ModelSignal.disconnect() does not work with lazy references

[Alex Hill]

ModelSignal.connect() lets you pass a string model reference as a sender, and will connect the signal as soon as the model is available.

For consistency, ModelSignal.disconnect() should work in the same way. Currently, if you call connect() followed by disconnect() before the model is available, the signal will remain connected:

>>> def receiver(sender, **kwargs):
...     print("post_init sent by %r" % sender)
... 
>>> post_init.connect(receiver, sender='some_app.SomeModel')
>>> post_init.disconnect(receiver, sender='some_app.SomeModel')
False
>>> 
>>> class SomeModel(models.Model):
...     class Meta:
...         app_label = 'some_app'
... 
>>> s = SomeModel()
post_init sent by <class 'SomeModel'>
>>> 

There's a patch with the necessary changes in PR 6629.

[Tim Graham]

Build/flake8/isort aren't passing.

[Alex Hill]

Sorry, that was sloppy. I've updated the patch. Strange for a circular import to only cause a problem in 2.7.

[Tim Graham <timograham@…>]

In ff6c6fe:

Fixed #26642 -- Made ModelSignal.disconnect() work with lazy references.

[Tim Graham <timograham@…>]

In f91247f:

[1.10.x] Fixed #26642 -- Made ModelSignal.disconnect() work with lazy references.

Backport of ff6c6feae17120c2c7df74fb6a9dc76826a1e233 from master