Use Object as supertype in face of invalid supertypes.

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 4093 matching lines @@
 
   DartType resolveType(TypeAnnotation node) {
     return typeResolver.resolveTypeAnnotation(this, node);
   }
 
   DartType resolveSupertype(ClassElement cls, TypeAnnotation superclass) {
     DartType supertype = resolveType(superclass);
     if (supertype != null) {
       if (identical(supertype.kind, TypeKind.MALFORMED_TYPE)) {
         compiler.reportError(superclass, MessageKind.CANNOT_EXTEND_MALFORMED);
-        return null;
+        return compiler.objectClass.computeType(compiler);

[karlklose, 2014/01/28 13:30:03]

Extract a getter for this type. Also it should be objectClass.rawType.

[Johnni Winther, 2014/01/29 10:26:09]

Done.

       } else if (!identical(supertype.kind, TypeKind.INTERFACE)) {
         compiler.reportError(superclass.typeName,
             MessageKind.CLASS_NAME_EXPECTED);
-        return null;
+        return compiler.objectClass.computeType(compiler);
       } else if (isBlackListed(supertype)) {
         compiler.reportError(superclass, MessageKind.CANNOT_EXTEND,
             {'type': supertype});
-        return null;
+        return compiler.objectClass.computeType(compiler);
       }
     }
     return supertype;
   }
 
   Link<DartType> resolveInterfaces(NodeList interfaces, Node superclass) {
     Link<DartType> result = const Link<DartType>();
     if (interfaces == null) return result;
     for (Link<Node> link = interfaces.nodes; !link.isEmpty; link = link.tail) {
       DartType interfaceType = resolveType(link.head);
@@ skipping 685 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);
 }