macOS: Implement basic bell features (no sound) (#7101)

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.

Note that neither of these respect the `system` `bell-features` config
because they're both unobtrusive (the dock icon bounces only once, the
title change is silent and similar to GTK tab attention) and unrelated
to system settings.

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.