X11: Fix panic when no monitors are available (#1158)

* X11: Fix panic when no monitors are available

* Set dummy monitor's dimensions to `(1, 1)`

* X11: Avoid panicking when there are no monitors in Window::new

CHANGELOG.md

@@ -17,6 +17,7 @@
 - On macOS, fix events not being emitted during modal loops, such as when windows are being resized
   by the user.
 - On Windows, fix hovering the mouse over the active window creating an endless stream of CursorMoved events.
+- On X11, return dummy monitor data to avoid panicking when no monitors exist.
 - On X11, prevent stealing input focus when creating a new window.
   Only steal input focus when entering fullscreen mode.
 

src/platform_impl/linux/x11/event_processor.rs

@@ -389,7 +389,11 @@ impl<T: 'static> EventProcessor<T> {
                             let window_rect = util::AaRect::new(new_outer_position, new_inner_size);
                             monitor = wt.xconn.get_monitor_for_window(Some(window_rect));
                             let new_hidpi_factor = monitor.hidpi_factor;
+
+                            // Avoid caching an invalid dummy monitor handle
+                            if monitor.id != 0 {
                                 shared_state_lock.last_monitor = Some(monitor.clone());
+                            }
                             new_hidpi_factor
                         };
                         if last_hidpi_factor != new_hidpi_factor {

src/platform_impl/linux/x11/monitor.rs

@@ -130,6 +130,19 @@ impl MonitorHandle {
         })
     }
 
+    fn dummy() -> Self {
+        MonitorHandle {
+            id: 0,
+            name: "<dummy monitor>".into(),
+            hidpi_factor: 1.0,
+            dimensions: (1, 1),
+            position: (0, 0),
+            primary: true,
+            rect: util::AaRect::new((0, 0), (1, 1)),
+            video_modes: Vec::new(),
+        }
+    }
+
     pub fn name(&self) -> Option<String> {
         Some(self.name.clone())
     }
@@ -167,9 +180,13 @@ impl MonitorHandle {
 impl XConnection {
     pub fn get_monitor_for_window(&self, window_rect: Option<util::AaRect>) -> MonitorHandle {
         let monitors = self.available_monitors();
-        let default = monitors
-            .get(0)
-            .expect("[winit] Failed to find any monitors using XRandR.");
+
+        if monitors.is_empty() {
+            // Return a dummy monitor to avoid panicking
+            return MonitorHandle::dummy();
+        }
+
+        let default = monitors.get(0).unwrap();
 
         let window_rect = match window_rect {
             Some(rect) => rect,
@@ -259,7 +276,7 @@ impl XConnection {
         self.available_monitors()
             .into_iter()
             .find(|monitor| monitor.primary)
-            .expect("[winit] Failed to find any monitors using XRandR.")
+            .unwrap_or_else(MonitorHandle::dummy)
     }
 
     pub fn select_xrandr_input(&self, root: Window) -> Result<c_int, XError> {

src/platform_impl/linux/x11/window.rs

@@ -119,7 +119,7 @@ impl UnownedWindow {
                     .unwrap_or(1.0)
             })
         } else {
-            return Err(os_error!(OsError::XMisc("No monitors were detected.")));
+            1.0
         };
 
         info!("Guessed window DPI factor: {}", dpi_factor);
@@ -637,6 +637,11 @@ impl UnownedWindow {
                     _ => unreachable!(),
                 };
 
+                // Don't set fullscreen on an invalid dummy monitor handle
+                if monitor.id == 0 {
+                    return None;
+                }
+
                 if let Some(video_mode) = video_mode {
                     // FIXME: this is actually not correct if we're setting the
                     // video mode to a resolution higher than the current
@@ -704,11 +709,11 @@ impl UnownedWindow {
     pub fn current_monitor(&self) -> X11MonitorHandle {
         let monitor = self.shared_state.lock().last_monitor.as_ref().cloned();
         monitor.unwrap_or_else(|| {
-            let monitor = self
-                .xconn
-                .get_monitor_for_window(Some(self.get_rect()))
-                .to_owned();
+            let monitor = self.xconn.get_monitor_for_window(Some(self.get_rect()));
+            // Avoid caching an invalid dummy monitor handle
+            if monitor.id != 0 {
                 self.shared_state.lock().last_monitor = Some(monitor.clone());
+            }
             monitor
         })
     }