Suggestion: syntax/rust.vim: Add highlighting for user-defined types

[Ploppz]

At the moment, I have this extra line (maybe not perfect) in rust.vim:
syn match Type "\v[A-Z]\w*[a-z0-9]"

Furthermore, if it's decided to add something like this, it would be nice if it could have precedence over rustModPath, for cases like Object::new();.

[chris-morgan]

Pretty sure there was an issue about this somewhere (maybe back in the days when this was in the rust-lang/rust repository?). My own preference with it was not to do this. Personally I think the capital letter is enough of a signal, and excessive highlighting is icky in most color schemes. As it is, we just highlight the prelude items.

[zacps]

Why don't we make it optional then? I'd personally like this added and I doubt I'm alone.

[chris-morgan]

If we do this, I think it’d make sense to have three “modes”:

1. Don’t highlight any items specially;
2. Highlight prelude items specially (as we currently do); and
3. Highlight CamelCase words as types, and maybe do something about tuple struct and tuple variant syntax (c.f. rustEnumVariant that we have at present).

I would suggest still keeping the current behaviour as the default, in order to (a) not change things gratuitously (well, I would perceive it as gratuitous), and (b) not mishighlight things when working with code bases that don’t adhere to the rustfmt conventions (e.g. working with the Windows API). Yet still this might be my own biases to simple highlighting showing.