[web] Don't send keyboard events from text fields to flutter (flutter/engine#13699)

engine/src/flutter/lib/web_ui/dev/chrome.dart

@@ -60,6 +60,7 @@ class Chrome extends Browser {
         '--window-size=$kMaxScreenshotWidth,$kMaxScreenshotHeight', // When headless, this is the actual size of the viewport
         '--disable-extensions',
         '--disable-popup-blocking',
+        // Indicates that the browser is in "browse without sign-in" (Guest session) mode.
         '--bwsi',
         '--no-first-run',
         '--no-default-browser-check',

engine/src/flutter/lib/web_ui/lib/src/engine/keyboard.dart

@@ -4,6 +4,23 @@
 
 part of engine;
 
+/// Contains a whitelist of keys that must be sent to Flutter under all
+/// circumstances.
+///
+/// When keys are pressed in a text field, we generally don't want to send them
+/// to Flutter. This list of keys is the exception to that rule. Keys in this
+/// list will be sent to Flutter even if pressed in a text field.
+///
+/// A good example is the "Tab" and "Shift" keys which are used by the framework
+/// to move focus between text fields.
+const List<String> _alwaysSentKeys = <String>[
+  'Alt',
+  'Control',
+  'Meta',
+  'Shift',
+  'Tab',
+];
+
 /// Provides keyboard bindings, such as the `flutter/keyevent` channel.
 class Keyboard {
   /// Initializes the [Keyboard] singleton.
@@ -50,6 +67,10 @@ class Keyboard {
   static const JSONMessageCodec _messageCodec = JSONMessageCodec();
 
   void _handleHtmlEvent(html.KeyboardEvent event) {
+    if (_shouldIgnoreEvent(event)) {
+      return;
+    }
+
     if (_shouldPreventDefault(event)) {
       event.preventDefault();
     }
@@ -66,6 +87,20 @@ class Keyboard {
         _messageCodec.encodeMessage(eventData), _noopCallback);
   }
 
+  /// Whether the [Keyboard] class should ignore the given [html.KeyboardEvent].
+  ///
+  /// When this method returns true, it prevents the keyboard event from being
+  /// sent to Flutter.
+  bool _shouldIgnoreEvent(html.KeyboardEvent event) {
+    // Keys in the [_alwaysSentKeys] list should never be ignored.
+    if (_alwaysSentKeys.contains(event.key)) {
+      return false;
+    }
+    // Other keys should be ignored if triggered on a text field.
+    return event.target is html.Element &&
+        HybridTextEditing.isEditingElement(event.target);
+  }
+
   bool _shouldPreventDefault(html.KeyboardEvent event) {
     switch (event.key) {
       case 'Tab':

engine/src/flutter/lib/web_ui/lib/src/engine/text_editing/text_editing.dart

@@ -17,6 +17,8 @@ void _emptyCallback(dynamic _) {}
 ///
 /// They are assigned once during the creation of the DOM element.
 void _setStaticStyleAttributes(html.HtmlElement domElement) {
+  domElement.classes.add(HybridTextEditing.textEditingClass);
+
   final html.CssStyleDeclaration elementStyle = domElement.style;
   elementStyle
     ..whiteSpace = 'pre-wrap'
@@ -534,6 +536,14 @@ class HybridTextEditing {
     return _defaultEditingElement;
   }
 
