cp: copy to readonly file should fail on mac

[tertsdiepraam]

Found here: nushell/nushell#10097 (comment)

This test should probably fail on mac too (it fails correctly on all other platforms). It is a port from a nushell test.

#[test]
fn dest_no_permissions() {
    let ts = TestScenario::new(util_name!());
    let at = &ts.fixtures;

    at.touch("valid.txt");
    at.touch("invalid_perms.txt");
    at.set_readonly("invalid_perms.txt");

    ts.ucmd()
        .args(&["valid.txt", "invalid_perms.txt"])
        .fails()
        .stderr_contains("invalid_perms.txt")
        .stderr_contains("denied");
}

[tertsdiepraam]

I have a theory for this failure:

• We use clonefile on mac to do a copy-on-write copy.
• According to comments in the code clonefile fails if the file already exists
• If it does we remove the file and try again.

Instead we should probably check the permissions before we remove the file.

However, I can't test that theory because I don't have a mac. If anyone wants to try this out, please do!

[PGIII]

Checked on my mac and this test does fail. I added a check if the dest file is read only and that does fix it. I will open a PR with the changes i made. Also it seems test_cp::test_cp_preserve_xattr is failing on my mac not sure if theres an open issue for that or not