tox fails without PATH environment variable

[mtelka]

The tox fails early without the PATH environment variable and does not run any tests:

$ env - /usr/bin/tox -e py39
GLOB sdist-make: [REDACTED]
py39 inst-nodeps: [REDACTED]
________________________________________________________________________________________________________________________ summary _________________________________________________________________________________________________________________________
  py39: commands succeeded
  congratulations :)
Traceback (most recent call last):
  File "/usr/bin/tox", line 8, in <module>
    sys.exit(cmdline())
  File "/usr/lib/python3.9/vendor-packages/tox/session/__init__.py", line 44, in cmdline
    main(args)
  File "/usr/lib/python3.9/vendor-packages/tox/session/__init__.py", line 69, in main
    exit_code = session.runcommand()
  File "/usr/lib/python3.9/vendor-packages/tox/session/__init__.py", line 197, in runcommand
    return self.subcommand_test()
  File "/usr/lib/python3.9/vendor-packages/tox/session/__init__.py", line 225, in subcommand_test
    run_sequential(self.config, self.venv_dict)
  File "/usr/lib/python3.9/vendor-packages/tox/session/commands/run/sequential.py", line 18, in run_sequential
    installpkg(venv, venv.package)
  File "/usr/lib/python3.9/vendor-packages/tox/session/commands/run/sequential.py", line 46, in installpkg
    venv.installpkg(path, action)
  File "/usr/lib/python3.9/vendor-packages/tox/venv.py", line 407, in installpkg
    self.install_pkg(sdistpath, action, "inst")
  File "/usr/lib/python3.9/vendor-packages/tox/venv.py", line 401, in install_pkg
    self._install(target, extraopts=pip_flags, action=action)
  File "/usr/lib/python3.9/vendor-packages/tox/venv.py", line 495, in _install
    self.run_install_command(packages=packages, options=options, action=action)
  File "/usr/lib/python3.9/vendor-packages/tox/venv.py", line 437, in run_install_command
    self._pcall(
  File "/usr/lib/python3.9/vendor-packages/tox/venv.py", line 598, in _pcall
    path = self.envconfig.setenv.get("PATH") or os.environ["PATH"]
  File "/usr/lib/python3.9/os.py", line 679, in __getitem__
    raise KeyError(key) from None
KeyError: 'PATH'
$ echo $?
1
$

Even empty PATH makes difference:

$ env - PATH= /usr/bin/tox -e py39
[...many lines skipped...]
================================================================================================= 16 failed, 560 passed, 21 skipped, 1 xfailed in 2.46s ==================================================================================================
ERROR: [REDACTED]
________________________________________________________________________________________________________________________ summary _________________________________________________________________________________________________________________________
ERROR:   py39: commands failed
$

[jugmac00]

Why is no $PATH available in your environment?

[mtelka]

Why is no $PATH available in your environment?

Because I tried to run tox with env - to make sure the current environment does not affect tests. It is easy to add PATH to the environment, but it is unclear why and how the PATH should be set (i.e. what tox needs to find in PATH?). I failed to find any documentation saying that PATH is need for tox. Maybe I just didn't try hard enough...

Thank you.