Avoid fast-path in --sh-boot script when PEX_TOOLS=1

[huonw]

This patch stops the "execute venv entrypoint directly" fast-path from happening when the user has set PEX_TOOLS=1 with a --sh-boot PEX, mimicking the similar check performed for Python bootstrapping:

pex/pex/pex_boot.py

Lines 204 to 205 in 17bd416

	if not ENV.PEX_TOOLS and Variables.PEX_VENV.value_or(ENV, is_venv):
	venv_dir = __maybe_run_venv__(

This change ensures that PEX_TOOLS=1 ./some.pex always works, no matter the state of the PEX_ROOT cache.

Fixes #2725

[huonw]

I haven't added a test yet, to confirm the direction: is the sh-boot script the right place to put this, or is it better placed in venv_pex.py somehow?

[jsirois]

You inverted your logic here which the existing IT caught. Also maybe just use -z instead of = to be (anti)parallel with the -n logic at the front of the line.

[huonw]

Oh, yes 🤦

-z is much better. Thanks.

[jsirois]

I haven't added a test yet, to confirm the direction: is the sh-boot script the right place to put this, or is it better placed in venv_pex.py somehow?

This is the right place. The venv does not contain any PEX .bootstrap/ code which is where the pex tools code lives; so the venv_pex.py code would need to re-exec back into the PEX exported by the sh-boot script. You'd have:

[PEX_TOOLS=1 PEX(sh-boot) ...] -> # Original PEX file invocation.
    <- exec `venv/bin/python venv/ ...` # The sh-boot script re-direction to existing venv.
[PEX_TOOLS=1 venv/bin/python venv/__main__.py ...] -> # The venv invocation.
    exec `PEX_TOOLS=1 sys.executable PEX ...` # The venv script re-direction to the original PEX file.
[PEX_TOOLS=1 venv/bin/python PEX ...] # Finally, the PEX_TOOLS=1 PEX file invocation.

So that's 2 Python binary startups.

My shortcut accounting for a Python invocation with some stdlib imports at least is ~50ms. With your change, you just have 1 Python binary startup. The clincher though is your change keeps the logic central instead of spreading it out in 2 files.

[jsirois]

@huonw if you want to update pex/version.py to 2.33.7 for this bug fix and add an entry in CHANGES.md I can get out a release today and save some trees.

[huonw]

I've updated:

• using -z
• added a test
• added the release metadata

Thanks for the initial review.

The venv does not contain any PEX .bootstrap/ code which is where the pex tools code lives

Ah, yes, that makes the "proper" approach (that in this PR) clearly the better one. Thank you.

[jsirois]

Thanks @huonw. This is now available in 2.33.7: https://github.com/pex-tool/pex/releases/tag/v2.33.7