x11/wayland: subscribe to xdg desktop portal for settings changes

We use this to detect changes in dark mode

refs: https://github.com/wez/wezterm/issues/2258

docs/changelog.md

@@ -27,7 +27,7 @@ As features stabilize some brief notes about them will accumulate here.
 * New [wezterm.json_parse()](config/lua/wezterm/json_parse.md) and [wezterm.json_encode()](config/lua/wezterm/json_encode.md) functions for working with JSON.
 * Hundreds of new color schemes have been imported from [base16](https://github.com/chriskempson/base16-schemes-source), [Gogh](https://gogh-co.github.io/Gogh/) and [terminal.sexy](https://terminal.sexy/). [Browse the schemes](colorschemes/index.md) and look for themes with `(base16)`, `(Gogh)` and `(terminal.sexy)` in the name to discover them!
 * [pane:is_alt_screen_active()](config/lua/pane/is_alt_screen_active.md) for testing whether the alt screen is active. Thanks to [@Funami580](https://github.com/Funami580)! [#2234](https://github.com/wez/wezterm/issues/2234)
-* X11/Wayland: XDG desktop portal is now used to determine whether dark mode is in use [#2258](https://github.com/wez/wezterm/issues/2258)
+* X11/Wayland: [XDG desktop portal](https://flatpak.github.io/xdg-desktop-portal/) is now used to determine whether dark mode is in use [#2258](https://github.com/wez/wezterm/issues/2258)
 
 #### Fixed
 * [ActivateKeyTable](config/lua/keyassignment/ActivateKeyTable.md)'s `replace_current` field was not actually optional. Made it optional. [#2179](https://github.com/wez/wezterm/issues/2179)

docs/config/lua/window/get_appearance.md

@@ -7,16 +7,12 @@ can be one of the following 4 values:
 
 * `"Light"` - the normal appearance, with dark text on a light background
 * `"Dark"` - "dark mode", with predominantly dark colors and probably a lighter, lower contrasting, text color on a dark background
-* `"LightHighContrast"` - light mode but with high contrast colors
+* `"LightHighContrast"` - light mode but with high contrast colors (not reported on all systems)
-* `"DarkHighContrast"` - dark mode but with high contrast colors
+* `"DarkHighContrast"` - dark mode but with high contrast colors (not reported on all systems)
 
-wezterm currently doesn't know how to interrogate the appearance on Wayland
+wezterm is able to detect when the appearance has changed and will generate a
-systems, and will always report `"Light"`.
+[window-config-reloaded](../window-events/window-config-reloaded.md) event for
-
+each window.
-On macOS, X11 and Windows systems, wezterm is able to detect when the
-appearance has changed and will generate a
-[window-config-reloaded](../window-events/window-config-reloaded.md) event for each
-window.
 
 This example configuration shows how you can have your color scheme
 automatically adjust to the current appearance:
@@ -48,6 +44,16 @@ return {
 
 ### Wayland GNOME Appearance
 
+*Since: nightly builds only*
+
+wezterm uses [XDG Desktop
+Portal](https://flatpak.github.io/xdg-desktop-portal/) to determine the
+appearance.
+
+In earlier versions you may wish to use an alternative method to determine the
+appearance, as wezterm didn't know how to interrogate the appearance on Wayland
+systems, and would always report `"Light"`.
+
 The GNOME desktop environment provides the `gsettings` tool that can
 inform us of the selected appearance even in a Wayland session. We can
 substitute the call to `window:get_appearance` above with a call to the
@@ -77,10 +83,10 @@ function query_appearance_gnome()
 end
 ```
 
-Since WezTerm will not fire a `window-config-reloaded`
+Since WezTerm will not fire a `window-config-reloaded` event on Wayland for
-event on Wayland, you will instead need to listen on the
+older versions of wezterm, you will instead need to listen on the
-[update-right-status](../window-events/update-right-status.md) event,
+[update-right-status](../window-events/update-right-status.md) event, which
-which will essentially poll for the appearance periodically:
+will essentially poll for the appearance periodically:
 
