`FileFinder._find_children` can loop forever on a persistently failing directory scan

• Location: Lib/importlib/_bootstrap_external.py:1469 (inside a while True: loop, backing the new PathEntryFinder.discover() API, added 2026 via gh-139899)

https://github.com/python/cpython/blob/1ad63ccc066a329180cfa8f4a8c4be8be47db973/Lib/importlib/_bootstrap_external.py#L1452-L1472

• Problem: Scans a directory via os.scandir(); any OSError from next() or from an entry's is_dir()/is_file() is caught and ignored without breaking the loop. For a transient single-entry failure this is reasonable (skip and continue). But if the underlying condition is persistent — e.g. an NFS "stale file handle," a disconnected removable volume — every subsequent next() raises the same error forever, and the loop never terminates: no break, no retry limit.
• Reproducer (verified): patched os.scandir to return an iterator whose __next__ unconditionally raises OSError forever; finder._find_children() under a 10-second timeout was killed (exit 124) — confirmed genuine hang. A companion test with a single transient injected error correctly skipped it and returned all real entries, confirming the "skip one bad entry" case works — it's specifically the persistent-failure case that hangs.
• Suggested fix: Add a break (or a bounded retry counter) in the except OSError: branch.
• Difficulty: Small, but a real hang bug (not just silent data loss) — worth flagging prominently. New code (2026), no existing discussion found.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-155939

Lib/importlib/_bootstrap_external.py の 1469 行目付近にある、FileFinder._find_children のスキャンループ内から始めます。issue に記載されている永続的な失敗の再現手順と、一時的なエラーの補助テストを実行します。永続的な OSError によるスキャンが終了し、一方で単一の一時的なエントリ失敗が発生しても残りのエントリが返されれば完了です。