Make 'current_monitor' return 'Option<MonitorHandle>'

On certain platforms window couldn't be on any monitor resulting in failures of 'current_monitor' function. Such issue was happening on Wayland, since the window isn't on any monitor, unless the user has drawn something into it. Returning 'Option<MonitorHandle>' will give an ability to handle such situations gracefully by properly indicating that there's no current monitor. Fixes rust-windowing#793.
kchibisov · Sep 6, 2020 · 7030548 · 7030548
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -25,9 +25,10 @@
 - **Breaking:** On Web, `set_cursor_position` and `set_cursor_grab` will now always return an error.
 - **Breaking:** `PixelDelta` scroll events now return a `PhysicalPosition`.
 - On NetBSD, fixed crash due to incorrect detection of the main thread.
-- **Breaking:** The virtual key code `Subtract` has been renamed to `NumpadSubtract`
-- **Breaking:** On X11, `-` key is mapped to the `Minus` virtual key code, instead of `Subtract`
+- **Breaking:** The virtual key code `Subtract` has been renamed to `NumpadSubtract`.
+- **Breaking:** On X11, `-` key is mapped to the `Minus` virtual key code, instead of `Subtract`.
 - On macOS, fix inverted horizontal scroll.
+- **Breaking:** `current_monitor` now returns `Option<MonitorHandle>`.
 
 # 0.22.2 (2020-05-16)
 

diff --git a/examples/multithreaded.rs b/examples/multithreaded.rs
@@ -21,7 +21,7 @@ fn main() {
             .build(&event_loop)
             .unwrap();
 
-        let mut video_modes: Vec<_> = window.current_monitor().video_modes().collect();
+        let mut video_modes: Vec<_> = window.current_monitor().unwrap().video_modes().collect();
         let mut video_mode_id = 0usize;
 
         let (tx, rx) = mpsc::channel();
@@ -34,7 +34,7 @@ fn main() {
                         // was moved to an another monitor, so that the window
                         // appears on this monitor instead when we go fullscreen
                         let previous_video_mode = video_modes.iter().cloned().nth(video_mode_id);
-                        video_modes = window.current_monitor().video_modes().collect();
+                        video_modes = window.current_monitor().unwrap().video_modes().collect();
                         video_mode_id = video_mode_id.min(video_modes.len());
                         let video_mode = video_modes.iter().nth(video_mode_id);
 
@@ -83,7 +83,7 @@ fn main() {
                             }
                             F => window.set_fullscreen(match (state, modifiers.alt()) {
                                 (true, false) => {
-                                    Some(Fullscreen::Borderless(window.current_monitor()))
+                                    Some(Fullscreen::Borderless(window.current_monitor().unwrap()))
                                 }
                                 (true, true) => Some(Fullscreen::Exclusive(
                                     video_modes.iter().nth(video_mode_id).unwrap().clone(),

diff --git a/examples/window_debug.rs b/examples/window_debug.rs
@@ -70,7 +70,7 @@ fn main() {
                             size.width * size.height
                         }
 
-                        let monitor = window.current_monitor();
+                        let monitor = window.current_monitor().unwrap();
                         if let Some(mode) = monitor
                             .video_modes()
                             .max_by(|a, b| area(a.size()).cmp(&area(b.size())))
@@ -84,7 +84,7 @@ fn main() {
                         if window.fullscreen().is_some() {
                             window.set_fullscreen(None);
                         } else {
-                            let monitor = window.current_monitor();
+                            let monitor = window.current_monitor().unwrap();
                             window.set_fullscreen(Some(Fullscreen::Borderless(monitor)));
                         }
                     }

diff --git a/src/platform_impl/android/mod.rs b/src/platform_impl/android/mod.rs
@@ -391,10 +391,10 @@ impl Window {
         v
     }
 
-    pub fn current_monitor(&self) -> monitor::MonitorHandle {
-        monitor::MonitorHandle {
+    pub fn current_monitor(&self) -> Option<monitor::MonitorHandle> {
+        Some(monitor::MonitorHandle {
             inner: MonitorHandle,
-        }
+        })
     }
 
     pub fn scale_factor(&self) -> f64 {

diff --git a/src/platform_impl/ios/window.rs b/src/platform_impl/ios/window.rs
@@ -224,7 +224,7 @@ impl Inner {
 
     pub fn fullscreen(&self) -> Option<Fullscreen> {
         unsafe {
-            let monitor = self.current_monitor();
+            let monitor = self.current_monitor_inner();
             let uiscreen = monitor.inner.ui_screen();
             let screen_space_bounds = self.screen_frame();
             let screen_bounds: CGRect = msg_send![uiscreen, bounds];
@@ -258,7 +258,7 @@ impl Inner {
         warn!("`Window::set_ime_position` is ignored on iOS")
     }
 
-    pub fn current_monitor(&self) -> RootMonitorHandle {
+    fn current_monitor_inner(&self) -> RootMonitorHandle {
         unsafe {
             let uiscreen: id = msg_send![self.window, screen];
             RootMonitorHandle {
@@ -267,6 +267,10 @@ impl Inner {
         }
     }
 
+    pub fn current_monitor(&self) -> Option<RootMonitorHandle> {
+        Some(self.current_monitor_inner())
+    }
+
     pub fn available_monitors(&self) -> VecDeque<MonitorHandle> {
         unsafe { monitor::uiscreens() }
     }

diff --git a/src/platform_impl/linux/mod.rs b/src/platform_impl/linux/mod.rs
@@ -425,9 +425,22 @@ impl Window {
     }
 
