Debugging Native Code
When you write a native module or a host component, you debug Rust or C++ code that runs inside the app's process. This page covers logging, and attaching a native debugger.
Accessing Logs
The app writes its logs to the terminal where you ran run-desktop. JavaScript console calls, React Native's own messages and your native logs all end up there.
The log level is controlled with the RUST_LOG environment variable, and defaults to info:
RUST_LOG=debug npx react-native run-desktop
RUST_LOG=my_module=trace,info npx react-native run-desktop # trace one module only
💡 Custom Native Logs
If you are writing a native module and want to add custom logs to your module for debugging purposes:
Rust
Use the log crate, as the platform does:
log::info!("[my-module] opened {}", path);
log::error!("[my-module] failed: {error}");
Add log = "0.4" to the crate's Cargo.toml.
C++
Use glog, which React Native's C++ code already uses:
LOG(INFO) << "[MyModule] opened " << path;
Debugging in a Native IDE
Debug builds are built with line tables, so a debugger can show source lines. For full variable information, build with full debug info:
CARGO_PROFILE_DEV_DEBUG=full npx react-native run-desktop
Run the app with run-desktop, and attach the native debugger of your platform to the process:
| Platform | Debugger |
|---|---|
| macOS | LLDB, from the terminal (lldb -p <pid>), from VS Code with CodeLLDB, or from Xcode with Debug > Attach to Process. |
| Windows | Visual Studio with Debug > Attach to Process, or VS Code with the C++ and Rust extensions. |
| Linux | GDB or LLDB (gdb -p <pid>), or VS Code with CodeLLDB. |
The process is named after your app. Set breakpoints in the Rust or C++ sources of your module, and trigger the code from JavaScript.
Panics
A panic in a Rust module method does not stop the app. It is caught and turned into a rejected promise or a thrown error, and the panic message is logged. To stop in the debugger at the panic, set a breakpoint on rust_panic.
JavaScript and native together
Native debugging and React Native DevTools can run at the same time. Use DevTools for the JavaScript side of a call, and the native debugger for the Rust or C++ side.