Access Denied error due to race saving cache file on Windows

[jaraco]

In pypa/setuptools#4467 and businho/pytest-ruff#28 and this Discord convo, I've captured an issue that's recently become apparent when pytest-ruff started failing on an exit code 2 (pytest-ruff 0.4).

In a test environment utilizing pytest-ruff and pytest-xdist, many tests will be run in parallel and since pytest-ruff passes each file to a separate ruff invocation, there may potentially be many instances of ruff launched for the same root directory and settings (and thus cache key).

As a result, Ruff will fail and exit with code 2 with the following output:

            Cause: Failed to rename temporary cache file to D:\a\setuptools\setuptools\.ruff_cache\0.5.1\13567325068112760734
            Cause: failed to persist temporary file: Access is denied. (os error 5)
            Cause: Access is denied. (os error 5)

Since it's a cache file, maybe the failure should be ignored, or maybe it could be retried.

At the very least, catching this error and exiting with a distinct exit code would allow tools like pytest-ruff to ignore the failure.

[jaraco]

My guess is the same behavior is happening on Linux too, but the file system allows the race to be resolved by replacing the file. Maybe there's a Windows file operation that's comparable.

[charliermarsh]

Yeah my guess is we're trying to replace the file while it's being read.

[charliermarsh]

My vote would be to make these non-fatal, and warn. Cache errors should generally be non-fatal IMO.