From 6327a678749b751033e4d885380e941eb7a18cce Mon Sep 17 00:00:00 2001
From: Thomas Adamcik <thomas@adamcik.no>
Date: Sat, 11 Apr 2015 00:47:53 +0200
Subject: [PATCH] models: Make sure we really only add __weakref__ once

---
 mopidy/models.py            |  8 +++++---
 tests/models/test_models.py | 11 +++++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/mopidy/models.py b/mopidy/models.py
index 4b268474..477b87a7 100644
--- a/mopidy/models.py
+++ b/mopidy/models.py
@@ -1,6 +1,7 @@
 from __future__ import absolute_import, unicode_literals
 
 import copy
+import inspect
 import json
 import weakref
 
@@ -145,11 +146,12 @@ class ImmutableObjectMeta(type):
                 value._name = key
 
         attrs['_fields'] = fields
-        attrs['__slots__'] = fields.values()
         attrs['_instances'] = weakref.WeakValueDictionary()
+        attrs['__slots__'] = fields.values()
 
-        for base in bases:
-            if '__weakref__' in getattr(base, '__slots__', []):
+        anncestors = [b for base in bases for b in inspect.getmro(base)]
+        for anncestor in anncestors:
+            if '__weakref__' in getattr(anncestor, '__slots__', []):
                 break
         else:
             attrs['__slots__'].append('__weakref__')
diff --git a/tests/models/test_models.py b/tests/models/test_models.py
index 0407056c..27d02382 100644
--- a/tests/models/test_models.py
+++ b/tests/models/test_models.py
@@ -8,6 +8,17 @@ from mopidy.models import (
     TlTrack, Track, model_json_decoder)
 
 
+class InheritanecTest(unittest.TestCase):
+
+    def test_weakref_and_slots_play_nice_in_subclass(self):
+        # Check that the following does not happen:
+        # TypeError: Error when calling the metaclass bases
+        #   __weakref__ slot disallowed: either we already got one...
+
+        class Foo(Track):
+            pass
+
+
 class CachingTest(unittest.TestCase):
 
     def test_same_instance(self):