fn main() {

    let features = std::env::vars()

        .filter_map(|(env_name, val)| feature_name(env_name, val))

        .map(|feature| feature.replace('_', "-").to_lowercase())

        .collect::<Vec<_>>()

        .join(",");

    println!("cargo:rustc-env=BUILD_FEATURES={features}");

    let opt_level = std::env::var("OPT_LEVEL").unwrap();

    println!("cargo:rustc-env=BUILD_OPT_LEVEL={opt_level}");

    let profile = std::env::var("PROFILE").unwrap();

    println!("cargo:rustc-env=BUILD_PROFILE={profile}");

    let debug = std::env::var("DEBUG").unwrap();

    println!("cargo:rustc-env=BUILD_DEBUG={debug}");

    let target = std::env::var("TARGET").unwrap();

    println!("cargo:rustc-env=BUILD_TARGET={target}");

    let host = std::env::var("HOST").unwrap();

    println!("cargo:rustc-env=BUILD_HOST={host}");

    let rustc = std::env::var("RUSTC").unwrap();

    let rustc_version = std::process::Command::new(rustc)

        .arg("--version")

        .output()

        .unwrap()

        .stdout;

    let rustc_version = String::from_utf8(rustc_version).unwrap();

    println!("cargo:rustc-env=BUILD_RUSTC_VERSION={rustc_version}");

}

fn feature_name(name: String, val: String) -> Option<String> {

    let feature = name.strip_prefix("CARGO_FEATURE_")?;

    if val != "1" {

    }

    Some(feature.to_string())

}