feat: Highlight exit and yield points

[Veykril]

Fixes #4691

[matklad]

Moves in the right direction! Couple of relevant thoughts:

• a related functionality is highlighting all exit points of the function, but we probably want a separate request for that (and support in client)
• document highlights is less than ideal name here. Perhaps just highlight_references?

[kjeremy]

* a related functionality is highlighting all exit points of the function, but we probably want a separate request for that (and support in client)

I don't think it needs to be a separate request See microsoft/language-server-protocol#1047

[Veykril]

Ye I think we don't need a separate request for that, but then the question is how we highlight exit points in regards to the trailing expression as that can overlap with the general ident highlight.

[matklad]

If the cursor is on ? / return or return type (-> Ty) we should highlight exit points, including expressions in the tail position.

if the cursor is on async / await, we should highlight all yield points.

if the cursor is within trailing expression, we should highlight references or nothing.

The name for all three I think is “highlight_related”?

[Veykril]

Yield point and exit point highlighting is implemented as well now. Gotta fix(and probably find) a few more special cases as well as do some minor cleanup still.

Also never type expressions being highlighted as exit points is missing still like intellij does, shouldnt be too hard to add as well I believe.

[Veykril]

Okay things are working but VSCode doesn't send a highlight request when the cursor goes onto non identifier symbols from what I can tell, that means clicking on ? and -> doesn't send a request currently. I suppose this is a bug on VSCode's side as I don't see anything in this regard in the lsp docs. Opened microsoft/vscode#127007

[Veykril]

Currently when the trailing expression is an if or match expression the entire expression gets highlighted as an exit point. Now I wonder if it would make more sense to only highlight the arm/branch expressions in this case? Seems more elegant to me.

[matklad]

Yeah, it’s better to highlight expressions in the tail position. I think we should have functionality for that implemented somewhere already, but I don’t remember where. Ok-wrapping maybe?

[matklad]

Got it! We have “change return type to Result” assist!

[Veykril]

Oh ye looks like that assist does similar things to what is wanted here, I'll take a look at that tomorrow

[Veykril]

I wonder if I overdid this a bit by also considering (labeled) breaks in loops 😄

[Veykril]

Managed to simplify things a bit more, but I couldn't really reuse the wrap_return_type_in_result logic for tails fully as its a bit different than whats needed here. Might be able to merge the logic somehow still but I'll take a look at that another time.
bors r+

[bors]

Build succeeded:

• Rust (macos-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• TypeScript (ubuntu-latest)
• TypeScript (windows-latest)