Deprecation warnings skip past packages named "django_*"

[Mike Edmunds]

The django_file_prefixes() utility doesn't include a trailing path separator, so also matches other packages whose installation directories start with "django". As a result, use of deprecated features in those packages will be mis-attributed to some other code outside those packages.

Django's implementation frequently has code like this:

# django.some_module

import warnings
from django.utils.deprecation import RemovedInDjangoXXWarning, django_file_prefixes

def _some_helper():
    ...
    warnings.warn(
        "This is deprecated.",
        RemovedInDjangoXXWarning,
        skip_file_prefixes=django_file_prefixes(),
    )

def some_django_feature():
    ...
    _some_helper()
    ...

The intent is a caller to some_django_feature() outside Django gets a deprecation warning pointed at their own code. (Not pointing at the call to _some_helper() in Django's implementation.)

As ​currently implemented, django_file_prefixes() returns the directory where Django is installed (in a tuple). E.g., ("/venv/site-packages/django",).

If some_django_feature() is called from a (hypothetical) django_goodies package installed in /venv/site-packages/django_goodies/__init__.py, the warning's skip_file_prefixes will skip it too. (That filename str.startswith() django_file_prefixes().) The resulting warning will point to the first stack frame outside django_goodies, which may be completely disconnected from the deprecated feature usage.