unsafe extern "C" fn data_source_handle_cancelled(
    data: *mut std::ffi::c_void,
    source: *mut wl_data_source,
) {
    let display: &mut WaylandPayload = &mut *(data as *mut _);

    assert!(!source.is_null());
    let proxy: *mut wl_proxy = source as *mut _;
    let version = (display.client.wl_proxy_get_version)(proxy);

    let id = (display.client.wl_proxy_marshal_flags)(
        source as _,
        1,
        std::ptr::null::<std::ffi::c_void>() as *const _,
        version,
        1 << 0
    );
    assert!(!id.is_null());
}