Add system check for the length of auth permissions codenames.

[Michael Mulholland]

I stumbled across this while performing some migrations on models with rather... descriptive names (my original model was dynamically created).

Anyway, it looks like in cases where a model name is just under the 100 character limit, and contrib.auth is used, the codenames generated for the default permissions (ie. add_*, change_*, delete_*, view_*) can exceed the maximum 100 characters on the Permission model.

As an example, the model below having a 98 character name allows migrations to be generated, but upon running the migration, a database error is raised when it tries to create permissions with codenames above 100 characters.

The model:

class SomeExcessivelyDescriptiveModelWithAnAbsolutelyRidiculousNameThatCouldntEverNeedToBeNearlyThisLong(models.Model):
    field1 = models.CharField(max_length=25)

The error:

django.db.utils.DataError: value too long for type character varying(100)

While I'm aware that you can override the default permissions by setting Meta.default_permissions on the model (this is how I fixed my app), and that the majority of people would never need model names this long, I figured it might be worth adding validation for this case since it uses contrib.auth's default behaviour. Also, the error message originally came up while using a flush command, which seemed counterintuitive.

[Mariusz Felisiak]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 5a68a223:

Fixed #31200 -- Added system checks for permissions codenames max length.