[Win32, Keyboard] Correctly process modifier events in IME mode (#30919)

Author: dkwingsmt

shell/platform/windows/keyboard_key_embedder_handler.cc

@@ -126,6 +126,10 @@ uint64_t KeyboardKeyEmbedderHandler::GetPhysicalKey(int scancode,
 uint64_t KeyboardKeyEmbedderHandler::GetLogicalKey(int key,
                                                    bool extended,
                                                    int scancode) {
+  if (key == VK_PROCESSKEY) {
+    return VK_PROCESSKEY;
+  }
+
   // Normally logical keys should only be derived from key codes, but since some
   // key codes are either 0 or ambiguous (multiple keys using the same key
   // code), these keys are resolved by scan codes.
@@ -220,6 +224,15 @@ void KeyboardKeyEmbedderHandler::KeyboardHookImpl(
     }
   }
 
+  if (result_logical_key == VK_PROCESSKEY) {
+    // VK_PROCESSKEY means that the key press is used by an IME. These key
+    // presses are considered handled and not sent to Flutter. These events must
+    // be filtered by result_logical_key because the key up event of such
+    // presses uses the "original" logical key.
+    callback(true);
+    return;
+  }
+
   UpdateLastSeenCritialKey(key, physical_key, result_logical_key);
   // Synchronize the toggled states of critical keys (such as whether CapsLocks
   // is enabled). Toggled states can only be changed upon a down event, so if
@@ -248,15 +261,6 @@ void KeyboardKeyEmbedderHandler::KeyboardHookImpl(
     pressingRecords_.erase(record_iter);
   }
 
-  if (result_logical_key == VK_PROCESSKEY) {
-    // VK_PROCESSKEY means that the key press is used by an IME. These key
-    // presses are considered handled and not sent to Flutter. These events must
-    // be filtered by result_logical_key because the key up event of such
-    // presses uses the "original" logical key.
-    callback(true);
-    return;
-  }
-
   FlutterKeyEvent key_data{
       .struct_size = sizeof(FlutterKeyEvent),
       .timestamp = static_cast<double>(

shell/platform/windows/keyboard_win32_unittests.cc

@@ -1545,7 +1545,7 @@ TEST(KeyboardTest, MultibyteCharacter) {
   tester.Responding(false);
 
   // Gothic Keyboard layout. (We need a layout that yields non-BMP characters
-  // without IME, which that is actually very rare.)
+  // without IME, which is actually very rare.)
 
   // Press key W of a US keyboard, which should yield character '𐍅'.
   tester.InjectMessages(
@@ -1617,6 +1617,33 @@ TEST(KeyboardTest, NeverRedispatchShiftRightKeyDown) {
   EXPECT_EQ(key_calls.size(), 0);
 }
 
+// Pressing modifiers during IME events should work properly by not sending any
+// events.
+//
+// Regression test for https://github.com/flutter/flutter/issues/95888 .
+TEST(KeyboardTest, ImeModifierEventsAreIgnored) {
+  KeyboardTester tester;
+  tester.Responding(false);
+
+  // US Keyboard layout.
+
+  // To make the keyboard into IME mode, there should have been events like
+  // letter key down with VK_PROCESSKEY. Omit them in this test since they don't
+  // seem significant.
+
+  // Press CtrlRight in IME mode.
+  tester.SetKeyState(VK_RCONTROL, true, false);
+  tester.InjectMessages(
+      1,
+      WmKeyDownInfo{VK_PROCESSKEY, kScanCodeControl, kExtended, kWasUp}.Build(
+          kWmResultZero));
+
+  EXPECT_EQ(key_calls.size(), 1);
+  EXPECT_CALL_IS_EVENT(key_calls[0], kFlutterKeyEventTypeDown, 0, 0, "",
+                       kNotSynthesized);
+  clear_key_calls();
+}
+
 TEST(KeyboardTest, DisorderlyRespondedEvents) {
   KeyboardTester tester;