X11: restore IME focus after replacing an input context

winit-x11/src/event_processor.rs

@@ -85,6 +85,7 @@ impl EventProcessor {
         self.process_xevent(xev, app);
 
         // Handle IME requests.
+        let mut ime_focus = None;
         while let Ok(request) = self.ime_receiver.try_recv() {
             let ime = match self.target.ime.as_mut() {
                 Some(ime) => ime,
@@ -97,11 +98,25 @@ impl EventProcessor {
                     ime.send_xim_area(window_id, x, y, w, h);
                 },
                 ImeRequest::Allow(window_id, allowed) => {
-                    ime.set_ime_allowed(window_id, allowed);
+                    let result = ime.set_ime_allowed(window_id, allowed);
+                    if self.active_window == Some(window_id as xproto::Window) {
+                        match result {
+                            Ok(true) => ime_focus = Some(window_id),
+                            Err(_) => ime_focus = None,
+                            Ok(false) => {},
+                        }
+                    }
                 },
             }
         }
 
+        // Replacing the context does not generate a window focus event. Transfer
+        // focus after draining requests, so contexts replaced again in this batch
+        // do not activate the input method unnecessarily.
+        if let (Some(window_id), Some(ime)) = (ime_focus, self.target.ime.as_mut()) {
+            let _ = ime.get_mut().focus(window_id);
+        }
+
         // Drain IME events.
         while let Ok((window, event)) = self.ime_event_receiver.try_recv() {
             let window_id = mkwid(window as xproto::Window);

winit-x11/src/ime/mod.rs

@@ -202,22 +202,26 @@ impl Ime {
         }
     }
 
-    pub fn set_ime_allowed(&mut self, window: ffi::Window, allowed: bool) {
+    pub fn set_ime_allowed(
+        &mut self,
+        window: ffi::Window,
+        allowed: bool,
+    ) -> Result<bool, ImeContextCreationError> {
         if self.is_destroyed() {
-            return;
+            return Ok(false);
         }
 
         if let Some(&mut Some(ref mut context)) = self.inner.contexts.get_mut(&window) {
             if allowed == context.is_allowed() {
-                return;
+                return Ok(false);
             }
         }
 
         // Remove context for that window.
         let _ = self.remove_context(window);
 
         // Create new context supporting IME input.
-        let _ = self.create_context(window, allowed);
+        self.create_context(window, allowed)
     }
 
     pub fn is_ime_allowed(&self, window: ffi::Window) -> bool {

winit/src/changelog/unreleased.md

@@ -46,6 +46,9 @@ changelog entry.
 - On Wayland, use the touch serial for `Window::drag_window`, `Window::drag_resize_window` and `Window::show_window_menu` when the interaction was started by touch.
 - On Windows, fix a crash when moving a window that owns windows not created by winit, such as native dialogs or application helper windows.
 
+- On X11, preserve input context focus when enabling or disabling IME on a
+  focused window.
+
 ### Changed
 
 - Removed the `url` dependency from `winit-core`, along with `SendData::from_file_paths`,