+  /// A CSS class name used to identify all elements used for text editing.
+  @visibleForTesting
+  static const String textEditingClass = 'flt-text-editing';
+
+  static bool isEditingElement(html.Element element) {
+    return element.classes.contains(textEditingClass);
+  }
+
   /// Requests that [customEditingElement] is used for managing text editing state
   /// instead of the hidden default element.
   ///

engine/src/flutter/lib/web_ui/test/keyboard_test.dart

@@ -13,6 +13,17 @@ import 'package:test/test.dart';
 
 void main() {
   group('Keyboard', () {
+    /// Used to save and restore [ui.window.onPlatformMessage] after each test.
+    ui.PlatformMessageCallback savedCallback;
+
+    setUp(() {
+      savedCallback = ui.window.onPlatformMessage;
+    });
+
+    tearDown(() {
+      ui.window.onPlatformMessage = savedCallback;
+    });
+
     test('initializes and disposes', () {
       expect(Keyboard.instance, isNull);
       Keyboard.initialize();
@@ -204,6 +215,12 @@ void main() {
     test('prevents default when "Tab" is pressed', () {
       Keyboard.initialize();
 
+      int count = 0;
+      ui.window.onPlatformMessage = (String channel, ByteData data,
+          ui.PlatformMessageResponseCallback callback) {
+        count += 1;
+      };
+
       final html.KeyboardEvent event = dispatchKeyboardEvent(
         'keydown',
         key: 'Tab',
@@ -211,14 +228,78 @@ void main() {
       );
 
       expect(event.defaultPrevented, isTrue);
+      expect(count, 1);
+
+      Keyboard.instance.dispose();
+    });
+
+    test('ignores keyboard events triggered on text fields', () {
+      Keyboard.initialize();
+
+      int count = 0;
+      ui.window.onPlatformMessage = (String channel, ByteData data,
+          ui.PlatformMessageResponseCallback callback) {
+        count += 1;
+      };
+
+      useTextEditingElement((html.Element element) {
+        final html.KeyboardEvent event = dispatchKeyboardEvent(
+          'keydown',
+          key: 'SomeKey',
+          code: 'SomeCode',
+          target: element,
+        );
+
+        expect(event.defaultPrevented, isFalse);
+        expect(count, 0);
+      });
+
+      Keyboard.instance.dispose();
+    });
+
+    test('the "Tab" key should never be ignored', () {
+      Keyboard.initialize();
+
+      int count = 0;
+      ui.window.onPlatformMessage = (String channel, ByteData data,
+          ui.PlatformMessageResponseCallback callback) {
+        count += 1;
+      };
+
+      useTextEditingElement((html.Element element) {
+        final html.KeyboardEvent event = dispatchKeyboardEvent(
+          'keydown',
+          key: 'Tab',
+          code: 'Tab',
+          target: element,
+        );
+
+        expect(event.defaultPrevented, isTrue);
+        expect(count, 1);
+      });
 
       Keyboard.instance.dispose();
     });
   });
 }
 
+typedef ElementCallback = void Function(html.Element element);
+
+void useTextEditingElement(ElementCallback callback) {
+  final html.InputElement input = html.InputElement();
+  input.classes.add(HybridTextEditing.textEditingClass);
+
+  try {
+    html.document.body.append(input);
+    callback(input);
+  } finally {
+    input.remove();
+  }
+}
+
 html.KeyboardEvent dispatchKeyboardEvent(
   String type, {
+  html.EventTarget target,
   String key,
   String code,
   bool repeat = false,
@@ -227,6 +308,8 @@ html.KeyboardEvent dispatchKeyboardEvent(
   bool isControlPressed = false,
   bool isMetaPressed = false,
 }) {
+  target ??= html.window;
+
   final Function jsKeyboardEvent =
       js_util.getProperty(html.window, 'KeyboardEvent');
   final List<dynamic> eventArgs = <dynamic>[
@@ -239,12 +322,13 @@ html.KeyboardEvent dispatchKeyboardEvent(
       'altKey': isAltPressed,
       'ctrlKey': isControlPressed,
       'metaKey': isMetaPressed,
+      'bubbles': true,
       'cancelable': true,
     }
   ];
   final html.KeyboardEvent event =
       js_util.callConstructor(jsKeyboardEvent, js_util.jsify(eventArgs));
-  html.window.dispatchEvent(event);
+  target.dispatchEvent(event);
 
   return event;
 }