Warn user if they attempt to have multiple templatetag libraries with the same name

[Daniel]

If a project has mulitple apps with templatetags with the same module name, django will load each of them, but drop all but the last one, and not inform the user at all, making it quite hard to diagnose.

For example, if you have:

• blog/templatetags/navigation_tags.py
• news/templatetags/navigation_tags.py
• pages/templatetags/navigation_tags.py

then try to use them in a template:

{% load navigation_tags %}

then only one of these will be loaded - and there's no report that there is a problem - but if you attempt to use one of the filters / tags from one of the libraries that's not the loaded one, it throws a generic template syntax error saying it's an invalid tag / filter.

Proposed solution:

Add a new 'check' to the django checks that warns the user if there are multiple templatetag libraries with the same name.

see PR:

​https://github.com/django/django/pull/14735

[Mariusz Felisiak]

Sounds reasonable.

[Shreya Bamne]

The PR (​https://github.com/django/django/pull/14735) mentioned in the ticket was closed due to inactivity. I would like to continue working on this. Would the correct next steps be to assign this ticket to myself, open a new PR and link the old one there? I am new to the Django community, any inputs are appreciated. Thank you.

[Shreya Bamne]

I have started working on this ticket and assigning the ticket to me.

[Shreya Bamne]

Continuing on the previous work done on this ticket, here is the link to the new PR: ​https://github.com/django/django/pull/15005

[Mariusz Felisiak <felisiak.mariusz@…>]

In b98394f:

Refs #32987 -- Refactored out get_template_tag_modules().

[Mariusz Felisiak <felisiak.mariusz@…>]

In 004b4620:

Fixed #32987 -- Added system check for template tag modules with the same name.

Co-authored-by: Daniel Fairhead <daniel@…>

[Claude Paroz]

I wonder if we should reconsider the new behavior here. The problem is that if in your project dependencies (which make sometimes a big list) you have two tag libraries with the same name, the project won't be able to migrate to Django 4.1. It's rather easily fixable when one of the libs is in your project, but not when they both are from external deps. See ​https://github.com/jazzband/sorl-thumbnail/issues/713

Could we at least make the check a warning, so it can be silenced?

[Mariusz Felisiak]

Replying to Claude Paroz:

Could we at least make the check a warning, so it can be silenced?

Sounds reasonable, see ​PR.

[GitHub <noreply@…>]

In f71b0cf7:

Refs #32987 -- Relaxed system check for template tag modules with the same name by turning into a warning.

Thanks Claude Paroz for the report.

Regression in 004b4620f6f4ad87261e149898940f2dcd5757ef.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 7843c43c:

[4.1.x] Refs #32987 -- Relaxed system check for template tag modules with the same name by turning into a warning.

Thanks Claude Paroz for the report.

Regression in 004b4620f6f4ad87261e149898940f2dcd5757ef.
Backport of f71b0cf769d9ac582ee3d1a8c33d73dad3a770da from main