chmod: fix GNU test 'chmod/usage'

[bbara]

fixes chmod/usage.

The description of the test says:

These test cases assume GNU behavior for "options" like -w.

The tests are (basically) combinations (and re-occurrences) of options, like (f considered as valid file):
chmod -- -w -- f, chmod -- -- -- f, chmod -w -w -- f

I then tried (testwise):

$ chmod -gw -w f -w
chmod: invalid mode: ‘-gw,-w,-w’

which seems to me like the options (like -w) are splitted from the files.
So my idea was to split the options from the files, keep order, and then "uniq" them before giving them to clap.

However, target is to find the not-working test cases, port them to the Rust unit tests, fix them, check for regression :)

[tertsdiepraam]

Nice! Could you be a bit more descriptive in the PR title and description? I.e. describe the actual change you're making or the bug you're fixing?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/timeout. tests/misc/timeout is passing on 'main'. Maybe you have to rebase?

[bbara]

Beside the not allowed re-occurence of options, I found another problem:
Symbolic Modes allow only one letter of 'ugo' after the sign (-+=) [1]. This wasn't considered so far. I guess this might fix GNU's usage test, but let's see.

[1] https://www.gnu.org/software/coreutils/manual/html_node/Symbolic-Modes.html

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/chmod/usage is no longer failing!
Congrats! The gnu test tests/tail-2/inotify-dir-recreate is no longer failing!
GNU test failed: tests/misc/timeout. tests/misc/timeout is passing on 'main'. Maybe you have to rebase?

[tertsdiepraam]

This utility seems to be a bit of a mess 😅 (which is by no means your fault), I'm glad you picked this to improve!

There's maybe an alternative approach here that's worth exploring where files can take hyphen values? Though I'm not sure we can get that to be just as compatible.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/chmod/usage is no longer failing!

[tertsdiepraam]

I think it's mostly good now! Just needs a bit more comments to explain why all this is necessary.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/chmod/usage is no longer failing!

[tertsdiepraam]

Excellent! Great work!