Add warning to collectstatic when static files have clashing names

[Markus Amalthea Magnuson]

If you have a project with several apps, some of which have static files directly in their static folder named identically, one of them will always be overwritten by the other when running collectstatic. The recommendation, and what is noted in the ​documentation, is to namespace by keeping all static files belonging to an app in an additional subdirectory in the static folder named like the app name. But if you're not doing that, the result can be very confusing. I've seen many developers run into this and spending quite some time before figuring it out through the documentation or otherwise.

I think there should be a default system check that looks for clashing static file names as described above, and warn if there are files that will overwrite each other when running collectstatic.

[Tim Graham]

I'm not sure a system check is a good idea since it seems such a check would involve a lot of disk reading and it could be expensive to do that each time the dev server is restarted (currently all system checks are simply static code analysis). Perhaps a warning when running collecstatic would be a better approach?

[Markus Amalthea Magnuson]

That sounds reasonable. Would it make sense to make such check as part of the management command itself? I'll probably work on this during the DjangoCon Europe sprints, so I'm assigning this ticket to myself for now :)

[Tim Graham]

Yes, I envisioned the warning as part of collectstatic's logging output.

[Markus Amalthea Magnuson]

I've open a pull request for this: ​https://github.com/django/django/pull/4740

A couple of thoughts:

• Would it make more sense to use warnings.warn() instead of logging with level 0?
• Any pointers on how to write tests for this change?

[Markus Amalthea Magnuson]

I did another commit to change the log level from 0 to 1, since it would show up in e.g. test output otherwise.

[Tim Graham]

You can grep for stdout=out in Django's test suit to see how to capture output from management commands.

[Markus Amalthea Magnuson]

Great, thanks a lot! Will have a look at that and add tests.

[Markus Amalthea Magnuson]

I've added tests to the pull request now, would love some review of it.

[Tim Graham]

Reviewed the PR.

[Markus Amalthea Magnuson]

I've updated the pull request according to code review. Should I squash all of the commits into a single one?

[Tim Graham <timograham@…>]

In 53044945:

Fixed #24890 -- Added warning to collectstatic when static files have clashing names