Misleading error message provided when custom permission names are too long

[Greatlemer]

Whilst adding a new custom permission to a model, I accidentally created one that was too long and instead of being informed the problem was an overly long name field, the validation error raised complained about the verbose name of my model being too long.

This was observed in Django 1.7.1 under python 2.7.

I was able to reproduce it by putting the following code in the models.py of an application listed in INSTALLED_APPS:

from django.db.models import Model

class Tmp(Model):
    class Meta:
        permissions = (
            (
                'can_do_something_long',
                'A custom permission name with greater than 50 chars',
            ),
        )

Then when I ran ./manage.py migrate I got the following error:

(env)blah> python ./manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: blah
  Apply all migrations: admin, contenttypes, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
    Creating table blah_tmp
  Installing custom SQL...
  Installing indexes...
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying sessions.0001_initial... OK
Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 164, in handle
    emit_post_migrate_signal(created_models, self.verbosity, self.interactive, connection.alias)
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/core/management/sql.py", line 268, in emit_post_migrate_signal
    using=db)
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/dispatch/dispatcher.py", line 198, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/data/home/ar/tmp/perm_issue/env/lib/python2.7/site-packages/django/contrib/auth/management/__init__.py", line 111, in create_permissions
    verbose_name_max_length,
django.core.exceptions.ValidationError: [u'The verbose_name of tmp is longer than 39 characters']

[Shai Berger]

This is actually fixed by #8162 which was fixed (only on master) by cf252dbea66d9c4a84aa1bc8da93b5e5cc759b9a. I'm not sure if we should backport.

[Tim Graham]

The message is still misleading in that it references verbose_name even for custom permissions.

[Shai Berger]

I'd thought for a second that the fix for #8162 fixed that too, because the test code included there uses permissions on permissions. I enjoy ironic recursion like anyone else, but it might be clearer to change that.

[Joeri Bekker]

The error is technically correct but in some cases doesn't point people to the most obvious cause. The cryptic database error mentioned in #18866 was replaced with the current message. It was an improvement but with custom permissions, the error is still cryptic.

[Joeri Bekker]

Separated 2 the two error cases with 2 separate error messages to help fix the user by developers.

See: ​https://github.com/django/django/pull/4274

[Tim Graham <timograham@…>]

In 0ed20d5:

Fixed #23926 -- Improved validation error for custom permissions that are too long.