How Rust is Bootstrapped

The Rust compiler (rustc) is written in Rust. To bootstrap Rust from scratch, you need a prior version of rustc — the compiler bootstraps itself through a stage-based process.

The Rust Bootstrap Process

Rust uses a multi-stage bootstrap:

Stage 0: Download a pre-compiled rustc binary (the "beta" channel release)
Stage 1: Use Stage 0 to compile the current rustc source code
Stage 2: Use Stage 1 to compile rustc again — this is the final compiler

Stage 2 is used because it ensures the compiler was compiled by the same-version compiler, catching any bootstrap-specific bugs.

Historical Bootstrap

Rust's original compiler (before it was rewritten in Rust) was written in OCaml. The transition to self-hosting happened around 2011–2012. The OCaml compiler was phased out once the Rust-in-Rust compiler was stable.

mrustc: An Alternative Bootstrap Path

mrustc is an alternative Rust compiler written in C++ that can compile older Rust code. It provides a bootstrap path that does not require a pre-compiled rustc binary, which is important for reproducible builds.

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