Fix seg-fault when using without a window (#1874)

* Fix seg-fault when using without a window #1869

* Update changelog

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
 
+- On macOS, fix segmentation fault after dropping the main window.
 - On Android, `InputEvent::KeyEvent` is partially implemented providing the key scancode.
 - Added `is_maximized` method to `Window`.
 - On Windows, fix bug where clicking the decoration bar would make the cursor blink.

src/platform_impl/macos/app_state.rs

@@ -341,9 +341,7 @@ impl AppState {
             unsafe {
                 let app: id = NSApp();
                 let windows: id = msg_send![app, windows];
-                let window: id = msg_send![windows, objectAtIndex:0];
                 let window_count: usize = msg_send![windows, count];
-                assert_ne!(window, nil);
 
                 let dialog_open = if window_count > 1 {
                     let dialog: id = msg_send![windows, lastObject];
@@ -373,10 +371,12 @@ impl AppState {
                         data2: 0
                     ];
                     // To stop event loop immediately, we need to post some event here.
-                    let _: () = msg_send![window, postEvent: dummy_event atStart: YES];
+                    let _: () = msg_send![app, postEvent: dummy_event atStart: YES];
                 }
                 pool.drain();
 
+                if window_count > 0 {
+                    let window: id = msg_send![windows, objectAtIndex:0];
                     let window_has_focus = msg_send![window, isKeyWindow];
                     if !dialog_open && window_has_focus && dialog_is_closing {
                         HANDLER.dialog_is_closing.store(false, Ordering::SeqCst);
@@ -384,6 +384,7 @@ impl AppState {
                     if dialog_open {
                         HANDLER.dialog_is_closing.store(true, Ordering::SeqCst);
                     }
+                }
             };
         }
         HANDLER.update_start_time();

src/platform_impl/macos/util/async.rs

@@ -207,7 +207,10 @@ pub unsafe fn set_title_async(ns_window: id, title: String) {
 
 // `close:` is thread-safe, but we want the event to be triggered from the main
 // thread. Though, it's a good idea to look into that more...
-pub unsafe fn close_async(ns_window: id) {
+//
+// ArturKovacs: It's important that this operation keeps the underlying window alive
+// through the `IdRef` because otherwise it would dereference free'd memory
+pub unsafe fn close_async(ns_window: IdRef) {
     let ns_window = MainThreadSafe(ns_window);
     Queue::main().exec_async(move || {
         autoreleasepool(move || {

src/platform_impl/macos/window.rs

@@ -1158,7 +1158,7 @@ impl Drop for UnownedWindow {
         trace!("Dropping `UnownedWindow` ({:?})", self as *mut _);
         // Close the window if it has not yet been closed.
         if *self.ns_window != nil {
-            unsafe { util::close_async(*self.ns_window) };
+            unsafe { util::close_async(self.ns_window.clone()) };
         }
     }
 }