     #[inline]
-    pub fn current_monitor(&self) -> RootMonitorHandle {
-        RootMonitorHandle {
-            inner: x11_or_wayland!(match self; Window(window) => window.current_monitor(); as MonitorHandle),
+    pub fn current_monitor(&self) -> Option<RootMonitorHandle> {
+        match self {
+            #[cfg(feature = "x11")]
+            &Window::X(ref window) => {
+                let current_monitor = window.current_monitor();
+                Some(RootMonitorHandle {
+                    inner: MonitorHandle::X(current_monitor),
+                })
+            }
+            #[cfg(feature = "wayland")]
+            &Window::Wayland(ref window) => {
+                let current_monitor = window.current_monitor()?;
+                Some(RootMonitorHandle {
+                    inner: MonitorHandle::Wayland(current_monitor),
+                })
+            }
         }
     }
 

diff --git a/src/platform_impl/linux/wayland/window.rs b/src/platform_impl/linux/wayland/window.rs
@@ -335,7 +335,7 @@ impl Window {
     pub fn fullscreen(&self) -> Option<Fullscreen> {
         if *(self.fullscreen.lock().unwrap()) {
             Some(Fullscreen::Borderless(RootMonitorHandle {
-                inner: PlatformMonitorHandle::Wayland(self.current_monitor()),
+                inner: PlatformMonitorHandle::Wayland(self.current_monitor().unwrap()),
             }))
         } else {
             None
@@ -396,12 +396,12 @@ impl Window {
         &self.surface
     }
 
-    pub fn current_monitor(&self) -> MonitorHandle {
-        let output = get_outputs(&self.surface).last().unwrap().clone();
-        MonitorHandle {
+    pub fn current_monitor(&self) -> Option<MonitorHandle> {
+        let output = get_outputs(&self.surface).last()?.clone();
+        Some(MonitorHandle {
             proxy: output,
             mgr: self.outputs.clone(),
-        }
+        })
     }
 
     pub fn available_monitors(&self) -> VecDeque<MonitorHandle> {

diff --git a/src/platform_impl/macos/window.rs b/src/platform_impl/macos/window.rs
@@ -972,7 +972,7 @@ impl UnownedWindow {
     }
 
     #[inline]
-    pub fn current_monitor(&self) -> RootMonitorHandle {
+    pub(crate) fn current_monitor_inner(&self) -> RootMonitorHandle {
         unsafe {
             let screen: id = msg_send![*self.ns_window, screen];
             let desc = NSScreen::deviceDescription(screen);
@@ -985,6 +985,11 @@ impl UnownedWindow {
         }
     }
 
+    #[inline]
+    pub fn current_monitor(&self) -> Option<RootMonitorHandle> {
+        Some(self.current_monitor_inner())
+    }
+
     #[inline]
     pub fn available_monitors(&self) -> VecDeque<MonitorHandle> {
         monitor::available_monitors()

diff --git a/src/platform_impl/macos/window_delegate.rs b/src/platform_impl/macos/window_delegate.rs
@@ -450,7 +450,8 @@ extern "C" fn window_will_enter_fullscreen(this: &Object, _: Sel, _: id) {
                 // Otherwise, we must've reached fullscreen by the user clicking
                 // on the green fullscreen button. Update state!
                 None => {
-                    shared_state.fullscreen = Some(Fullscreen::Borderless(window.current_monitor()))
+                    let current_monitor = window.current_monitor_inner();
+                    shared_state.fullscreen = Some(Fullscreen::Borderless(current_monitor))
                 }
             }
             shared_state.in_fullscreen_transition = true;

diff --git a/src/platform_impl/web/window.rs b/src/platform_impl/web/window.rs
@@ -201,7 +201,7 @@ impl Window {
     #[inline]
     pub fn fullscreen(&self) -> Option<Fullscreen> {
         if self.canvas.is_fullscreen() {
-            Some(Fullscreen::Borderless(self.current_monitor()))
+            Some(Fullscreen::Borderless(self.current_monitor_inner()))
         } else {
             None
         }
@@ -237,12 +237,17 @@ impl Window {
     }
 
     #[inline]
-    pub fn current_monitor(&self) -> RootMH {
+    fn current_monitor_inner(&self) -> RootMH {
         RootMH {
             inner: monitor::Handle,
         }
     }
 
+    #[inline]
+    pub fn current_monitor(&self) -> Option<RootMH> {
+        Some(self.current_monitor_inner())
+    }
+
     #[inline]
     pub fn available_monitors(&self) -> VecDequeIter<monitor::Handle> {
         VecDeque::new().into_iter()

diff --git a/src/platform_impl/windows/window.rs b/src/platform_impl/windows/window.rs
@@ -577,10 +577,10 @@ impl Window {
     }
 
     #[inline]
-    pub fn current_monitor(&self) -> RootMonitorHandle {
-        RootMonitorHandle {
+    pub fn current_monitor(&self) -> Option<RootMonitorHandle> {
+        Some(RootMonitorHandle {
             inner: monitor::current_monitor(self.window.0),
-        }
+        })
     }
 
     #[inline]

diff --git a/src/window.rs b/src/window.rs
@@ -736,13 +736,15 @@ impl Window {
 
 /// Monitor info functions.
 impl Window {
-    /// Returns the monitor on which the window currently resides
+    /// Returns the monitor on which the window currently resides.
+    ///
+    /// Returns `None` if current monitor can't be detected.
     ///
     /// ## Platform-specific
     ///
     /// **iOS:** Can only be called on the main thread.
     #[inline]
-    pub fn current_monitor(&self) -> MonitorHandle {
+    pub fn current_monitor(&self) -> Option<MonitorHandle> {
         self.window.current_monitor()
     }