move synthetic fasta closers into the token stream

pkg/front_end/lib/src/fasta/scanner/abstract_scanner.dart

 // 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 fasta.scanner.abstract_scanner;
 
 import 'dart:collection' show ListMixin;
 
 import 'dart:typed_data' show Uint16List, Uint32List;
 
 import '../scanner.dart'
     show ErrorToken, Scanner, buildUnexpectedCharacterToken;
 
-import 'error_token.dart' show UnmatchedToken, UnterminatedToken;
+import 'error_token.dart' show UnterminatedToken;
 
 import 'keyword.dart' show KeywordState, Keyword;
 
 import 'precedence.dart';
 
 import 'token.dart' show BeginGroupToken, CommentToken, SymbolToken, Token;
 
 import 'token_constants.dart';
 
 import 'characters.dart';
@@ skipping 1084 matching lines @@
   }
 
   int advanceAfterError(bool shouldAdvance) {
     if (atEndOfFile()) return $EOF;
     if (shouldAdvance) {
       return advance(); // Ensure progress.
     } else {
       return -1;
     }
   }
-
-  void unmatchedBeginGroup(BeginGroupToken begin) {
-    // We want to ensure that unmatched BeginGroupTokens are reported as
-    // errors.  However, the diet parser assumes that groups are well-balanced
-    // and will never look at the endGroup token.  This is a nice property that
-    // allows us to skip quickly over correct code. By inserting an additional
-    // synthetic token in the stream, we can keep ignoring endGroup tokens.
-    //
-    // [begin] --next--> [tail]
-    // [begin] --endG--> [synthetic] --next--> [next] --next--> [tail]
-    //
-    // This allows the diet parser to skip from [begin] via endGroup to
-    // [synthetic] and ignore the [synthetic] token (assuming it's correct),
-    // then the error will be reported when parsing the [next] token.
-    //
-    // For example, tokenize("{[1};") produces:
-    //
-    // SymbolToken({) --endGroup-----+
-    //      |                        |
-    //     next                      |
-    //      v                        |
-    // SymbolToken([) --endGroup--+  |
-    //      |                     |  |
-    //     next                   |  |
-    //      v                     |  |
-    // StringToken(1)             |  |
-    //      |                     v  |
-    //     next       SymbolToken(]) | <- Synthetic token.
-    //      |                     |  |
-    //      |                   next |
-    //      v                     |  |
-    // UnmatchedToken([)<---------+  |
-    //      |                        |
-    //     next                      |
-    //      v                        |
-    // SymbolToken(})<---------------+
-    //      |
-    //     next
-    //      v
-    // SymbolToken(;)
-    //      |
-    //     next
-    //      v
-    //     EOF
-    Token synthetic =
-        new SymbolToken(closeBraceInfoFor(begin), begin.charOffset);
-    UnmatchedToken next = new UnmatchedToken(begin);
-    begin.endGroup = synthetic;
-    synthetic.next = next;
-    appendErrorToken(next);
-  }
 }
 
 PrecedenceInfo closeBraceInfoFor(BeginGroupToken begin) {
   return const {
     '(': CLOSE_PAREN_INFO,
     '[': CLOSE_SQUARE_BRACKET_INFO,
     '{': CLOSE_CURLY_BRACKET_INFO,
     '<': GT_INFO,
     r'${': CLOSE_CURLY_BRACKET_INFO,
   }[begin.lexeme];
@@ skipping 68 matching lines @@
       switchToUint32(newLength);
     }
   }
 
   void switchToUint32(int newLength) {
     final newArray = new Uint32List(newLength);
     newArray.setRange(0, arrayLength, array);
     array = newArray;
   }
 }