Function write_rust 

pub fn write_rust<P: AsRef<Path>, E: Prebindgen>(
    registry: &Registry<E::Metadata>,
    ext: &E,
    out_path: P,
) -> Result<PathBuf, WriteError>

Emit the resolved registry to a Rust file.

out_path may be relative (resolved against OUT_DIR by prebindgen) or absolute. Returns the path actually written.