add GeneratedField

[taraskuzyk]

GeneratedField was added in Django 5.0. I am making this pull request as a draft as I'd like to find out how to contribute to this repository (would love to also document that in a CONTRIBUTING.md).

I based this on JSONField implementation and main changes were taken based on the __init__ in source:

def __init__(self, *, expression, output_field, db_persist=None, **kwargs):
        if kwargs.setdefault("editable", False):
            raise ValueError("GeneratedField cannot be editable.")
        if not kwargs.setdefault("blank", True):
            raise ValueError("GeneratedField must be blank.")
        if kwargs.get("default", NOT_PROVIDED) is not NOT_PROVIDED:
            raise ValueError("GeneratedField cannot have a default.")
        if kwargs.get("db_default", NOT_PROVIDED) is not NOT_PROVIDED:
            raise ValueError("GeneratedField cannot have a database default.")
        if db_persist not in (True, False):
            raise ValueError("GeneratedField.db_persist must be True or False.")

[sbdchd]

Yeah seems good, if you want to test it, you can add some code inside https://github.com/sbdchd/django-types/blob/main/tests/trout/models.py and the type checker will make sure it works with the types!

[taraskuzyk]

Will do. Had an unrelated question - I'm using grep for searching across codebase, and the .ignore contains django-stubs. I can only see it being edited once before, is there a reason that file exists?

[sbdchd]

Oh I think that's a remnant of how the project used to be structured, there was like a dupe folder that was symbolic linked to another folder so you'd get dupes in vscode without the .ignore file