gh-101283: Try to load the fallback cmd.exe by an absolute path

[arhadthedev]

• Issue: Undocumented risky behaviour in subprocess module #101283

[arhadthedev]

PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: 'D:\a\cpython\cpython\build\test_python_2036�\test_python_worker_5676�'

Looks like a fluke; restarting.

[arhadthedev]

@eryksun Thank you for improvements! Since none of my code is left, I've reattributed the news entry to you.

[gpshead]

Should a RuntimeWarning be raised or logging.warn call made in this case as an FYI?

[eryksun]

That's a good idea. How about this?

                        comspec = 'cmd.exe'
                        warnings.warn(f'spawning "{comspec}" using a '
                                      'relative file path',
                                      RuntimeWarning)

[gpshead]

if we keep the fallback at all rather than just make it an error, something like that. probably with a stacklevel= set.

related to my other comment, i wouldn't want to add a new warning in a security backport either.

[miss-islington]

Thanks @arhadthedev for the PR, and @zooba for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[miss-islington]

Sorry @arhadthedev and @zooba, I had trouble checking out the 3.11 backport branch.
Please retry by removing and re-adding the "needs backport to 3.11" label.
Alternatively, you can backport using cherry_picker on the command line.
cherry_picker 23751ed826ee63fb486e874ec25934ea87dd8519 3.11

[miss-islington]

Thanks @arhadthedev for the PR, and @zooba for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[bedevere-bot]

GH-101711 is a backport of this pull request to the 3.11 branch.

[zooba]

Bah, just noticed in the backports that now there's a case where comspec may be used without being defined. We should fix and backport that immediately

[zooba]

Turns out I can commit directly to the backports, so those will be fine. But we need an else: comspec = executable branch in main

[bedevere-bot]

GH-101713 is a backport of this pull request to the 3.7 branch.

[zooba]

GH-101712 is the comspec=executable fix for main.

[gpshead]

This version number is wrong. 3.11.2 was released before this change was merged. As this PR is in the main branch, listing it as 3.12 in these docs is more appropriate. Documentation readers should not be expected to know which patch release versions came before a major release.

We lack the ability to list all versions in versionchanged markers in our docs so have done it this way elsewhere as well when a visible API change has been made in patch releases.

[arhadthedev]

Bah, just noticed in the backports that now there's a case where comspec may be used without being defined. We should fix and backport that immediately

This version number is wrong. 3.11.2 was released before this change was merged. As this PR is in the main branch, listing it as 3.12 in these docs is more appropriate. Documentation readers should not be expected to know which patch release versions came before a major release.

Got working on it; the PR will follow in a few hours.

[arhadthedev]

Bah, just noticed in the backports that now there's a case where comspec may be used without being defined. We should fix and backport that immediately

To be fixed by gh-101712. Thank you, @zooba!

This version number is wrong. 3.11.2 was released before this change was merged. As this PR is in the main branch, listing it as 3.12 in these docs is more appropriate. Documentation readers should not be expected to know which patch release versions came before a major release.

Addressed in gh-101728.