Pass environment variables to tox _build_ environment

[nschloe]

I'm trying to tox-test a package that needs a particular env variable when building the package. This config

[tox]
envlist = py3

[testenv]
passenv = *
; [...]

only seems to pass the env variables when testing. (Makes sense, it's the [testenv] after all.)

How can I pass environment variables to the tox build process?

[jugmac00]

Does this help (untested)?

[testenv:.pkg]
pass_env = *

If so, I think we'd need to update our documentation.

[nschloe]

Yup, that did the trick. Thanks!

[jugmac00]

I think this is somehow sufficiently documented in https://tox.wiki/en/latest/upgrading.html#packaging-environments, so I do not see an immediate need to update our documentation. In the long term I would like to see things from the FAQ and the upgrading documentation moved or duplicated to the configuration section where appropriate.