anyio.Path.iterdir blocks in Python 3.13

[cbornet]

Things to check first

• I have searched the existing issues and didn't find my bug already reported there

• I have checked that my bug is still present in the latest release

AnyIO version

HEAD

Python version

3.13

What happened?

Python 3.13 introduced a breaking change on how pathlib.Path.iterdir behaves.
iterdir now materializes the list of files eagerly. See python/cpython#129871 .
The reason for this change was to raise OS errors directly and not at the first iteration : python/cpython#78722

anyio.Path.iterdir is calling pathlib.Path.iterdir directly (not in a thread)

anyio/src/anyio/_core/_fileio.py

Line 548 in 8bad9c0

gen = self._path.iterdir()

and probably users would expect it not to block.

Some possibilities to fix would be:

• Reimplement anyio.Path.iterdir to not use pathlib.Path.iterdir and use os.scandir directly without materializing the iterator. In this case, there will be a small difference with pathlib.Path.iterdir that OS errors will only happen when we start iterating.
• Make anyio.Path.iterdir async which is a breaking change.

LMK what you think. I can do a PR.

How can we reproduce the bug?

N/A

[agronholm]

I would prefer not to introduce any breaking changes, but instead reimplement the async iterator in a way that defers any I/O until the first iteration, like how it used to work.