Crate rustc_log

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" }

fn main() {
    rustc_log::init_logger(rustc_log::LoggerConfig::from_env("LOG")).unwrap();
    /* ... */
}

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.

Structs

BacktraceFormatter 🔒

LoggerConfig

The values of all the environment variables that matter for configuring a logger. Errors are explicitly preserved so that we can share error handling.

Enums

Error

Traits

BuildSubscriberRet

Trait alias for the complex return type of build_subscriber in init_logger_with_additional_layer. A Registry with any composition of tracing::Subscribers (e.g. Registry::default().with(custom_layer)) should be compatible with this type. Having an alias is also useful so rustc_driver_impl does not need to explicitly depend on tracing_subscriber.

Functions

init_logger

Initialize the logger with the given values for the filter, coloring, and other options env variables.

init_logger_with_additional_layer

Initialize the logger with the given values for the filter, coloring, and other options env variables. Additionally add a custom layer to collect logging and tracing events via build_subscriber, for example: || Registry::default().with(custom_layer).

stderr_isatty

stdout_isatty