[3.7] bpo-22490: Remove __PYVENV_LAUNCHER__ from environment during launch (GH-9516)

[jaraco]

• bpo-22490: Remove "PYVENV_LAUNCHER" from the shell environment on macOS

This changeset removes the environment varialbe "PYVENV_LAUNCHER"
during interpreter launch as it is only needed to communicate between
the stub executable in framework installs and the actual interpreter.

Leaving the environment variable present may lead to misbehaviour when
launching other scripts.

• Actually commit the changes for issue 22490...

• Correct typo

Co-Authored-By: Nicola Soranzo nicola.soranzo@gmail.com

• Run make patchcheck

Co-authored-by: Jason R. Coombs jaraco@jaraco.com
Co-authored-by: Nicola Soranzo nicola.soranzo@gmail.com.
(cherry picked from commit 044cf94)

Co-authored-by: Ronald Oussoren ronaldoussoren@mac.com

https://bugs.python.org/issue22490

[telamonian]

Thanks for backporting this!

I stumbled accross this issue when I found yet another weird bug caused by __PYVENV_LAUNCHER__, which broke IPython kernels launched from a Jupyter server running in a venv. Because __PYVENV_LAUNCHER__ was polluting the environment when the Python process in the kernel started, include-system-site-packages = false could get picked up from the venv's pyvenv.cfg, which meant that the site-packages dir would get left off of sys.path for that kernel's Python instance.

For reference, which Python version did this first get included in? For me, upgrading from 3.7.6 -> 3.7.9 fixed the above issue.

[jaraco]

Looks like it was added in 3.7.8rc1

[telamonian]

thanks!