 ```lua
 local wezterm = require 'wezterm'

window/src/os/wayland/connection.rs

@@ -412,6 +412,12 @@ impl WaylandConnection {
         }
         Ok(())
     }
+
+    pub(crate) fn advise_of_appearance_change(&self, appearance: crate::Appearance) {
+        for win in self.windows.borrow().values() {
+            win.borrow_mut().appearance_changed(appearance);
+        }
+    }
 }
 
 impl ConnectionOps for WaylandConnection {

window/src/os/wayland/window.rs

@@ -6,9 +6,9 @@ use crate::os::wayland::connection::WaylandConnection;
 use crate::os::wayland::wl_id;
 use crate::os::x11::keyboard::Keyboard;
 use crate::{
-    Clipboard, Connection, Dimensions, MouseCursor, Point, Rect, RequestedWindowGeometry,
+    Appearance, Clipboard, Connection, Dimensions, MouseCursor, Point, Rect,
-    ResolvedGeometry, ScreenPoint, Window, WindowEvent, WindowEventSender, WindowKeyEvent,
+    RequestedWindowGeometry, ResolvedGeometry, ScreenPoint, Window, WindowEvent, WindowEventSender,
-    WindowOps, WindowState,
+    WindowKeyEvent, WindowOps, WindowState,
 };
 use anyhow::{anyhow, bail, Context};
 use async_io::Timer;
@@ -146,6 +146,7 @@ pub struct WaylandWindowInner {
     invalidated: bool,
     font_config: Rc<FontConfiguration>,
     text_cursor: Option<Rect>,
+    appearance: Appearance,
     config: Option<ConfigHandle>,
     // cache the title for comparison to avoid spamming
     // the compositor with updates that don't actually change it
@@ -372,6 +373,7 @@ impl WaylandWindow {
             gl_state: None,
             wegl_surface: None,
             text_cursor: None,
+            appearance: Appearance::Light,
         }));
 
         let window_handle = Window::Wayland(WaylandWindow(window_id));
@@ -401,6 +403,14 @@ unsafe impl HasRawWindowHandle for WaylandWindowInner {
 }
 
 impl WaylandWindowInner {
+    pub(crate) fn appearance_changed(&mut self, appearance: Appearance) {
+        if appearance != self.appearance {
+            self.appearance = appearance;
+            self.events
+                .dispatch(WindowEvent::AppearanceChanged(appearance));
+        }
+    }
+
     pub(crate) fn keyboard_event(&mut self, event: WlKeyboardEvent) {
         let conn = WaylandConnection::get().unwrap().wayland();
         let mut mapper = conn.keyboard_mapper.borrow_mut();

window/src/os/x11/connection.rs

@@ -313,6 +313,12 @@ impl XConnection {
         *self.default_dpi.borrow_mut() = dpi;
     }
 
+    pub(crate) fn advise_of_appearance_change(&self, appearance: crate::Appearance) {
+        for win in self.windows.borrow().values() {
+            win.lock().unwrap().appearance_changed(appearance);
+        }
+    }
+
     fn process_queued_xcb(&self) -> anyhow::Result<()> {
         if let Some(event) = self
             .conn

window/src/os/x11/window.rs

@@ -523,11 +523,7 @@ impl XWindowInner {
                     conn.update_xrm();
                     self.check_dpi_and_synthesize_resize();
                     let appearance = conn.get_appearance();
-                    if appearance != self.appearance {
+                    self.appearance_changed(appearance);
-                        self.appearance = appearance;
-                        self.events
-                            .dispatch(WindowEvent::AppearanceChanged(appearance));
-                    }
                 }
 
                 if msg.atom() == conn.atom_net_wm_state {
@@ -555,6 +551,14 @@ impl XWindowInner {
         Ok(())
     }
 
