bpo-41994: Fix refcount issues in Python/import.c

[serhiy-storchaka]

https://bugs.python.org/issue41994

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @pablogsal for commit 25ba819 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[serhiy-storchaka]

@ericsnowcurrently, please take a look. It has relation to the code added by you (support of arbitrary mapping as sys.modules).

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[encukou]

I went through the changes and they look OK to me!
To review, I needed to merge current master & resolve a small conflict; I hope you don't mind me pushing that into this PR.

@ericsnowcurrently, do you want to review as well? I might have missed some big-picture issue.

[serhiy-storchaka]

Thank you @encukou. I planned to merge with master, but it needed some time because there is easy to miss some detail in large image when change how reference counted. Good opportunity to do one more review.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @serhiy-storchaka for commit 03e405f 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[encukou]

Unfortunately that last merge was with a leaking master, which is now fixed. Another merge should fix the tests.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @serhiy-storchaka for commit c31124f 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[encukou]

And now the tests failed because of bpo-42794. This PR seems cursed :(

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @encukou for commit bc4ba0c 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[miss-islington]

Thanks @serhiy-storchaka for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

[miss-islington]

Sorry, @serhiy-storchaka and @encukou, I could not cleanly backport this to 3.9 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 4db8988420e0a122d617df741381b0c385af032c 3.9