There isn't a Rust language specification, and you can use #![allow(dead_code)] at the root of the crate I'm not sure what you mean by "optimizing away unu

There isn't a Rust language specification, and you can use #![allow(dead_code)] at the root of the crate I'm not sure what you mean by "optimizing away unused variables", so I'm interpreting it as variables that are literally unused after declaration.