Report errors on repeated interfaces.

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

Index: sdk/lib/_internal/compiler/implementation/resolution/members.dart
diff --git a/sdk/lib/_internal/compiler/implementation/resolution/members.dart b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
index 278e8009aefd1f5e80cbc64889ec83823f4221ee..f1d2008df6d7612aa1043e488bbc6561b835e822 100644
--- a/sdk/lib/_internal/compiler/implementation/resolution/members.dart
+++ b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
@@ -2709,6 +2709,14 @@ class ClassResolverVisitor extends TypeDefinitionVisitor {
           TypeAnnotation typeAnnotation = link.head;
           error(typeAnnotation.typeName, MessageKind.CLASS_NAME_EXPECTED, []);
         } else {
+          if (interfaceType == element.supertype) {
+            error(link.head,

[ahe, 2013/01/09 13:15:31]

As these errors are recoverable, it would be nice to use reportMessage instead.

[Johnni Winther, 2013/01/10 06:55:13]

Done.

+                  MessageKind.DUPLICATE_EXTENDS_IMPLEMENTS,
+                  [interfaceType]);
+          }
+          if (interfaces.contains(interfaceType)) {
+            error(link.head, MessageKind.DUPLICATE_IMPLEMENTS, [interfaceType]);
+          }
           interfaces = interfaces.prepend(interfaceType);
           if (isBlackListed(interfaceType)) {
             error(link.head, MessageKind.CANNOT_IMPLEMENT, [interfaceType]);