Fix stuck HUD on fast modifier release

src/main.rs

@@ -40,6 +40,7 @@ enum DaemonMessage {
 }
 
 struct Session {
+    id: u64,
     groups: Vec<AppGroup>,
     selected: usize,
     original: usize,
@@ -49,6 +50,7 @@ struct Session {
 struct RuntimeState {
     history: FocusHistory,
     session: Option<Session>,
+    next_session_id: u64,
     window_cycle: Option<WindowCycleSession>,
     ignore_focus_until: Option<Instant>,
 }
@@ -107,6 +109,7 @@ impl Switcher {
             state: RefCell::new(RuntimeState {
                 history,
                 session: None,
+                next_session_id: 0,
                 window_cycle: None,
                 ignore_focus_until: None,
             }),
@@ -149,7 +152,57 @@ impl Switcher {
             }
         });
 
+        let switcher = Rc::clone(self);
+        controller.connect_modifiers(move |_controller, modifiers| {
+            if !switch_modifier_is_pressed(modifiers) {
+                switcher.finish(true);
+            }
+            Propagation::Proceed
+        });
+
         self.window.add_controller(controller);
+
+        let focus_controller = gtk::EventControllerLegacy::new();
+        let switcher = Rc::clone(self);
+        focus_controller.connect_event(move |_controller, event| {
+            let Some(focus_event) = event.downcast_ref::<gdk::FocusEvent>() else {
+                return Propagation::Proceed;
+            };
+            if !focus_event.is_in() {
+                return Propagation::Proceed;
+            }
+
+            let session_id = switcher
+                .state
+                .borrow()
+                .session
+                .as_ref()
+                .map(|session| session.id);
+            let Some(session_id) = session_id else {
+                return Propagation::Proceed;
+            };
+
+            let switcher = Rc::clone(&switcher);
+            // The Wayland keyboard-enter and modifier updates can arrive in
+            // adjacent dispatches. Let GDK apply both before checking whether
+            // Super was released before the exclusive grab took effect.
+            glib::timeout_add_local_once(Duration::from_millis(10), move || {
+                let is_current_session = switcher
+                    .state
+                    .borrow()
+                    .session
+                    .as_ref()
+                    .is_some_and(|session| session.id == session_id);
+                if is_current_session
+                    && current_keyboard_modifiers()
+                        .is_some_and(|modifiers| !switch_modifier_is_pressed(modifiers))
+                {
+                    switcher.finish(true);
+                }
+            });
+            Propagation::Proceed
+        });
+        self.window.add_controller(focus_controller);
     }
 
     fn handle_message(&self, message: DaemonMessage) {
@@ -247,7 +300,10 @@ impl Switcher {
             (false, Direction::Next) => (original + 1) % groups.len(),
             (false, Direction::Previous) => (original + groups.len() - 1) % groups.len(),
         };
+        let session_id = state.next_session_id;
+        state.next_session_id = state.next_session_id.wrapping_add(1);
         state.session = Some(Session {
+            id: session_id,
             groups,
             selected,
             original,
@@ -503,6 +559,17 @@ impl Switcher {
     }
 }
 
+fn switch_modifier_is_pressed(modifiers: gdk::ModifierType) -> bool {
+    modifiers.intersects(gdk::ModifierType::SUPER_MASK | gdk::ModifierType::META_MASK)
+}
+
+fn current_keyboard_modifiers() -> Option<gdk::ModifierType> {
+    gdk::Display::default()?
+        .default_seat()?
+        .keyboard()
+        .map(|keyboard| keyboard.modifier_state())
+}
+
 fn install_css() {
     let provider = gtk::CssProvider::new();
     provider.load_from_data(
@@ -657,3 +724,26 @@ fn main() -> Result<()> {
         Some(command) => anyhow::bail!("unknown command: {command}"),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn switch_modifier_accepts_super_and_meta_mappings() {
+        assert!(switch_modifier_is_pressed(gdk::ModifierType::SUPER_MASK));
+        assert!(switch_modifier_is_pressed(gdk::ModifierType::META_MASK));
+        assert!(switch_modifier_is_pressed(
+            gdk::ModifierType::SHIFT_MASK | gdk::ModifierType::SUPER_MASK
+        ));
+    }
+
+    #[test]
+    fn switch_modifier_rejects_unrelated_modifiers() {
+        assert!(!switch_modifier_is_pressed(gdk::ModifierType::empty()));
+        assert!(!switch_modifier_is_pressed(gdk::ModifierType::SHIFT_MASK));
+        assert!(!switch_modifier_is_pressed(
+            gdk::ModifierType::CONTROL_MASK | gdk::ModifierType::ALT_MASK
+        ));
+    }
+}