windows: fix layout-switch freeze (Punto Switcher) via WM_INPUTLANGCHANGE

src/changelog/unreleased.md

@@ -217,6 +217,11 @@ changelog entry.
 
 ### Fixed
 
+- On Windows, fix deadlock when switching keyboard layout via tools like PuntoSwitcher or IME
+  switchers. The `LAYOUT_CACHE` mutex was held across a `PeekMessageW` call in the `WM_KEYDOWN`
+  handler, which could dispatch re-entrant messages that tried to re-acquire the same lock.
+- On Windows, handle `WM_INPUTLANGCHANGE` explicitly to refresh the layout cache and avoid
+  re-entrant deadlocks through `DefWindowProc`.
 - On Orbital, `MonitorHandle::name()` now returns `None` instead of a dummy name.
 - On iOS, fixed `SurfaceResized` and `Window::surface_size` not reporting the size of the actual surface.
 - On macOS, fixed the scancode conversion for audio volume keys.

src/platform_impl/windows/event_loop.rs

@@ -49,12 +49,12 @@ use windows_sys::Win32::UI::WindowsAndMessaging::{
     WMSZ_BOTTOMRIGHT, WMSZ_LEFT, WMSZ_RIGHT, WMSZ_TOP, WMSZ_TOPLEFT, WMSZ_TOPRIGHT,
     WM_CAPTURECHANGED, WM_CLOSE, WM_CREATE, WM_DESTROY, WM_DPICHANGED, WM_ENTERSIZEMOVE,
     WM_EXITSIZEMOVE, WM_GETMINMAXINFO, WM_IME_COMPOSITION, WM_IME_ENDCOMPOSITION,
-    WM_IME_SETCONTEXT, WM_IME_STARTCOMPOSITION, WM_INPUT, WM_KEYDOWN, WM_KEYUP, WM_KILLFOCUS,
-    WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MBUTTONDOWN, WM_MBUTTONUP, WM_MENUCHAR, WM_MOUSEHWHEEL,
-    WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_NCACTIVATE, WM_NCCALCSIZE, WM_NCCREATE, WM_NCDESTROY,
-    WM_NCLBUTTONDOWN, WM_PAINT, WM_POINTERDOWN, WM_POINTERUP, WM_POINTERUPDATE, WM_RBUTTONDOWN,
-    WM_RBUTTONUP, WM_SETCURSOR, WM_SETFOCUS, WM_SETTINGCHANGE, WM_SIZE, WM_SIZING, WM_SYSCOMMAND,
-    WM_SYSKEYDOWN, WM_SYSKEYUP, WM_TOUCH, WM_WINDOWPOSCHANGED, WM_WINDOWPOSCHANGING,
+    WM_IME_SETCONTEXT, WM_IME_STARTCOMPOSITION, WM_INPUT, WM_INPUTLANGCHANGE, WM_KEYDOWN, WM_KEYUP,
+    WM_KILLFOCUS, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MBUTTONDOWN, WM_MBUTTONUP, WM_MENUCHAR,
+    WM_MOUSEHWHEEL, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_NCACTIVATE, WM_NCCALCSIZE, WM_NCCREATE,
+    WM_NCDESTROY, WM_NCLBUTTONDOWN, WM_PAINT, WM_POINTERDOWN, WM_POINTERUP, WM_POINTERUPDATE,
+    WM_RBUTTONDOWN, WM_RBUTTONUP, WM_SETCURSOR, WM_SETFOCUS, WM_SETTINGCHANGE, WM_SIZE, WM_SIZING,
+    WM_SYSCOMMAND, WM_SYSKEYDOWN, WM_SYSKEYUP, WM_TOUCH, WM_WINDOWPOSCHANGED, WM_WINDOWPOSCHANGING,
     WM_XBUTTONDOWN, WM_XBUTTONUP, WNDCLASSEXW, WS_EX_LAYERED, WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW,
     WS_EX_TRANSPARENT, WS_OVERLAPPED, WS_POPUP, WS_VISIBLE,
 };
@@ -1569,6 +1569,22 @@ unsafe fn public_window_callback_inner(
             result = ProcResult::DefWindowProc(wparam);
         },
 
+        WM_INPUTLANGCHANGE => {
+            // Refresh the layout cache so subsequent key events use the new
+            // layout. This message is sent by Windows (or tools like
+            // PuntoSwitcher) when the keyboard layout changes. We handle it
+            // explicitly to avoid re-entrant deadlocks: without this handler
+            // the message falls through to DefWindowProc which may
+            // synchronously dispatch IME messages while LAYOUT_CACHE is held
+            // by a parent WNDPROC frame.
+            {
+                let mut layouts = LAYOUT_CACHE.lock().unwrap();
+                layouts.get_current_layout();
+            }
+            update_modifiers(window, userdata);
+            result = ProcResult::Value(1);
+        },
+
         // this is necessary for us to maintain minimize/restore state
         WM_SYSCOMMAND => {
             if wparam == SC_RESTORE as usize {

src/platform_impl/windows/keyboard.rs

@@ -111,15 +111,22 @@ impl KeyEventBuilder {
                     let pending_token = self.pending.add_pending();
                     *result = ProcResult::Value(0);
 
-                    let next_msg = next_kbd_msg(hwnd);
-
                     let mut layouts = LAYOUT_CACHE.lock().unwrap();
                     let mut finished_event_info = Some(PartialKeyEventInfo::from_message(
                         wparam,
                         lparam,
                         ElementState::Pressed,
                         &mut layouts,
                     ));
+                    // We MUST release the layout lock before calling `next_kbd_msg`,
+                    // otherwise PeekMessageW may dispatch re-entrant messages (e.g.
+                    // WM_INPUTLANGCHANGE from PuntoSwitcher or other IME switchers)
+                    // that try to re-acquire LAYOUT_CACHE on the same thread, causing
+                    // a deadlock.
+                    drop(layouts);
+
+                    let next_msg = next_kbd_msg(hwnd);
+
                     let mut event_info = self.event_info.lock().unwrap();
                     *event_info = None;
                     if let Some(next_msg) = next_msg {
@@ -133,6 +140,7 @@ impl KeyEventBuilder {
                             // store the partial information, and add to it in the upcoming events
                             *event_info = finished_event_info.take();
                         } else {
+                            let mut layouts = LAYOUT_CACHE.lock().unwrap();
                             let (_, layout) = layouts.get_current_layout();
                             let is_fake = {
                                 let curr_event = finished_event_info.as_ref().unwrap();