tox4: env substitution does not uses values from set_env

[astrojuanlu]

Configuration:

$ cat tox.ini 
[testenv]
skip_install = True
allowlist_externals =
    /bin/echo
setenv =
    MSG = "Normal tests"
    fast: MSG = "Only fast tests"
commands =
    echo {env:MSG}

tox 3:

$ python -m tox -e py3
py3 run-test-pre: PYTHONHASHSEED='561195256'
py3 run-test: commands[0] | echo 'Normal tests'
Normal tests
___________________________________________ summary ___________________________________________
  py3: commands succeeded
  congratulations :)
$ python -m tox -e py3-fast
py3-fast run-test-pre: PYTHONHASHSEED='3471543899'
py3-fast run-test: commands[0] | echo 'Only fast tests'
Only fast tests
___________________________________________ summary ___________________________________________
  py3-fast: commands succeeded
  congratulations :)

tox 4:

$ python -m tox -e py3
py3: commands[0]> echo

py3: OK ✔ in 0.04 seconds
  py3: OK (0.04=setup[0.04]+cmd[0.00] seconds)
  congratulations :) (0.07 seconds)
$ python -m tox -e py3-fast
py3-fast: commands[0]> echo

py3-fast: OK ✔ in 0.04 seconds
  py3-fast: OK (0.04=setup[0.04]+cmd[0.00] seconds)
  congratulations :) (0.07 seconds)

[gaborbernat]

Thanks for the report. It seems the commands are evaluated before the setenv part, hence though the command is run in a subprocess with that environment variable set, it does not actually is populated within the executed commands argument list.

[gaborbernat]

Resolved via #1784

[astrojuanlu]

I confirm the fix 👍🏽

[gaborbernat]

Released now via https://tox.readthedocs.io/en/rewrite/changelog.html#v4-0-0a3-2021-01-13