Add notifications.

src/SettingsDialog.zig

@@ -109,6 +109,9 @@ colors: *PaletteEditor,
 /// one place and read in another; nothing re-checks it.
 confirm_quit: *gtk.Switch,
 
+/// The notifications toggle, held for the same reason.
+notifications: *gtk.Switch,
+
 /// Container the startup rows live in, so rows can be added and removed after
 /// the page is already on screen.
 startup_box: *gtk.Box,
@@ -145,6 +148,7 @@ pub fn present(alloc: std.mem.Allocator, parent: *gtk.Window, opts: Options) !vo
         .theme_buttons = undefined,
         .colors = undefined,
         .confirm_quit = gtk.Switch.new(),
+        .notifications = gtk.Switch.new(),
         .startup_box = gtk.Box.new(.vertical, 6),
         .error_label = gtk.Label.new(null),
     };
@@ -165,6 +169,7 @@ pub fn present(alloc: std.mem.Allocator, parent: *gtk.Window, opts: Options) !vo
     content.as(gtk.Widget).addCssClass("playpen-dialog-content");
 
     content.append(self.buildAppearance());
+    content.append(self.buildNotifications());
     content.append(self.buildQuitting());
     content.append(self.buildStartup());
 
@@ -219,7 +224,7 @@ pub fn close() void {
 // -------------------------------------------------------------------------
 // Appearance
 
-/// The Appearance section: the colour scheme, and the palette it resolves to.
+/// The Appearance section: the color scheme, and the palette it resolves to.
 fn buildAppearance(self: *SettingsDialog) *gtk.Widget {
     const group = gtk.Box.new(.vertical, 10);
     group.as(gtk.Widget).addCssClass("playpen-settings-group");
@@ -266,7 +271,7 @@ fn onEditorReport(ctx: ?*anyopaque, message: ?[:0]const u8) void {
 /// The scheme picker: one toggle per choice, drawn as a single linked control.
 ///
 /// They are not put in a GTK radio group. Grouped toggles can't be unchecked by
-/// clicking the active one, which is the behaviour we want, but the group also
+/// clicking the active one, which is the behavior we want, but the group also
 /// emits `toggled` twice per change — once off, once on — and the off half
 /// would apply whichever scheme happened to be next in the list. Handling the
 /// exclusivity here instead makes each click exactly one decision.
@@ -326,13 +331,82 @@ fn onThemeToggled(button: *gtk.ToggleButton, self: *SettingsDialog) callconv(.c)
     appearance.setTheme(values[index]);
 
     // The palette editor edits whichever scheme is on screen, and that is what
-    // just changed: its swatches now stand for the other palette's colours.
+    // just changed: its swatches now stand for the other palette's colors.
     self.colors.refresh();
 }
 
 // -------------------------------------------------------------------------
 // Quitting
 
+/// The Notifications section: whether a finish reaches the desktop.
+///
+/// The whole-app half of the mute. The per-tab half lives in each row's menu,
+/// because it is a thing you decide about one tab while looking at it, and
+/// walking to a settings window to say "not this one, for the next hour" would
+/// mean nobody ever did.
+fn buildNotifications(self: *SettingsDialog) *gtk.Widget {
+    const group = gtk.Box.new(.vertical, 10);
+    group.as(gtk.Widget).addCssClass("playpen-settings-group");
+
+    const title = gtk.Label.new("Notifications");
+    title.setXalign(0);
+    title.as(gtk.Widget).addCssClass("playpen-settings-title");
+    group.append(title.as(gtk.Widget));
+
+    const row = gtk.Box.new(.horizontal, 12);
+
+    const labels = gtk.Box.new(.vertical, 2);
+    labels.as(gtk.Widget).setHexpand(1);
+    labels.as(gtk.Widget).setValign(.center);
+
+    const name = gtk.Label.new("Tell me when a pane finishes");
+    name.setXalign(0);
+    name.as(gtk.Widget).addCssClass("playpen-dialog-label");
+    labels.append(name.as(gtk.Widget));
+
+    const hint_label = gtk.Label.new(
+        "A desktop notification when something running in a tab goes quiet, " ++
+            "for the tabs you aren't looking at. Off, the sidebar dots are the " ++
+            "only word you get. One tab at a time can be muted from its row menu.",
+    );
+    hint_label.setXalign(0);
+    hint_label.setWrap(1);
+    hint_label.as(gtk.Widget).addCssClass("playpen-dialog-sublabel");
+    labels.append(hint_label.as(gtk.Widget));
+
+    row.append(labels.as(gtk.Widget));
+
+    self.notifications.setActive(@intFromBool(Settings.get().notifications));
+    self.notifications.as(gtk.Widget).setValign(.center);
+    _ = gobject.Object.signals.notify.connect(
+        self.notifications,
+        *SettingsDialog,
+        &onNotificationsChanged,
+        self,
+        .{ .detail = "active" },
+    );
+    row.append(self.notifications.as(gtk.Widget));
+
+    group.append(row.as(gtk.Widget));
+
+    return group.as(gtk.Widget);
+}
+
+/// Straight to the file, for the same reason `onConfirmQuitChanged` is.
+fn onNotificationsChanged(
+    toggle: *gtk.Switch,
+    _: *gobject.ParamSpec,
+    self: *SettingsDialog,
+) callconv(.c) void {
+    Settings.get().notifications = toggle.getActive() != 0;
+
+    Settings.get().save() catch {
+        self.showError("Could not write the settings file.");
+        return;
+    };
+    self.showError(null);
+}
+
 /// The Quitting section: whether closing the window asks first.
 ///
 /// Above the startup list rather than below it. That list grows with the number