Bootstrapping the compiler

Bootstrapping is the process of using a compiler to compile itself. More accurately, it means using an older compiler to compile a newer version of the same compiler.

This raises a chicken-and-egg paradox: where did the first compiler come from? It must have been written in a different language. In Rust's case it was written in OCaml. However, it was abandoned long ago, and the only way to build a modern version of rustc is with a slightly less modern version.

This is exactly how x.py works: it downloads the current beta release of rustc, then uses it to compile the new compiler.

In this section, we give a high-level overview of what Bootstrap does, followed by a high-level introduction to how Bootstrap does it.

Additionally, see debugging bootstrap to learn about debugging methods.