This is repo illustrates the problem with rls-vscode. With this project setup running cargo check produces following output:

cargo check
    Checking adder v0.1.0 (/Users/gozala/Projects/ws-rs/adder)
error: cannot find macro `println2` in this scope
  --> adder/src/main.rs:2:5
   |
2  |       println2!("Hello, world!");
   |       ^^^^^^^^ help: a macro with a similar name exists: `println`

error: aborting due to previous error

error: could not compile `adder`.

To learn more, run the command again with --verbose.

Plugin however does not display this error, instead it reports error in Cargo.toml.

VSCode settings are included in the .vscode/settings.json.

Including additional setup information:

rustup show
Default host: x86_64-apple-darwin
rustup home:  /Users/gozala/.rustup

installed toolchains
--------------------

stable-x86_64-apple-darwin
nightly-x86_64-apple-darwin (default)

active toolchain
----------------

nightly-x86_64-apple-darwin (default)
rustc 1.44.0-nightly (f509b26a7 2020-03-18)