Function write_if_changed

build.rs:653–664

Write the generated file only if its content has actually changed. This avoids bumping the mtime on `stub_map_generated.rs` when nothing changed, which in turn prevents `rustc` from unnecessarily recompiling the main crate.

(content: &str)

/// changed, which in turn prevents `rustc` from unnecessarily recompiling
/// the main crate.
fn write_if_changed(content: &str) {
    let out_dir = env::var("OUT_DIR").expect("OUT_DIR not set");
    let dest_path = Path::new(&out_dir).join("stub_map_generated.rs");

    if let Ok(existing) = fs::read_to_string(&dest_path)
        && existing == content
    {
        return;
    }

    fs::write(&dest_path, content).expect("Failed to write generated stub map");
}