Migrate Rust completer to Rust Language Server

[Saldivarcher]

So it seems that racerd, has stalled and hasn't been updated in a year. Were there plans to move to a different rust completion server?

[puremourning]

Such as?

[bstaletic]

Last I heard RLS was in a fairly good shape. As in Rust Language Server.

[Saldivarcher]

Yeah I think RLS would be nice, it seems like it's heavily used and updated regularly.

[puremourning]

Do you have specific issues that it would address?

[bstaletic]

@puremourning We already have a couple unresolved rust related issues that might go away with RLS. It might be worth a try.

[puremourning]

Fair enough. As always provided there is a benefit and no regression and a completely free migration path... :)

Then again I don’t Rust so PRs welcome?

[micbou]

There is a rough implementation in that branch. If people are interested, I may polish it and submit a PR.

[Saldivarcher]

Oh awesome @micbou 😎, if you need any help let me know and I'll try to find some time to help.
@puremourning a bunch of small things like: auto completion on types from extern blocks.

[Valloric]

We'll eventually need to migrate to RLS since racer is deadish. Also, RLS is powered by racer internally (for the initial RLS implementation).

@jwilm Thoughts?

[bstaletic]

@micbou Says there's not too much work left to polish his branch enough for migration.

[jwilm]

RLS capabilities are a super set of Racer's; there's no technical reasons ycmd shouldn't use RLS at this point. There may be some other benefits like eliminating a Rust build step in ycmd in favor of "make sure rls is installed on your system". I believe this comes as a component with rustup today.

[bstaletic]

Because of rust-lang/rls#641, I'd really prefer if we were to stick to installing RLS in third_party.

[puremourning]

We are currently working on significantly reducing the overhead in adding new LSP based completers.

When this is complete we will review which servers offer value and stability. We'll keep this in mind.

[Valloric]

While RLS has its problems, it's the obvious next step for our Rust integration.

@puremourning I love that we're making integrating LSP completers easier! Great work and thank you! :) This will pay off a lot going forward since lots of semantic engines are moving towards implementing the LSP spec.

[bstaletic]

The RLS PR has been merged.