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

src/platform_impl/windows/event_loop.rs

@@ -53,14 +53,15 @@ use windows_sys::Win32::UI::WindowsAndMessaging::{
     WMSZ_BOTTOM, WMSZ_BOTTOMLEFT, 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_INPUT_DEVICE_CHANGE, 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,
+    WM_IME_SETCONTEXT, WM_IME_STARTCOMPOSITION, WM_INPUT, WM_INPUTLANGCHANGE,
+    WM_INPUT_DEVICE_CHANGE, 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,
 };
 
 use crate::dpi::{PhysicalPosition, PhysicalSize};
@@ -1778,6 +1779,16 @@ unsafe fn public_window_callback_inner(
             }
         },
 
+        // The active input layout changed (e.g. the user switched keyboard layout/IME, or a
+        // layout-switching tool such as Punto Switcher activated one). `LAYOUT_CACHE` is keyed
+        // by `HKL`, and Windows can reuse an `HKL` value after the layout it identified is
+        // unloaded and a different one is loaded in its place, so re-derive the layout instead
+        // of trusting whatever is already cached for it.
+        WM_INPUTLANGCHANGE => {
+            LAYOUT_CACHE.lock().unwrap().refresh_current_layout();
+            result = ProcResult::DefWindowProc(wparam);
+        },
+
         WM_LBUTTONDOWN => {
             use crate::event::ElementState::Pressed;
             use crate::event::MouseButton::Left;

src/platform_impl/windows/keyboard_layout.rs

@@ -272,6 +272,13 @@ impl LayoutCache {
         }
     }
 
+    pub fn refresh_current_layout(&mut self) -> (u64, &Layout) {
+        let locale_id = unsafe { GetKeyboardLayout(0) } as u64;
+        let layout = Self::prepare_layout(locale_id);
+        self.layouts.insert(locale_id, layout);
+        (locale_id, self.layouts.get(&locale_id).unwrap())
+    }
+
     pub fn get_agnostic_mods(&mut self) -> ModifiersState {
         let (_, layout) = self.get_current_layout();
         let filter_out_altgr = layout.has_alt_graph && key_pressed(VK_RMENU);
@@ -984,3 +991,22 @@ fn vkey_to_non_char_key(
         _ => Key::Unidentified(native_code),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn refresh_current_layout_replaces_a_stale_entry() {
+        let mut cache = LayoutCache::default();
+        let (locale_id, _) = cache.get_current_layout();
+
+        let poisoned_hkl = !locale_id;
+        cache.layouts.get_mut(&locale_id).unwrap().hkl = poisoned_hkl;
+        assert_eq!(cache.get_current_layout().1.hkl, poisoned_hkl);
+
+        let (refreshed_id, refreshed_layout) = cache.refresh_current_layout();
+        assert_eq!(refreshed_id, locale_id);
+        assert_eq!(refreshed_layout.hkl, locale_id);
+    }
+}