Add warnings and hints to for-in.

pkg/compiler/lib/src/diagnostics/messages.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.
 
 
 /**
  * The messages in this file should meet the following guide lines:
  *
  * 1. The message should be a complete sentence starting with an uppercase
  * letter, and ending with a period.
@@ skipping 179 matching lines @@
   EXPONENT_MISSING,
   EXPORT_BEFORE_PARTS,
   EXTERNAL_WITH_BODY,
   EXTRA_CATCH_DECLARATION,
   EXTRA_FORMALS,
   EXTRANEOUS_MODIFIER,
   EXTRANEOUS_MODIFIER_REPLACE,
   FACTORY_REDIRECTION_IN_NON_FACTORY,
   FINAL_FUNCTION_TYPE_PARAMETER,
   FINAL_WITHOUT_INITIALIZER,
+  FORIN_NOT_ASSIGNABLE,
   FORMAL_DECLARED_CONST,
   FORMAL_DECLARED_STATIC,
   FUNCTION_TYPE_FORMAL_WITH_DEFAULT,
   FUNCTION_WITH_INITIALIZER,
   GENERIC,
   GETTER_MISMATCH,
   GETTER_NOT_FOUND,
   HEX_DIGIT_EXPECTED,
   HIDDEN_HINTS,
   HIDDEN_IMPLICIT_IMPORT,
@@ skipping 275 matching lines @@
     const <MessageKind, MessageTemplate>{
       /// Do not use this. It is here for legacy and debugging. It violates item
       /// 4 of the guide lines for error messages in the beginning of the file.
       MessageKind.GENERIC:
         const MessageTemplate(MessageKind.GENERIC, '#{text}'),
 
       MessageKind.NOT_ASSIGNABLE:
         const MessageTemplate(MessageKind.NOT_ASSIGNABLE,
           "'#{fromType}' is not assignable to '#{toType}'."),
 
+      MessageKind.FORIN_NOT_ASSIGNABLE:
+        const MessageTemplate(MessageKind.FORIN_NOT_ASSIGNABLE,
+          "The element type '#{currentType}' of '#{expressionType}' "
+          "is not assignable to '#{elementType}'."),
+
       MessageKind.VOID_EXPRESSION:
         const MessageTemplate(MessageKind.VOID_EXPRESSION,
           "Expression does not yield a value."),
 
       MessageKind.VOID_VARIABLE:
         const MessageTemplate(MessageKind.VOID_VARIABLE,
           "Variable cannot be of type void."),
 
       MessageKind.RETURN_VALUE_IN_VOID:
         const MessageTemplate(MessageKind.RETURN_VALUE_IN_VOID,
@@ skipping 2857 matching lines @@
   static String convertToString(value) {
     if (value is ErrorToken) {
       // Shouldn't happen.
       return value.assertionMessage;
     } else if (value is Token) {
       value = value.value;
     }
     return '$value';
   }
 }