Check that const-map keys don't override equals.

sdk/lib/_internal/compiler/implementation/resolution/members.dart

 // 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.
 
 part of resolution;
 
 abstract class TreeElements {
   Element get currentElement;
   Setlet<Node> get superUses;
 
@@ skipping 3080 matching lines @@
     } else if (isMirrorsUsedConstant) {
       compiler.mirrorUsageAnalyzerTask.validate(node, mapping);
     }
     if (node.isConst()) {
       analyzeConstant(node);
     }
 
     return null;
   }
 
+  void checkConstMapKeysDontOverrideEquals(Spannable spannable,
+                                           MapConstant map) {
+    for (Constant key in map.keys.entries) {
+      if (!key.isObject()) continue;
+      ObjectConstant objectConstant = key;
+      DartType keyType = objectConstant.type;
+      ClassElement cls = keyType.element;
+      if (cls == compiler.stringClass) continue;
+      Element equals = cls.lookupMember('==');
+      if (equals.getEnclosingClass() != compiler.objectClass) {
+        compiler.reportError(spannable,
+                             MessageKind.CONST_MAP_KEY_OVERRIDES_EQUALS,
+                             {'type': keyType});
+      }
+    }
+  }
+
   void analyzeConstant(Node node, {bool isConst: true}) {
     addDeferredAction(enclosingElement, () {
       Constant constant = compiler.constantHandler.compileNodeWithDefinitions(
           node, mapping, isConst: isConst);
 
+      if (isConst && constant != null && constant.isMap()) {
+        checkConstMapKeysDontOverrideEquals(node, constant);
+      }
+
       // The type constant that is an argument to JS_INTERCEPTOR_CONSTANT names
       // a class that will be instantiated outside the program by attaching a
       // native class dispatch record referencing the interceptor.
       if (argumentsToJsInterceptorConstant != null &&
           argumentsToJsInterceptorConstant.contains(node)) {
         if (constant.isType()) {
           TypeConstant typeConstant = constant;
           if (typeConstant.representedType is InterfaceType) {
             world.registerInstantiatedType(typeConstant.representedType,
                 mapping);
@@ skipping 1407 matching lines @@
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }
 
 /// Looks up [name] in [scope] and unwraps the result.
 Element lookupInScope(Compiler compiler, Node node,
                       Scope scope, String name) {
   return Elements.unwrap(scope.lookup(name), compiler, node);
 }