macOS: Implement basic bell features (no sound)

Fixes #7099

This adds basic bell features to macOS to conceptually match the GTK
implementation. When a bell is triggered, macOS will do the following:

  1. Bounce the dock icon once, if the app isn't already in focus.
  2. Add a bell emoji (🔔) to the title of the surface that triggered
     the bell. This emoji will be removed after the surface is focused
     or a keyboard event if the surface is already focused. This
     behavior matches iTerm2.

This doesn't add an icon badge because macOS's dockTitle.badgeLabel API
wasn't doing anything for me and I wasn't able to fully figure out
why...

macos/Sources/App/macOS/AppDelegate.swift

@@ -186,6 +186,12 @@ class AppDelegate: NSObject,
             name: .ghosttyConfigDidChange,
             object: nil
         )
+        NotificationCenter.default.addObserver(
+            self,
+            selector: #selector(ghosttyBellDidRing(_:)),
+            name: .ghosttyBellDidRing,
+            object: nil
+        )
 
         // Configure user notifications
         let actions = [
@@ -502,6 +508,11 @@ class AppDelegate: NSObject,
         ghosttyConfigDidChange(config: config)
     }
 
+    @objc private func ghosttyBellDidRing(_ notification: Notification) {
+        // Bounce the dock icon if we're not focused.
+        NSApp.requestUserAttention(.informationalRequest)
+    }
+
     private func ghosttyConfigDidChange(config: Ghostty.Config) {
         // Update the config we need to store
         self.derivedConfig = DerivedConfig(config)

macos/Sources/Ghostty/Ghostty.App.swift

@@ -538,6 +538,9 @@ extension Ghostty {
             case GHOSTTY_ACTION_COLOR_CHANGE:
                 colorChange(app, target: target, change: action.action.color_change)
 
+            case GHOSTTY_ACTION_RING_BELL:
+                ringBell(app, target: target)
+
             case GHOSTTY_ACTION_CLOSE_ALL_WINDOWS:
                 fallthrough
             case GHOSTTY_ACTION_TOGGLE_TAB_OVERVIEW:
@@ -747,6 +750,30 @@ extension Ghostty {
             appDelegate.toggleVisibility(self)
         }
 
+        private static func ringBell(
+            _ app: ghostty_app_t,
+            target: ghostty_target_s) {
+            switch (target.tag) {
+            case GHOSTTY_TARGET_APP:
+                // Technically we could still request app attention here but there
+                // are no known cases where the bell is rang with an app target so
+                // I think its better to warn.
+                Ghostty.logger.warning("ring bell does nothing with an app target")
+                return
+
+            case GHOSTTY_TARGET_SURFACE:
+                guard let surface = target.target.surface else { return }
+                guard let surfaceView = self.surfaceView(from: surface) else { return }
+                NotificationCenter.default.post(
+                    name: .ghosttyBellDidRing,
+                    object: surfaceView
+                )
+
+            default:
+                assertionFailure()
+            }
+        }
+
         private static func moveTab(
             _ app: ghostty_app_t,
             target: ghostty_target_s,

macos/Sources/Ghostty/Ghostty.Config.swift

@@ -116,6 +116,14 @@ extension Ghostty {
         /// details on what each means. We only add documentation if there is a strange conversion
         /// due to the embedded library and Swift.
 
+        var bellFeatures: BellFeatures {
+            guard let config = self.config else { return .init() }
+            var v: CUnsignedInt = 0
+            let key = "bell-features"
+            guard ghostty_config_get(config, &v, key, UInt(key.count)) else { return .init() }
+            return .init(rawValue: v)
+        }
+
         var initialWindow: Bool {
             guard let config = self.config else { return true }
             var v = true;
@@ -543,6 +551,12 @@ extension Ghostty.Config {
         case download
     }
 
+    struct BellFeatures: OptionSet {
+        let rawValue: CUnsignedInt
+
+        static let system = BellFeatures(rawValue: 1 << 0)
+    }
+
     enum MacHidden : String {
         case never
         case always

macos/Sources/Ghostty/Package.swift

@@ -253,6 +253,9 @@ extension Notification.Name {
 
     /// Resize the window to a default size.
     static let ghosttyResetWindowSize = Notification.Name("com.mitchellh.ghostty.resetWindowSize")
+
+    /// Ring the bell
+    static let ghosttyBellDidRing = Notification.Name("com.mitchellh.ghostty.ghosttyBellDidRing")
 }
 
