`pip_library` outputs typically contain the `none` module from PyPI

[chrisnovakovic]

This happens whenever a pip_library is declared without pip_flags and the PipFlags plugin configuration option is also unset:

$ plz build //third_party/python:wheel_filename
Build finished; total time 40ms, incrementality 50.0%. Outputs:
//third_party/python:wheel_filename:
 plz-out/gen/third_party/python/wheel_filename.whl
$ unzip -l plz-out/gen/third_party/python/wheel_filename.whl
Archive: plz-out/gen/third_party/python/wheel_filename.whl
 Length Date Time Name
--------- ---------- ----- ----
 1175 2001-01-01 00:00 third_party/python/AUTHORS.rst
 6934 2001-01-01 00:00 third_party/python/CONTRIBUTORS.rst
 720 2001-01-01 00:00 third_party/python/none/__init__.py
 20253 2001-01-01 00:00 third_party/python/none/callable.py
 681 2001-01-01 00:00 third_party/python/none/collection/__init__.py
 25229 2001-01-01 00:00 third_party/python/none/collection/a.py
 2314 2001-01-01 00:00 third_party/python/none/collection/i.py
 662 2001-01-01 00:00 third_party/python/none/hash/__init__.py
 656 2001-01-01 00:00 third_party/python/none/hash/cdc/__init__.py
 14141 2001-01-01 00:00 third_party/python/none/hash/cdc/fastcdc.py
 11372 2001-01-01 00:00 third_party/python/none/hash/tree.py
 0 2001-01-01 00:00 third_party/python/none/py.typed
 640 2001-01-01 00:00 third_party/python/none/task/__init__.py
 29149 2001-01-01 00:00 third_party/python/none/task/abc.py
 679 2001-01-01 00:00 third_party/python/none/text/__init__.py
 3470 2001-01-01 00:00 third_party/python/none/text/case.py
 1063 2001-01-01 00:00 third_party/python/none/typeset.py
 5522 2001-01-01 00:00 third_party/python/none/url.py
 4 2001-01-01 00:00 third_party/python/none-0.1.1.dist-info/INSTALLER
 1182 2001-01-01 00:00 third_party/python/none-0.1.1.dist-info/LICENSE.rst
 3024 2001-01-01 00:00 third_party/python/none-0.1.1.dist-info/METADATA
 1827 2001-01-01 00:00 third_party/python/none-0.1.1.dist-info/RECORD
 0 2001-01-01 00:00 third_party/python/none-0.1.1.dist-info/REQUESTED
 83 2001-01-01 00:00 third_party/python/none-0.1.1.dist-info/WHEEL
 3736 2001-01-01 00:00 third_party/python/wheel_filename/__init__.py
 0 2001-01-01 00:00 third_party/python/wheel_filename/py.typed
 4 2001-01-01 00:00 third_party/python/wheel_filename-1.3.0.dist-info/INSTALLER
 1095 2001-01-01 00:00 third_party/python/wheel_filename-1.3.0.dist-info/LICENSE
 4790 2001-01-01 00:00 third_party/python/wheel_filename-1.3.0.dist-info/METADATA
 778 2001-01-01 00:00 third_party/python/wheel_filename-1.3.0.dist-info/RECORD
 0 2001-01-01 00:00 third_party/python/wheel_filename-1.3.0.dist-info/REQUESTED
 92 2001-01-01 00:00 third_party/python/wheel_filename-1.3.0.dist-info/WHEEL
 15 2001-01-01 00:00 third_party/python/wheel_filename-1.3.0.dist-info/top_level.txt
--------- -------
 141290 33 files

It happens because {pip_flags} is stringified as None here:

python-rules/build_defs/python.build_defs

Line 487 in a18ff0d

pip_cmd += f' {repo_flag} {index_flag} {pip_flags} {package_name}'

so the arguments passed to pip end up being none and the name and version of the module to install, and none is actually the name of a module on PyPI so pip installs that as well as the desired module instead of failing.