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+# Debugging VSCode plugin and the language server
+
+## Prerequisites
+
+- Install [LLDB](https://lldb.llvm.org/) and the [LLDB Extension](https://marketplace.visualstudio.com/items?itemName=vadimcn.vscode-lldb).
+- Open the root folder in VSCode. Here you can access the preconfigured debug setups.
+
+  <img height=150px src="https://user-images.githubusercontent.com/36276403/74611090-92ec5380-5101-11ea-8a41-598f51f3f3e3.png" alt="Debug options view">
+
+- Install all TypeScript dependencies
+  ```bash
+  cd editors/code
+  npm ci
+  ```
+
+## Common knowledge
+
+* All debug configurations open a new `[Extension Development Host]` VSCode instance
+where **only** the `rust-analyzer` extension being debugged is enabled.
+* To activate the extension you need to open any Rust project folder in `[Extension Development Host]`.
+
+
+## Debug TypeScript VSCode extension
+
+- `Run Installed Extension` - runs the extension with the globally installed `rust-analyzer` binary.
+- `Run Extension (Debug Build)` - runs extension with the locally built LSP server (`target/debug/rust-analyzer`).
+
+TypeScript debugging is configured to watch your source edits and recompile.
+To apply changes to an already running debug process, press <kbd>Ctrl+Shift+P</kbd> 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
+  ```
+
+
+- By default, the LSP server is built without debug information. To enable it, you'll need to change `Cargo.toml`:
+  ```toml
+    [profile.dev]
+    debug = 2
+  ```
+
+- Select `Run Extension (Debug Build)` to run your locally built `target/debug/rust-analyzer`.
+
+- In the original VSCode window once again select the `Attach To Server` debug configuration.
+
+- A list of running processes should appear. Select the `rust-analyzer` from this repo.
+
+- Navigate to `crates/rust-analyzer/src/main_loop.rs` and add a breakpoint to the `on_request` function.
+
+- Go back to the `[Extension Development Host]` instance and hover over a Rust variable and your breakpoint should hit.
+
+If you need to debug the server from the very beginning, including its initialization code, you can use the `--wait-dbg` command line argument or `RA_WAIT_DBG` environment variable. The server will spin at the beginning of the `try_main` function (see `crates\rust-analyzer\src\bin\main.rs`)
+```rust
+    let mut d = 4;
+    while d == 4 { // set a breakpoint here and change the value
+        d = 4;
+    }
+```
+
+However for this to work, you will need to enable debug_assertions in your build
+```rust
+RUSTFLAGS='--cfg debug_assertions' cargo build --release
+```
+
+## Demo
+
+- [Debugging TypeScript VScode extension](https://www.youtube.com/watch?v=T-hvpK6s4wM).
+- [Debugging Rust LSP server](https://www.youtube.com/watch?v=EaNb5rg4E0M).
+
+## Troubleshooting
+
+### Can't find the `rust-analyzer` process
+
+It could be a case of just jumping the gun.
+
+The `rust-analyzer` 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 `rust-analyzer`
+
+Make sure you have run `echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope`.
+
+By default this should reset back to 1 every time 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`.