rust-analyzer/docs/dev/debugging.md

Debugging vs Code plugin and the Language Server

Prerequsities

• Install LLDB and the LLDB Extension VSCode extensions.

• Open the root folder in VSCode. Here you can access the preconfigured debug setups.

  

• Install all TypeScript dependencies

  cd editors/code
  npm install
  

Common knowledge

• All debug configurations open new [Extension Development Host] VSCode instance where only your rust-analyzer extension is enabled.
• To activate the extension you need to open any Rust project folder in [Extension Development Host].

Debug TypeScript VSCode extension

• Run Extension - runs the extension with the globally installed ra_lsp_server binary.
• Run Extension (Dev Server) - runs extension with the locally built LSP server (target/debug/ra_lsp_server).

TypeScript debugging is configured to watch your source edits and recompile. To apply changes to an already running debug process press Ctrl+Shift+P and run the following command in your [Extension Development Host]

> Developer: Reload Window

Debug Rust LSP server

• When attaching a debugger to an already running rust-analyzer server on Linux you might need to enable ptrace for unrelated processes by running:

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

  This enables ptrace on non-forked processes

• By default, the LSP server is built without debug information. To enable it, you'll need to change Cargo.toml:

    [profile.dev]
    debug = 2
  

• Select Run Extension (Dev Server) to run your locally built target/debug/ra_lsp_server.

• In the original VSCode window once again select the Attach To Server debug configuration.

• 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

• Debugging TypeScript VScode extension.
• Debugging Rust LSP server.

Troubleshooting

Can't find the ra_lsp_server process

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.

Can't connect to ra_lsp_server

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.

Breakpoints are never being hit

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.