Notably, mrustc is a Rust compiler in the sense that it is able to compile valid Rust code. It does not provide a guarantee that it will reject invalid input. T

Notably, mrustc is a Rust compiler in the sense that it is able to compile valid Rust code. It does not provide a guarantee that it will reject invalid input. The user is on the hook to work out themselves through some other mechanism that their code is valid before calling mrustc. This is fine for a project with the goal of providing an alternative bootstrapping path for rustc. The rustc codebase is known to be valid Rust, more or less by definition, since rustc is self-hosting and Rust is defined by rustc’s implementation rather than by a specification.