Proper way to write stub file for abstract models

[miaachan]

Bug report

What's wrong

I ran into a situation where I had to write stubs for my abstract model. But, mypy
is treating the inherited fields as Any.

Setup:

# base.py
from django.db import models

class TestModelBase(models.Model):
    date_created = models.DateTimeField(auto_now_add=True)
    date_modified = models.DateTimeField(auto_now=True)

    class Meta:
        abstract = True

# base.pyi - stub of base.py
from django.db import models

class TestModelBase(models.Model):
    date_created: models.DateTimeField
    date_modified: models.DateTimeField
    
    class Meta:
        abstract: bool

# models.py
from django.db import models
from .base import TestModelBase

class ModelA(TestModelBase):
    own_datetime = models.DateTimeField(null=True, blank=True)

reveal_type(ModelA.date_modified) # -> OK! Revealed type is "django.db.models.fields.DateTimeField[Any, Any]"
reveal_type(ModelA.own_datetime) # -> Revealed type is "django.db.models.fields.DateTimeField[Union[builtins.str, datetime.date, django.db.models.expressions.Combinable, None], Union[datetime.datetime, None]]"

It is weird that reveal_type(ModelA.date_modified) is able to yield DateTimeField
but fails in the next case.

Interact with model:

# t.py
from .models import ModelA

class A:
    foo: ModelA

    def bar(self) -> None:
        reveal_type(self.foo) # -> Revealed type is "pg.models.ModelA"
        reveal_type(self.foo.date_modified) # -> Revealed type is "Any"
        reveal_type(self.foo.own_datetime) # -> Revealed type is "Union[datetime.datetime, None]"

If the stub base.pyi is removed, the revealed type of self.foo.date_modified becomes
normal -> Revealed type is "datetime.datetime*". Am I missing something in the stub?

How is that should be

self.foo.date_modified should be datetime.datetime instead of Any

System information

• OS:
• python version: 3.9.5
• django version: 3.2.5
• mypy version: 0.931
• django-stubs version: 1.9.0
• django-stubs-ext version: 0.3.1

[intgr]

I think typing model classes in .pyi files isn't well supported by django-stubs.

You may get away with hinting the fields as date_created: datetime.datetime, but I'm not sure.