Improve display of const unstable display feature info

[GuillaumeGomez]

Fixes #131618.

It looks like this:

And like this for methods:

You can check it online here.

r? @notriddle

[notriddle]

If this works with methods, can you add an example and test case for that? Or, if not, mention that it doesn't work in the PR?

[GuillaumeGomez]

Same code for both but you're right, better ensure it.

[GuillaumeGomez]

Extended test to check on methods as well and added screenshot.

[notriddle]

@rfcbot poll

[rfcbot]

Team member @notriddle has asked teams: T-rustdoc-frontend, for consensus on:

• @GuillaumeGomez
• @camelid
• @jsha
• @notriddle

[Nemo157]

This seems a little too similar to normal unstable API annotations to me. Skimming the docs I think I would miss the const word and just overlook the method as unstable.

[camelid]

What if we showed the const in the function header, but highlighted it differently somehow to show it was unstable? This could be in addition to the current change, maybe. Just wanted to bring it up as an idea. This would match how we handle normal instability: still show it, but mark it differently. Rather than hiding the fact that it's const unless you look at the version.

[GuillaumeGomez]

The important part here is to have the feature name accessible and copyable.

[notriddle]

If that's the only problem, then we can reuse the popover mechanics from Notable Traits to power the tooltip.

[camelid]

This seems a little too similar to normal unstable API annotations to me. Skimming the docs I think I would miss the const word and just overlook the method as unstable.

Yeah, I agree. I actually didn't even notice that the unstable-info box was just about the const-instability at first.

[camelid]

@rfcbot concern too similar to regular unstable box EDIT: forgot that doesn't work for polls

[GuillaumeGomez]

If that's the only problem, then we can reuse the popover mechanics from Notable Traits to power the tooltip.

It's extra JS when we can have it inlined without. I'm definitely not a big fan.

[bors]

☔ The latest upstream changes (presumably #140695) made this pull request unmergeable. Please resolve the merge conflicts.