USERPROFILE is not automatically forwarded on Windows

[AndreLouisCaron]

Hi there!

Given the following tox.ini:

[tox]
skipsdist = true

[testenv]
commands =
  python -c 'import os.path; print(os.path.expanduser("~"))'

Then, on Windows, this will incorrectly print ~.

If you add a passenv section to forward USERPROFILE, then it gives the right output:

[tox]
skipsdist = true

[testenv]
passenv =
  USERPROFILE
commands =
  python -c 'import os.path; print(os.path.expanduser("~"))'

This prints C:\Users\... as you would expect.

If I'm not mistaken, I believe HOME is forwarded by default on other systems, I would assume USERPROFILE should also be forwarded by default on Windows.

I'll gladly work on a patch if you're willing to accept such a contribution!

[AndreLouisCaron]

Note that, apart from os.path.expanduser(), I also need to pass this when running pip-compile inside a virtual environment when using a private package index (such as DevPI); it seems like pip relies on this variable to find pip.ini.

[yan12125]

$HOME is not automatically forwarded on Unix-like systems (Linux, Mac, ...), either. I don't know the design philosophy of tox, though. I was bitten by this when trying to use homebrew on Mac.

[AndreLouisCaron]

IIRC, Tox 1.x used to forward the entire environment by default, but this created issues with reproducing builds (env-dependent builds are really annoying). Then, Tox 2.0 changed this to forward as few things as possible. I remember the port from Tox 1.9 to 2.0+ because I debugged a lot of these hidden dependencies on environment variables (see PR #520 for another example).

It makes sense from a testing standpoint, but (in addition to testing) I've been using Tox more and more as a one-liner for "find Python, install deps without affecting the system and run this command"-style automation. In that context, having random stdlib stuff breaking for obscure reasons is less fun :-/

[obestwalter]

I agree that these hidden dependencies should be taken into account and hopefully we caught all of them by now, but I opened an issue asking for help to take a closer look: #539.