Move --help option defaults from its class to its decorator

[kdeldycke]

This is a proposal to fix #2832, which points to a subtle change in behavior of the help option introduced in 8.1.8.

The root of the problem is that by deduplicating code in 8.1.8 (see: #2563), I introduced a HelpOption class, to centralize the setup necessary to make a standard Option behave like an help option.

In #2832, a user is relying on a custom class to feed the @help_option decorator. This bypass all the custom setup made by HelpOption, and produce the discrepancy in behavior between 8.1.7 and 8.1.8.

This PR:

• Reverts back to setting up all parameters of the help option in the decorator instead of the HelpOption class
• Aligns @help_option implementation with the way Click is doing for the others (like @password_option, @version_option, ...)
• Removes the click.decorators.HelpOption class as a consequence
• Adds a complete unit test to check combination of custom class and option names leads to expected results

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[AndreasBackx]

Can you rebase this on stable then we can include this in 8.1.9?

I assume we can keep this in 8.2.0, though we'll need to document it.

[kdeldycke]

Yes! I can rebase it to 8.1.9. I was targeting 8.2.0 as I didn't know if a 8.1.9 would see the light of day given that 8.2.0 seems imminent.

Also, something I realized, when #2563 was merged back into main branch (i.e. the future 8.2.0 release), the new HelpOption class was properly merged, but the duplicate in-place Option creation in get_help_option() was not replaced with the new HelpOption. See:

click/src/click/core.py

Lines 1028 to 1035 in 8fcf9b0

	return Option(
	help_options,
	is_flag=True,
	is_eager=True,
	expose_value=False,
	callback=show_help,
	help=_("Show this message and exit."),
	)

So I felt like this PR, by targeting main could solve both issues at the same time. What do you think?

[davidism]

Approved with the suggestions I just commented.

[kdeldycke]

I just merged the changes proposed by @davidism and rebase this PR on top of main.

All tests are passing but the typing workflow job, which is also failing for the same reason on the vanilla main branch. Same thing for the pre-commit.yaml workflow that is failing for reasons not related to this PR.

So unless you have other issues to point to, I think this PR is ready to be merged upstream.