Recover after #909 (#925)

* Fix stubs related to `(Async)RequestFactory` and `(Async)Client`

* Revert incorrect removal.

* Allow set as `unique_together`, use shared type alias.

* Revert `Q.__init__` to use only `*args, **kwargs` to remove false-positive with `Q(**{...})`

* Add abstract methods to `HttpResponseBase` to create common interface.

* Remove monkey-patched attributes from `HttpResponseBase` subclasses.

* Add QueryDict mutability checks (+ plugin support)

* Fix lint

* Return back GenericForeignKey to `Options.get_fields`

* Minor fixup

* Make plugin code typecheck with `--warn-unreachable`, minor performance increase.

* Better types for `{unique, index}_together` and Options.

* Fix odd type of `URLResolver.urlconf_name` which isn't a str actually.

* Better types for field migration operations.

* Revert form.files to `MultiValueDict[str, UploadedFile]`

* Compatibility fix (#916)

* Do not assume that `Annotated` is always related to django-stubs (fixes #893)

* Restrict `FormView.get_form` return type to `_FormT` (class type argument). Now it is resolved to `form_class` argument if present, but also errors if it is not subclass of _FormT

* Fix CI (make test runnable on 3.8)

* Fix CI (make test runnable on 3.8 _again_)

mypy_django_plugin/transformers/request.py

@@ -1,7 +1,7 @@
-from mypy.plugin import AttributeContext
+from mypy.plugin import AttributeContext, MethodContext
 from mypy.types import Instance
 from mypy.types import Type as MypyType
-from mypy.types import UnionType
+from mypy.types import UninhabitedType, UnionType
 
 from mypy_django_plugin.django.context import DjangoContext
 from mypy_django_plugin.lib import helpers
@@ -35,3 +35,10 @@ def set_auth_user_model_as_type_for_request_user(ctx: AttributeContext, django_c
         return ctx.default_attr_type
 
     return UnionType([Instance(user_info, []), Instance(anonymous_user_info, [])])
+
+
+def check_querydict_is_mutable(ctx: MethodContext, django_context: DjangoContext) -> MypyType:
+    ret_type = ctx.default_return_type
+    if isinstance(ret_type, UninhabitedType):
+        ctx.api.fail("This QueryDict is immutable.", ctx.context)
+    return ret_type