[5.0.3 regression] error: "type[RealmFilter]" has no attribute "objects" [attr-defined]

[andersk]

When trying to upgrade to django-stubs 5.0.3 or 5.0.4 in Zulip, I get 25 unexpected errors like error: "type[RealmFilter]" has no attribute "objects" [attr-defined]. This is not #1684; RealmFilter is a normal concrete model class. The issue seems to depend on the structure of the project’s import graph.

Based on git bisect, it first occurs at

• 2f5a494 (lookup manager type via mro #2276, cc @asottile).

I’ve reduced the issue to this minimized test case: https://github.com/andersk/no-attribute-objects

$ mypy .
zerver/models/__init__.py:6: error: "type[RealmFilter]" has no attribute "objects"  [attr-defined]
Found 1 error in 1 file (checked 10 source files)

pyproject.toml

[tool.django-stubs]
django_settings_module = "zproject.settings"

[tool.mypy]
plugins = ["mypy_django_plugin.main"]

confirmation/__init__.py (empty)

confirmation/models.py

from django.db import models

from zerver.models import Realm


class Confirmation(models.Model):
    realm = models.ForeignKey(Realm, on_delete=models.RESTRICT)

zerver/__init__.py (empty)

zerver/models/__init__.py

from zerver.models.linkifiers import RealmFilter as RealmFilter
from zerver.models.realms import Realm as Realm
from zerver.models.streams import Stream as Stream
from zerver.models.users import UserProfile as UserProfile

RealmFilter.objects

zerver/models/linkifiers.py

from django.db import models


class RealmFilter(models.Model):
    pass

zerver/models/realms.py

from django.db import models


class Realm(models.Model):
    pass

zerver/models/streams.py

from django.db import models

from zerver.models.realms import Realm
from zerver.models.users import UserProfile


class Stream(models.Model):
    realm = models.ForeignKey(Realm, on_delete=models.RESTRICT)
    creator = models.ForeignKey(UserProfile, on_delete=models.RESTRICT)

zerver/models/users.py

from django.contrib.auth.models import AbstractBaseUser, PermissionsMixin


class UserProfile(AbstractBaseUser, PermissionsMixin):
    pass

zproject/__init__.py (empty)

zproject/settings.py

INSTALLED_APPS = [
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "confirmation",
    "zerver",
]

[asottile]

appears to be a weird ordering thing -- #2280 will fix this probably (that or the objects removal needs to happen earlier)

what's happening is the plugin does a pass over your class -- notices the correct type exists (Manager[Self]) from models.Model and leaves it -- and then later the plugin deletes models.Model.objects

I'm surprised none of the tests hits this -- and we don't hit this at sentry because we turn off deletion of objects and friends in our fork

[flaeppe]

I couldn't get the case above to reproduce in django-stubs test suite, but I was able to check out https://github.com/andersk/no-attribute-objects and run it against #2280 successfully

[flaeppe]

I just want to reference that djangorestframework-stubs also ran in to this issue for rest_framework.authtoken.models.Token.objects(some additional info in typeddjango/djangorestframework-stubs#644). Which, in some way, means that project also has a structure with the ability to make mypy process files in an order that breaks the plugin.

[flaeppe]

I realised that our plugin tries to adjust the model class from the get_customize_class_mro_hook which, per its definition, is called:

get_customize_class_mro_hook() can be used to modify class MRO (for example insert some entries there) before the class body is analyzed.

Ref: https://mypy.readthedocs.io/en/stable/extending_mypy.html#current-list-of-plugin-hooks

But the code tries to expect and look through the class body...

A fix for this is instead to move to adjust the model class via the get_metaclass_hook. Which is called before get_base_class_hook: See https://github.com/python/mypy/blob/570b90a7a368f04c64f60af339d0ac1808c49c15/mypy/semanal.py#L1998-L2010

---

Anyways, above is some quite specific details, in the end it's just to change the plugin to use another hook. I'll add a fix for this.