Workspace mode builds the whole workspace, even if not necessary

[nrc]

If we have a crate inside a workspace and we open the crate in the RLS (not the whole workspace), the RLS builds the entire workspace and any deps, not just the crate which was opened.

This causes problems in the Rust distro where in order to run each test in workspace mode, we end up building the entire Rust distro.

cc @Xanewok

[DSpeckhals]

I was wondering why I was getting beginBuild messages but nothing else when running tests locally in rust-lang/rust after preparing an RLS update there...

[Xanewok]

Oh crap. Sorry, I didn't foresee that problem before. @nrc thanks for looking into this, it seems that's the case.

So in workspace_mode, without analyze_package specified, we fall back to compiling as if we were running cargo check --all. It turns out that if you run cargo check --all inside a member package, it check-builds the whole workspace, including other member packages and their deps and so forth. If one just runs cargo check inside, it seems to implicitly call cargo check -p <cur_pkg_name> instead, limiting the build scope to only that package.

The quick Rust CI hack fix now would be to specify manually analyze_package for each test (I'll have to test that one, though), while ideally we would infer those config options, just like with build_bin etc.
So if user initialized RLS inside a workspace member package, we would infer analyze_package: <cur_pkg>, unless explicitly set by the user. We'd have to allow the user to explicitly say "null", so this might need introducing additional build_every_package: boolean | null or similar config option.

[sfackler]

#613 happens with analyze_package set, so I think it'd be a separate issue.

[nrc]

So if user initialized RLS inside a workspace member package, we would infer analyze_package: <cur_pkg>, unless explicitly set by the user. We'd have to allow the user to explicitly say "null", so this might need introducing additional build_every_package: boolean | null or similar config option.

Yeah, I agree we should do this. I don't think we need to have a build_every_package option - if the user wants to build everything they should open the whole workspace, whereas if they want to build one crate, they should just open that crate (in fact, I hope this would mean we don't need analyze_package at all in the long term).