The problem is indeed a double definition. Within the library the same function is defined twice (window_window in this case).

More specifically it was defined within a C library as shown above, but also within the rust project as follows:

    #[no_mangle]
    unsafe extern "C" fn window_window(handle: *const ()) -> bool {
      println!("THIS IS NOT GOOD");
      /* snip */
    }

The #[no_mangle] attribute makes it so the name is preserved in the binary, hence there are two definitions.