cp: correct error message on copying dir to itself

[jfinkels]

Correct the error message produced when attempting to copy a directory into itself with cp. Before this commit, the error message was

$ cp -R d d
cp: cannot copy a directory, 'd', into itself, 'd'

After this commit, the error message is

$ cp -R d d
cp: cannot copy a directory, 'd', into itself, 'd/d'

This makes GNU test suite file tests/cp/into-self.sh pass.

[tertsdiepraam]

I think this is good enough to merge, but if you're up for a challenge, I found a case where the output still differs from GNU :)

❯ mkdir -p foo/bar/baz

❯ cp -r foo/bar foo/bar/baz
cp: cannot copy a directory, 'foo/bar', into itself, 'foo/bar/baz/bar'

❯ cargo run -- cp -r foo/bar foo/bar/baz
cp: cannot copy a directory, 'foo/bar', into itself, 'foo/bar/foo/bar/baz'

[jfinkels]

Another good catch. I added a fixup! commit that corrects the behavior to satisfy both the simple and nested test cases

[sylvestre]

I guess you saw

---- test_cp::test_copy_nested_directory_to_itself_disallowed stdout ----
current_directory_resolved: 
mkdir: C:\Users\RUNNER~1\AppData\Local\Temp\.tmpeJUUl8\a
mkdir: C:\Users\RUNNER~1\AppData\Local\Temp\.tmpeJUUl8\a/b
mkdir: C:\Users\RUNNER~1\AppData\Local\Temp\.tmpeJUUl8\a/b/c
run: D:\a\coreutils\coreutils\target\debug\coreutils.exe cp -R a/b a/b/c
thread 'test_cp::test_copy_nested_directory_to_itself_disallowed' panicked at 'assertion failed: `(left == right)`

Diff < left / right > :
<cp: cannot copy a directory, 'a/b', into itself, 'a/b/c\b'
>cp: cannot copy a directory, 'a\b', into itself, 'a\b\c\b'

', tests\common\util.rs:328:9


failures:
    test_cp::test_copy_nested_directory_to_itself_disallowed

[sylvestre]

Cool:
Congrats! The gnu test tests/cp/into-self is no longer failing!