Revise duplicate interface check

runtime/vm/class_finalizer.cc

 // Copyright (c) 2013, 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.
 
 #include "vm/class_finalizer.h"
 
 #include "vm/flags.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
 #include "vm/longjump.h"
@@ skipping 1427 matching lines @@
     FinalizeType(cls, sig_type, kCanonicalizeWellFormed);
     return;
   }
   // Finalize interface types (but not necessarily interface classes).
   Array& interface_types = Array::Handle(cls.interfaces());
   AbstractType& interface_type = AbstractType::Handle();
   for (intptr_t i = 0; i < interface_types.Length(); i++) {
     interface_type ^= interface_types.At(i);
     interface_type = FinalizeType(cls, interface_type, kCanonicalizeWellFormed);
     interface_types.SetAt(i, interface_type);
+
+    // Check whether the interface is duplicated. We need to wait with
+    // this check until the super type and interface types are finalized,
+    // so that we can use Type::Equals() for the test.
+    ASSERT(interface_type.IsFinalized());
+    ASSERT(super_type.IsFinalized());
+    if (interface_type.Equals(super_type)) {
+      const Script& script = Script::Handle(cls.script());
+      ReportError(script, cls.token_pos(),
+                  "super type '%s' may not be listed in "
+                  "implements clause of class '%s'",
+                  String::Handle(super_type.Name()).ToCString(),
+                  String::Handle(cls.Name()).ToCString());
+    }
+    AbstractType& seen_interf = AbstractType::Handle();
+    for (intptr_t j = 0; j < i; j++) {
+      seen_interf ^= interface_types.At(j);
+      if (interface_type.Equals(seen_interf)) {
+        const Script& script = Script::Handle(cls.script());
+        ReportError(script, cls.token_pos(),
+                    "interface '%s' appears twice in "
+                    "implements clause of class '%s'",
+                    String::Handle(interface_type.Name()).ToCString(),
+                    String::Handle(cls.Name()).ToCString());
+      }
+    }
   }
   // Mark as finalized before resolving type parameter upper bounds and member
   // types in order to break cycles.
   cls.Finalize();
   // Finalize bounds even if running in production mode, so that a snapshot
   // contains them.
   ResolveAndFinalizeUpperBounds(cls);
   ResolveAndFinalizeMemberTypes(cls);
   // Run additional checks after all types are finalized.
   if (cls.is_const()) {
@@ skipping 500 matching lines @@
 void ClassFinalizer::ReportError(const char* format, ...) {
   va_list args;
   va_start(args, format);
   const Error& error = Error::Handle(
       Parser::FormatError(Script::Handle(), -1, "Error", format, args));
   va_end(args);
   ReportError(error);
 }
 
 }  // namespace dart