Fixed #29970, #30041 -- Made ModelBase.__new__() pass attrs without contribute_to_class() to type.__new__().

django/db/models/base.py

@@ -58,6 +58,11 @@ def subclass_exception(name, bases, module, attached_to):
     })
 
 
+def _has_contribute_to_class(value):
+    # Only call contribute_to_class() if it's bound.
+    return not inspect.isclass(value) and hasattr(value, 'contribute_to_class')
+
+
 class ModelBase(type):
     """Metaclass for all models."""
     def __new__(cls, name, bases, attrs, **kwargs):
@@ -75,8 +80,15 @@ class ModelBase(type):
         classcell = attrs.pop('__classcell__', None)
         if classcell is not None:
             new_attrs['__classcell__'] = classcell
-        new_class = super_new(cls, name, bases, new_attrs, **kwargs)
         attr_meta = attrs.pop('Meta', None)
+        # Pass all attrs without a (Django-specific) contribute_to_class()
+        # method to type.__new__() so that they're properly initialized
+        # (i.e. __set_name__()).
+        for obj_name, obj in list(attrs.items()):
+            if not _has_contribute_to_class(obj):
+                new_attrs[obj_name] = attrs.pop(obj_name)
+        new_class = super_new(cls, name, bases, new_attrs, **kwargs)
+
         abstract = getattr(attr_meta, 'abstract', False)
         meta = attr_meta or getattr(new_class, 'Meta', None)
         base_meta = getattr(new_class, '_meta', None)
@@ -300,8 +312,7 @@ class ModelBase(type):
         return new_class
 
     def add_to_class(cls, name, value):
-        # We should call the contribute_to_class method only if it's bound
-        if not inspect.isclass(value) and hasattr(value, 'contribute_to_class'):
+        if _has_contribute_to_class(value):
             value.contribute_to_class(cls, name)
         else:
             setattr(cls, name, value)

tests/model_inheritance/tests.py

@@ -181,18 +181,33 @@ class ModelInheritanceTests(TestCase):
     def test_init_subclass(self):
         saved_kwargs = {}
 
-        class A:
+        class A(models.Model):
             def __init_subclass__(cls, **kwargs):
                 super().__init_subclass__()
                 saved_kwargs.update(kwargs)
 
         kwargs = {'x': 1, 'y': 2, 'z': 3}
 
-        class B(A, models.Model, **kwargs):
+        class B(A, **kwargs):
             pass
 
         self.assertEqual(saved_kwargs, kwargs)
 
+    @unittest.skipUnless(PY36, '__set_name__ is new in Python 3.6')
+    @isolate_apps('model_inheritance')
+    def test_set_name(self):
+        class ClassAttr:
+            called = None
+
+            def __set_name__(self_, owner, name):
+                self.assertIsNone(self_.called)
+                self_.called = (owner, name)
+
+        class A(models.Model):
+            attr = ClassAttr()
+
+        self.assertEqual(A.attr.called, (A, 'attr'))
+
 
 class ModelInheritanceDataTests(TestCase):
     @classmethod