[macOS] Issues with `window.is_maximized()`

Description

I apologize for the poor title, but I'm not quite sure how to phrase this as the bug originates in the relationship between egui and winit, and I believe the root cause lies on the winit side.

While investigating a reported deadlock in https://github.com/emilk/egui/issues/3494 involving fetching window.is_maximized() at runtime I found that its implementation can impact egui's ability to make forward progress on rendering.

The call stack for it can be found here: https://gist.github.com/landaire/bf648a199411a4a813cb7e1419bbc4d9

This isn't actually a deadlock, but it looks like in is_zoomed() we change the window style which causes egui to receive consistent redraw requests. I do not have good knowledge of egui, or really any rendering for that fact, but I think the style change somehow prevents us from making significant rendering progress.

This prevents the issue from happening:

diff --git a/src/platform_impl/macos/window_delegate.rs b/src/platform_impl/macos/window_delegate.rs
index 19dc605e..3691ab88 100644
--- a/src/platform_impl/macos/window_delegate.rs
+++ b/src/platform_impl/macos/window_delegate.rs
@@ -1191,14 +1191,14 @@ impl WindowDelegate {
         let required = NSWindowStyleMask::Titled | NSWindowStyleMask::Resizable;
         let needs_temp_mask = !curr_mask.contains(required);
         if needs_temp_mask {
-            self.set_style_mask(required);
+            // self.set_style_mask(required);
         }
 
         let is_zoomed = self.window().isZoomed();
 
         // Roll back temp styles
         if needs_temp_mask {
-            self.set_style_mask(curr_mask);
+            // self.set_style_mask(curr_mask);
         }
 
         is_zoomed

A candidate fix for winit could be the following:

diff --git a/src/platform_impl/macos/window_delegate.rs b/src/platform_impl/macos/window_delegate.rs
index 19dc605e..ba6004ae 100644
--- a/src/platform_impl/macos/window_delegate.rs
+++ b/src/platform_impl/macos/window_delegate.rs
@@ -1288,7 +1288,7 @@ impl WindowDelegate {
 
     #[inline]
     pub fn is_maximized(&self) -> bool {
-        self.is_zoomed()
+        self.ivars().maximized.get()
     }
 
     #[inline]

But I don't know if there are scenarios where the ivar does not match what is returned from is_zoomed(). But it looks like it's set on window_will_enter_fullscreen and set_maximized which I think should keep it in sync?

I can't really explain why the window styling change prevents egui from making forward progress either, but the behavior is very obvious in a debugger. If you set a breakpoint in update_viewport_info you'll notice it's called consistently. However, if you take either of the above patches you'll notice that it's only called a handful of times (egui is running in the background, so it normally shouldn't be redrawing when it doesn't have focus I believe).

macOS version

ProductName:            macOS
ProductVersion:         15.1
BuildVersion:           24B83

Winit version

0.30.7

Start in src/platform_impl/macos/window_delegate.rs, comparing is_maximized, is_zoomed, set_style_mask, and the maximized state updates. Reproduce the macOS 15.1 behavior with winit 0.30.7 and observe update_viewport_info while querying window.is_maximized(). Done means the query remains accurate without causing repeated redraw activity or blocking egui's rendering progress.