Fix autoreload regression for empty template DIRS (swev-id: django__django-15572)

[casey-brooks]

Summary

• filter empty string entries before normalizing template directories
• ensure template loaders ignore empty strings and add regression coverage

Testing

• PYTHONPATH=$PWD:$HOME/.nix-profile/lib/python3.11/site-packages DJANGO_SETTINGS_MODULE=tests.test_sqlite python3 tests/runtests.py template_tests.test_autoreloader_empty_dirs --parallel=1
• flake8 django/template/autoreload.py tests/template_tests/test_autoreloader_empty_dirs.py

Regression details

Reproduction steps

1. Configure TEMPLATES[0]['DIRS'] = [''] in a Django project (or via settings override).
2. Start the development server with python manage.py runserver.
3. Edit any non-.py file under the project root (e.g., requirements.txt).

Observed behavior

• get_template_directories() normalizes the empty string to Path.cwd(), so template_changed() returns True for unrelated filesystem changes, and the autoreloader never schedules a full restart.

DEBUG signal output (before fix)

DEBUG django.utils.autoreload: /abs/path/requirements.txt notified as changed. Signal results: [(<function template_changed at django/template/autoreload.py:73>, True)]

Upstream context

• Issue Django 3.2.4+ autoreload regression: empty DIRS ("") expands to project root and suppresses reloads #506
• Regression introduced by django@68357b2 and django@c0d506f (Ticket https://code.djangoproject.com/ticket/32744)

[casey-brooks]

Local Verification

• PYTHONPATH=$PWD:$HOME/.nix-profile/lib/python3.11/site-packages DJANGO_SETTINGS_MODULE=tests.test_sqlite python3 tests/runtests.py template_tests.test_autoreloader_empty_dirs --parallel=1 # 1 passed
• flake8 django/template/autoreload.py tests/template_tests/test_autoreloader_empty_dirs.py # no issues

[noa-lucent]

Looks good

[noa-lucent]

Fix looks good — empty template dirs are filtered safely and the regression test covers the scenario.