Check field overrides

pkg/analyzer/lib/src/task/strong/info.dart

 // Copyright (c) 2015, 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.
 
 /// Defines static information collected by the type checker and used later by
 /// emitters to generate code.
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.info;
 
@@ skipping 434 matching lines @@
 // Invalid override due to incompatible type.  I.e., the overridden signature
 // is not compatible with the original.
 class InvalidMethodOverride extends InvalidOverride {
   InvalidMethodOverride(AstNode node, ExecutableElement element,
       InterfaceType base, FunctionType subType, FunctionType baseType)
       : super(node, element, base, subType, baseType);
 
   String get message => _messageHelper('Invalid override');
 }
 
+class InvalidFieldOverride extends InvalidOverride {
+  InvalidFieldOverride(AstNode node, ExecutableElement element,
+      InterfaceType base, DartType subType, DartType baseType)
+      : super(node, element, base, subType, baseType);
+
+  String get message => 'Field declaration {3}.{1} cannot be '
+      'overridden in {0}.';
+}
+
 /// Dart constructors have one weird quirk, illustrated with this example:
 ///
 ///     class Base {
 ///       var x;
 ///       Base() : x = print('Base.1') {
 ///         print('Base.2');
 ///       }
 ///     }
 ///
 ///     class Derived extends Base {
@@ skipping 15 matching lines @@
 /// Better to have `super` at the end, as required by the Dart style guide:
 /// <http://goo.gl/q1T4BB>
 ///
 /// For now this is the only pattern we support.
 class InvalidSuperInvocation extends StaticError {
   InvalidSuperInvocation(SuperConstructorInvocation node) : super(node);
 
   @override String get message => "super call must be last in an initializer "
       "list (see http://goo.gl/q1T4BB): {0}";
 }