 // NOTE: I am moving all of these to Notification.Name extensions over time. This

macos/Sources/Ghostty/SurfaceView.swift

@@ -59,6 +59,15 @@ extension Ghostty {
 
         @EnvironmentObject private var ghostty: Ghostty.App
 
+        var title: String {
+            var result = surfaceView.title
+            if (surfaceView.bell) {
+                result = "🔔 \(result)"
+            }
+
+            return result
+        }
+
         var body: some View {
             let center = NotificationCenter.default
 
@@ -74,7 +83,7 @@ extension Ghostty {
 
                     Surface(view: surfaceView, size: geo.size)
                         .focused($surfaceFocus)
-                        .focusedValue(\.ghosttySurfaceTitle, surfaceView.title)
+                        .focusedValue(\.ghosttySurfaceTitle, title)
                         .focusedValue(\.ghosttySurfacePwd, surfaceView.pwd)
                         .focusedValue(\.ghosttySurfaceView, surfaceView)
                         .focusedValue(\.ghosttySurfaceCellSize, surfaceView.cellSize)

macos/Sources/Ghostty/SurfaceView_AppKit.swift

@@ -63,6 +63,9 @@ extension Ghostty {
         /// dynamically updated. Otherwise, the background color is the default background color.
         @Published private(set) var backgroundColor: Color? = nil
 
+        /// True when the bell is active. This is set inactive on focus or event.
+        @Published private(set) var bell: Bool = false
+
         // An initial size to request for a window. This will only affect
         // then the view is moved to a new window.
         var initialSize: NSSize? = nil
@@ -190,6 +193,11 @@ extension Ghostty {
                 selector: #selector(ghosttyColorDidChange(_:)),
                 name: .ghosttyColorDidChange,
                 object: self)
+            center.addObserver(
+                self,
+                selector: #selector(ghosttyBellDidRing(_:)),
+                name: .ghosttyBellDidRing,
+                object: self)
             center.addObserver(
                 self,
                 selector: #selector(windowDidChangeScreen),
@@ -300,9 +308,12 @@ extension Ghostty {
                 SecureInput.shared.setScoped(ObjectIdentifier(self), focused: focused)
             }
 
-            // On macOS 13+ we can store our continuous clock...
             if (focused) {
+                // On macOS 13+ we can store our continuous clock...
                 focusInstant = ContinuousClock.now
+
+                // We unset our bell state if we gained focus
+                bell = false
             }
         }
 
@@ -556,6 +567,11 @@ extension Ghostty {
             }
         }
 
+        @objc private func ghosttyBellDidRing(_ notification: SwiftUI.Notification) {
+            // Bell state goes to true
+            bell = true
+        }
+
         @objc private func windowDidChangeScreen(notification: SwiftUI.Notification) {
             guard let window = self.window else { return }
             guard let object = notification.object as? NSWindow, window == object else { return }
@@ -855,6 +871,9 @@ extension Ghostty {
                 return
             }
 
+            // On any keyDown event we unset our bell state
+            bell = false
+
             // We need to translate the mods (maybe) to handle configs such as option-as-alt
             let translationModsGhostty = Ghostty.eventModifierFlags(
                 mods: ghostty_surface_key_translation_mods(

macos/Sources/Ghostty/SurfaceView_UIKit.swift

@@ -35,6 +35,9 @@ extension Ghostty {
         // on supported platforms.
         @Published var focusInstant: ContinuousClock.Instant? = nil
 
+        /// True when the bell is active. This is set inactive on focus or event.
+        @Published var bell: Bool = false
+
         // Returns sizing information for the surface. This is the raw C
         // structure because I'm lazy.
         var surfaceSize: ghostty_surface_size_s? {

src/config/Config.zig

@@ -1874,7 +1874,13 @@ keybind: Keybinds = .{},
 ///    for instance under the "Sound > Alert Sound" setting in GNOME,
 ///    or the "Accessibility > System Bell" settings in KDE Plasma.
 ///
-/// Currently only implemented on Linux.
+///    On macOS this has no affect.
+///
+/// On macOS, if the app is unfocused, it will bounce the app icon in the dock
+/// once. Additionally, the title of the window with the alerted terminal
+/// surface will contain a bell emoji (🔔) until the terminal is focused
+/// or a key is pressed. These are not currently configurable since they're
+/// considered unobtrusive.
 @"bell-features": BellFeatures = .{},
 
 /// Control the in-app notifications that Ghostty shows.