improve fasta interpolation recovery

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;
 
@@ skipping 204 matching lines @@
    *
    * Note that [extraOffset] can only be used if the covered character(s) are
    * known to be ASCII.
    */
   DartDocToken createDartDocToken(TokenType type, int start, bool asciiOnly,
       [int extraOffset = 0]);
 
   /** Documentation in subclass [ArrayBasedScanner]. */
   void discardOpenLt();
 
+  /** Documentation in subclass [ArrayBasedScanner]. */
+  void discardInterpolation();
+
   /// Return true when at EOF.
   bool atEndOfFile();
 
   Token tokenize() {
     while (!atEndOfFile()) {
       int next = advance();
       while (!identical(next, $EOF)) {
         next = bigSwitch(next);
       }
       if (atEndOfFile()) {
@@ skipping 809 matching lines @@
     }
   }
 
   int tokenizeInterpolatedExpression(int next) {
     appendBeginGroup(TokenType.STRING_INTERPOLATION_EXPRESSION);
     beginToken(); // The expression starts here.
     next = advance(); // Move past the curly bracket.
     while (!identical(next, $EOF) && !identical(next, $STX)) {
       next = bigSwitch(next);
     }
-    if (identical(next, $EOF)) return next;
+    if (identical(next, $EOF)) {
+      beginToken();
+      discardInterpolation();
+      return next;
+    }
     next = advance(); // Move past the $STX.
     beginToken(); // The string interpolation suffix starts here.
     return next;
   }
 
   int tokenizeInterpolatedIdentifier(int next) {
     appendPrecedenceToken(TokenType.STRING_INTERPOLATION_IDENTIFIER);
 
     if ($a <= next && next <= $z ||
         $A <= next && next <= $Z ||
@@ skipping 233 matching lines @@
       switchToUint32(newLength);
     }
   }
 
   void switchToUint32(int newLength) {
     final newArray = new Uint32List(newLength);
     newArray.setRange(0, arrayLength, array);
     array = newArray;
   }
 }