Expand description
This crate allows tools to enable rust logging without having to magically match rustc’s tracing crate version.
For example if someone is working on rustc_ast and wants to write some
minimal code against it to run in a debugger, with access to the debug!
logs emitted by rustc_ast, that can be done by writing:
[dependencies]
rustc_ast = { path = "../rust/compiler/rustc_ast" }
rustc_log = { path = "../rust/compiler/rustc_log" }
rustc_span = { path = "../rust/compiler/rustc_span" }
fn main() {
rustc_log::init_env_logger("LOG").unwrap();
let edition = rustc_span::edition::Edition::Edition2021;
rustc_span::create_session_globals_then(edition, || {
/* ... */
});
}Now LOG=debug cargo +nightly run will run your minimal main.rs and show
rustc’s debug logging. In a workflow like this, one might also add
std::env::set_var("LOG", "debug") to the top of main so that cargo +nightly run by itself is sufficient to get logs.
The reason rustc_log is a tiny separate crate, as opposed to exposing the same things in rustc_driver only, is to enable the above workflow. If you had to depend on rustc_driver in order to turn on rustc’s debug logs, that’s an enormously bigger dependency tree; every change you make to rustc_ast (or whichever piece of the compiler you are interested in) would involve rebuilding all the rest of rustc up to rustc_driver in order to run your main.rs. Whereas by depending only on rustc_log and the few crates you are debugging, you can make changes inside those crates and quickly run main.rs to read the debug logs.