cp: treat an empty file name as a non-existing file

[samueltardieu]

The PathBuf value parser from clap cannot be used directly as it does not (rightly) accept empty file names.

Fix #6177

[BenWiederhake]

Straight-forward implementation, tests, lovely.

Can you make the tests a bit more specific, just in case cp encounters an unrelated issue?

[BenWiederhake]

LGTM!

The unhelpful error message on windows is a pity, but out of scope for this PR.

Let's see if known issue #6534 remains the only CI failure.

EDIT: Oops, I celebrated too early.

thread 'test_cp::test_cp_multiple_files_with_empty_file_name' panicked at tests\by-util\test_cp.rs:182:10:
'cp: The system cannot find the path specified. (os error 3)
' does not contain 'The system cannot find the file specified'

[samueltardieu]

LGTM!

The unhelpful error message on windows is a pity, but out of scope for this PR.

Let's see if known issue #6534 remains the only CI failure.

EDIT: Oops, I celebrated too early.

thread 'test_cp::test_cp_multiple_files_with_empty_file_name' panicked at tests\by-util\test_cp.rs:182:10:
'cp: The system cannot find the path specified. (os error 3)
' does not contain 'The system cannot find the file specified'

The message on Windows is different for the empty file name and other non-existent file names. I've entered a new version.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)

[samueltardieu]

@BenWiederhake The only failing test is the Windows test coverage which has since be disabled in the CI.

[BenWiederhake]

Thanks!