Fix message dialog sync on macOS as well. Re-order parent in panel_ffi.

src/backend/macos/file_dialog/panel_ffi.rs

@@ -30,9 +30,9 @@ fn make_nsstring(s: &str) -> Id<NSString> {
 
 pub struct Panel {
     pub(crate) panel: Id<Object>,
+    parent: Option<Id<NSWindow, Shared>>,
     _focus_manager: FocusManager,
     _policy_manager: PolicyManager,
-    parent: Option<Id<NSWindow, Shared>>,
 }
 
 impl AsModal for Panel {

src/backend/macos/message_dialog.rs

@@ -1,3 +1,4 @@
+use std::mem;
 use std::ops::DerefMut;
 
 use crate::backend::DialogFutureType;
@@ -35,6 +36,7 @@ enum NSAlertReturn {
 pub struct NSAlert {
     buttons: MessageButtons,
     alert: Id<Object>,
+    parent: Option<Id<NSWindow>>,
     _focus_manager: FocusManager,
     _policy_manager: PolicyManager,
 }
@@ -93,13 +95,24 @@ impl NSAlert {
 
         Self {
             alert: unsafe { Id::from_retained_ptr(alert) },
+            parent: opt.parent.map(|x| NSWindow::from_raw_window_handle(&x)),
             buttons: opt.buttons,
             _focus_manager,
             _policy_manager,
         }
     }
 
-    pub fn run(self) -> MessageDialogResult {
+    pub fn run(mut self) -> MessageDialogResult {
+        if let Some(parent) = self.parent.take() {
+            let completion = { block::ConcreteBlock::new(|_: u32| {}) };
+
+            unsafe {
+                msg_send![self.alert, beginSheetModalForWindow: parent completionHandler: &completion]
+            }
+
+            mem::forget(completion);
+        }
+
         let ret: i64 = unsafe { msg_send![self.alert, runModal] };
         dialog_result(&self.buttons, ret)
     }