Choose a channel for the RLS based on the current Rustup default.

[nrc]

E.g., if the user is using the stable channel by default, then we should use the stable channel for launching the RLS with Rustup.

This should not be used, if the user has set rust-client.channel, which means we will need to change the default for that setting to null rather than "nightly".

To get started, look at rustup.ts. I think you'll need to parse the result of rustup show.

[lnicola]

I wonder if there shouldn't be a rustup run default foo that uses the default channel instead. Would running rls instead of rustup run channel rls work?

[lnicola]

@nrc is there any reason to invoke rls through rustup when the channel hasn't been customized?

[nrc]

Yeah, that might work. I can't think of a reason why it would not. We'd need to experiment to make sure.

We'd need to use rustup if just calling rls didn't work (to install RLS or whatever), but then I think we could just use rustup without specifying a channel to get the default.

[lnicola]

I can't think of a reason why it would not.

Maybe rustup is in PATH, but ~/.cargo/bin isn't.

I think we could just use rustup without specifying a channel to get the default.

The thing is that rustup run seems to require a channel name.

[lnicola]

I opened rust-lang/rustup#1279, maybe we'll get this.