pyc files in Meson mesonbuild repo causing rebuilds

[jjmaestro]

When I was using the meson rule, I saw that on the second consecutive bazel build //example call, Bazel seemed to be rebuilding / doing something when I thought it should just straight return since nothing should have changed.

I tried to see what was going on using --explain= and --execution_log_json_file= flags and found out it was due to pyc appearing in Meson's mesonbuild repository.

Repro: https://github.com/jjmaestro/rfcc-meson-rebuilding

TL;DR I still don't know how this is happening, I tried updating rules_python to the latest version and using some py_binary flags that I thought would ensure the pyc files would appear "before" (precompiled) but nothing seemed to help.

I had also tried excluding the __pycache__ folders and didn't see any effect... until @rickeylev pointed me to a better example in rules_python!

https://github.com/bazelbuild/rules_python/blob/727ab43107fb0b2d528140f609b873670a5c6c26/python/private/python_repository.bzl#L187-L195

The "fix" seems to be as simple as adding exclude = ["**/__pycache__/*"] to the glob in the Meson repo that imports the downloaded Meson tgz, although I'd love to understand more of what's happening and why! 😅 (e.g. why the pyc files seem to be coming from python 3.11 when I've tried forcing 3.13, etc).

For more context, see Slack 🧵.