Hi, I've been running into rare crashes via notmuch-vim for a while now and finally got around to tracking down the problem. I apologize for the size of the reproduction case, but at least it can be reproduced!

To summarize the problem, notmuch_tags_get appears to occasionally cause crashes when called from Ruby (I'm not sure if that method or the bindings are actually at fault or simply exposing some other memory corruption in the program, but it does appear to consistently trigger the crash).

I've attached my test case and parts of my logs showing the problem, but you can also view the full logs online: https://github.com/arcnmx/notmuch-vim/runs/6242139879

The most interesting part is the valgrind segment, while the ruby crash logs pinpoint the issue to line 43 of test.rb: https://github.com/arcnmx/notmuch-vim/blob/e981e3374250a8a04709b8a5143dee6f33ed04ce/test.rb#L43

To reproduce the issue, I created a github actions workflow that triggers the issue: https://github.com/arcnmx/notmuch-vim/tree/notmuch-segfault-repro

The ruby script is pared-down from the vim plugin that's been triggering it, so is still a little large. The repo also includes mbox test data that triggers the issue, and can be run locally using nix: nix-shell --run "initmail; debugtest; runtest"