Check if default_app_config is used on Django 1.7+

[denizdogan]

From https://docs.djangoproject.com/en/2.2/ref/applications/#configuring-applications:

default_app_config allows applications that predate Django 1.7 such as django.contrib.admin to opt-in to AppConfig features without requiring users to update their INSTALLED_APPS.
New applications should avoid default_app_config. Instead they should require the dotted path to the appropriate AppConfig subclass to be configured explicitly in INSTALLED_APPS.

Unless someone opposes this idea, I'll try to throw together a PR for this soon.

[stefan6419846]

As recent Django versions are going to remove the default_app_config support, this might not be required anymore in the future: https://docs.djangoproject.com/en/4.0/ref/applications/#configuring-applications, django/django#12310.

[denizdogan]

@stefan6419846 Sorry, I'm not sure I understand what you mean. :) My PR/issue was created to warn users about using default_app_config if they do use it. It's been about three years since I made it, so if it's obsolete, I'll happily close the issue and PR, I just don't understand if it is obsolete?

[stefan6419846]

Since Django 3.2, Django will detect the AppConfig from apps.py automatically without the user to require to set default_app_config (ultimately deprecating it). For this reason, your proposed check should become obsolete with Django 3.2, as Django would not use it anyway. Upstream documentation on this is available from https://docs.djangoproject.com/en/4.0/releases/3.2/#automatic-appconfig-discovery.

According to https://www.djangoproject.com/download/#supported-versions, Django 3.2 is the oldest release still supported. In theory this check should be obsolete, although versions < 3.2 probably are still in use.

One might argue that this check might make more sense now to finally remove it, as this value will not be used any more at all, but I am not sure.