToken, Token forToken) {
    if (token != forToken.next) {
      token =
          parseVariablesDeclarationRest(token, /* endWithSemicolon = */ false);
      listener.handleForInitializerLocalVariableDeclaration(
          token, optional('in', token.next));
    } else if (optional(';', token.next)) {
      listener.handleForInitializerEmptyStatement(token.next);
    } else {
      token = parseExpression(token);
      listener.handleForInitializerExpressionStatement(
          token,
          optional('in', token.next) ||
              optional(':', token.next) ||
              // If this is an empty `await for`, we rewrite it into an
              // `await for (_ in _)`.
              (awaitToken != null && optional(')', token.next)));
    }
    Token next = token.next;
    if (optional(';', next)) {
      if (awaitToken != null) {
        reportRecoverableError(awaitToken, codes.messageInvalidAwaitFor);
      }
    } else if (!optional('in', next)) {
      // Recovery
      if (optional(':', next)) {
        reportRecoverableError(next, codes.messageColonInPlaceOfIn);
      } else if (awaitToken != null) {
        reportRecoverableError(
            next, codes.templateExpectedButGot.withArguments('in'));
        token.setNext(
            new SyntheticKeywordToken(Keyword.IN, next.offset)..setNext(next));
      }
    }
    return token;
  }

  /// This method parses the portion of the forLoopParts that starts with the
  /// first semicolon (the one that terminates the forInitializerStatement).
  ///
  /// ```
  ///  forLoopParts:
  ///      localVariableDeclaration ';' expression? ';' expressionList?
  ///    | expression? ';' expression? ';' expressionList?
  ///    | localVariableDeclaration 'in' expression
  ///    | identifier 'in' expression
  /// ;
  /// ```
  Token parseForRest(Token awaitToken, Token token, Token forToken) {
    token = parseForLoopPartsRest(token, forToken, awaitToken);
    listener.beginForStatementBody(token.next);
    LoopState savedLoopState = loopState;
    loopState = LoopState.InsideLoop;
    token = parseStatement(token);
    loopState = savedLoopState;
    listener.endForStatementBody(token.next);
    listener.endForStatement(token.next);
    return token;
  }

  Token parseForLoopPartsRest(Token token, Token forToken, Token awaitToken) {
    Token leftParenthesis = forToken.next;
    assert(optional('for', forToken));
    assert(optional('(', leftParenthesis));

    Token leftSeparator = ensureSemicolon(token);
    if (optional(';', leftSeparator.next)) {
      token = parseEmptyStatement(leftSeparator);
    } else {
      token = parseExpressionStatement(leftSeparator);
    }
    int expressionCount = 0;
    while (true) {
      Token next = token.next;
      if (optional(')', next)) {
        token = next;
        break;
      }
      token = parseExpression(token).next;
      ++expressionCount;
      if (!optional(',', token)) {
        break;
      }
    }
    if (token != leftParenthesis.endGroup) {
      reportRecoverableErrorWithToken(token, codes.templateUnexpectedToken);
      token = leftParenthesis.endGroup;
    }
    listener.handleForLoopParts(
        forToken, leftParenthesis, leftSeparator, expressionCount);
    return token;
  }

  /// This method parses the portion of the forLoopParts that starts with the
  /// keyword 'in'. For the sake of recovery, we accept a colon in place of the
  /// keyword.
  ///
  /// ```
  ///  forLoopParts:
  ///      localVariableDeclaration ';' expression? ';' expressionList?
  ///    | expression? ';' expression? ';' expressionList?
  ///    | localVariableDeclaration 'in' expression
  ///    | identifier 'in' expression
  /// ;
  /// ```
  Token parseForInRest(
      Token token, Token awaitToken, Token forToken, Token identifier) {
    token = parseForInLoopPartsRest(token, awaitToken, forToken, identifier);
    listener.beginForInBody(token.next);
    LoopState savedLoopState = loopState;
    loopState = LoopState.InsideLoop;
    token = parseStatement(token);
    loopState = savedLoopState;
    listener.endForInBody(token.next);
    listener.endForIn(token.next);
    return token;
  }

  Token parseForInLoopPartsRest(
      Token token, Token awaitToken, Token forToken, Token identifier) {
    Token inKeyword = token.next;
    assert(optional('for', forToken));
    assert(optional('(', forToken.next));
    assert(optional('in', inKeyword) || optional(':', inKeyword));

    if (!identifier.isIdentifier) {
      reportRecoverableErrorWithToken(
          identifier, codes.templateExpectedIdentifier);
    } else if (identifier != token) {
      if (optional('=', identifier.next)) {
        reportRecoverableError(
            identifier.next, codes.messageInitializedVariableInForEach);
      } else {
        reportRecoverableErrorWithToken(
            identifier.next, codes.templateUnexpectedToken);
      }
    } else if (awaitToken != null && !inAsync) {
      // TODO(danrubel): consider reporting the error on awaitToken
      reportRecoverableError(inKeyword, codes.messageAwaitForNotAsync);
    }

    listener.beginForInExpression(inKeyword.next);
    token = parseExpression(inKeyword);
    token = ensureCloseParen(token, forToken.next);
    listener.endForInExpression(token);
    listener.handleForInLoopParts(
        awaitToken, forToken, forToken.next, inKeyword);
    return token;
  }

