nox uses PATH to find executables

[dhermes]

This is a bit tox-like to suggest, so feel free to reject.

I was recently migrating my Pelican blog from a Makefile to a noxfile. I had pelican installed in a few of my base environments, but forgot to install it into the virtual environment. However, the sessions ran just fine because they referenced the pelican executable on my ${PATH} even though none existed in the virtualenv.

[theacodes]

hrm. This is tricky. I never was a fan of tox being onerous about stuff needing to be in the virtualenv, but I can definitely see why its useful. How can we handle this gracefully?

[dhermes]

I've been using os.path.join(session.bin, "pelican") to be explicit. I'm not sure what the right move is, you could have both options supported (i.e. one with an empty PATH and one with PATH passed down from the calling shell). Then it's up to you to decide which one should be the default.

[theacodes]

yeah it's tricky. We could do something like:

nox.run(..., external=True)

or flip-side:

nox.run(..., virtualenv_only=True)

We could also have a flag, such as --warn-on-external-tools / --no-warn-on-external-tools or something.

[dhermes]

ISTM that external=True (i.e. opt-in to non-virtualenv scripts) should be the default. That's just 1 vote though.

[theacodes]

So by default you can only use tools that are in the virtualenv, otherwise, we error?

[dhermes]

Correct.

[theacodes]

Hrm, what is your take @lukesneeringer?

I am in favor of this with one caveat - by default we warn but a flag could be passed to error instead.