Union return values with generics from queryset methods resolve wrong when the queryset is used on multiple models.

[jkaikkosplk]

Bug report

What's wrong

Returning a union type that includes a generic from a queryset method results with the generic getting resolved wrong on subsequent models.

-   case: handles_type_var_in_subclasses_of_subclasses_of_queryset
    main: |
        from myapp.models import MyModel, MyOtherModel
        reveal_type(MyModel.objects.example_other_mixin())  # N: Revealed type is "myapp.models.MyModel"
        reveal_type(MyModel.objects.example_union())  # N: Revealed type is "Union[myapp.models.MyModel, None]"
        reveal_type(MyOtherModel.objects.example_other_mixin())  # N: Revealed type is "myapp.models.MyOtherModel"
        reveal_type(MyOtherModel.objects.example_union())  # N: Revealed type is "Union[myapp.models.MyOtherModel, None]"
    installed_apps:
        - myapp
    files:
        -   path: myapp/__init__.py
        -   path: myapp/models.py
            content: |
              from typing import TypeVar, Generic, Optional
              from django.db import models
              from typing_extensions import Self

              T = TypeVar("T", bound=models.Model)
              T_2 = TypeVar("T_2", bound=models.Model)

              class SomeMixin:
                  def example_mixin(self, a: T) -> T: ...

              class OtherMixin(models.QuerySet[T]):
                  def example_other_mixin(self) -> T: ...
                  def example_union(self) -> Optional[T]: ...

              class _MyModelQuerySet(OtherMixin[T], models.QuerySet[T], Generic[T]):
                  def example(self) -> T: ...
                  def override(self) -> T: ...
                  def override2(self) -> T: ...
                  def dummy_override(self) -> int: ...
                  def test_sub_self(self) -> Self: ...

              class _MyModelQuerySet2(SomeMixin, _MyModelQuerySet[T_2]):
                  def example_2(self) -> T_2: ...
                  def override(self) -> T_2: ...
                  def override2(self) -> T_2: ...
                  def dummy_override(self) -> T_2: ...  # type: ignore[override]
                  def test_self(self) -> Self: ...

              class MyModelQuerySet(_MyModelQuerySet2["MyModel"]):
                  def override(self) -> "MyModel": ...

              class MyModel(models.Model):
                  objects = MyModelQuerySet.as_manager()

              class MyOtherModel(models.Model):
                  objects = _MyModelQuerySet2.as_manager()

Result:
both reveal_type(MyModel.objects.example_union()) and reveal_type(MyOtherModel.objects.example_union()) get resolved to "Union[myapp.models.MyModel, None]"

============================================================================================ FAILURES ============================================================================================
____________________________________________________________________ handles_type_var_in_subclasses_of_subclasses_of_queryset ____________________________________________________________________
/Users/jkaikko/Projects/django-stubs/tests/typecheck/managers/querysets/test_as_manager.yml:249:
E   pytest_mypy_plugins.utils.TypecheckAssertionError: Invalid output:
E   Actual:
E     ...
E     main:20: note: Revealed type is "Union[myapp.models.MyModel, None]" (diff)
E   Expected:
E     ...
E     main:20: note: Revealed type is "Union[myapp.models.MyOtherModel, None]" (diff)
E   Alignment of first line difference:
E     E: ...s "Union[myapp.models.MyOtherModel, None]"
E     A: ...s "Union[myapp.models.MyModel, None]"
E                                   ^

How is that should be

reveal_type(MyModel.objects.example_union()) should be resolve to Union[myapp.models.MyModel, None] and MyOtherModel.objects.example_union() should resolve to Union[myapp.models.MyOtherModel, None]

System information

• OS:
• python version: 3.9.9, 3.11.9
• django version: 4.2, 5.0
• mypy version: 1.11.1
• django-stubs version: 5.0.4
• django-stubs-ext version: 5.0.4

[jkaikkosplk]

Aaaand right after submitting, I find #1917, which I think this is a duplicate of.