  /// ```
  /// whileStatement:
  ///   'while' '(' expression ')' statement
  /// ;
  /// ```
  Token parseWhileStatement(Token token) {
    Token whileToken = token.next;
    assert(optional('while', whileToken));
    listener.beginWhileStatement(whileToken);
    token = ensureParenthesizedCondition(whileToken);
    listener.beginWhileStatementBody(token.next);
    LoopState savedLoopState = loopState;
    loopState = LoopState.InsideLoop;
    token = parseStatement(token);
    loopState = savedLoopState;
    listener.endWhileStatementBody(token.next);
    listener.endWhileStatement(whileToken, token.next);
    return token;
  }

  /// ```
  /// doStatement:
  ///   'do' statement 'while' '(' expression ')' ';'
  /// ;
  /// ```
  Token parseDoWhileStatement(Token token) {
    Token doToken = token.next;
    assert(optional('do', doToken));
    listener.beginDoWhileStatement(doToken);
    listener.beginDoWhileStatementBody(doToken.next);
    LoopState savedLoopState = loopState;
    loopState = LoopState.InsideLoop;
    token = parseStatement(doToken);
    loopState = savedLoopState;
    listener.endDoWhileStatementBody(token);
    Token whileToken = token.next;
    if (!optional('while', whileToken)) {
      reportRecoverableError(
          whileToken, codes.templateExpectedButGot.withArguments('while'));
      whileToken = rewriter.insertSyntheticKeyword(token, Keyword.WHILE);
    }
    token = ensureParenthesizedCondition(whileToken);
    token = ensureSemicolon(token);
    listener.endDoWhileStatement(doToken, whileToken, token);
    return token;
  }

  /// ```
  /// block:
  ///   '{' statement* '}'
  /// ;
  /// ```
  Token parseBlock(Token token, BlockKind blockKind) {
    Token begin = token =
        ensureBlock(token, /* template = */ null, blockKind.missingBlockName);
    listener.beginBlock(begin, blockKind);
    int statementCount = 0;
    Token startToken = token.next;
    while (notEofOrValue('}', startToken)) {
      token = parseStatement(token);
      if (identical(token.next, startToken)) {
        // No progress was made, so we report the current token as being invalid
        // and move forward.
        token = token.next;
        reportRecoverableError(
            token, codes.templateUnexpectedToken.withArguments(token));
      }
      ++statementCount;
      startToken = token.next;
    }
    token = token.next;
    assert(token.isEof || optional('}', token));
    listener.endBlock(statementCount, begin, token, blockKind);
    return token;
  }

  Token parseInvalidBlock(Token token) {
    Token begin = token.next;
    assert(optional('{', begin));
    // Parse and report the invalid block, but suppress errors
    // because an error has already been reported by the caller.
    Listener originalListener = listener;
    listener = new ForwardingListener(listener)..forwardErrors = false;
    // The scanner ensures that `{` always has a closing `}`.
    token = parseBlock(token, BlockKind.invalid);
    listener = originalListener;
    listener.handleInvalidTopLevelBlock(begin);
    return token;
  }

  /// Determine if the following tokens look like an expression and not a local
  /// variable or local function declaration.
  bool looksLikeExpression(Token token) {
    // TODO(srawlins): Consider parsing the potential expression once doing so
    //  does not modify the token stream. For now, use simple look ahead and
    //  ensure no false positives.

    token = token.next;
    if (token.isIdentifier) {
      token = token.next;
      if (optional('(', token)) {
        token = token.endGroup.next;
        if (isOneOf(token, [';', '.', '..', '?', '?.'])) {
          return true;
        }
      } else if (isOneOf(token, ['.', ')', ']'])) {
        // TODO(srawlins): Also consider when `token` is `;`. There is still not
        // good error recovery on `yield x;`. This would also require
        // modification to analyzer's
        // test_parseCompilationUnit_pseudo_asTypeName.
        return true;
      }
    } else if (token == Keyword.NULL) {
      return true;
    }
    // TODO(srawlins): Consider other possibilities for `token` which would
    //  imply it looks like an expression, for example beginning with `<`, as
    //  part of a collection literal type argument list, `(`, other literals,
    //  etc. For example, there is still not good error recovery on
    //  `yield <int>[]`.

    return false;
  }

  /// Determine if the following tokens look like an 'await' expression
  /// and not a local variable or local function declaration.
  bool looksLikeAwaitExpression(Token token) {
    token = token.next;
    assert(optional('await', token));

    return looksLikeExpression(token);
  }

  /// Determine if the following tokens look like a 'yield' expression and not a
  /// local variable or local function declaration.
  bool looksLikeYieldStatement(Token token) {
    token = token.next;
    assert(optional('yield', token));

    return looksLikeExpression(token);
  }

  /// ```
  /// awaitExpression:
  ///   'await' unaryExpression
  /// ;
  /// ```
  Token parseAwaitExpression(Token token, bool allowCascades) {
    Token awaitToken = token.next;
    assert(optional('await', awaitToken));
    listener.beginAwaitExpression(awaitToken);
    token = parsePrecedenceExpression(
        awaitToken, POSTFIX_PRECEDENCE, allowCascades);
    if (inAsync) {
      listener.endAwaitExpression(awaitToken, token.next);
    } else {
      codes.MessageCode errorCode = codes.messageAwaitNotAsync;
      reportRecoverableError(awaitToken, errorCode);
      listener.endInvalidAwaitExpression(awaitToken, token.next, errorCode);
    }
    return token;
  }

