launcher/build.rs

//! Build identity for the dashboard badge.
//!
//! `SM121_VERSION` is passed by the add-on image build (`--build-arg` →
//! `ENV` in the builder stage). Two things are needed for it to survive a
//! warm cargo cache: this script must declare the env var as an input, and the
//! value must reach the compiler as a *generated source*, not through
//! `option_env!` alone (a cached fingerprint can otherwise keep the old
//! literal). The value is echoed as a cargo warning so the CI log shows what
//! the image actually got.
fn main() {
    println!("cargo:rerun-if-env-changed=SM121_VERSION");
    let version = std::env::var("SM121_VERSION").unwrap_or_else(|_| "dev".into());
    println!("cargo:warning=SM121_VERSION={version}");
    let out = std::path::PathBuf::from(std::env::var("OUT_DIR").expect("OUT_DIR"))
        .join("build_version.rs");
    std::fs::write(out, format!("pub const VERSION: &str = {version:?};\n"))
        .expect("write build_version.rs");
}