danjgo-admin fails with "ModuleNotFoundError: No module named 'pkg_resources'"

[peti]

The GNU Mailman django project has stopped working in current versions of master. When I run it in b425012, I get the following error:

Traceback (most recent call last):
  File "/nix/store/has52f9ds9cf95vb6d8pwfbpr3190qnj-python3.7-Django-1.11.24/bin/..django-admin-wrapped-wrapped", line 12, in <module>
    sys.exit(execute_from_command_line())
  File "/nix/store/049xih271v339wm1hdvlf5xv6vqm39dx-python3-3.7.4-env/lib/python3.7/site-packages/django/core/management/__init__.py", line 364, in
 execute_from_command_line
    utility.execute()
  File "/nix/store/049xih271v339wm1hdvlf5xv6vqm39dx-python3-3.7.4-env/lib/python3.7/site-packages/django/core/management/__init__.py", line 338, in execute
    django.setup()
  File "/nix/store/049xih271v339wm1hdvlf5xv6vqm39dx-python3-3.7.4-env/lib/python3.7/site-packages/django/__init__.py", line 27, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/nix/store/049xih271v339wm1hdvlf5xv6vqm39dx-python3-3.7.4-env/lib/python3.7/site-packages/django/apps/registry.py", line 85, in populate
    app_config = AppConfig.create(entry)
  File "/nix/store/049xih271v339wm1hdvlf5xv6vqm39dx-python3-3.7.4-env/lib/python3.7/site-packages/django/apps/config.py", line 94, in create
    module = import_module(entry)
  File "/nix/store/k0igqpz995nmxwf6piyd5jjpcc7gcnyc-python3-3.7.4/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/nix/store/049xih271v339wm1hdvlf5xv6vqm39dx-python3-3.7.4-env/lib/python3.7/site-packages/haystack/__init__.py", line 7, in <module>
    from pkg_resources import DistributionNotFound, get_distribution, parse_version
ModuleNotFoundError: No module named 'pkg_resources'

The same commands succeeds fine in the older 8136744.

The error can be reproduced as follows:

1. Check out the branch t/mailmain from https://github.com/peti/nixpkgs.
2. cd pkgs/servers/mail/mailman
3. sed -e s/@ALLOWED_HOSTS@// settings.py >tmp.py
4. nix-shell -p 'python3.withPackages (x: with x; [postorius hyperkitty])' --run 'django-admin collectstatic --pythonpath $PWD --settings tmp'

Ping: @FRidh

[peti]

According to git bisect, the commit that broke this build is f7e28bf by @FRidh.

[FRidh]

See #68314. setuptools is no longer implicitly included. Unfortunately this can only be detected at run-time

[FRidh]

in this case the package haystack needs to have setuptools.

[peti]

OK. Thank you for the pointer. I suppose more explicit dependencies are a good thing albeit less convenient. I'll test whether that change fixes the issue and push a fix if it does.