  /// ```
  /// throwExpression:
  ///   'throw' expression
  /// ;
  ///
  /// throwExpressionWithoutCascade:
  ///   'throw' expressionWithoutCascade
  /// ;
  /// ```
  Token parseThrowExpression(Token token, bool allowCascades) {
    Token throwToken = token.next;
    assert(optional('throw', throwToken));
    if (optional(';', throwToken.next)) {
      // TODO(danrubel): Find a better way to intercept the parseExpression
      // recovery to generate this error message rather than explicitly
      // checking the next token as we are doing here.
      reportRecoverableError(
          throwToken.next, codes.messageMissingExpressionInThrow);
      rewriter.insertToken(
          throwToken,
          new SyntheticStringToken(TokenType.STRING, '""',
              throwToken.next.charOffset, /* _length = */ 0));
    }
    token = allowCascades
        ? parseExpression(throwToken)
        : parseExpressionWithoutCascade(throwToken);
    listener.handleThrowExpression(throwToken, token.next);
    return token;
  }

  /// ```
  /// rethrowStatement:
  ///   'rethrow' ';'
  /// ;
  /// ```
  Token parseRethrowStatement(Token token) {
    Token throwToken = token.next;
    assert(optional('rethrow', throwToken));
    listener.beginRethrowStatement(throwToken);
    token = ensureSemicolon(throwToken);
    listener.endRethrowStatement(throwToken, token);
    return token;
  }

  /// ```
  /// tryStatement:
  ///   'try' block (onPart+ finallyPart? | finallyPart)
  /// ;
  ///
  /// onPart:
  ///   catchPart block |
  ///   'on' type catchPart? block
  /// ;
  ///
  /// catchPart:
  ///   'catch' '(' identifier (',' identifier)? ')'
  /// ;
  ///
  /// finallyPart:
  ///   'finally' block
  /// ;
  /// ```
  Token parseTryStatement(Token token) {
    Token tryKeyword = token.next;
    assert(optional('try', tryKeyword));
    listener.beginTryStatement(tryKeyword);
    Token lastConsumed = parseBlock(tryKeyword, BlockKind.tryStatement);
    token = lastConsumed.next;
    int catchCount = 0;

    String value = token.stringValue;
    while (identical(value, 'catch') || identical(value, 'on')) {
      listener.beginCatchClause(token);
      Token onKeyword = null;
      if (identical(value, 'on')) {
        // 'on' type catchPart?
        onKeyword = token;
        lastConsumed = computeType(token, /* required = */ true)
            .ensureTypeNotVoid(token, this);
        token = lastConsumed.next;
        value = token.stringValue;
      }
      Token catchKeyword = null;
      Token comma = null;
      if (identical(value, 'catch')) {
        catchKeyword = token;

        Token openParens = catchKeyword.next;
        if (!optional("(", openParens)) {
          reportRecoverableError(openParens, codes.messageCatchSyntax);
          openParens = rewriter.insertParens(
              catchKeyword, /* includeIdentifier = */ true);
        }

        Token exceptionName = openParens.next;
        if (exceptionName.kind != IDENTIFIER_TOKEN) {
          exceptionName = IdentifierContext.catchParameter
              .ensureIdentifier(openParens, this);
        }

        if (optional(")", exceptionName.next)) {
          // OK: `catch (identifier)`.
        } else {
          comma = exceptionName.next;
          if (!optional(",", comma)) {
            // Recovery
            if (!exceptionName.isSynthetic) {
              reportRecoverableError(comma, codes.messageCatchSyntax);
            }

            // TODO(danrubel): Consider inserting `on` clause if
            // exceptionName is preceded by type and followed by a comma.
            // Then this
            //   } catch (E e, t) {
            // will recover to
            //   } on E catch (e, t) {
            // with a detailed explanation for the user in the error
            // indicating what they should do to fix the code.

            // TODO(danrubel): Consider inserting synthetic identifier if
            // exceptionName is a non-synthetic identifier followed by `.`.
            // Then this
            //   } catch (
            //   e.f();
            // will recover to
            //   } catch (_s_) {}
            //   e.f();
            // rather than
            //   } catch (e) {}
            //   _s_.f();

            if (openParens.endGroup.isSynthetic) {
              // The scanner did not place the synthetic ')' correctly.
              rewriter.moveSynthetic(exceptionName, openParens.endGroup);
              comma = null;
            } else {
              comma =
                  rewriter.insertSyntheticToken(exceptionName, TokenType.COMMA);
            }
          }
          if (comma != null) {
            Token traceName = comma.next;
            if (traceName.kind != IDENTIFIER_TOKEN) {
              traceName = IdentifierContext.catchParameter
                  .ensureIdentifier(comma, this);
            }
            if (!optional(")", traceName.next)) {
              // Recovery
              if (!traceName.isSynthetic) {
                reportRecoverableError(
                    traceName.next, codes.messageCatchSyntaxExtraParameters);
              }
              if (openParens.endGroup.isSynthetic) {
                // The scanner did not place the synthetic ')' correctly.
                rewriter.moveSynthetic(traceName, openParens.endGroup);
              }
            }
          }
        }
        lastConsumed = parseFormalParameters(catchKeyword, MemberKind.Catch);
        token = lastConsumed.next;
      }
      listener.endCatchClause(token);
      lastConsumed = parseBlock(lastConsumed, BlockKind.catchClause);
      token = lastConsumed.next;
      ++catchCount;
      listener.handleCatchBlock(onKeyword, catchKeyword, comma);
      value = token.stringValue; // while condition
    }

