A simple Rust compiler plugin macro for generating an i64 specifying, in seconds, the time that the target crate was built in relation to epoch (1970-01-01T00:00:00Z).

#![feature(plugin)]
#![plugin(build_epoch)]

fn main() {
    // At the time of writing, this prints "1437740236":
    println!("{}", build_epoch!());
}

The static value of build_epoch!() is determined when the compiler expands its first occurrence.