Diagnose unterminated "grouping" characters.

dart/frog/leg/scanner/array_based_scanner.dart

 // Copyright (c) 2011, 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.
 
 class ArrayBasedScanner<S> extends AbstractScanner<S> {
   int get charOffset() => byteOffset + extraCharOffset;
   final Token tokens;
   Token tail;
   int tokenStart;
   int byteOffset;
 
   /** Since the input is UTF8, some characters are represented by more
    * than one byte. [extraCharOffset] tracks the difference. */
   int extraCharOffset;
-  Link<Token> groupingStack = const EmptyLink<Token>();
+  Link<BeginGroupToken> groupingStack = const EmptyLink<BeginGroupToken>();
 
   ArrayBasedScanner()
     : this.extraCharOffset = 0,
       this.tokenStart = -1,
       this.byteOffset = -1,
       this.tokens = new Token(EOF_INFO, -1) {
     this.tail = this.tokens;
   }
 
   int advance() {
@@ skipping 25 matching lines @@
   void appendKeywordToken(Keyword keyword) {
     tail.next = new KeywordToken(keyword, tokenStart);
     tail = tail.next;
   }
 
   void appendEofToken() {
     tail.next = new Token(EOF_INFO, charOffset);
     tail = tail.next;
     // EOF points to itself so there's always infinite look-ahead.
     tail.next = tail;
+    if (!groupingStack.isEmpty()) {
+      BeginGroupToken begin = groupingStack.head;
+      throw new MalformedInputException('Unbalanced ${begin.stringValue}',
+                                        begin);
+    }
   }
 
   void beginToken() {
     tokenStart = charOffset;
   }
 
   Token firstToken() {
     return tokens.next;
   }
 
@@ skipping 22 matching lines @@
     appendStringToken(info, value);
     if (groupingStack.isEmpty()) {
       return advance();
     }
     discardOpenLt();
     BeginGroupToken begin = groupingStack.head;
     if (begin.kind !== openKind) {
       if (openKind !== OPEN_CURLY_BRACKET_TOKEN ||
           begin.kind !== STRING_INTERPOLATION_TOKEN) {
         // Not ending string interpolation.
-        throw new MalformedInputException('Unmatched ${begin.stringValue}');
+        throw new MalformedInputException('Unmatched ${begin.stringValue}',
+                                          begin);
       }
       // We're ending an interpolated expression.
       begin.endGroup = tail;
       groupingStack = groupingStack.tail;
       // Using "start-of-text" to signal that we're back in string
       // scanning mode.
       return $STX;
     }
     begin.endGroup = tail;
     groupingStack = groupingStack.tail;
@@ skipping 41 matching lines @@
 
   void discardOpenLt() {
     while (!groupingStack.isEmpty() && groupingStack.head.kind === LT_TOKEN) {
       groupingStack = groupingStack.tail;
     }
   }
 
   // TODO(ahe): make class abstract instead of adding an abstract method.
   abstract peek();
 }