Fix FilterSet proxy (#4620)

rest_framework/filters.py

@@ -37,15 +37,32 @@ class BaseFilterBackend(object):
         return []
 
 
-class FilterSet(object):
-    def __new__(cls, *args, **kwargs):
-        warnings.warn(
-            "The built in 'rest_framework.filters.FilterSet' is pending deprecation. "
-            "You should use 'django_filters.rest_framework.FilterSet' instead.",
-            PendingDeprecationWarning
-        )
-        from django_filters.rest_framework import FilterSet
-        return FilterSet(*args, **kwargs)
+if django_filters:
+    from django_filters.filterset import FilterSetMetaclass as DFFilterSetMetaclass
+    from django_filters.rest_framework.filterset import FilterSet as DFFilterSet
+
+    class FilterSetMetaclass(DFFilterSetMetaclass):
+        def __new__(cls, name, bases, attrs):
+            warnings.warn(
+                "The built in 'rest_framework.filters.FilterSet' is pending deprecation. "
+                "You should use 'django_filters.rest_framework.FilterSet' instead.",
+                PendingDeprecationWarning
+            )
+            return super(FilterSetMetaclass, cls).__new__(cls, name, bases, attrs)
+    _BaseFilterSet = DFFilterSet
+else:
+    # Dummy metaclass just so we can give a user-friendly error message.
+    class FilterSetMetaclass(type):
+        def __init__(self, name, bases, attrs):
+            # Assert only on subclasses, so we can define FilterSet below.
+            if bases != (object,):
+                assert False, 'django-filter must be installed to use the `FilterSet` class'
+            super(FilterSetMetaclass, self).__init__(name, bases, attrs)
+    _BaseFilterSet = object
+
+
+class FilterSet(six.with_metaclass(FilterSetMetaclass, _BaseFilterSet)):
+    pass
 
 
 class DjangoFilterBackend(BaseFilterBackend):

tests/test_filters.py

@@ -79,12 +79,23 @@ if django_filters:
             model = BaseFilterableItem
             fields = '__all__'
 
+    # Test the same filter using the deprecated internal FilterSet class.
+    class BaseFilterableItemFilterWithProxy(filters.FilterSet):
+        text = django_filters.CharFilter()
+
+        class Meta:
+            model = BaseFilterableItem
+            fields = '__all__'
+
     class BaseFilterableItemFilterRootView(generics.ListCreateAPIView):
         queryset = FilterableItem.objects.all()
         serializer_class = FilterableItemSerializer
         filter_class = BaseFilterableItemFilter
         filter_backends = (filters.DjangoFilterBackend,)
 
+    class BaseFilterableItemFilterWithProxyRootView(BaseFilterableItemFilterRootView):
+        filter_class = BaseFilterableItemFilterWithProxy
+
     # Regression test for #814
     class FilterFieldsQuerysetView(generics.ListCreateAPIView):
         queryset = FilterableItem.objects.all()
@@ -296,6 +307,18 @@ class IntegrationTestFiltering(CommonFilteringTestCase):
         self.assertEqual(response.status_code, status.HTTP_200_OK)
         self.assertEqual(len(response.data), 1)
 
+    @unittest.skipUnless(django_filters, 'django-filter not installed')
+    def test_base_model_filter_with_proxy(self):
+        """
+        The `get_filter_class` model checks should allow base model filters.
+        """
+        view = BaseFilterableItemFilterWithProxyRootView.as_view()
+
+        request = factory.get('/?text=aaa')
+        response = view(request).render()
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertEqual(len(response.data), 1)
+
     @unittest.skipUnless(django_filters, 'django-filter not installed')
     def test_unknown_filter(self):
         """