gpui: set and clear the dock icon's badge

crates/gpui/src/app.rs

@@ -1317,6 +1317,16 @@ impl App {
         self.platform.unhide_other_apps();
     }
 
+    /// Sets the label drawn on the application's dock icon, or clears it with
+    /// `None`.
+    ///
+    /// Only macOS implements it; elsewhere the call does nothing. A
+    /// menu-bar-only app (`ActivationPolicy::Accessory`) has no dock icon, so
+    /// the label has nowhere to appear.
+    pub fn set_dock_badge(&self, label: Option<&str>) {
+        self.platform.set_dock_badge(label);
+    }
+
     /// Returns the list of currently active displays.
     pub fn displays(&self) -> Vec<Rc<dyn PlatformDisplay>> {
         self.platform.displays()

crates/gpui/src/platform.rs

@@ -143,6 +143,11 @@ pub trait Platform: 'static {
     fn hide_other_apps(&self);
     fn unhide_other_apps(&self);
 
+    /// Sets the label drawn on the application's dock icon, or clears it.
+    ///
+    /// Only macOS implements it; the default is a no-op.
+    fn set_dock_badge(&self, _label: Option<&str>) {}
+
     fn displays(&self) -> Vec<Rc<dyn PlatformDisplay>>;
     fn primary_display(&self) -> Option<Rc<dyn PlatformDisplay>>;
     fn active_window(&self) -> Option<AnyWindowHandle>;

crates/gpui_macos/Cargo.toml

@@ -51,7 +51,7 @@ media.workspace = true
 metal.workspace = true
 objc.workspace = true
 objc2.workspace = true
-objc2-app-kit.workspace = true
+objc2-app-kit = { workspace = true, features = ["NSApplication", "NSDockTile"] }
 objc2-foundation.workspace = true
 objc2-user-notifications.workspace = true
 parking_lot.workspace = true

crates/gpui_macos/src/dock.rs

@@ -0,0 +1,21 @@
+//! The dock icon's badge, the one label macOS draws outside the app's windows.
+//!
+//! The badge belongs to the dock tile, so it only exists while the app has a
+//! dock icon: a menu-bar-only app (activation policy `Accessory`) has nothing
+//! to draw it on and this becomes a no-op.
+
+use objc2::MainThreadMarker;
+use objc2_app_kit::NSApplication;
+use objc2_foundation::NSString;
+
+/// Sets the dock icon's badge, or clears it with `None`.
+pub(crate) fn set_dock_badge(label: Option<&str>) {
+    let Some(mtm) = MainThreadMarker::new() else {
+        log::warn!("the dock badge must be set on the main thread");
+        return;
+    };
+    let label = label.map(NSString::from_str);
+    NSApplication::sharedApplication(mtm)
+        .dockTile()
+        .setBadgeLabel(label.as_deref());
+}

crates/gpui_macos/src/gpui_macos.rs

@@ -7,6 +7,7 @@
 mod dispatcher;
 mod display;
 mod display_link;
+mod dock;
 mod events;
 mod keyboard;
 mod pasteboard;

crates/gpui_macos/src/platform.rs

@@ -837,6 +837,10 @@ impl Platform for MacPlatform {
         }
     }
 
+    fn set_dock_badge(&self, label: Option<&str>) {
+        crate::dock::set_dock_badge(label);
+    }
+
     fn primary_display(&self) -> Option<Rc<dyn PlatformDisplay>> {
         Some(Rc::new(MacDisplay::primary()))
     }