fix: Fix FilterBackendProtocol for django-filter

rest_framework-stubs/decorators.pyi

@@ -10,7 +10,7 @@ from typing import (
 from django.db.models import QuerySet
 from django.http.response import HttpResponseBase
 from rest_framework.authentication import BaseAuthentication
-from rest_framework.filters import _FilterBackendProtocol
+from rest_framework.filters import FilterBackendProtocol
 from rest_framework.parsers import BaseParser
 from rest_framework.permissions import _PermissionClass
 from rest_framework.renderers import BaseRenderer
@@ -112,7 +112,7 @@ def action(
     authentication_classes: _AuthClassesParam = ...,
     renderer_classes: _RenderClassesParam = ...,
     parser_classes: _ParserClassesParam = ...,
-    filter_backends: Sequence[type[_FilterBackendProtocol]] = ...,
+    filter_backends: Sequence[type[FilterBackendProtocol]] = ...,
     lookup_field: str = ...,
     lookup_url_kwarg: str | None = ...,
     queryset: QuerySet[Any] = ...,

rest_framework-stubs/filters.pyi

@@ -10,13 +10,12 @@ from rest_framework.request import Request
 from rest_framework.views import APIView
 
 _MT = TypeVar("_MT", bound=Model)
-_Q = TypeVar("_Q", bound=QuerySet[Any])
 
-class _FilterBackendProtocol(Protocol):
-    def filter_queryset(self, request: Any, queryset: _Q, view: APIView) -> _Q: ...
+class FilterBackendProtocol(Protocol):
+    def filter_queryset(self, request: Request, queryset: QuerySet[_MT], view: APIView) -> QuerySet[_MT]: ...
 
 class BaseFilterBackend:
-    def filter_queryset(self, request: Any, queryset: _Q, view: APIView) -> _Q: ...
+    def filter_queryset(self, request: Request, queryset: QuerySet[_MT], view: APIView) -> QuerySet[_MT]: ...
     def get_schema_fields(self, view: APIView) -> list[Any]: ...
     def get_schema_operation_parameters(self, view: APIView) -> Any: ...
 

rest_framework-stubs/generics.pyi

@@ -5,7 +5,7 @@ from django.db.models import Manager, Model
 from django.db.models.query import QuerySet
 from django.http.response import HttpResponse
 from rest_framework import mixins, views
-from rest_framework.filters import _FilterBackendProtocol
+from rest_framework.filters import FilterBackendProtocol
 from rest_framework.pagination import BasePagination
 from rest_framework.request import Request
 from rest_framework.response import Response
@@ -24,7 +24,7 @@ class GenericAPIView(views.APIView):
     serializer_class: type[BaseSerializer] | None = ...
     lookup_field: str = ...
     lookup_url_kwarg: str | None = ...
-    filter_backends: Sequence[type[_FilterBackendProtocol]] = ...
+    filter_backends: Sequence[type[FilterBackendProtocol]] = ...
     pagination_class: type[BasePagination] | None = ...
     def get_object(self) -> Any: ...
     def get_serializer(self, *args: Any, **kwargs: Any) -> BaseSerializer: ...

tests/test_restframework.py

@@ -1,4 +1,8 @@
+from typing import Sequence
+
 from rest_framework.decorators import permission_classes
+from rest_framework.filters import FilterBackendProtocol
+from rest_framework.generics import GenericAPIView
 from rest_framework.permissions import IsAdminUser, IsAuthenticated
 from rest_framework.test import APIClient
 from typing_extensions import assert_type
@@ -15,3 +19,26 @@ def test_test_client_types() -> None:
 def test_decorator_types() -> None:
     permission_classes([IsAuthenticated])
     permission_classes([IsAuthenticated | IsAdminUser])
+
+
+def test_filter_backends_types() -> None:
+    """
+    django-filter does not use typing, so we're testing if untyped code also works fine
+    with our types.
+
+    https://github.com/carltongibson/django-filter/pull/1585
+    """
+
+    class DjangoFilterBackend:
+        def filter_queryset(self, request, queryset, view):  # type: ignore
+            filterset = self.get_filterset(request, queryset, view)  # type: ignore
+            return filterset.qs
+
+    class BookAPIView(GenericAPIView):
+        filter_backends = (DjangoFilterBackend,)
+
+    # mypy and pyright works differently here:
+    # mypy: Expression is of type "tuple[type[DjangoFilterBackend]]", not "Sequence[type[FilterBackendProtocol]]"  [assert-type]
+    # Disable this check for now in mypy.
+    # At least assigning to filter_backends works fine, that's our main concern here.
+    assert_type(BookAPIView.filter_backends, Sequence[type[FilterBackendProtocol]])  # type: ignore[assert-type]