[Help wanted / bug ?] Trying to create UserModelMixins and ModelMixins; trouble typing manager.

[PedroPerpetua]

I've tried the Gitter help link, but it appears to not be an active place (I left a question there a couple months ago and it never got an answer - and there's only about 5 more messages since then), so I'm trying my luck here.

For boilerplate purposes, I'm trying to provide multiple model Mixins, as well as a base abstract user model to be used in projects. This abstract user model should implement one of these Mixins (SoftDeleteMixin); this mixin implements it's own custom manager. That appears to be the start of the mess, as I can't make the types coherent.

Here are some snippets of the models and what I'm trying to achieve:

# The mixin manager
SoftDeleteModel = TypeVar("SoftDeleteModel", bound=SoftDeleteMixin)
class SoftDeleteManager(models.Manager[SoftDeleteModel]):
    def get_queryset(self) -> models.QuerySet[SoftDeleteModel]: ...
    def include_deleted(self) -> models.QuerySet[SoftDeleteModel]: ...

# The mixin
class SoftDeleteMixin(models.Model):
     objects = SoftDeleteManager[Self]()

# The manager for the users - inherits from the other manager because the GenericUser type will subclass SoftDeleteMixin
GenericUser = TypeVar("GenericUser", bound=BaseAbstractUser)
class BaseUserManager(SoftDeleteManager[GenericUser], DjangoBaseUserManager[GenericUser]):
    def create_user(self, password: str, **fields: Any) -> GenericUser: ...
    def create_superuser(self, password: str, **fields: Any) -> GenericUser: ...

# The abstract user model
class BaseAbstractUser(PermissionsMixin, SoftDeleteMixin, DjangoAbstractBaseUser):
    objects = BaseUserManager[Self]()  # By default uses the base manager

Now this is generating loads of errors with mypy:

• Incompatible types in assignment (expression has type "BaseUserManager[BaseAbstractUser]", base class "SoftDeleteMixin" defined the type as "SoftDeleteManager[SoftDeleteMixin]"
  • This appears to be related to Incompatible types in assignment with User subclass #174
• Subclasses have incompatible return type in the objects property; for example:

class UserModel(BaseAbstractUser): ...
instance = UserModel.objects.create(...)  # instance will evaluate to BaseAbstractUser instead of UserModel
# Notably, Pylance on VSCode appears to correctly identify that `create` returns a UserModel, which seems weird to me.

Is this some sort of bug, or am I doing some kind of "anti-pattern" here, typing things incorrectly, etc? I've tried multiple changes with Generics and all that and always end up with some kind of issue in the end. Help would be greatly appreciated.