    Token finallyKeyword = null;
    if (optional('finally', token)) {
      finallyKeyword = token;
      lastConsumed = parseBlock(token, BlockKind.finallyClause);
      token = lastConsumed.next;
      listener.handleFinallyBlock(finallyKeyword);
    } else {
      if (catchCount == 0) {
        reportRecoverableError(tryKeyword, codes.messageOnlyTry);
      }
    }
    listener.endTryStatement(catchCount, tryKeyword, finallyKeyword);
    return lastConsumed;
  }

  /// ```
  /// switchStatement:
  ///   'switch' parenthesizedExpression switchBlock
  /// ;
  /// ```
  Token parseSwitchStatement(Token token) {
    Token switchKeyword = token.next;
    assert(optional('switch', switchKeyword));
    listener.beginSwitchStatement(switchKeyword);
    token = ensureParenthesizedCondition(switchKeyword);
    LoopState savedLoopState = loopState;
    if (loopState == LoopState.OutsideLoop) {
      loopState = LoopState.InsideSwitch;
    }
    token = parseSwitchBlock(token);
    loopState = savedLoopState;
    listener.endSwitchStatement(switchKeyword, token);
    return token;
  }

  /// ```
  /// switchBlock:
  ///   '{' switchCase* defaultCase? '}'
  /// ;
  /// ```
  Token parseSwitchBlock(Token token) {
    Token beginSwitch =
        token = ensureBlock(token, /* template = */ null, 'switch statement');
    listener.beginSwitchBlock(beginSwitch);
    int caseCount = 0;
    Token defaultKeyword = null;
    Token colonAfterDefault = null;
    while (notEofOrValue('}', token.next)) {
      Token beginCase = token.next;
      int expressionCount = 0;
      int labelCount = 0;
      Token peek = peekPastLabels(beginCase);
      while (true) {
        // Loop until we find something that can't be part of a switch case.
        String value = peek.stringValue;
        if (identical(value, 'default')) {
          while (!identical(token.next, peek)) {
            token = parseLabel(token);
            labelCount++;
          }
          if (defaultKeyword != null) {
            reportRecoverableError(
                token.next, codes.messageSwitchHasMultipleDefaults);
          }
          defaultKeyword = token.next;
          colonAfterDefault = token = ensureColon(defaultKeyword);
          peek = token.next;
          break;
        } else if (identical(value, 'case')) {
          while (!identical(token.next, peek)) {
            token = parseLabel(token);
            labelCount++;
          }
          Token caseKeyword = token.next;
          if (defaultKeyword != null) {
            reportRecoverableError(
                caseKeyword, codes.messageSwitchHasCaseAfterDefault);
          }
          listener.beginCaseExpression(caseKeyword);
          token = parseExpression(caseKeyword);
          token = ensureColon(token);
          listener.endCaseExpression(token);
          listener.handleCaseMatch(caseKeyword, token);
          expressionCount++;
          peek = peekPastLabels(token.next);
        } else if (expressionCount > 0) {
          break;
        } else {
          // Recovery
          reportRecoverableError(
              peek, codes.templateExpectedToken.withArguments("case"));
          Token endGroup = beginSwitch.endGroup;
          while (token.next != endGroup) {
            token = token.next;
          }
          peek = peekPastLabels(token.next);
          break;
        }
      }
      token = parseStatementsInSwitchCase(token, peek, beginCase, labelCount,
          expressionCount, defaultKeyword, colonAfterDefault);
      ++caseCount;
    }
    token = token.next;
    listener.endSwitchBlock(caseCount, beginSwitch, token);
    assert(token.isEof || optional('}', token));
    return token;
  }

  /// Peek after the following labels (if any). The following token
  /// is used to determine if the labels belong to a statement or a
  /// switch case.
  Token peekPastLabels(Token token) {
    while (token.isIdentifier && optional(':', token.next)) {
      token = token.next.next;
    }
    return token;
  }

  /// Parse statements after a switch `case:` or `default:`.
  Token parseStatementsInSwitchCase(
      Token token,
      Token peek,
      Token begin,
      int labelCount,
      int expressionCount,
      Token defaultKeyword,
      Token colonAfterDefault) {
    listener.beginSwitchCase(labelCount, expressionCount, begin);
    // Finally zero or more statements.
    int statementCount = 0;
    while (!identical(token.next.kind, EOF_TOKEN)) {
      String value = peek.stringValue;
      if ((identical(value, 'case')) ||
          (identical(value, 'default')) ||
          ((identical(value, '}')) && (identical(token.next, peek)))) {
        // A label just before "}" will be handled as a statement error.
        break;
      } else {
        Token startToken = token.next;
        token = parseStatement(token);
        Token next = token.next;
        if (identical(next, startToken)) {
          // No progress was made, so we report the current token as being
          // invalid and move forward.
          reportRecoverableError(
              next, codes.templateUnexpectedToken.withArguments(next));
          token = next;
        }
        ++statementCount;
      }
      peek = peekPastLabels(token.next);
    }
    listener.endSwitchCase(labelCount, expressionCount, defaultKeyword,
        colonAfterDefault, statementCount, begin, token.next);
    return token;
  }

