Debugging vs Code plugin and the Language Server

Checkout rust rust-analyzer and open it in vscode.

$ git clone https://github.com/rust-analyzer/rust-analyzer.git --depth 1
$ cd rust-analyzer
$ code .

To attach to the lsp server in linux you'll have to run:

echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope

This enables ptrace on non forked processes
Ensure the dependencies for the extension are installed, run the npm: install - editors/code task in vscode.
Launch the Debug Extension, this will build the extension and the lsp server.
A new instance of vscode with [Extension Development Host] in the title.

Don't worry about disabling rls all other extensions will be disabled but this one.
In the new vscode instance open a rust project, and navigate to a rust file
In the original vscode start an additional debug session (the three periods in the launch) and select Debug Lsp Server.
A list of running processes should appear select the ra_lsp_server from this repo.
Navigate to crates/ra_lsp_server/src/main_loop.rs and add a breakpoint to the on_task function.
Go back to the [Extension Development Host] instance and hover over a rust variable and your breakpoint should hit.

Demo

It could be a case of just jumping the gun.

The ra_lsp_server is only started once the onLanguage:rust activation.

Make sure you open a rust file in the [Extension Development Host] and try again.

Make sure you have run echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope.

By default this should reset back to 1 everytime you log in.

Check your version of lldb if it's version 6 and lower use the classic adapter type. It's lldb.adapterType in settings file.

If you're running lldb version 7 change the lldb adapter type to bundled or native.