`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.