  /// ```
  /// breakStatement:
  ///   'break' identifier? ';'
  /// ;
  /// ```
  Token parseBreakStatement(Token token) {
    Token breakKeyword = token = token.next;
    assert(optional('break', breakKeyword));
    bool hasTarget = false;
    if (token.next.isIdentifier) {
      token = ensureIdentifier(token, IdentifierContext.labelReference);
      hasTarget = true;
    } else if (!isBreakAllowed) {
      reportRecoverableError(breakKeyword, codes.messageBreakOutsideOfLoop);
    }
    token = ensureSemicolon(token);
    listener.handleBreakStatement(hasTarget, breakKeyword, token);
    return token;
  }

  /// ```
  /// assertion:
  ///   'assert' '(' expression (',' expression)? ','? ')'
  /// ;
  /// ```
  Token parseAssert(Token token, Assert kind) {
    token = token.next;
    assert(optional('assert', token));
    listener.beginAssert(token, kind);
    Token assertKeyword = token;
    Token leftParenthesis = token.next;
    if (!optional('(', leftParenthesis)) {
      // Recovery
      reportRecoverableError(
          leftParenthesis, codes.templateExpectedButGot.withArguments('('));
      leftParenthesis =
          rewriter.insertParens(token, /* includeIdentifier = */ true);
    }
    token = leftParenthesis;
    Token commaToken = null;
    bool old = mayParseFunctionExpressions;
    mayParseFunctionExpressions = true;

    token = parseExpression(token);
    if (optional(',', token.next)) {
      token = token.next;
      if (!optional(')', token.next)) {
        commaToken = token;
        token = parseExpression(token);
        if (optional(',', token.next)) {
          // Trailing comma is ignored.
          token = token.next;
        }
      }
    }

    Token endGroup = leftParenthesis.endGroup;
    if (token.next == endGroup) {
      token = endGroup;
    } else {
      // Recovery
      if (endGroup.isSynthetic) {
        // The scanner did not place the synthetic ')' correctly, so move it.
        token = rewriter.moveSynthetic(token, endGroup);
      } else {
        reportRecoverableErrorWithToken(
            token.next, codes.templateUnexpectedToken);
        token = endGroup;
      }
    }

    assert(optional(')', token));
    mayParseFunctionExpressions = old;
    if (kind == Assert.Expression) {
      reportRecoverableError(assertKeyword, codes.messageAssertAsExpression);
    } else if (kind == Assert.Statement) {
      ensureSemicolon(token);
    }
    listener.endAssert(
        assertKeyword, kind, leftParenthesis, commaToken, token.next);
    return token;
  }

  /// ```
  /// assertStatement:
  ///   assertion ';'
  /// ;
  /// ```
  Token parseAssertStatement(Token token) {
    assert(optional('assert', token.next));
    // parseAssert ensures that there is a trailing semicolon.
    return parseAssert(token, Assert.Statement).next;
  }

  /// ```
  /// continueStatement:
  ///   'continue' identifier? ';'
  /// ;
  /// ```
  Token parseContinueStatement(Token token) {
    Token continueKeyword = token = token.next;
    assert(optional('continue', continueKeyword));
    bool hasTarget = false;
    if (token.next.isIdentifier) {
      token = ensureIdentifier(token, IdentifierContext.labelReference);
      hasTarget = true;
      if (!isContinueWithLabelAllowed) {
        reportRecoverableError(
            continueKeyword, codes.messageContinueOutsideOfLoop);
      }
    } else if (!isContinueAllowed) {
      reportRecoverableError(
          continueKeyword,
          loopState == LoopState.InsideSwitch
              ? codes.messageContinueWithoutLabelInCase
              : codes.messageContinueOutsideOfLoop);
    }
    token = ensureSemicolon(token);
    listener.handleContinueStatement(hasTarget, continueKeyword, token);
    return token;
  }

  /// ```
  /// emptyStatement:
  ///   ';'
  /// ;
  /// ```
  Token parseEmptyStatement(Token token) {
    token = token.next;
    assert(optional(';', token));
    listener.handleEmptyStatement(token);
    return token;
  }

  /// Given a token ([beforeToken]) that is known to be before another [token],
  /// return the token that is immediately before the [token].
  Token previousToken(Token beforeToken, Token token) {
    Token next = beforeToken.next;
    while (next != token && next != beforeToken) {
      beforeToken = next;
      next = beforeToken.next;
    }
    return beforeToken;
  }

  /// Recover from finding an operator declaration missing the `operator`
  /// keyword. The metadata for the member, if any, has already been parsed
  /// (and events have already been generated).
  Token parseInvalidOperatorDeclaration(
      Token beforeStart,
      Token abstractToken,
      Token externalToken,
      Token staticToken,
      Token covariantToken,
      Token lateToken,
      Token varFinalOrConst,
      Token beforeType,
      DeclarationKind kind,
      String enclosingDeclarationName) {
    TypeInfo typeInfo = computeType(
        beforeStart, /* required = */ false, /* inDeclaration = */ true);
    Token beforeName = typeInfo.skipType(beforeType);
    Token next = beforeName.next;

    if (optional('operator', next)) {
      next = next.next;
    } else {
      // The 'operator' keyword is missing, but we may or may not have a type
      // before the token that is the actual operator.
      Token operator = next;
      if (!next.isOperator && next.next.isOperator) {
        beforeName = next;
        operator = next.next;
      }
      reportRecoverableError(operator, codes.messageMissingOperatorKeyword);
      rewriter.insertSyntheticKeyword(beforeName, Keyword.OPERATOR);

