Apply OS theme via native-theme on desktop

desktop/Cargo.toml

@@ -44,6 +44,9 @@ gpui-kit.workspace = true
 gpui_linux.workspace = true
 gpui_windows.workspace = true
 gpui_macos.workspace = true
+native-theme.workspace = true
+native-theme-gpui.workspace = true
+flume.workspace = true
 reqwest_client.workspace = true
 
 log.workspace = true

desktop/src/main.rs

@@ -1,17 +1,23 @@
 use std::sync::{Arc, Mutex};
 
 use gpui::{
-    App, Bounds, KeyBinding, Menu, MenuItem, SharedString, TitlebarOptions,
+    App, Bounds, Global, KeyBinding, Menu, MenuItem, SharedString, TitlebarOptions,
     WindowBackgroundAppearance, WindowBounds, WindowDecorations, WindowKind, WindowOptions,
     actions, point, px, size,
 };
+use gpui_kit::component::{Theme, ThemeMode};
 use gpui_platform::application;
+use native_theme::watch::ThemeSubscription;
+use native_theme_gpui::apply_system_theme;
 use nostr_sdk::prelude::SecretKey;
+use settings::{AppSettings, AppearanceMode};
 use state::{APP_ID, CLIENT_NAME};
 use workspace::TAB_BAR_HEIGHT;
 
 actions!(coop, [Quit]);
 
+const BASE_FONT_SIZE: f32 = 16.0;
+
 fn main() {
     // Initialize logging
     tracing_subscriber::fmt::init();
@@ -59,6 +65,15 @@ fn main() {
             // Initialize settings
             settings::init(cx);
 
+            let appearance = settings::persisted_appearance_mode();
+            match apply_native_theme(appearance, cx) {
+                Ok(()) => start_theme_watcher(appearance, cx),
+                Err(error) => {
+                    log::warn!("native theme unavailable ({error})");
+                    apply_appearance(appearance, cx);
+                }
+            }
+
             // Initialize the nostr client
             state::init(cx, cli_key);
 
@@ -155,3 +170,69 @@ fn quit(_ev: &Quit, cx: &mut App) {
     log::info!("Gracefully quitting the application . . .");
     cx.quit();
 }
+
+/// Apply the native theme to the app, and then apply the persisted appearance mode
+fn apply_native_theme(appearance: AppearanceMode, cx: &mut App) -> native_theme::Result<()> {
+    let mut system = native_theme_gpui::SystemTheme::from_system()?;
+    let native = system.light.defaults.font.size;
+
+    if native > 0.0 {
+        system.accessibility.text_scaling_factor *= BASE_FONT_SIZE / native;
+    }
+
+    apply_system_theme(&system, cx);
+    apply_appearance(appearance, cx);
+
+    Ok(())
+}
+
+/// Honor the appearance mode against the installed (native) palettes.
+fn apply_appearance(appearance: AppearanceMode, cx: &mut App) {
+    match 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),
+    }
+}
+
+/// Holds the watcher subscription so it lives as long as the app.
+struct ThemeWatcher {
+    _subscription: ThemeSubscription,
+    /// The appearance mode the observer in `workspace` was registered with.
+    appearance: std::cell::Cell<AppearanceMode>,
+}
+
+impl Global for ThemeWatcher {}
+
+/// Start a background task to watch for OS theme changes and re-apply the native theme.
+fn start_theme_watcher(initial_appearance: AppearanceMode, cx: &mut App) {
+    let (sender, receiver) = flume::unbounded();
+    match native_theme::watch::on_theme_change(move |event| {
+        if let Err(error) = sender.send(event) {
+            log::warn!("theme change dropped ({error})");
+        }
+    }) {
+        Ok(subscription) => {
+            cx.set_global(ThemeWatcher {
+                _subscription: subscription,
+                appearance: std::cell::Cell::new(initial_appearance),
+            });
+            cx.spawn(async move |cx| {
+                while receiver.recv_async().await.is_ok() {
+                    log::info!("OS theme changed; re-applying");
+                    cx.update(|cx| {
+                        let appearance = AppSettings::get_appearance_mode(cx);
+                        if let Some(watcher) = cx.try_global::<ThemeWatcher>() {
+                            watcher.appearance.set(appearance);
+                        }
+                        if let Err(error) = apply_native_theme(appearance, cx) {
+                            log::warn!("failed to apply updated OS theme ({error})");
+                        }
+                    });
+                }
+            })
+            .detach();
+        }
+        Err(error) => log::warn!("OS theme watching unavailable ({error})"),
+    }
+}