Dev Server fails to restart after adding BASE_DIR to TEMPLATES[0]['DIRS'] in settings

[craiglabenz]

Repro steps:

$ pip install -U django
$ django-admin startproject <name>

Open settings.py, copy the BASE_DIR variable from line 16 and paste it into the empty DIRS list on line 57

$ ./manage.py runserver

Back in your IDE, save a file and watch the dev server *NOT* restart.

Back in settings.py, remove BASE_DIR from the templates DIRS list. Manually CTRL-C your dev server (as it won't restart on its own when you save), restart the dev server. Now return to your settings.py file, re-save it, and notice the development server once again detects changes and restarts.

This bug prevents the dev server from restarting no matter where you make changes - it is not just scoped to edits to settings.py.

[Hrushikesh Vaidya]

I don't think this is a bug, really. Adding BASE_DIR to the list of template directories causes the entire project directory
to be marked as a template directory, and Django does not watch for changes in template directories by design.

[Keryn Knight]

I think I encountered this recently while making examples for #33461, though I didn't get fully to the bottom of what was going on.

Django does not watch for changes in template directories by design.

It does, via the template_changed signal listener, which from my brief poking around when I saw it, is I believe the one which prevented trigger_reload from executing. But that mostly led to my realising I don't know what function is responsible for reloading for python files, rather than template/i18n files, so I moved on.

I would tentatively accept this, personally.

[Hrushikesh Vaidya]

Replying to Keryn Knight:

Django does not watch for changes in template directories by design.

It does, via the template_changed signal listener

My bad, I meant that Django does not watch for changes in template directories to reload the server. The template_changed signal listener returns True if the change occurs in a file located in a designated template directory, which causes notify_file_changed to not trigger the reload.

AFAIK from browsing the code, for a python file (or actually any file not in a template directory), the template_changed signal listener returns None, which causes notify_file_changed to trigger the reload, right?

So could we fix this by checking if the changed file is a python file inside the template_changed signal listener, regardless of whether it is in a template directory?

def template_changed(sender, file_path, **kwargs):
    if file_path.suffix == '.py': 
        return
    # Now check if the file was a template file

This seems to work on a test project, but I have not checked for side effects, although I don't think there should be any.

[Carlton Gibson]

I would tentatively accept this, personally.

😀 I was thinking I'd tentatively wontfix, as not worth the complication — but let's accept for review and see what the consensus is.

Hrushikesh, would you like to prepare a PR based on your suggestion?

Thanks!

[Hrushikesh Vaidya]

Sure! ​PR

At first I thought keeping python files in a template directory does not seem so intuitive, at least to me, same with marking a more general purpose directory as a template directory. But I guess if someone does want to do it that way, it would be nice to support autoreload in that scenario as well.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 832adb31:

Fixed #33473 -- Fixed detecting changes by autoreloader in .py files inside template directories.