through attribute not defined within model definition

[mfosterw]

Bug report

What's wrong

Mypy cannot detect the through attribute of a ManyToManyField within the definition of the enclosing model. To reproduce, add the following test method to MyModel in tests/typecheck/fields/test_related.yml::test_many_to_many:

class MyModel(models.Model):
    auto_through = models.ManyToManyField(Other, related_name="autos")
    # Have multiple M2Ms with implicit through
    other_again = models.ManyToManyField(Other, related_name="others_again")
    custom_through = models.ManyToManyField(Other, through=CustomThrough, related_name="customs")

    objects = MyModelManager()

    def test(self) -> None:
        reveal_type(self.custom_through.through)

Results in:

myapp/models/__init__:31: error: "Other_ManyRelatedManager" has no attribute "through"  [attr-defined]
myapp/models/__init__:31: note: Revealed type is "Any"

How is that should be

Revealed type should be "CustomThrough"

System information

• OS: macOS 14.2.1
• python version: 3.12.1
• django version: 4.2.9
• mypy version: 1.7.1
• django-stubs version: 4.2.7
• django-stubs-ext version: 4.2.7