Add cache for _find_maturin_project_above

[mrcljx]

I noticed my app's launch to take forever (nearly half a minute) with most of time spent in _find_maturin_project_above which is called repeatedly for every search path whenever a module is loaded.

Adding a cache ensures that search paths aren't analyzed over and over again.

AFAIK using functools.cache (added in 3.9) should be okay as this project requires Python 3.9. If compatibility is a concern, one could use functools.lru_cache(maxsize=None) instead.

[mbway]

Thanks for your PR. Can you explain some more about what situation is causing such a long time to be spent inside the import hook?

• The hook only runs for top level imports (so not import foo.bar)
• for each top level import, it checks each directory and parent directories in sys.path
• The _find_maturin_project_above first checks if pyproject.toml exists and only does a slightly more expensive search if it finds that.

So does your app import a huge number of different packages in a virtual environment with many editable-installed packages installed into it?

I would think there would need to be thousands of packages in the environment to take >15 seconds of searching (30 second startup with 'most of the time' inside the import hook).

Can you run with debug logging enabled in the import hook? (modified from the docs)

import logging
logging.basicConfig(format='%(name)s %(asctime)s [%(levelname)s] %(message)s', level=logging.DEBUG)
import maturin_import_hook
maturin_import_hook.reset_logger()
maturin_import_hook.install()

If you are able, can you share the log? Otherwise, can you look at the log and confirm that a significant time is being spent in the import hook.

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Regarding the PR itself, I'm open to adding caching functionality but I would rather it be done in a way that can be disabled (opt-out) so it does not interfere with the importlib.reload() support, where things on the filesystem may have changed significantly between reloads.

I can provide a PR with this alternative approach. I hope that's OK with you?