Watch for OS theme changes at runtime

Cargo.lock

@@ -5699,6 +5699,7 @@ dependencies = [
  "fontdb",
  "inventory",
  "native-theme-derive",
+ "notify",
  "objc2 0.6.5",
  "objc2-app-kit 0.3.2",
  "objc2-core-foundation",
@@ -8337,11 +8338,13 @@ version = "0.2.0-alpha"
 dependencies = [
  "assets",
  "dock",
+ "flume 0.11.1",
  "gpui-component",
  "gpui-pre",
  "gpui-pre-platform",
  "gpui-pre-reqwest-client",
  "metadata",
+ "native-theme",
  "native-theme-gpui",
  "paths",
  "settings",

Cargo.toml

@@ -18,6 +18,7 @@ reqwest_client = { package = "gpui-pre-reqwest-client", version = "0.3.8" }
 gpui-component = { version = "=0.7.1", features = ["tree-sitter-languages"] }
 gpui-base = "=0.7.1"
 
+native-theme = { version = "0.6.1", features = ["watch"] }
 native-theme-gpui = { version = "0.6.1", default-features = false, features = ["system-fonts"] }
 
 dock = { path = "crates/dock" }

desktop/Cargo.toml

@@ -38,7 +38,9 @@ gpui.workspace = true
 gpui_platform.workspace = true
 dock = { workspace = true }
 gpui-component.workspace = true
+native-theme.workspace = true
 native-theme-gpui.workspace = true
+flume.workspace = true
 reqwest_client.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true

desktop/src/main.rs

@@ -5,8 +5,9 @@ use dock::TAB_BAR_HEIGHT;
 use gpui::*;
 use gpui_component::{Theme, ThemeMode, ThemeRegistry, theme};
 use gpui_platform::application;
+use native_theme::watch::ThemeSubscription;
 use native_theme_gpui::{SystemTheme, apply_system_theme};
-use settings::{AppearanceMode, SettingsStore};
+use settings::{AppearanceMode, Settings, SettingsStore};
 
 actions!(signed, [Quit]);
 
@@ -28,26 +29,21 @@ fn main() {
             SettingsStore::set_global(store.clone(), cx);
 
             let settings = store.read(cx).settings().clone();
-            let registry = ThemeRegistry::global_mut(cx);
-
-            for (name, content) in Assets.themes() {
-                if let Err(err) = registry.load_themes_from_str(&content) {
-                    tracing::error!("Failed to load theme {name}: {err}");
+            {
+                let registry = ThemeRegistry::global_mut(cx);
+                for (name, content) in Assets.themes() {
+                    if let Err(err) = registry.load_themes_from_str(&content) {
+                        tracing::error!("Failed to load theme {name}: {err}");
+                    }
                 }
             }
 
-            match SystemTheme::from_system() {
-                Ok(mut system) => {
-                    let native = system.light.defaults.font.size;
-                    if native > 0.0 {
-                        let scaling = settings.theme.font_size / native;
-                        system.accessibility.text_scaling_factor *= scaling;
-                    }
-                    apply_system_theme(&system, cx);
-                }
+            match apply_native_theme(&settings, cx) {
+                Ok(()) => start_theme_watcher(cx),
                 Err(error) => {
                     tracing::warn!("native theme unavailable ({error})");
 
+                    let registry = ThemeRegistry::global_mut(cx);
                     let light_theme = registry
                         .themes()
                         .get(settings.theme.light_theme.as_str())
@@ -77,13 +73,13 @@ fn main() {
                     } else {
                         tracing::warn!("{} theme is missing", settings.theme.dark_theme);
                     }
-                }
-            }
 
