Admin System Checks do not run for custom AdminSite sites

[Andrew Mosson]

The admin section of the System checks only runs for ModelAdmin subclasses that are registered with the main AdminSite (admin.site.register(...))

To replicate place something similar to the following in a urls.py file

books/admin.py
from django.contrib import admin

class BookAdmin(admin.ModelAdmin):
    list_display = 'a field'  # intentional error

- urls.py
from django.admin.sites import AdminSite
from books.models import Book
from books.admin import BookAdmin

custom_site = AdminSite()
custom_site.register(Book, BookAdmin)

> python manage.py check
Expect to see an error here (specifically that list display must be a list of a tuple)

In actuality, this runs fine.

One potential fix for this problem would be to create a module level variable in django.contrib.admin.sites (or directly in django.contrib.admin), run the checks on register (this is already being done but the result of the checks are being ignored), and store the results in the module level variable.

Patch with this approach is attached

[Andrew Mosson]

Patch at ​https://github.com/amosson/django/tree/ticket_23497

[Simon Charette]

Could you submit a PR against Django's master instead? It makes reviewing easier.

[Andrew Mosson]

Sure. Here you go

​https://github.com/django/django/pull/3227

[Berker Peksag]

I've opened ​PR #3728 to revise ​PR #3227.

Changes:

• Fixed merge conflicts
• Added a release note
• Rewrote tests
• Updated commit message as suggested by Tim

[Tim Graham <timograham@…>]

In b7219c7ba5fdfbf9349948b5a91af50e32822ee6:

Fixed #23497 -- Made admin system checks run for custom AdminSites.

[Tim Graham <timograham@…>]

In 6d8c14621e2878ea2051ee56326c66969a1d18d0:

[1.7x.] Fixed #23497 -- Made admin system checks run for custom AdminSites.

Backport of b7219c7ba5fdfbf9349948b5a91af50e32822ee6 from master