Better error message for const loop variables

runtime/vm/parser.cc

 // 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.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 5250 matching lines @@
   return is_function_literal;
 }
 
 
 // Current token position is the token after the opening ( of the for
 // statement. Returns true if we recognize a for ( .. in expr)
 // statement.
 bool Parser::IsForInStatement() {
   const intptr_t saved_pos = TokenPos();
   bool result = false;
-  if (CurrentToken() == Token::kVAR || CurrentToken() == Token::kFINAL) {
+  // Allow const modifier as well when recognizing a for-in statement
+  // pattern. We will get an error later if the loop variable is
+  // declared with const.
+  if (CurrentToken() == Token::kVAR ||
+      CurrentToken() == Token::kFINAL ||
+      CurrentToken() == Token::kCONST) {
     ConsumeToken();
   }
   if (IsIdentifier()) {
     if (LookaheadToken(1) == Token::kIN) {
       result = true;
     } else if (TryParseOptionalType()) {
       if (IsIdentifier()) {
         ConsumeToken();
       }
       result = (CurrentToken() == Token::kIN);
@@ skipping 4413 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart