https://blog.rust-lang.org/2017/02/02/Rust-1.15.html "The build system for Rust has been re-written in Rust, using Cargo. It is now the default. This process has been long, but has finally borne fruit. Given that all Rust development happens on the master branch, we’ve been using it since December of last year, and it’s working well. There is an open PR to remove the Makefiles entirely, landing in Rust 1.17. This will pave the way for rustc to use packages from crates.io in the compiler like any other Rust project, and is a further demonstration of the maturity of Cargo. Rust has gained Tier 3 support for i686-unknown-openbsd, MSP430, and ARMv5TE."