improve fasta closing brace recovery

pkg/analyzer/lib/src/generated/parser.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.parser;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 6893 matching lines @@
 
       if (type == TokenType.CLOSE_SQUARE_BRACKET) {
         rightSquareBracket = getAndAdvance();
         if (leftSquareBracket == null) {
           if (leftCurlyBracket != null) {
             _reportErrorForCurrentToken(
                 ParserErrorCode.WRONG_TERMINATOR_FOR_PARAMETER_GROUP,
                 ['}', ']']);
             rightCurlyBracket = rightSquareBracket;
             rightSquareBracket = null;
+            // Skip over synthetic closer inserted by fasta
+            // since we've already reported an error
+            if (_currentToken.type == TokenType.CLOSE_CURLY_BRACKET &&
+                _currentToken.isSynthetic) {
+              _advance();
+            }
           } else {
             _reportErrorForCurrentToken(
                 ParserErrorCode.UNEXPECTED_TERMINATOR_FOR_PARAMETER_GROUP,
                 ["["]);
           }
         }
         kind = ParameterKind.REQUIRED;
       } else if (type == TokenType.CLOSE_CURLY_BRACKET) {
         rightCurlyBracket = getAndAdvance();
         if (leftCurlyBracket == null) {
           if (leftSquareBracket != null) {
             _reportErrorForCurrentToken(
                 ParserErrorCode.WRONG_TERMINATOR_FOR_PARAMETER_GROUP,
                 [']', '}']);
             rightSquareBracket = rightCurlyBracket;
             rightCurlyBracket = null;
+            // Skip over synthetic closer inserted by fasta
+            // since we've already reported an error
+            if (_currentToken.type == TokenType.CLOSE_SQUARE_BRACKET &&
+                _currentToken.isSynthetic) {
+              _advance();
+            }
           } else {
             _reportErrorForCurrentToken(
                 ParserErrorCode.UNEXPECTED_TERMINATOR_FOR_PARAMETER_GROUP,
                 ["{"]);
           }
         }
         kind = ParameterKind.REQUIRED;
       }
     } while (!_matches(TokenType.CLOSE_PAREN) &&
         !identical(initialToken, _currentToken));
@@ skipping 1709 matching lines @@
     }
   }
 }
 
 /**
  * Instances of this class are thrown when the parser detects that AST has
  * too many nested expressions to be parsed safely and avoid possibility of
  * [StackOverflowError] in the parser or during later analysis.
  */
 class _TooDeepTreeError {}