Highlight `box` about tree-sitter-rust

[Nokel81]

Sure, here says that is is a reserved keyword (even in Rust2015 it seems). And here is the uses of box, which are currently unstable in nightly but do work.

[maxbrunsfeld]

Can you share a link to the docs for this? Upon first search, all I'm seeing is very old discussions about the box syntax that was eventually removed.

[GrayJack]

For reference:

1. rust-lang/rust#49733
2. https://doc.rust-lang.org/unstable-book/language-features/box-syntax.html

[Nokel81]

@GrayJack So if I read correctly, they are removing the let x = box 1; syntax but might be keeping the if let box Some(y) = Box::new(Some(10))?

[GrayJack]

What I understood was that nothing is clear LOL

[GrayJack]

On another dive into the comments on those features using the box keyword:

Looks like box as expression will probably never go to stable and probably remain as a unstable feature till some problems related to the Box can be fixed, a possible fix for those problems would be this RFC, but it wasn't accepted yet (21/10/2020). Once Box type problems fixed, this feature will probably be removed.

About the box pattern, it also looks like it will never face the light of a stable release (there some thoughts about removing it and adding a deref pattern that will work on any type that can de dereferenced).

Either way, I think it's ok for us to implement those in the parser, since those features are used inside the stdlib and when we open those std files in a editor using tree-sitter the syntax usually breaks. Implementing them would mean that we can get closer to be possible to highlight and parse any Rust code.

[amaanq]

I think we're gonna close this out since it probably will never be stabilized, and might be removed in the future, seems like deref patterns will supersede box patterns