-            match settings.appearance {
-                AppearanceMode::System => Theme::sync_system_appearance(None, cx),
-                AppearanceMode::Light => Theme::change(ThemeMode::Light, None, cx),
-                AppearanceMode::Dark => Theme::change(ThemeMode::Dark, None, cx),
+                    match settings.appearance {
+                        AppearanceMode::System => Theme::sync_system_appearance(None, cx),
+                        AppearanceMode::Light => Theme::change(ThemeMode::Light, None, cx),
+                        AppearanceMode::Dark => Theme::change(ThemeMode::Dark, None, cx),
+                    }
+                }
             }
 
             std::fs::create_dir_all(paths::nostr_dir()).ok();
@@ -128,3 +124,62 @@ fn main() {
             cx.activate(true);
         });
 }
+
+/// Apply the OS theme to the app, scaling the font size to match the system font size.
+fn apply_native_theme(settings: &Settings, cx: &mut App) -> native_theme::Result<()> {
+    let mut system = SystemTheme::from_system()?;
+    let native = system.light.defaults.font.size;
+    if native > 0.0 {
+        let scaling = settings.theme.font_size / native;
+        system.accessibility.text_scaling_factor *= scaling;
+    }
+
+    apply_system_theme(&system, cx);
+
+    match settings.appearance {
+        AppearanceMode::System => Theme::sync_system_appearance(None, cx),
+        AppearanceMode::Light => Theme::change(ThemeMode::Light, None, cx),
+        AppearanceMode::Dark => Theme::change(ThemeMode::Dark, None, cx),
+    }
+
+    Ok(())
+}
+
+/// Holds the watcher subscription so it lives as long as the app.
+struct ThemeWatcher {
+    _subscription: ThemeSubscription,
+}
+
+impl Global for ThemeWatcher {}
+
+/// Re-apply the OS theme whenever it changes at runtime.
+fn start_theme_watcher(cx: &mut App) {
+    let (sender, receiver) = flume::unbounded();
+    match native_theme::watch::on_theme_change(move |event| {
+        if let Err(error) = sender.send(event) {
+            tracing::warn!("theme change dropped ({error})");
+        }
+    }) {
+        Ok(subscription) => {
+            cx.set_global(ThemeWatcher {
+                _subscription: subscription,
+            });
+            cx.spawn(async move |cx| {
+                while receiver.recv_async().await.is_ok() {
+                    tracing::info!("OS theme changed; re-applying");
+                    cx.update(|cx| {
+                        let store = SettingsStore::global(cx);
+                        let settings = store.read(cx).settings().clone();
+                        if let Err(error) = apply_native_theme(&settings, cx) {
+                            tracing::warn!("failed to apply updated OS theme ({error})");
+                        }
+                    });
+                }
+            })
+            .detach();
+        }
+        Err(error) => {
+            tracing::warn!("OS theme watching unavailable ({error})")
+        }
+    }
+}

docs/NATIVE-THEME-MIGRATION.md

@@ -169,11 +169,14 @@ and overwriting them fights its observer.
 - `Theme::change(mode, None, cx)` reproduces the native palette for the mode
   because the connector installed a `ThemeConfig` per variant.
 
-Known gap (not addressed here): gpui-component's system-appearance follow is
-driven by window-activation events. A live OS theme change while the window
-is focused may not propagate on Linux until the window is re-focused;
-native-theme's `watch` feature (a theme-change watcher) is a possible
-follow-up, out of scope.
+Known gap (addressed since): gpui-component's system-appearance follow is
+driven by window-activation events. The app now enables native-theme's
+`watch` feature and re-applies the theme on its signal (`start_theme_watcher`
+in `desktop/src/main.rs`), so live OS changes apply without re-focusing or
+restarting. macOS reports appearance changes only (`AppleInterfaceTheme-
+ChangedNotification`); an accent-only change posts a different notification
+the watcher does not observe yet — Windows (`UISettings::ColorValuesChanged`),
+KDE (inotify on `kdeglobals`) and GNOME (portal `SettingChanged`) cover accent.
 
 ### 4.4 Settings dialog (`settings_dialog.rs`)
 
@@ -278,6 +281,5 @@ Unchanged:
   SVG assets.
 - theme-drawn widgets (`widgets` feature).
 - a preset-picker UI (`from_preset`) in settings.
-- runtime OS-theme watching (`watch` feature).
 - per-field user overrides layered on the native theme.
 - migrating `signed.json` into a native-theme `Theme` definition.