We need this bug solved for 3.9.0 rc2. Łukasz, you're the one to make the call about the approach; how can we make your job easier?

My view is:

- Victor's PR 21961 is going in the right direction. But, as far as I know (correct me if I'm wrong), Victor unfortunately has less time for CPython than usual, for personal reasons. So, the PR is unexpectedly stalled. I don't think there's enough time to fix and test it for RC 2.

- My PR 21973 essentially just provides a better error message (and might prevent segfaults in more convoluted cases -- essentially ones where the _ast module is replaced maliciously). We can merge it, backport to 3.9; then iterate on Victor's PR to have a better solution in 3.10.

But Pablo an Victor should chime in as well.