Fix has_registry_receivers when super.__new__ is object.__new__

This change updates has_registry_receivers implementation in order to
call super.__new__ without args, kwargs parameters if super.__new__ is
object.__new__ (which forbids args, kwargs parameters). Without this fix
decorated class instantiation with positional or/and keyword arguments
fail.

Change-Id: I25880f6142f294fdde9db7f453d5e649c79029d0

neutron/callbacks/registry.py

@@ -83,7 +83,12 @@ def has_registry_receivers(klass):
     def replacement_new(cls, *args, **kwargs):
         if new_inherited:
             # class didn't define __new__ so we need to call inherited __new__
-            instance = super(klass, cls).__new__(cls, *args, **kwargs)
+            super_new = super(klass, cls).__new__
+            if super_new is object.__new__:
+                # object.__new__ doesn't accept args nor kwargs
+                instance = super_new(cls)
+            else:
+                instance = super_new(cls, *args, **kwargs)
         else:
             instance = orig_new(cls, *args, **kwargs)
         if getattr(instance, '_DECORATED_METHODS_SUBSCRIBED', False):

neutron/tests/unit/callbacks/test_registry.py

@@ -52,6 +52,13 @@ class AnotherObjectWithDecoratedCallback(ObjectWithDecoratedCallback,
         self.counter2 += 1
 
 
+@registry.has_registry_receivers
+class CallbackClassWithParameters(object):
+
+    def __init__(self, dummy):
+        pass
+
+
 class CallBacksManagerTestCase(base.BaseTestCase):
 
     def test_decorated_inst_method_receives(self):
@@ -81,3 +88,6 @@ class CallBacksManagerTestCase(base.BaseTestCase):
 
     def test_new_inheritance_not_broken(self):
         self.assertTrue(AnotherObjectWithDecoratedCallback().new_called)
+
+    def test_object_new_not_broken(self):
+        CallbackClassWithParameters('dummy')