This directory contains the source code of the rust project, including:
- `rustc` and its tests
- `libstd`
- Various submodules for tools, like rustdoc, rls, etc.

For more information on how various parts of the compiler work, see the [rustc guide].

There is also useful content in the following READMEs, which are gradually being moved over to the guide:
- https://github.com/rust-lang/rust/tree/master/src/librustc/ty/query
- https://github.com/rust-lang/rust/tree/master/src/librustc/dep_graph
- https://github.com/rust-lang/rust/tree/master/src/librustc/infer/higher_ranked
- https://github.com/rust-lang/rust/tree/master/src/librustc/infer/lexical_region_resolve

[rustc guide]: https://rust-lang.github.io/rustc-guide/about-this-guide.html