env: fix only long options are allowed to contain '='

[jovielarue]

This fixes #6165 and was adapted from #6711.

This PR contains changes that ensure short options (-u) do not have '=' as their arguments' first character in accordance with GNU/POSIX standards.

Tests were added to ensure this change does not regress.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/printenv. tests/misc/printenv is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[sylvestre]

great progress, thanks!

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

Looks like a regression

[jovielarue]

I'm having trouble replicating the printenv test failure from github-actions. ./run-gnu-test.sh tests/misc/printenv.sh and cargo test test_printenv are both passing for me with my changes. I'm not sure how to proceed. Do you have any suggestions on how I can debug this?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/printenv. tests/misc/printenv is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[sylvestre]

The log says:

2024-12-28T21:05:03.0260690Z FAIL: tests/misc/printenv
2024-12-28T21:05:03.0260751Z =========================
2024-12-28T21:05:03.0260755Z 
2024-12-28T21:05:03.0260843Z env: cannot unset '=b': Invalid argument
2024-12-28T21:05:03.0260916Z --- exp	2024-12-28 20:53:00.649621280 +0000
2024-12-28T21:05:03.0260997Z +++ out	2024-12-28 20:53:00.649621280 +0000
2024-12-28T21:05:03.0261058Z @@ -1 +0,0 @@
2024-12-28T21:05:03.0261117Z -b
2024-12-28T21:05:03.0261218Z FAIL tests/misc/printenv.sh (exit status: 1)

[sylvestre]

i guess it is this line:
https://github.com/coreutils/coreutils/blob/master/tests/misc/printenv.sh#L75

[jovielarue]

Oh, got it. I was ensuring that all short options could not contain '=', but that is not correct. It should just be the short unset option (-u) that cannot contain '=' as its first character. I committed a change to fix this.

I've tested this with that line of code directly (not sure why it wasn't catching on my system as it was running the same tests; I suppose it could be because I am using fish shell to run these tests), and run all relevant tests. I believe it should pass now.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[cakebaker]

Thanks for your PR :)