Add warning for invalid JavaScriptCatalog 'packages'

[James Bennett]

The javascript_catalog i18n view's packages argument only accepts modules which are either django.conf or which are also in INSTALLED_APPS. But there are two issues with this:

1. The documentation for the view hides this a bit, and can create the impression that the restriction only applies to a packages argument passed through the URL.

2. The view itself does not give you any warning if you're violating this restriction; it just silently discards anything in packages that doesn't meet the requirements.

At the very least, the documentation should be more up-front that this requirement always applies no matter how you're passing packages to the view. Possibly as a bonus, the view should warn that it's discarding any packages that don't conform to the requirements, to aid in debugging.

[Aymeric Augustin]

Two problems are reported in this ticket:

(a) the ​documentation of javascript_catalog is confusing

(b) invalid package names are silently dropped: yes, silent failure is bad and we should do something. Raising an exception would be backwards incompatible. Raising a warning could be a good compromise.

I've created #18596 to track (a). Let's focus this ticket on (b).

[Tim Graham]

Claude, I know made some improvements when you created the new JavaScriptCatalog class-based view in 1.10. Is this ticket still relevant for that view?

[Claude Paroz]

Yes, this is still relevant (now in JavaScriptCatalog.get_paths method).

[Claude Paroz]

​PR

[Tim Graham]

Instead of a RuntimeWarning as proposed in the PR, would it make more sense to raise a deprecation warning and eventually error out (or even error out now)? I usually favor raising an error straight away, rather than delaying that notice with a deprecation path, if it reveals a mistake a developer made (a past case was QuerySet.select_related() validating the values it receives) but I'll defer a decision here since I'm not a JavaScriptCatalog user.

[Claude Paroz]

Aymeric, would you like to develop about your backwards compatibility concerns?
Would erroring out be acceptable (considering a release note about that new behavior)?

[Aymeric Augustin]

When I made this comment five years ago, I was learning to triage tickets and clearly I didn't know James... Don't take what I wrote too seriously!

I think raising an error and documenting the change is fine, since the code isn't working as intended anyway in that case.

[Claude Paroz]

Thanks for your input!

[Claude Paroz <claude@…>]

In 23142eea:

Fixed #18394 -- Added error for invalid JavaScriptCatalog packages

Thanks Tim Graham for the review.