Change switch to give errors when cases don't follow the newest syntax.

lib/compiler/implementation/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.
 
 class MessageKind {
   final String template;
   const MessageKind(this.template);
 
   static const GENERIC = const MessageKind('#{1}');
 
@@ skipping 112 matching lines @@
   static const TYPE_VARIABLE_AS_CONSTRUCTOR = const MessageKind(
       'cannot use type variable as constructor');
   static const DUPLICATE_TYPE_VARIABLE_NAME = const MessageKind(
       'type variable #{1} already declared');
   static const INVALID_BREAK = const MessageKind(
       'target of break is not a statement');
   static const INVALID_USE_OF_SUPER = const MessageKind(
       'super not allowed here');
   static const INVALID_CASE_DEFAULT = const MessageKind(
       'default only allowed on last case of a switch');
-  static const INVALID_CASE_EXPRESSION = const MessageKind(
-      'case expression is not a compile-time constant int or string.');
-  static const INVALID_CASE_EXPRESSION_TYPE = const MessageKind(
-      "case expressions don't all have the same type "
-      "(must be all int or String).");
+
+  static const SWITCH_CASE_TYPES_NOT_EQUAL = const MessageKind(
+      "case expressions don't all have the same type.");
+  static const SWITCH_CASE_VALUE_OVERRIDES_EQUALS = const MessageKind(
+      "case expression value overrides 'operator=='.");
+  static const SWITCH_INVALID = const MessageKind(
+      "switch cases contain invalid expressions.");
+
   static const INVALID_ARGUMENT_AFTER_NAMED = const MessageKind(
       'non-named argument after named argument');
 
   static const NOT_A_COMPILE_TIME_CONSTANT = const MessageKind(
       'not a compile-time constant');
   static const CYCLIC_COMPILE_TIME_CONSTANTS = const MessageKind(
       'cycle in the compile-time constant computation');
 
   static const KEY_NOT_A_STRING_LITERAL = const MessageKind(
       'map-literal key not a string literal');
@@ skipping 171 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, List arguments)
     : super(kind, arguments);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, List arguments)
     : super(kind, arguments);
 }