apps.get_app_config() could give better errors on fully-qualified package names

[Peter Inglesby]

Running eg ./manage.py dumpdata django.contrib.auth fails with CommandError: Unknown application: django.contrib.auth. Instead, you need to call the command with just auth.

This is because it calls through to apps.get_app_config which does not expect a fully-qualified package name.

There is a similar problem with other management commands that take an app's name.

There are a handful of approaches to fixing this:

1. apps.get_app_config should split a package name on dots, throw away all but the last token, and use this for looking up the app. I've not thought through all the consequences of this -- could an app name legitimately contain dots?
2. As for 1, but only if the package name begins django.contrib.
3. When apps.get_app_config raises a LookupError, it could check to see whether its argument contains dots, and its message could be something like No installed app with label 'x.y.z'. Did you mean 'z'?.
4. Whenever a management command calls apps.get_app_config, it could strip off django.contrib. if present.

I'm happy to code up a fix if/when the right approach is settle on.

[Aymeric Augustin]

These commands are documented to take app labels in argument rather than app names.

Option 3 is a decent idea but it should be implemented by inspecting the app cache to figure out if there's an app with the provided name and find its label. This cannot be done simply by splitting on dots because it's possible to give any label to an app with a customized AppConfig class.

[Tim Graham <timograham@…>]

In 0688a794:

Fixed #24776 -- Improved apps.get_app_config() error message on fully-qualified package names.