Feature Request: Support django-polymorphic models in ManyToMany field

[khink]

Feature request

Sorry for filing this as a bug, i saw no other place to create a feature request.

And I thought posting here would make it easy for people with the same issue to find the reason.

What's wrong

When running mypy after upgrading to django-stubs[compatible-mypy]==4.2.6, i get error: Need type annotation for "articles".

Here, articles is defined as follows:

class ArticlePreset(models.Model):
    ...
    articles = models.ManyToManyField(Article, related_name="presets")

This is not due to the class being a string name as was the case in #1802.

We get four of these errors, and they are all for ManyToMany fields to the Article model.

The Article model is a polymorphic (https://github.com/django-polymorphic/django-polymorphic/) model:

class Article(PolymorphicModel):
    ...

This almost certainly is the reason for the error message. All other ManyToManyFields don't give this error.

How it should be

It would be nice if django-stubs could also support polymorphic models.

I realize that django-polymorphic has seen no activity in the last two years, and supporting it is not a priority. Also, I have no involvement with that project, we just use it (i wish we hadn't).

System information

• OS: Ubuntu Linux
• python version: 3.11.6
• django version: 4.2.7
• mypy version: 1.6.1
• django-stubs version: 4.2.6
• django-stubs-ext version: 4.2.5

[intgr]

Looks unrelated, but we have another issue with django-polymorphic as well: #1158. There are 8 thumbs up reactions so it has a considerable number of users.

[flaeppe]

Since django-polymorphic doesn't export types. Could it be possible to conditionally declare the PolymorphicModel base?

e.g.

from django.db import models
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    PolymorphicModel = models.Model
else:
    from xyz import PolymorphicModel

class Article(PolymorphicModel):
    ...

This wouldn't start showing any declarations from django-polymorphic but would set a default to interpret PolymorphicModel as a models.Model

[flaeppe]

This might be off topic, but I keep wondering if it's possible to use typing_extensions.Annotated to solve these kind of problems.

But I haven't gotten around to try it out myself. What I'm thinking about is doing:

from django.db import models
from typing_extensions import Annotated
from xyz import PolymorphicModel as _PolymorphicModel

PolymorphicModel = Annotated[models.Model, _PolymorphicModel]

class Article(PolymorphicModel):
    ...

[intgr]

Anyway I think the "proper" solution would be to get type stubs for django-polymorphic? Either add them to upstream if they want it, or create a new django-polymorphic-stubs project. Would that be sufficient to fix these issues?

[flaeppe]

Yes, getting typing for django-polymorphic is what should resolve these issues

django-stubs can't really do anything here

[flaeppe]

I'm going to close this off with the reasoning that this is an issue for django-polymorphic and should be brought there

[khink]

Thanks for looking into this and suggesting workarounds!