[macOS, Keyboard] Duplicate down events are no longer ignored, but kept and preceded by up events

shell/platform/darwin/macos/framework/Source/FlutterEmbedderKeyResponder.mm

@@ -680,12 +680,23 @@ - (void)handleDownEvent:(NSEvent*)event callback:(FlutterKeyCallbackGuard*)callb
   bool isARepeat = event.isARepeat;
   NSNumber* pressedLogicalKey = _pressingRecords[@(physicalKey)];
   if (pressedLogicalKey != nil && !isARepeat) {
-    // Normally the key up events won't be missed since macOS always sends the
-    // key up event to the window where the corresponding key down occurred.
-    // However this might happen in add-to-app scenarios if the focus is changed
+    // This might happen in add-to-app scenarios if the focus is changed
     // from the native view to the Flutter view amid the key tap.
-    [callback resolveTo:TRUE];
-    return;
+    //
+    // This might also happen when a key event is forged (such as by an
+    // IME) using the same keyCode as an unreleased key. See
+    // https://github.com/flutter/flutter/issues/82673#issuecomment-988661079
+    FlutterKeyEvent flutterEvent = {
+        .struct_size = sizeof(FlutterKeyEvent),
+        .timestamp = GetFlutterTimestampFrom(event.timestamp),
+        .type = kFlutterKeyEventTypeUp,
+        .physical = physicalKey,
+        .logical = [pressedLogicalKey unsignedLongLongValue],
+        .character = nil,
+        .synthesized = true,
+    };
+    [self sendSynthesizedFlutterEvent:flutterEvent guard:callback];
+    pressedLogicalKey = nil;
   }
 
   if (pressedLogicalKey == nil) {

shell/platform/darwin/macos/framework/Source/FlutterEmbedderKeyResponderUnittests.mm

@@ -306,7 +306,7 @@ - (void)dealloc {
   [events removeAllObjects];
 }
 
-TEST(FlutterEmbedderKeyResponderUnittests, IgnoreDuplicateDownEvent) {
+TEST(FlutterEmbedderKeyResponderUnittests, SynthesizeForDuplicateDownEvent) {
   __block NSMutableArray<TestKeyEvent*>* events = [[NSMutableArray<TestKeyEvent*> alloc] init];
   __block BOOL last_handled = TRUE;
   FlutterKeyEvent* event;
@@ -319,7 +319,7 @@ - (void)dealloc {
                                                      userData:user_data]];
       }];
 
-  last_handled = FALSE;
+  last_handled = TRUE;
   [responder handleEvent:keyEvent(NSEventTypeKeyDown, 0x100, @"a", @"a", FALSE, kKeyCodeKeyA)
                 callback:^(BOOL handled) {
                   last_handled = handled;
@@ -332,44 +332,35 @@ - (void)dealloc {
   EXPECT_EQ(event->logical, kLogicalKeyA);
   EXPECT_STREQ(event->character, "a");
   EXPECT_EQ(event->synthesized, false);
-  EXPECT_EQ(last_handled, FALSE);
-  [[events lastObject] respond:TRUE];
   EXPECT_EQ(last_handled, TRUE);
+  [[events lastObject] respond:FALSE];
+  EXPECT_EQ(last_handled, FALSE);
 
   [events removeAllObjects];
 
-  last_handled = FALSE;
-  [responder handleEvent:keyEvent(NSEventTypeKeyDown, 0x100, @"a", @"a", FALSE, kKeyCodeKeyA)
+  last_handled = TRUE;
+  [responder handleEvent:keyEvent(NSEventTypeKeyDown, 0x100, @"à", @"à", FALSE, kKeyCodeKeyA)
                 callback:^(BOOL handled) {
                   last_handled = handled;
                 }];
 
-  EXPECT_EQ([events count], 1u);
-  EXPECT_EQ(last_handled, TRUE);
-  event = [events lastObject].data;
-  EXPECT_EQ(event->physical, 0ull);
-  EXPECT_EQ(event->logical, 0ull);
-  EXPECT_FALSE([[events lastObject] hasCallback]);
-  EXPECT_EQ(last_handled, TRUE);
-
-  [events removeAllObjects];
-
-  last_handled = FALSE;
-  [responder handleEvent:keyEvent(NSEventTypeKeyUp, 0x100, @"a", @"a", FALSE, kKeyCodeKeyA)
-                callback:^(BOOL handled) {
-                  last_handled = handled;
-                }];
+  EXPECT_EQ([events count], 2u);
 
-  EXPECT_EQ([events count], 1u);
-  event = [events lastObject].data;
+  event = [events firstObject].data;
   EXPECT_EQ(event->type, kFlutterKeyEventTypeUp);
   EXPECT_EQ(event->physical, kPhysicalKeyA);
   EXPECT_EQ(event->logical, kLogicalKeyA);
-  EXPECT_STREQ(event->character, nullptr);
+  EXPECT_STREQ(event->character, NULL);
+  EXPECT_EQ(event->synthesized, true);
+
+  event = [events lastObject].data;
+  EXPECT_EQ(event->type, kFlutterKeyEventTypeDown);
+  EXPECT_EQ(event->physical, kPhysicalKeyA);
+  EXPECT_EQ(event->logical, 0xE0ull /* à */);
+  EXPECT_STREQ(event->character, "à");
   EXPECT_EQ(event->synthesized, false);
+  [[events lastObject] respond:FALSE];
   EXPECT_EQ(last_handled, FALSE);
-  [[events lastObject] respond:TRUE];
-  EXPECT_EQ(last_handled, TRUE);
 
   [events removeAllObjects];
 }