[Keyboard] Accept empty events (#87152)

packages/flutter/lib/src/services/hardware_keyboard.dart

@@ -787,8 +787,15 @@ class KeyEventManager {
         assert(false, 'Should never encounter KeyData when transitMode is rawKeyData.');
         return false;
       case KeyDataTransitMode.keyDataThenRawKeyData:
+        assert((data.physical == 0 && data.logical == 0) ||
+               (data.physical != 0 && data.logical != 0));
         // Postpone key event dispatching until the handleRawKeyMessage.
-        _keyEventsSinceLastMessage.add(_eventFromData(data));
+        //
+        // Having 0 as the physical or logical ID indicates an empty key data,
+        // transmitted to ensure that the transit mode is correctly inferred.
+        if (data.physical != 0 && data.logical != 0) {
+          _keyEventsSinceLastMessage.add(_eventFromData(data));
+        }
         return false;
     }
   }

packages/flutter/test/services/hardware_keyboard_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui' as ui;
+
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -162,4 +164,60 @@ void main() {
     expect(logs, <int>[3, 2, 1]);
     logs.clear();
   }, variant: KeySimulatorTransitModeVariant.all());
+
+  // The first key data received from the engine might be an empty key data.
+  // In that case, the key data should not be converted to any [KeyEvent]s,
+  // but is only used so that *a* key data comes before the raw key message
+  // and makes [KeyEventManager] infer [KeyDataTransitMode.keyDataThenRawKeyData].
+  testWidgets('Empty keyData yields no event but triggers inferrence', (WidgetTester tester) async {
+    final List<KeyEvent> events = <KeyEvent>[];
+    final List<RawKeyEvent> rawEvents = <RawKeyEvent>[];
+    tester.binding.keyboard.addHandler((KeyEvent event) {
+      events.add(event);
+      return true;
+    });
+    RawKeyboard.instance.addListener((RawKeyEvent event) {
+      rawEvents.add(event);
+    });
+    tester.binding.keyEventManager.handleKeyData(const ui.KeyData(
+      type: ui.KeyEventType.down,
+      timeStamp: Duration.zero,
+      logical: 0,
+      physical: 0,
+      character: 'a',
+      synthesized: false,
+    ));
+    tester.binding.keyEventManager.handleRawKeyMessage(<String, dynamic>{
+      'type': 'keydown',
+      'keymap': 'windows',
+      'keyCode': 0x04,
+      'scanCode': 0x04,
+      'characterCodePoint': 0,
+      'modifiers': 0,
+    });
+    expect(events.length, 0);
+    expect(rawEvents.length, 1);
+
+    // Dispatch another key data to ensure it's in
+    // [KeyDataTransitMode.keyDataThenRawKeyData] mode (otherwise assertion
+    // will be thrown upon a KeyData).
+    tester.binding.keyEventManager.handleKeyData(const ui.KeyData(
+      type: ui.KeyEventType.down,
+      timeStamp: Duration.zero,
+      logical: 0x22,
+      physical: 0x70034,
+      character: '"',
+      synthesized: false,
+    ));
+    tester.binding.keyEventManager.handleRawKeyMessage(<String, dynamic>{
+      'type': 'keydown',
+      'keymap': 'windows',
+      'keyCode': 0x04,
+      'scanCode': 0x04,
+      'characterCodePoint': 0,
+      'modifiers': 0,
+    });
+    expect(events.length, 1);
+    expect(rawEvents.length, 2);
+  });
 }