Report error on duplicate supertypes

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 3368)
+++ runtime/vm/parser.cc	(working copy)
@@ -2984,9 +2984,19 @@
   ASSERT((CurrentToken() == Token::kIMPLEMENTS) ||
          (CurrentToken() == Token::kEXTENDS));
   GrowableArray<AbstractType*> interfaces;
+  String& interface_name = String::Handle();
   do {
     ConsumeToken();
+    intptr_t supertype_pos = token_index_;
     AbstractType& interface = AbstractType::ZoneHandle(ParseType(kCanResolve));
+    interface_name = interface.Name();
+    for (int i = 0; i < interfaces.length(); i++) {
+      String& other_name = String::Handle(interfaces[i]->Name());
+      if (interface_name.Equals(other_name)) {

[hausner, 2012/01/18 01:06:16]

I tried to use Equals on the type object directly, but ran into asserts because
the types may be not finalized when we run this code. Any better idea to check
whether two types are identical?

[regis, 2012/01/18 01:29:40]

Using the name seems brittle. How about using AbstractType::Equals() in the
class finalizer? See the code finalizing interfaces around line 1030 in
class_finalizer.cc.
 

[hausner, 2012/01/18 17:44:00]

As discussed in person: doing the check in the finalizer does not work, since
the implements lists of the whole class hierarchy is flattened into one list.
However, we only need to find duplicate interfaces per implements clause.

I think we can get away with comparing type names for this, at least as long as
we don't have arbitrary type aliases.

+        ErrorMsg(supertype_pos, "Duplicate supertype '%s'",
+                 interface_name.ToCString());
+      }
+    }
     interfaces.Add(&interface);
   } while (CurrentToken() == Token::kCOMMA);
   return NewArray<AbstractType>(interfaces);