Function pio_package_to_json 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_package_to_json(
    pkg: *const PioPackage,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut c_char

Serialize a package handle to compact .pio.json. Returns an owned C string (free with pio_string_free) or NULL on error.