winit: [MacOS] Dialogues freeze when used in winit event loop

OS: OSX 10.15.6

Hi I’m working on RustyFileDialog crate, and in the process I found out weird issue related to winit event loop.

(To make it easier to reproduce I’ll use nfd2 as an example instead of my impl.) File dialogs, for example from nfd2 freeze when opened from winit event loop. Example:

fn main() {
    let el = EventLoop::new();
    let win = WindowBuilder::new().build(&el).unwrap();

    // This dialog works as expected
    nfd2::open_file_dialog(None,None).unwrap();

    el.run(move |event, _, control_flow| {
        match event {
            event::Event::WindowEvent {
                event: event::WindowEvent::MouseInput { .. },
                ..
            } => {
                // This dialog freezes
                nfd2::open_file_dialog(None,None).unwrap();
            }
            _ => {}
        }
    })
}

More info

• For this test NSOpenPanel is used, and it is opened with runModal (blocking)
• If I use beginWithCompletionHandler (non-blocking) dialog works as expected
• SDL2-rs does not have this issue
• winit window stays responsive, only NSOpenPanel is frozen