Make super.foo= erroneous if they are not assignable.

pkg/compiler/lib/src/warnings.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.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "Computer says no!";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 112 matching lines @@
 
   static const MessageKind METHOD_NOT_FOUND = const MessageKind(
       "No method named '#{memberName}' in class '#{className}'.");
 
   static const MessageKind OPERATOR_NOT_FOUND = const MessageKind(
       "No operator '#{memberName}' in class '#{className}'.");
 
   static const MessageKind SETTER_NOT_FOUND = const MessageKind(
       "No setter named '#{memberName}' in class '#{className}'.");
 
+  static const MessageKind SETTER_NOT_FOUND_IN_SUPER = const MessageKind(
+      "No setter named '#{name}' in superclass of '#{className}'.");
+
   static const MessageKind GETTER_NOT_FOUND = const MessageKind(
       "No getter named '#{memberName}' in class '#{className}'.");
 
   static const MessageKind NOT_CALLABLE = const MessageKind(
       "'#{elementName}' is not callable.");
 
   static const MessageKind MEMBER_NOT_STATIC = const MessageKind(
       "'#{className}.#{memberName}' is not static.");
 
   static const MessageKind NO_INSTANCE_AVAILABLE = const MessageKind(
@@ skipping 976 matching lines @@
 
   static const MessageKind CANNOT_RESOLVE_GETTER = const MessageKind(
       "Cannot resolve getter.");
 
   static const MessageKind CANNOT_RESOLVE_SETTER = const MessageKind(
       "Cannot resolve setter.");
 
   static const MessageKind ASSIGNING_METHOD = const MessageKind(
       "Cannot assign a value to a method.");
 
+  static const MessageKind ASSIGNING_METHOD_IN_SUPER = const MessageKind(
+      "Cannot assign a value to method '#{name}' "
+      "in superclass '#{superclassName}'.");
+
   static const MessageKind ASSIGNING_TYPE = const MessageKind(
       "Cannot assign a value to a type.");
 
   static const MessageKind VOID_NOT_ALLOWED = const MessageKind(
       "Type 'void' can't be used here because it isn't a return type.",
       howToFix: "Try removing 'void' keyword or replace it with 'var', 'final',"
           " or a type.",
       examples: const [
           "void x; main() {}",
           "foo(void x) {} main() { foo(null); }",
@@ skipping 1360 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';
   }
 }