vim: Tweak how comment nesting works

[lilyball]

Don't try to match line comments inside of a comment block. That makes
no sense and can highlight differently for people who override their
highlights.

Similarly, don't match a doc-comment inside of a comment block. It
shouldn't be highlighted differently unless it's actually a doc-comment
(and nested comments are obviously not doc comments).

Fixes#12307.

[lilyball]

r? @chris-morgan

[flaper87]

LGTM

[chris-morgan]

In /** x /* y */ z */, this highlights the /* and */ as rustCommentBlock, unlike the rest which is rustCommentBlockDoc. Au contraire, /** inside /* is notrustCommentBlockDoc.

Apart from that, the behaviour (as distinct from highlighting) of the previous implementation remains, including all the caveats: good.

[lilyball]

@chris-morgan I intentionally made /** inside of /* not be rustCommentBlockDoc. As for the /* and */ delimiters inside of /** being rustCommentBlock, that's unfortunate. The solution would be to duplicate rustCommentBlockNest into a rustCommentBlockDocNest so it can give the delimiters the same rustCommentBlockDoc syntax. Is it worth it?

Incidentally, I wish I could just remove the matchgroup=rustCommentBlock from rustCommentBlockNest, but I believe that makes it search for contained syntaxes starting from the first character of the delimiter, which is bad, instead of just in the enclosed content.

[chris-morgan]

Yes, the matchgroup stuff is there for a reason.

Is it worth duplicating the Nest rules for Doc and non-Doc? Well, if you want to get highlighting consistent, I guess it is.

[lilyball]

I think I can use ms= and me= instead to adjust the contained area.

[lilyball]

Nevermind, it doesn't work right, and there's no way to debug this.

[lilyball]

I've gone ahead and duplicated the rule so it can highlight correctly.