functools.partial does not carry over type of ForeignKey

[StefanBrand]

Bug report

What's wrong

I have two models:

ProtectedForeignKey = partial(models.ForeignKey, on_delete=models.PROTECT)

class Model(models.Model):
    config = ProtectedForeignKey("Config")

class Config(models.Model):
    version = models.IntegerField()

model = Model.objects.get()
model.config.version  # "_GT" has no attribute "version"

---

Without partial, it works fine:

class Model(models.Model):
    config = models.ForeignKey("Config", on_delete=models.PROTECT)  # ForeignKey[Union[Config, Combinable], Config]

---

Edit: And casting works in 1.8.0 (but not in 1.9.0 due to #725)

class Model(models.Model):
    config = cast("Config", ProtectedForeignKey("Config"))

How it should be

partial should carry over the ForeignKey type.

System information

• OS: Ubuntu 20.04
• python version: 3.9.1
• django version: 3.1.5
• mypy version: 0.910
• django-stubs version: 1.9.0
• django-stubs-ext version:

[flaeppe]

ProtectedForeignKey = partial(models.ForeignKey, on_delete=models.PROTECT)

class Model(models.Model):
    config = ProtectedForeignKey("Config")

ForeignKey is generic, but in this situation having unbound arguments. That's why e.g. there's a _GT in the error message. That's why I'll close this off.