tac: support non-UTF-8 separator

[victor-prokhorov]

fixes #9502

open question: GNU tac also accepts non-UTF-8 separators in regex mode. right now, in this pr i return an error. should i handle this in the same PR, or i should do it in another?

[ChrisDryden]

The ultimate goal it to get the non utf-8 stuff to be fully matching how gnu handles it, can you try to handle it in the same pr?

[codspeed-hq]

Merging this PR will improve performance by 3.55%

⚡ 1 improved benchmark
✅ 287 untouched benchmarks
⏩ 40 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	cp_large_file[16]	389.6 µs	376.3 µs	+3.55%

---

_{Comparing victor-prokhorov:tac-non-utf8-separator (5bde2a8) with main (a972eee)}

Footnotes

1. 40 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. ↩

[ChrisDryden]

By fixing this it should also fix the tac-locale test so you can use that to guide you on whether the fix is working properly

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/date/date-locale-hour. tests/date/date-locale-hour is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/misc/usage_vs_getopt (fails in this run but passes 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/tac/tac is no longer failing!
Congrats! The gnu test tests/tac/tac-locale is no longer failing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/symlink (fails in this run but passes 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/tac/tac is no longer failing!
Congrats! The gnu test tests/tac/tac-locale is no longer failing!

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/date/date-locale-hour. tests/date/date-locale-hour is passing on 'main'. Maybe you have to rebase?
Congrats! The gnu test tests/tac/tac is no longer failing!
Congrats! The gnu test tests/tac/tac-locale is no longer failing!
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[victor-prokhorov]

i found this trick of turning the u flag here https://docs.rs/regex/1.10.4/regex/#opt-out-of-unicode-support, should it be included in the inline documentation?
i used expect because the invariance is upheld by construction, is returning a result preferred? please advise
the integration tests i wrote somewhat overlap gnu test scripts, let me know if you prefer them removed

[ChrisDryden]

TIL GNU also ignores non-ASCII bytes inside bracket expressions

[ChrisDryden]

Great find!

[ChrisDryden]

Thanks!