Error when setting `gettext_lazy` as class attribute

[browniebroke]

Bug report

What's wrong

We received an update in cookiecutter-django to update to the latest django-stubs, but the type checks fail:

https://github.com/cookiecutter/cookiecutter-django/actions/runs/3385553002/jobs/5623835120#step:5:2492

The reason is because the success_message attribute for SuccessMessageMixin should accept lazy string.

django-stubs/django-stubs/contrib/messages/views.pyi

Lines 6 to 9 in 8f97bf8

	class SuccessMessageMixin:
	success_message: str = ...
	def form_valid(self, form: BaseForm) -> HttpResponse: ...
	def get_success_message(self, cleaned_data: Dict[str, str]) -> str: ...

References:

• Return Promise for lazy functions. #689
• Error while passing gettext_lazy to arguments expecting strings #1137

I assume there are a other mixin with the same problem.

Related error:

Note that the CI run above also have a similar error regarding the model admin fieldsets attribute (defined here) - I'm happy to open a separate issue about it, but maybe we should consider a overall fix?

How is that should be

The type annotation for success_message should accept lazy strings too:

class SuccessMessageMixin: 
     success_message: _StrOrPromise = ... 

System information

• OS:
• python version: 3.10
• django version: 4.0
• mypy version: 0.982
• django-stubs version: 1.13.0
• django-stubs-ext version: n/a (I don't think this package is installed?)

[sobolevn]

CC @PIG208

[sobolevn]

@browniebroke thank you for the report! I think that one issue is fine.

This was pretty big change, I hope we can find and fix corner cases in a patch release soon.