cp: Fix panic when recursively copying a directory with a non-UTF8 name

[aweinstock314]

Comparative output from GNU cp and uu cp prior to the fix:

root@b082d601e194:/tmp# cp --version
cp (GNU coreutils) 9.7
Packaged by Debian (9.7-3)
Copyright (C) 2025 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Torbjorn Granlund, David MacKenzie, and Jim Meyering.
root@b082d601e194:/tmp# mkdir dir$'\x80' dir2
root@b082d601e194:/tmp# touch dir$'\x80'/a
root@b082d601e194:/tmp# cp -r dir$'\x80'/. dir2
root@b082d601e194:/tmp# ls -l dir2/
total 0
-rw-r--r-- 1 root root 0 Feb 25 23:46 a

root@03081849be59:/tmp# cp --version
cp (uutils coreutils) 0.6.0
root@03081849be59:/tmp# mkdir dir$'\x80' dir2
root@03081849be59:/tmp# touch dir$'\x80'/a
root@03081849be59:/tmp# cp -r dir$'\x80'/. dir2

thread 'main' (1659) panicked at src/uu/cp/src/copydir.rs:113:64:
called `Option::unwrap()` on a `None` value
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Aborted

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[codspeed-hq]

Merging this PR will improve performance by 6.49%

⚡ 2 improved benchmarks
✅ 292 untouched benchmarks
⏩ 42 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	shuf_input_range[1000000]	89.7 ms	84.2 ms	+6.49%
⚡	Simulation	cp_large_file[16]	391.3 µs	379 µs	+3.25%

---

_{Comparing Zellic:cp-fix-nonutf8-panic (40d7ba7) with main (a611f98)}

Footnotes

1. 42 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. ↩

[xtqqczze]

Suggested change

	if target.exists() && !root.as_os_str().as_encoded_bytes().ends_with(b"/.") {
	if target.exists() && !root.ends_with("/.") {

I don't know whether this suggestion works, but converting to bytes might not be correct. Maybe the os_str_bytes crate would be helpful.

[julian-klode]

Since we are querying for a two byte sequence at the end of it, what do you foresee could be the problem? Encoding issues should be out of the question at this point

[xtqqczze]

It could be more complicated than that, maybe some platform uses multi-byte encoding?

[xtqqczze]

Well, that suggestion compiled but didn't pass tests.

[xtqqczze]

@oech3 why is shuf_input_range[1000000] so noisy?

[oech3]

I don't know. But I think the test is not using frozen seed at least for.