Fix http://dartbug.com/8669 by making sure we do not crash when trying to use Object as a mixin.

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;
   Set<Node> get superUses;
 
@@ skipping 88 matching lines @@
   }
 
   void setOperatorSelectorInComplexSendSet(SendSet node, Selector selector) {
     selectors[node.assignmentOperator] = selector;
   }
 
   Selector getOperatorSelectorInComplexSendSet(SendSet node) {
     return selectors[node.assignmentOperator];
   }
 
-  // The following methods set selectors on the "for in" node. Since    
-  // we're using three selectors, we need to use children of the node,  
-  // and we arbitrarily choose which ones.      
- 
+  // The following methods set selectors on the "for in" node. Since
+  // we're using three selectors, we need to use children of the node,
+  // and we arbitrarily choose which ones.

[ngeoffray, 2013/05/30 06:53:01]

Thank you :)

+
   Selector setIteratorSelector(ForIn node, Selector selector) {
     selectors[node] = selector;
   }
 
   Selector getIteratorSelector(ForIn node) {
     return selectors[node];
   }
 
   Selector setMoveNextSelector(ForIn node, Selector selector) {
     selectors[node.forToken] = selector;
   }
-        
+
   Selector getMoveNextSelector(ForIn node) {
     return selectors[node.forToken];
   }
 
   Selector setCurrentSelector(ForIn node, Selector selector) {
     selectors[node.inToken] = selector;
   }
 
   Selector getCurrentSelector(ForIn node) {
     return selectors[node.inToken];
@@ skipping 460 matching lines @@
           MessageKind.ILLEGAL_MIXIN_APPLICATION_MODIFIERS,
           {'modifiers': illegalModifiers});
     }
 
     // In case of cyclic mixin applications, the mixin chain will have
     // been cut. If so, we have already reported the error to the
     // user so we just return from here.
     ClassElement mixin = mixinApplication.mixin;
     if (mixin == null) return;
 
+    // Check that we're not trying to use Object as a mixin.
+    if (mixin.superclass == null) {
+      compiler.reportErrorCode(mixinApplication,
+                               MessageKind.ILLEGAL_MIXIN_OBJECT);
+      // Avoid reporting additional errors for the Object class.

[ngeoffray, 2013/05/30 06:53:01]

I'd drop "for the Object class", it confused me.

+      return;
+    }
+
     // Check that the mixed in class has Object as its superclass.
     if (!mixin.superclass.isObject(compiler)) {
       compiler.reportErrorCode(mixin, MessageKind.ILLEGAL_MIXIN_SUPERCLASS);
     }
 
     // Check that the mixed in class doesn't have any constructors and
     // make sure we aren't mixing in methods that use 'super'.
     mixin.forEachLocalMember((Element member) {
       if (member.isGenerativeConstructor() && !member.isSynthesized) {
         compiler.reportErrorCode(member, MessageKind.ILLEGAL_MIXIN_CONSTRUCTOR);
@@ skipping 3375 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }