Watch for OS theme changes at runtime

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})")
+        }
+    }
+}