ls: prevent ReadDir from closing before entries are processed

[vikram-kangotra]

The issue occurred because ReadDir was being consumed by the for loop, causing it to be dropped immediately after iteration. This closed the directory file descriptor (FD 3) before metadata() could be called on the entries, since /proc/self/fd shows the process's own open FDs.

By using read_dir.by_ref() in the loop, we borrow the iterator instead of consuming it, keeping the ReadDir (and its underlying FD) alive until enter_directory() completes.

Fixes: #9332

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/fold/fold is no longer failing!

[codspeed-hq]

CodSpeed Performance Report

Merging #9410 will degrade performances by 2.09%

_{Comparing vikram-kangotra:fix/ls-proc-self-fd-regression (d469b5c) with main (2a314c7)}

Summary

⚡ 1 improvement
❌ 1 regression
✅ 124 untouched
⏩ 6 skipped¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	ls_recursive_long_all_deep_tree[(100, 4)]	3.2 ms	3.3 ms	-2.09%
⚡	ls_recursive_wide_tree[(10000, 1000)]	52.6 ms	51.4 ms	+2.46%

Footnotes

1. 6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)

[sylvestre]

Would it be possible to add a test to make sure we don't regress in the future? Thanks

[vikram-kangotra]

Would it be possible to add a test to make sure we don't regress in the future? Thanks

Sure. Will add test

[sylvestre]

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