Make SomeModel._default_manager return a BaseManager[SomeModel] instead of BaseManager[Model] (#817)

* _default_manager has more specific type for TypeVars

* remove unnecessary # type: ignore

* add test for _base_manager

* add overloads for classproperty.__get__

* readd # type: ignore for WSGIRequestHandler.connection, fails in github's pipeline

* fix _base_manager test: mypy reveals an inferred type

Co-authored-by: Michael Pöhle <michael.poehle@polyteia.de>

django-stubs/db/models/base.pyi

@@ -5,6 +5,7 @@ from django.core.exceptions import MultipleObjectsReturned as BaseMultipleObject
 from django.core.exceptions import ObjectDoesNotExist, ValidationError
 from django.db.models.manager import BaseManager
 from django.db.models.options import Options
+from django.utils.functional import classproperty
 
 _Self = TypeVar("_Self", bound="Model")
 
@@ -22,8 +23,12 @@ class Model(metaclass=ModelBase):
     class MultipleObjectsReturned(BaseMultipleObjectsReturned): ...
     class Meta: ...
     _meta: Options[Any]
-    _default_manager: BaseManager[Model]
-    _base_manager: BaseManager[Model]
+    @classproperty
+    @classmethod
+    def _default_manager(cls: Type[_Self]) -> BaseManager[_Self]: ...
+    @classproperty
+    @classmethod
+    def _base_manager(cls: Type[_Self]) -> BaseManager[_Self]: ...
     objects: BaseManager[Any]
     pk: Any = ...
     _state: ModelState

django-stubs/utils/functional.pyi

@@ -62,8 +62,14 @@ def partition(
     predicate: Callable, values: List[_PartitionMember]
 ) -> Tuple[List[_PartitionMember], List[_PartitionMember]]: ...
 
-class classproperty:
-    fget: Optional[Callable] = ...
-    def __init__(self, method: Optional[Callable] = ...) -> None: ...
-    def __get__(self, instance: Any, cls: Optional[type] = ...) -> Any: ...
-    def getter(self, method: Callable) -> classproperty: ...
+_Get = TypeVar("_Get")
+_Self = TypeVar("_Self")
+
+class classproperty(Generic[_Get]):
+    fget: Optional[Callable[[Type[_Self]], _Get]] = ...
+    def __init__(self, method: Optional[Callable[[Type[_Self]], _Get]] = ...) -> None: ...
+    @overload
+    def __get__(self, instance: None, cls: Type[_Self] = ...) -> _Get: ...
+    @overload
+    def __get__(self, instance: _Self, cls: Type[_Self] = ...) -> _Get: ...
+    def getter(self, method: Callable[[Type[_Self]], _Get]) -> classproperty[_Get]: ...

tests/typecheck/managers/test_managers.yml

@@ -48,13 +48,38 @@
                 class Base(Generic[_T]):
                     def __init__(self, model_cls: Type[_T]):
                         self.model_cls = model_cls
-                        reveal_type(self.model_cls._default_manager)  # N: Revealed type is "django.db.models.manager.BaseManager[django.db.models.base.Model]"
+                        reveal_type(self.model_cls._default_manager)  # N: Revealed type is "django.db.models.manager.BaseManager[_T`1]"
                 class MyModel(models.Model):
                     pass
                 class Child(Base[MyModel]):
                     def method(self) -> None:
                         reveal_type(self.model_cls._default_manager)  # N: Revealed type is "django.db.models.manager.Manager[myapp.models.MyModel]"
 
+-   case: test_base_manager_called_on_model_cls_as_generic_parameter
+    main: |
+        from myapp.models import Base, MyModel
+        base_instance = Base(MyModel)
+        reveal_type(base_instance.model_cls._base_manager)  # N: Revealed type is "django.db.models.manager.BaseManager[myapp.models.MyModel*]"
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                from typing import TypeVar, Generic, Type
+                from django.db import models
+
+                _T = TypeVar('_T', bound=models.Model)
+                class Base(Generic[_T]):
+                    def __init__(self, model_cls: Type[_T]):
+                        self.model_cls = model_cls
+                        reveal_type(self.model_cls._base_manager)  # N: Revealed type is "django.db.models.manager.BaseManager[_T`1]"
+                class MyModel(models.Model):
+                    pass
+                class Child(Base[MyModel]):
+                    def method(self) -> None:
+                        reveal_type(self.model_cls._base_manager)  # N: Revealed type is "django.db.models.manager.BaseManager[myapp.models.MyModel*]"
+
 -   case: if_custom_manager_defined_it_is_set_to_default_manager
     main: |
         from myapp.models import MyModel