Issue 14112

[evanwilson2123]

Summary

Handled an intermittent OSError: [Errno 5] Input/output error raised from _read_pyc during parallel collection with pytest-xdist.

The failure occurred when open(pyc, "rb") succeeded, but an OSError was raised from the file context-manager path (with fp: / __exit__). _read_pyc now treats that as a cache-read failure and returns None, matching existing cache-miss behavior.

Closes #14112.

What changed

• Wrapped the with fp: block in _read_pyc with except OSError handling.
• Kept trace logging for diagnosis.
• Added a regression test:
  • test_read_pyc_handles_context_manager_oserror
  • Simulates open() success + context-manager OSError(errno.EIO) and asserts _read_pyc(...) is None.

Why this is correct

_read_pyc is a best-effort assertion-rewrite cache read path. Returning None on I/O failure is the intended cache-miss fallback and avoids hard-failing collection due to transient filesystem errors under parallel execution.

Validation

python3.12 -m pytest testing/test_assertrewrite.py -k "test_read_pyc_handles_context_manager_oserror" -q
python3.12 -m pytest testing/test_assertrewrite.py -k "read_pyc" -q
python3.12 -m pytest -n 8 testing/test_assertrewrite.py -k "read_pyc" -q