Allow hiding a parameter set from test name

[Anton3]

Closes #13228

[RonnyPfannschmidt]

The edge cases are well handled

We might want to bikeshed on whether to use explicit None vs missing instead of a new singleton

[Anton3]

@RonnyPfannschmidt None is often used in those places to signify "fall back to other ways to get id", so I think the new sigil is justified.

There are currently no public CONSTANTS exported in pytest, so I wondered whether I should use a function instead, but ultimately thought that there are no good reasons not to use a constant there.

Are there any other requirements before merge? If not, then merge when ready :)
Please squash

[RonnyPfannschmidt]

Thanks for the elaboration 👍

Id like to see the input of some more core members before merge

[Anton3]

@Zac-HD @The-Compiler @jakkdl [pinging random members] Would anyone be willing to also review the PR?

[RonnyPfannschmidt]

Please avoid eagerly pinging volunteers
Most of us are pretty thin stretched and appreciate the lack of accidental pressure

I understand the desire to finally Lan and previously have been in the same position

[nicoddemus]

Great work!

Left a few comments related mostly to docs.

[nicoddemus]

Can you move this so the list is kept sorted?

[Anton3]

Formatter forces ALL_CAPS names to the top of the list

[nicoddemus]

This section is shown here: https://pytest--13229.org.readthedocs.build/en/13229/reference/reference.html#pytest.Metafunc.parametrize

Although a bit hidden, perhaps it helps to show the version where this was added, and mentioning the restriction of it being used at most 1 time:

Suggested change

	``pytest.HIDDEN_PARAM`` means to hide the parameter set
	from the test name.
	.. versionadded: 8.4
	``pytest.HIDDEN_PARAM`` means to hide the parameter set
	from the test name. Can only be used at most 1 time, as
	test names need to be unique.

Also HIDDEN_PARAM should appear under the Constants at the top of the page, and then the pytest.HIDDEN_PARAM should be a link to it.

Also it should be mentioned here: https://pytest--13229.org.readthedocs.build/en/13229/reference/reference.html#pytest-param

[nicoddemus]

Change pytest.HIDDEN_PARAM to a link to the Constants section in the "API Reference" (see my other comment).

[nicoddemus]

Btw while reviewing #13192 I noticed we will be using NotChecked for a singleton there, should we follow suit here and use HiddenParam too?

[Anton3]

I haven't managed to find any mentions of NotChecked in #13192.
I've copied the naming from NOTSET, which is also used around parameter set naming, although not public.
And they both follow PEP8 style for constants.

[Anton3]

@nicoddemus done, please review again