+    pub(crate) fn appearance_changed(&mut self, appearance: Appearance) {
+        if appearance != self.appearance {
+            self.appearance = appearance;
+            self.events
+                .dispatch(WindowEvent::AppearanceChanged(appearance));
+        }
+    }
+
     fn focus_changed(&mut self, focused: bool) {
         log::trace!("focus_changed {focused}, flagging geometry as unsure");
         self.sure_about_geometry = false;

window/src/os/x_and_wayland.rs

@@ -104,6 +104,15 @@ impl Connection {
             _ => panic!("attempted to get wayland reference on non-wayland connection"),
         }
     }
+
+    pub(crate) fn advise_of_appearance_change(&self, appearance: Appearance) {
+        log::trace!("Appearance changed to {appearance:?}");
+        match self {
+            Self::X11(x) => x.advise_of_appearance_change(appearance),
+            #[cfg(feature = "wayland")]
+            Self::Wayland(w) => w.advise_of_appearance_change(appearance),
+        }
+    }
 }
 
 impl ConnectionOps for Connection {
@@ -124,6 +133,7 @@ impl ConnectionOps for Connection {
     }
 
     fn run_message_loop(&self) -> anyhow::Result<()> {
+        crate::os::xdg_desktop_portal::subscribe();
         match self {
             Self::X11(x) => x.run_message_loop(),
             #[cfg(feature = "wayland")]
@@ -132,17 +142,8 @@ impl ConnectionOps for Connection {
     }
 
     fn get_appearance(&self) -> Appearance {
-        match promise::spawn::block_on(crate::os::xdg_desktop_portal::read_setting(
+        match promise::spawn::block_on(crate::os::xdg_desktop_portal::get_appearance()) {
-            "org.freedesktop.appearance",
+            Ok(appearance) => return appearance,
-            "color-scheme",
-        )) {
-            Ok(value) => match value.downcast_ref::<u32>() {
-                Some(1) => return Appearance::Dark,
-                Some(_) => return Appearance::Light,
-                None => {
-                    log::debug!("Unable to resolve appearance using xdg-desktop-portal: expected a u32 value but got {value:#?}");
-                }
-            },
             Err(err) => {
                 log::debug!("Unable to resolve appearance using xdg-desktop-portal: {err:#}");
             }

window/src/os/xdg_desktop_portal.rs

@@ -2,7 +2,9 @@
 
 //! <https://github.com/flatpak/xdg-desktop-portal/blob/main/data/org.freedesktop.portal.Settings.xml>
 
+use crate::{Appearance, Connection, ConnectionOps};
 use anyhow::Context;
+use futures_util::stream::StreamExt;
 use std::collections::HashMap;
 use zbus::dbus_proxy;
 use zvariant::OwnedValue;
@@ -31,3 +33,43 @@ pub async fn read_setting(namespace: &str, key: &str) -> anyhow::Result<OwnedVal
         .context("make proxy")?;
     proxy.Read(namespace, key).await.context("Read")
 }
+
+fn value_to_appearance(value: OwnedValue) -> anyhow::Result<Appearance> {
+    Ok(match value.downcast_ref::<u32>() {
+        Some(1) => Appearance::Dark,
+        Some(_) => Appearance::Light,
+        None => {
+            anyhow::bail!(
+                "Unable to resolve appearance \
+                 using xdg-desktop-portal: expected a u32 value but got {value:#?}"
+            );
+        }
+    })
+}
+
+pub async fn get_appearance() -> anyhow::Result<Appearance> {
+    let value = read_setting("org.freedesktop.appearance", "color-scheme").await?;
+    value_to_appearance(value)
+}
+
+pub fn subscribe() {
+    promise::spawn::spawn(async move {
+        let connection = zbus::ConnectionBuilder::session()?.build().await?;
+        let proxy = PortalSettingsProxy::new(&connection)
+            .await
+            .context("make proxy")?;
+        let mut stream = proxy.receive_SettingChanged().await?;
+        while let Some(signal) = stream.next().await {
+            let args = signal.args()?;
+            if args.namespace == "org.freedesktop.appearance" && args.key == "color-scheme" {
+                if let Ok(appearance) = value_to_appearance(args.value) {
+                    let conn =
+                        Connection::get().ok_or_else(|| anyhow::anyhow!("connection is dead"))?;
+                    conn.advise_of_appearance_change(appearance);
+                }
+            }
+        }
+        Result::<(), anyhow::Error>::Ok(())
+    })
+    .detach();
+}