      // Having inserted the keyword the type now possibly compute differently.
      typeInfo = computeType(
          beforeStart, /* required = */ true, /* inDeclaration = */ true);
      beforeName = typeInfo.skipType(beforeType);
      next = beforeName.next;

      // The 'next' token can be the just-inserted 'operator' keyword.
      // If it is, change it so it points to the actual operator.
      if (!next.isOperator &&
          next.next.isOperator &&
          identical(next.stringValue, 'operator')) {
        next = next.next;
      }
    }

    assert((next.isOperator && next.endGroup == null) ||
        optional('===', next) ||
        optional('!==', next));

    Token token = parseMethod(
        beforeStart,
        abstractToken,
        externalToken,
        staticToken,
        covariantToken,
        lateToken,
        varFinalOrConst,
        beforeType,
        typeInfo,
        /* getOrSet = */ null,
        beforeName.next,
        kind,
        enclosingDeclarationName,
        /* nameIsRecovered = */ false);
    listener.endMember();
    return token;
  }

  /// Recover from finding an invalid class member. The metadata for the member,
  /// if any, has already been parsed (and events have already been generated).
  /// The member was expected to start with the token after [token].
  Token recoverFromInvalidMember(
      Token token,
      Token beforeStart,
      Token abstractToken,
      Token externalToken,
      Token staticToken,
      Token covariantToken,
      Token lateToken,
      Token varFinalOrConst,
      Token beforeType,
      TypeInfo typeInfo,
      Token getOrSet,
      DeclarationKind kind,
      String enclosingDeclarationName) {
    Token next = token.next;
    String value = next.stringValue;

    if (identical(value, 'class')) {
      return reportAndSkipClassInClass(next);
    } else if (identical(value, 'enum')) {
      return reportAndSkipEnumInClass(next);
    } else if (identical(value, 'typedef')) {
      return reportAndSkipTypedefInClass(next);
    } else if (next.isOperator && next.endGroup == null) {
      return parseInvalidOperatorDeclaration(
          beforeStart,
          abstractToken,
          externalToken,
          staticToken,
          covariantToken,
          lateToken,
          varFinalOrConst,
          beforeType,
          kind,
          enclosingDeclarationName);
    }

    if (getOrSet != null ||
        identical(value, '(') ||
        identical(value, '=>') ||
        identical(value, '{')) {
      token = parseMethod(
          beforeStart,
          abstractToken,
          externalToken,
          staticToken,
          covariantToken,
          lateToken,
          varFinalOrConst,
          beforeType,
          typeInfo,
          getOrSet,
          token.next,
          kind,
          enclosingDeclarationName,
          /* nameIsRecovered = */ false);
    } else if (token == beforeStart) {
      // TODO(danrubel): Provide a more specific error message for extra ';'.
      reportRecoverableErrorWithToken(next, codes.templateExpectedClassMember);
      listener.handleInvalidMember(next);
      if (!identical(value, '}')) {
        // Ensure we make progress.
        token = next;
      }
    } else {
      token = parseFields(
          beforeStart,
          abstractToken,
          externalToken,
          staticToken,
          covariantToken,
          lateToken,
          varFinalOrConst,
          beforeType,
          typeInfo,
          token.next,
          kind,
          enclosingDeclarationName,
          /* nameIsRecovered = */ false);
    }

    listener.endMember();
    return token;
  }

  /// Report that the nesting depth of the code being parsed is too large for
  /// the parser to safely handle. Return the next `}` or EOF.
  Token recoverFromStackOverflow(Token token) {
    Token next = token.next;
    reportRecoverableError(next, codes.messageStackOverflow);
    next = rewriter.insertSyntheticToken(token, TokenType.SEMICOLON);
    listener.handleEmptyStatement(next);

    while (notEofOrValue('}', next)) {
      token = next;
      next = token.next;
    }
    return token;
  }

  void reportRecoverableError(Token token, codes.Message message) {
    // Find a non-synthetic token on which to report the error.
    token = findNonZeroLengthToken(token);
    listener.handleRecoverableError(message, token, token);
  }

  void reportRecoverableErrorWithEnd(
      Token startToken, Token endToken, codes.Message message) {
    listener.handleRecoverableError(message, startToken, endToken);
  }

  void reportRecoverableErrorWithToken(
      Token token, codes.Template<_MessageWithArgument<Token>> template) {
    // Find a non-synthetic token on which to report the error.
    token = findNonZeroLengthToken(token);
    listener.handleRecoverableError(
        template.withArguments(token), token, token);
  }

  Token reportAllErrorTokens(Token token) {
    while (token is ErrorToken) {
      listener.handleErrorToken(token);
      token = token.next;
    }
    return token;
  }

  Token skipErrorTokens(Token token) {
    while (token is ErrorToken) {
      token = token.next;
    }
    return token;
  }

