Implement a 'check' target for 'rust_binary' and 'rust_library'.

[semtexzv]

I'd be nice to support a target similar to 'cargo check' entirely inside bazel.

Idea:

By running rustc <file> --error-format=json -Z no-codegen we get an output expected by rust analyzer. With some clever code generation It could allow the user to set checkOnSave.overrideCommand in the rust-project.json to run this target, generating necessary info for rust-analyzer to get proper error highlighting.

Details:

For each generated binary/library/crate, generate a <name>_check target. When running this target, we execute appropriate rustc <files...> --error-format=json -Z no-codegen, returning the errors, warnings in json fomat.

Then, when generating rust-project.json for rust-analyzer, insert "checkOnSave.overrideCommand" : "bazel run <path>_check"

[googleson78]

The "check" part of this is already somewhat possible and working today, with some config options. See #1649

I also gave the "json output" somewhat of a shot in #1657.

The "automatically insert the target into rust-project.json" isn't currently possible afaik, due to the fact that rust-project.json doesn't currently store info about that. See

rust-lang/rust-analyzer#13529
rust-lang/rust-analyzer#13446