UserAdmin returns incorrect fieldsets when model has overridden __bool__.

[krnr]

in cases when model has "soft-delete" fields and defined __bool__ like these:

class CustomUser(models.User):
    is_deleted = models.BooleanField(default=False)

    def __bool__(self):
        return not self.is_deleted

the UserAdmin will use add_fieldsets because of comparison in get_fieldsets.

I have a simple fix for this: just check against None instead of boolean evaluation.

[Mariusz Felisiak]

I know that this fix is quite small but you will find other places where we use if instance/obj pattern, e.g. in SingleObjectMixin. Defining __bool__ on a model instance is an edge case and your issue can be worked around by defining and using e.g. is_active(self): return not self.is_deleted. See also arguments for closing a similar ticket.

[krnr]

I was fine with the existing admin class (because I seldom meet such user models), but recently I saw this PR: ​https://github.com/django/django/commit/5cd4c3e5595128bc1a3f28f2e30bab2e4dd3b1b7 and I was thinking "why does it have nice check against None in one method and doesn't have in another?"

and it's not about checking against all possible if instance (yeah, it doesn't worth it), just about fieldsets.

but that's OK. just leave it be if anyone else will be curious.