Reapply this reverted change:

runtime/vm/class_finalizer.cc

 // 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.
 
 #include "vm/class_finalizer.h"
 
 #include "vm/flags.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
 #include "vm/longjump.h"
@@ skipping 79 matching lines @@
       ReportError("Duplicate definition : %s\n", str.ToCString());
     }
   } else {
     retval = false;
   }
   isolate->set_long_jump_base(base);
   return retval;
 }
 
 
-#if defined (DEBUG)
 // Adds all interfaces of cls into 'collected'. Duplicate entries may occur.
 // No cycles are allowed.
 void ClassFinalizer::CollectInterfaces(const Class& cls,
                                        const GrowableObjectArray& collected) {
   const Array& interface_array = Array::ZoneHandle(cls.interfaces());
   AbstractType& interface = AbstractType::Handle();
   Class& interface_class = Class::Handle();
   for (intptr_t i = 0; i < interface_array.Length(); i++) {
     interface ^= interface_array.At(i);
     interface_class = interface.type_class();
     collected.Add(interface_class);
     CollectInterfaces(interface_class, collected);
   }
 }
 
 
+#if defined (DEBUG)
 // Collect all interfaces of the class 'cls' and check that every function
 // defined in each interface can be found in the class.
 // No need to check instance fields since they have been turned into
 // getters/setters.
 void ClassFinalizer::VerifyClassImplements(const Class& cls) {
   ASSERT(!cls.is_interface());
   const GrowableObjectArray& interfaces =
       GrowableObjectArray::Handle(GrowableObjectArray::New());
   CollectInterfaces(cls, interfaces);
   const String& class_name = String::Handle(cls.Name());
@@ skipping 817 matching lines @@
       const Script& script = Script::Handle(cls.script());
       ReportError(script, field.token_index(),
                   "field '%s' of class '%s' conflicts with instance "
                   "member '%s' of super class '%s'",
                   name.ToCString(),
                   class_name.ToCString(),
                   name.ToCString(),
                   super_class_name.ToCString());
     }
   }
-  // Resolve function signatures and check for conflicts in super classes.
+  // Collect interfaces, super interfaces, and super classes of this class.
+  const GrowableObjectArray& interfaces =
+      GrowableObjectArray::Handle(GrowableObjectArray::New());
+  CollectInterfaces(cls, interfaces);
+  // Include superclasses in list of interfaces and super interfaces.
+  super_class = cls.SuperClass();
+  while (!super_class.IsNull()) {
+    interfaces.Add(super_class);
+    super_class = super_class.SuperClass();
+  }
+  // Resolve function signatures and check for conflicts in super classes and
+  // interfaces.
   array = cls.functions();
   Function& function = Function::Handle();
   Function& overridden_function = Function::Handle();
   intptr_t num_functions = array.Length();
   String& function_name = String::Handle();
   for (intptr_t i = 0; i < num_functions; i++) {
     function ^= array.At(i);
     ResolveAndFinalizeSignature(cls, function);
     function_name = function.name();
     if (function.is_static()) {
       super_class = FindSuperOwnerOfInstanceMember(cls, function_name);
       if (!super_class.IsNull()) {
         const String& class_name = String::Handle(cls.Name());
         const String& super_class_name = String::Handle(super_class.Name());
         const Script& script = Script::Handle(cls.script());
         ReportError(script, function.token_index(),
                     "static function '%s' of class '%s' conflicts with "
                     "instance member '%s' of super class '%s'",
                     function_name.ToCString(),
                     class_name.ToCString(),
                     function_name.ToCString(),
                     super_class_name.ToCString());
       }
     } else {
-      // TODO(regis): This arity check is still being debated. Revisit.
-      super_class = cls.SuperClass();
-      while (!super_class.IsNull()) {
+      for (int i = 0; i < interfaces.Length(); i++) {
+        super_class ^= interfaces.At(i);
         overridden_function = super_class.LookupDynamicFunction(function_name);
         if (!overridden_function.IsNull() &&
-          !function.HasCompatibleParametersWith(overridden_function)) {
+            !function.HasCompatibleParametersWith(overridden_function)) {
           // Function types are purposely not checked for subtyping.
           const String& class_name = String::Handle(cls.Name());
           const String& super_class_name = String::Handle(super_class.Name());
           const Script& script = Script::Handle(cls.script());
           ReportError(script, function.token_index(),
-                      "class '%s' overrides function '%s' of super class '%s' "
+                      "class '%s' overrides function '%s' of %s '%s' "
                       "with incompatible parameters",
                       class_name.ToCString(),
                       function_name.ToCString(),
+                      super_class.is_interface() ? "interface" : "super class",
                       super_class_name.ToCString());
         }
-        super_class = super_class.SuperClass();
       }
     }
     if (function.kind() == RawFunction::kGetterFunction) {
       name = Field::NameFromGetter(function_name);
       super_class = FindSuperOwnerOfFunction(cls, name);
       if (!super_class.IsNull()) {
         const String& class_name = String::Handle(cls.Name());
         const String& super_class_name = String::Handle(super_class.Name());
         const Script& script = Script::Handle(cls.script());
         ReportError(script, function.token_index(),
@@ skipping 476 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