Don't panic when getting refresh rate failed (#2533)

This fixes a crash on macOS when trying to get the monitor
refresh rate from the disabled monitor.

Co-authored-by: Jet Spark <lixiaopeng.jetspark@bytedance.com>
Co-authored-by: Mads Marquart <mads@marquart.dk>

CHANGELOG.md

@@ -8,6 +8,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 # Unreleased
 
+- On macOS, fix panic when getting current monitor without any monitor attached.
 - On Windows and MacOS, add API to enable/disable window buttons (close, minimize, ...etc).
 - On Windows, macOS, X11 and Wayland, add `Window::set_theme`.
 - **Breaking:** Remove `WindowExtWayland::wayland_set_csd_theme` and `WindowBuilderExtX11::with_gtk_theme_variant`.
@@ -41,7 +42,6 @@ And please only add new entries to the top of this list, right below the `# Unre
 - **Breaking:** Removed `WindowBuilderExtWindows::with_theme` and `WindowBuilderExtWayland::with_wayland_csd_theme` in favour of `WindowBuilder::with_theme`.
 - **Breaking:** Removed `WindowExtWindows::theme` in favour of `Window::theme`.
 - Enabled `doc_auto_cfg` when generating docs on docs.rs for feature labels.
-- On macOS, fix panic when getting current monitor without any monitor attached.
 - **Breaking:** On Android, switched to using [`android-activity`](https://github.com/rib/android-activity) crate as a glue layer instead of [`ndk-glue](https://github.com/rust-windowing/android-ndk-rs/tree/master/ndk-glue). See [README.md#Android](https://github.com/rust-windowing/winit#Android) for more details. ([#2444](https://github.com/rust-windowing/winit/pull/2444))
 
 # 0.27.5

src/monitor.rs

@@ -143,6 +143,9 @@ impl MonitorHandle {
 
     /// The monitor refresh rate used by the system.
     ///
+    /// Return `Some` if succeed, or `None` if failed, which usually happens when the monitor
+    /// the window is on is removed.
+    ///
     /// When using exclusive fullscreen, the refresh rate of the [`VideoMode`] that was used to
     /// enter fullscreen should be used instead.
     #[inline]

src/platform_impl/macos/monitor.rs

@@ -215,15 +215,18 @@ impl MonitorHandle {
     pub fn refresh_rate_millihertz(&self) -> Option<u32> {
         unsafe {
             let mut display_link = std::ptr::null_mut();
-            assert_eq!(
-                ffi::CVDisplayLinkCreateWithCGDisplay(self.0, &mut display_link),
-                ffi::kCVReturnSuccess
-            );
+            if ffi::CVDisplayLinkCreateWithCGDisplay(self.0, &mut display_link)
+                != ffi::kCVReturnSuccess
+            {
+                return None;
+            }
             let time = ffi::CVDisplayLinkGetNominalOutputVideoRefreshPeriod(display_link);
             ffi::CVDisplayLinkRelease(display_link);
 
             // This value is indefinite if an invalid display link was specified
-            assert!(time.flags & ffi::kCVTimeIsIndefinite == 0);
+            if time.flags & ffi::kCVTimeIsIndefinite != 0 {
+                return None;
+            }
 
             Some((time.time_scale as i64 / time.time_value * 1000) as u32)
         }

src/platform_impl/windows/monitor.rs

@@ -192,7 +192,7 @@ impl MonitorHandle {
 
     #[inline]
     pub fn refresh_rate_millihertz(&self) -> Option<u32> {
-        let monitor_info = get_monitor_info(self.0).unwrap();
+        let monitor_info = get_monitor_info(self.0).ok()?;
         let device_name = monitor_info.szDevice.as_ptr();
         unsafe {
             let mut mode: DEVMODEW = mem::zeroed();