[Django] #34438: In Django 4.2 UserCreationForm fails with Manager isn't available; 'auth.User' has been swapped for 'users.User'

[Django]

#34438: In Django 4.2 UserCreationForm fails with Manager isn't available;
'auth.User' has been swapped for 'users.User'
----------------------------------------+------------------------
Reporter: Gary Jarrel | Owner: nobody
Type: Bug | Status: new
Component: contrib.auth | Version: 4.2
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
----------------------------------------+------------------------
Our project users a custom user model defined in settings via
{{{AUTH_USER_MODEL}}}

There is a basic test case:
{{{#!python
def test_username_validation_error_msg(self, user: User):
# The user already exists,
# hence cannot be created.
form = UserAdminCreationForm(
{
"username": user.username,
"password1": user.password,
"password2": user.password,
}
)

assert not form.is_valid()
assert len(form.errors) == 1
assert "username" in form.errors
assert form.errors["username"][0] == _("This username has already
been taken.")
}}}

This works in Django 4.1, however when I ran the test suite against 4.2rc1
and the current main branch, I get failures.

{{{
AttributeError: Manager isn't available; 'auth.User' has been swapped for
'users.User'
}}}

with the trace

{{{
../../contrib/django/django/forms/forms.py:197: in is_valid
return self.is_bound and not self.errors
../../contrib/django/django/forms/forms.py:192: in errors
self.full_clean()
../../contrib/django/django/forms/forms.py:327: in full_clean
self._clean_fields()
../../contrib/django/django/forms/forms.py:342: in _clean_fields
value = getattr(self, "clean_%s" % name)()
../../contrib/django/django/contrib/auth/forms.py:158: in clean_username
if username and
User.objects.filter(username__iexact=username).exists():
}}}

I believe it relates to this
[[https://github.com/django/django/commit/298d02a77a69321af8c0023df3250663e9d1362d
| commit]]

The line
{{{
#!python
if username and User.objects.filter(username__iexact=username).exists()
}}}

When I changed the line to:

{{{
#!python
if username and
UserModel.objects.filter(username__iexact=username).exists()
}}}

The error was resolved.

This could potentially be related to:
[https://code.djangoproject.com/ticket/28608 28608], but it seems like a
very old ticket, when compared to the
[[https://github.com/django/django/commit/298d02a77a69321af8c0023df3250663e9d1362d
| commit]] which was done in December 22

''As a side note, the test then failed due to the change in the error
message from:''

{{{
"This username has already been taken."
}}}

to
{{{
A user with that username already exists.
}}}

But that's not a big issue.

--
Ticket URL: <https://code.djangoproject.com/ticket/34438>
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