django-filter: preserve queryset model and row types in filter_queryset

stubs/django-filter/@tests/test_cases/check_rest_framework_backends.py

@@ -0,0 +1,36 @@
+from typing import Any, TypedDict
+from typing_extensions import assert_type
+
+from django.db.models import Model, QuerySet
+from django.http import HttpRequest
+from django_filters.rest_framework import DjangoFilterBackend
+
+
+class Product(Model): ...
+
+
+class Customer(Model): ...
+
+
+class ProductRow(TypedDict):
+    name: str
+
+
+def check_filter_queryset(
+    request: HttpRequest,
+    view: object,
+    models: QuerySet[Product],
+    values: QuerySet[Product, ProductRow],
+    tuples: QuerySet[Product, tuple[int, str]],
+    dynamic_rows: QuerySet[Product, Any],
+) -> None:
+    backend = DjangoFilterBackend()
+    assert_type(backend.filter_queryset(request, models, view), QuerySet[Product])
+    assert_type(backend.filter_queryset(request, values, view), QuerySet[Product, ProductRow])
+    assert_type(backend.filter_queryset(request, tuples, view), QuerySet[Product, tuple[int, str]])
+
+    assert_type(backend.filter_queryset(request, dynamic_rows, view), QuerySet[Product, Any])
+
+    filtered = backend.filter_queryset(request, values, view)
+    _wrong_model: QuerySet[Customer, ProductRow] = filtered  # type: ignore[assignment]
+    _wrong_row: QuerySet[Product, str] = filtered  # type: ignore[assignment]

stubs/django-filter/django_filters/rest_framework/backends.pyi

@@ -1,6 +1,7 @@
 from typing import Any, TypeAlias
+from typing_extensions import TypeVar
 
-from django.db.models import QuerySet
+from django.db.models import Model, QuerySet
 from django.http import HttpRequest
 from django_filters.filterset import FilterSetMetaclass
 
@@ -9,6 +10,9 @@ from . import filterset
 # APIView placeholder - djangorestframework is optional, so we use Any for compatibility
 _APIView: TypeAlias = Any
 
+_Model = TypeVar("_Model", bound=Model)
+_Row = TypeVar("_Row", default=_Model)
+
 class DjangoFilterBackend:
     filterset_base: FilterSetMetaclass = ...
     raise_exception: bool
@@ -25,5 +29,7 @@ class DjangoFilterBackend:
     def get_filterset_kwargs(self, request: HttpRequest, queryset: QuerySet[Any], view: _APIView) -> dict[str, Any]: ...
 
     # Filters any model type
-    def filter_queryset(self, request: HttpRequest, queryset: QuerySet[Any], view: _APIView) -> QuerySet[Any]: ...
+    def filter_queryset(
+        self, request: HttpRequest, queryset: QuerySet[_Model, _Row], view: _APIView
+    ) -> QuerySet[_Model, _Row]: ...
     def to_html(self, request: HttpRequest, queryset: QuerySet[Any], view: _APIView) -> str: ...  # Renders form for any model