  Token parseInvalidTopLevelDeclaration(Token token) {
    Token next = token.next;
    reportRecoverableErrorWithToken(
        next,
        optional(';', next)
            ? codes.templateUnexpectedToken
            : codes.templateExpectedDeclaration);
    if (optional('{', next)) {
      next = parseInvalidBlock(token);
    }
    listener.handleInvalidTopLevelDeclaration(next);
    return next;
  }

  Token reportAndSkipClassInClass(Token token) {
    assert(optional('class', token));
    reportRecoverableError(token, codes.messageClassInClass);
    listener.handleInvalidMember(token);
    Token next = token.next;
    // If the declaration appears to be a valid class declaration
    // then skip the entire declaration so that we only generate the one
    // error (above) rather than a plethora of unhelpful errors.
    if (next.isIdentifier) {
      // skip class name
      token = next;
      next = token.next;
      // TODO(danrubel): consider parsing (skipping) the class header
      // with a recovery listener so that no events are generated
      if (optional('{', next) && next.endGroup != null) {
        // skip class body
        token = next.endGroup;
      }
    }
    listener.endMember();
    return token;
  }

  Token reportAndSkipEnumInClass(Token token) {
    assert(optional('enum', token));
    reportRecoverableError(token, codes.messageEnumInClass);
    listener.handleInvalidMember(token);
    Token next = token.next;
    // If the declaration appears to be a valid enum declaration
    // then skip the entire declaration so that we only generate the one
    // error (above) rather than a plethora of unhelpful errors.
    if (next.isIdentifier) {
      // skip enum name
      token = next;
      next = token.next;
      if (optional('{', next) && next.endGroup != null) {
        // TODO(danrubel): Consider replacing this `skip enum` functionality
        // with something that can parse and resolve the declaration
        // even though it is in a class context
        token = next.endGroup;
      }
    }
    listener.endMember();
    return token;
  }

  Token reportAndSkipTypedefInClass(Token token) {
    assert(optional('typedef', token));
    reportRecoverableError(token, codes.messageTypedefInClass);
    listener.handleInvalidMember(token);
    // TODO(brianwilkerson): If the declaration appears to be a valid typedef
    // then skip the entire declaration so that we generate a single error
    // (above) rather than many unhelpful errors.
    listener.endMember();
    return token;
  }

  /// Create a short token chain from the [beginToken] and [endToken] and return
  /// the [beginToken].
  Token link(BeginToken beginToken, Token endToken) {
    beginToken.setNext(endToken);
    beginToken.endGroup = endToken;
    return beginToken;
  }

  /// Create and return a token whose next token is the given [token].
  Token syntheticPreviousToken(Token token) {
    // Return the previous token if there is one so that any token inserted
    // before `token` will be properly inserted into the token stream.
    // TODO(danrubel): remove this once all methods have been converted to
    // use and return the last token consumed and the `previous` field
    // has been removed.
    if (token.previous != null) {
      return token.previous;
    }
    Token before = new Token.eof(/* offset = */ -1);
    before.next = token;
    return before;
  }

  /// Return the first dartdoc comment token preceding the given token
  /// or `null` if no dartdoc token is found.
  Token findDartDoc(Token token) {
    Token comments = token.precedingComments;
    Token dartdoc = null;
    bool isMultiline = false;
    while (comments != null) {
      String lexeme = comments.lexeme;
      if (lexeme.startsWith('///')) {
        if (!isMultiline) {
          dartdoc = comments;
          isMultiline = true;
        }
      } else if (lexeme.startsWith('/**')) {
        dartdoc = comments;
        isMultiline = false;
      }
      comments = comments.next;
    }
    return dartdoc;
  }

  /// Parse the comment references in a sequence of comment tokens
  /// where [dartdoc] (not null) is the first token in the sequence.
  /// Return the number of comment references parsed.
  int parseCommentReferences(Token dartdoc) {
    return dartdoc.lexeme.startsWith('///')
        ? parseReferencesInSingleLineComments(dartdoc)
        : parseReferencesInMultiLineComment(dartdoc);
  }

  /// Parse the comment references in a multi-line comment token.
  /// Return the number of comment references parsed.
  int parseReferencesInMultiLineComment(Token multiLineDoc) {
    String comment = multiLineDoc.lexeme;
    assert(comment.startsWith('/**'));
    int count = 0;
    int length = comment.length;
    int start = 3;
    bool inCodeBlock = false;
    int codeBlock = comment.indexOf('```', /* start = */ 3);
    if (codeBlock == -1) {
      codeBlock = length;
    }
    while (start < length) {
      if (isWhitespace(comment.codeUnitAt(start))) {
        ++start;
        continue;
      }
      int end = comment.indexOf('\n', start);
      if (end == -1) {
        end = length;
      }
      if (codeBlock < end) {
        inCodeBlock = !inCodeBlock;
        codeBlock = comment.indexOf('```', end);
        if (codeBlock == -1) {
          codeBlock = length;
        }
      }
      if (!inCodeBlock && !comment.startsWith('*     ', start)) {
        count += parseCommentReferencesInText(multiLineDoc, start, end);
      }
      start = end + 1;
    }
    return count;
  }

