select_related changes the manager class

[canassa]

Bug report

What's wrong

select_related breaks custom managers.

Take the following example:

class TransactionQuerySet(models.QuerySet):
    def with_status(self):
        return self.filter(status=...)


class TransactionManager(models.Manager):

    def get_queryset(self) -> TransactionQuerySet:
        return TransactionQuerySet(self.model, using=self._db)

    def with_status(self):
        return self.get_queryset().with_status()

class Transaction(models.Model):
    ...
    objects = TransactionManager()

The following code has no type errors:

Transaction.objects.with_status()

But the following fails:

Transaction.objects.select_related().with_status()

error: "_QuerySet[Transaction, Transaction]" has no attribute "with_status"

The revealed types:

reveal_type(Transaction.objects)
reveal_type(Transaction.objects.select_related())

note: Revealed type is "core.core.models.Transaction_TransactionManager5[core.core.models.Transaction]"
note: Revealed type is "django.db.models.query._QuerySet[core.core.models.Transaction*, core.core.models.Transaction*]"

This problem started after I updated django-stubs from 1.8.0 to 1.9.0

System information

• OS:
• python version: 3.9.7
• django version: 3.2.8
• mypy version: 0.910
• django-stubs version: 1.9.0
• django-stubs-ext version: Not using it