Do we know what in meson 0.17 broke? Is there an upstream bug report? - I'm asking because thats the prerequisite for getting it fixed / unpinning in the future.

Yes, it arose from mesonbuild/meson-python#587; I am still investigating if there is a quick way to fix it on our side or whether it will need changes on their side.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout v3.9.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 a23ef5a8176c08c7f3de4d1a78f9bf075554b2bd

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #29295: BLD: Pin meson-python to <0.17.0'

4. Push to a named branch:

git push YOURFORK v3.9.x:auto-backport-of-pr-29295-on-v3.9.x

5. Create a PR against branch v3.9.x, I would have named this PR:

"Backport PR #29295 on branch v3.9.x (BLD: Pin meson-python to <0.17.0)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

I've opened mesonbuild/meson-python#713 for meson-python upstream, and we can unpin once that is out in a release.