use std::process::Command;

fn main() {

    // Set a build-time `GIT_HEAD` env var which includes the commit id;

    // such that we can tell which code is running.

    let hash = Command::new("git")

        .arg("rev-parse")

        .arg("--short")

        .arg("HEAD")

        .output()

        .ok()

        .and_then(|output| {

            if output.status.success() {

                String::from_utf8(output.stdout).ok()

            } else {

                None

            }

        })

        .unwrap_or_else(|| String::from("unknown"));

    println!("cargo:rustc-env=GIT_HEAD={}", hash);

    println!("cargo:rustc-rerun-if-changed=.git/HEAD");

}