  /// Parse the comment references in a sequence of single line comment tokens
  /// where [token] is the first comment token in the sequence.
  /// Return the number of comment references parsed.
  int parseReferencesInSingleLineComments(Token token) {
    int count = 0;
    bool inCodeBlock = false;
    while (token != null && !token.isEof) {
      String comment = token.lexeme;
      if (comment.startsWith('///')) {
        if (comment.indexOf('```', /* start = */ 3) != -1) {
          inCodeBlock = !inCodeBlock;
        }
        if (!inCodeBlock && !comment.startsWith('///    ')) {
          count += parseCommentReferencesInText(
              token, /* start = */ 3, comment.length);
        }
      }
      token = token.next;
    }
    return count;
  }

  /// Parse the comment references in the text between [start] inclusive
  /// and [end] exclusive. Return a count indicating how many were parsed.
  int parseCommentReferencesInText(Token commentToken, int start, int end) {
    String comment = commentToken.lexeme;
    int count = 0;
    int index = start;
    while (index < end) {
      int ch = comment.codeUnitAt(index);
      if (ch == 0x5B /* `[` */) {
        ++index;
        if (index < end && comment.codeUnitAt(index) == 0x3A /* `:` */) {
          // Skip old-style code block.
          index = comment.indexOf(':]', index + 1) + 1;
          if (index == 0 || index > end) {
            break;
          }
        } else {
          int referenceStart = index;
          index = comment.indexOf(']', index);
          if (index == -1 || index >= end) {
            // Recovery: terminating ']' is not typed yet.
            index = findReferenceEnd(comment, referenceStart, end);
          }
          if (ch != 0x27 /* `'` */ && ch != 0x22 /* `"` */) {
            if (isLinkText(comment, index)) {
              // TODO(brianwilkerson) Handle the case where there's a library
              // URI in the link text.
            } else {
              listener.handleCommentReferenceText(
                  comment.substring(referenceStart, index),
                  commentToken.charOffset + referenceStart);
              ++count;
            }
          }
        }
      } else if (ch == 0x60 /* '`' */) {
        // Skip inline code block if there is both starting '`' and ending '`'
        int endCodeBlock = comment.indexOf('`', index + 1);
        if (endCodeBlock != -1 && endCodeBlock < end) {
          index = endCodeBlock;
        }
      }
      ++index;
    }
    return count;
  }

  /// Given a comment reference without a closing `]`,
  /// search for a possible place where `]` should be.
  int findReferenceEnd(String comment, int index, int end) {
    // Find the end of the identifier if there is one
    if (index >= end || !isLetter(comment.codeUnitAt(index))) {
      return index;
    }
    while (index < end && isLetterOrDigit(comment.codeUnitAt(index))) {
      ++index;
    }

    // Check for a trailing `.`
    if (index >= end || comment.codeUnitAt(index) != 0x2E /* `.` */) {
      return index;
    }
    ++index;

    // Find end of the identifier after the `.`
    if (index >= end || !isLetter(comment.codeUnitAt(index))) {
      return index;
    }
    ++index;
    while (index < end && isLetterOrDigit(comment.codeUnitAt(index))) {
      ++index;
    }
    return index;
  }

  /// Parse the tokens in a single comment reference and generate either a
  /// `handleCommentReference` or `handleNoCommentReference` event.
  /// Return `true` if a comment reference was successfully parsed.
  bool parseOneCommentReference(Token token, int referenceOffset) {
    Token begin = token;
    Token newKeyword = null;
    if (optional('new', token)) {
      newKeyword = token;
      token = token.next;
    }
    Token prefix, period;
    if (token.isIdentifier && optional('.', token.next)) {
      prefix = token;
      period = token.next;
      token = period.next;
    }
    if (token.isEof) {
      // Recovery: Insert a synthetic identifier for code completion
      token = rewriter.insertSyntheticIdentifier(
          period ?? newKeyword ?? syntheticPreviousToken(token));
      if (begin == token.next) {
        begin = token;
      }
    }
    Token operatorKeyword = null;
    if (optional('operator', token)) {
      operatorKeyword = token;
      token = token.next;
    }
    if (token.isUserDefinableOperator) {
      if (token.next.isEof) {
        parseOneCommentReferenceRest(
            begin, referenceOffset, newKeyword, prefix, period, token);
        return true;
      }
    } else {
      token = operatorKeyword ?? token;
      if (token.next.isEof) {
        if (token.isIdentifier) {
          parseOneCommentReferenceRest(
              begin, referenceOffset, newKeyword, prefix, period, token);
          return true;
        }
        Keyword keyword = token.keyword;
        if (newKeyword == null &&
            prefix == null &&
            (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.
        }
      }
    }
    listener.handleNoCommentReference();
    return false;
  }

  void parseOneCommentReferenceRest(
      Token begin,
      int referenceOffset,
      Token newKeyword,
      Token prefix,
      Token period,
      Token identifierOrOperator) {
    // Adjust the token offsets to match the enclosing comment token.
    Token token = begin;
    do {
      token.offset += referenceOffset;
      token = token.next;
    } while (!token.isEof);

    listener.handleCommentReference(
        newKeyword, prefix, period, identifierOrOperator);
  }

  /// 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 ch = comment.codeUnitAt(index);
    if (ch == 0x28 || ch == 0x3A) {
      return true;
    }
    while (isWhitespace(ch)) {
      index = index + 1;
      if (index >= length) {
        return false;
      }
      ch = comment.codeUnitAt(index);
    }
    return ch == 0x5B;
  }
}

// TODO(ahe): Remove when analyzer supports generalized function syntax.
typedef _MessageWithArgument<T> = codes.Message Function(T);