The Rustc Driver and Interface
rustc_driver is essentially
main() function. It acts as
the glue for running the various phases of the compiler in the correct order,
using the interface defined in the
rustc_interface crate provides external users with an (unstable) API
for running code at particular times during the compilation process, allowing
third parties to effectively use
rustc's internals as a library for
analysing a crate or emulating the compiler in-process (e.g. the RLS or rustdoc).
For those using
rustc as a library, the
interface::run_compiler() function is the main
entrypoint to the compiler. It takes a configuration for the compiler and a closure that
run_compiler creates a
Compiler from the configuration and passes
it to the closure. Inside the closure, you can use the
Compiler to drive queries to compile
a crate and get the results. This is what the
rustc_driver does too.
You can see what queries are currently available through the rustdocs for
You can see an example of how to use them by looking at the
rustc_driver::run_compiler function (not to be confused with
rustc_driver::run_compiler function takes a bunch of
command-line args and some other configurations and drives the compilation to completion.
rustc_driver::run_compiler also takes a
Callbacks. In the past, when
rustc_driver::run_compiler was the primary way to use the compiler as a
library, these callbacks were used to have some custom code run after different
phases of the compilation. If you read Appendix A, you may notice the use of the
CompileController, which no longer exist.
replaces this functionality.
Warning: By its very nature, the internal compiler APIs are always going to be unstable. That said, we do try not to break things unnecessarily.
A Note On Lifetimes
The Rust compiler is a fairly large program containing lots of big data
structures (e.g. the AST, HIR, and the type system) and as such, arenas and
references are heavily relied upon to minimize unnecessary memory use. This
manifests itself in the way people can plug into the compiler, preferring a
"push"-style API (callbacks) instead of the more Rust-ic "pull" style (think
Thread-local storage and interning are used a lot through the compiler to reduce
duplication while also preventing a lot of the ergonomic issues due to many
pervasive lifetimes. The
rustc::ty::tls module is used to access these
thread-locals, although you should rarely need to touch it.