Framework can receive TextEditingDeltas from engine

packages/flutter/lib/services.dart

@@ -42,6 +42,7 @@ export 'src/services/system_chrome.dart';
 export 'src/services/system_navigator.dart';
 export 'src/services/system_sound.dart';
 export 'src/services/text_editing.dart';
+export 'src/services/text_editing_delta.dart';
 export 'src/services/text_formatter.dart';
 export 'src/services/text_input.dart';
 export 'src/services/text_layout_metrics.dart';

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

@@ -23,6 +23,7 @@ import 'platform_channel.dart';
 import 'system_channels.dart';
 import 'system_chrome.dart';
 import 'text_editing.dart';
+import 'text_editing_delta.dart';
 
 export 'dart:ui' show TextAffinity;
 
@@ -467,6 +468,7 @@ class TextInputConfiguration {
     this.textCapitalization = TextCapitalization.none,
     this.autofillConfiguration = AutofillConfiguration.disabled,
     this.enableIMEPersonalizedLearning = true,
+    this.enableDeltaModel = false,
   }) : assert(inputType != null),
        assert(obscureText != null),
        smartDashesType = smartDashesType ?? (obscureText ? SmartDashesType.disabled : SmartDashesType.enabled),
@@ -476,7 +478,8 @@ class TextInputConfiguration {
        assert(keyboardAppearance != null),
        assert(inputAction != null),
        assert(textCapitalization != null),
-       assert(enableIMEPersonalizedLearning != null);
+       assert(enableIMEPersonalizedLearning != null),
+       assert(enableDeltaModel != null);
 
   /// The type of information for which to optimize the text input control.
   final TextInputType inputType;
@@ -622,6 +625,7 @@ class TextInputConfiguration {
     TextCapitalization? textCapitalization,
     bool? enableIMEPersonalizedLearning,
     AutofillConfiguration? autofillConfiguration,
+    bool? enableDeltaModel,
   }) {
     return TextInputConfiguration(
       inputType: inputType ?? this.inputType,
@@ -636,8 +640,30 @@ class TextInputConfiguration {
       keyboardAppearance: keyboardAppearance ?? this.keyboardAppearance,
       enableIMEPersonalizedLearning: enableIMEPersonalizedLearning?? this.enableIMEPersonalizedLearning,
       autofillConfiguration: autofillConfiguration ?? this.autofillConfiguration,
+      enableDeltaModel: enableDeltaModel ?? this.enableDeltaModel,
     );
   }
+
+  /// Whether to enable that the engine sends text input updates to the
+  /// framework as [TextEditingDelta]'s or as one [TextEditingValue].
+  ///
+  /// When this is enabled platform text input updates will
+  /// come through [TextInputClient.updateEditingValueWithDeltas].
+  ///
+  /// When this is disabled platform text input updates will come through
+  /// [TextInputClient.updateEditingValue].
+  ///
+  /// Enabling this flag results in granular text updates being received from the
+  /// platforms text input control rather than a single new bulk editing state
+  /// given by [TextInputClient.updateEditingValue].
+  ///
+  /// If the platform does not currently support the delta model then updates
+  /// for the editing state will continue to come through the
+  /// [TextInputClient.updateEditingValue] channel.
+  ///
+  /// Defaults to false. Cannot be null.
+  final bool enableDeltaModel;
+
   /// Returns a representation of this object as a JSON object.
   Map<String, dynamic> toJson() {
     final Map<String, dynamic>? autofill = autofillConfiguration.toJson();
@@ -655,6 +681,7 @@ class TextInputConfiguration {
       'keyboardAppearance': keyboardAppearance.toString(),
       'enableIMEPersonalizedLearning': enableIMEPersonalizedLearning,
       if (autofill != null) 'autofill': autofill,
+      'enableDeltaModel' : enableDeltaModel,
     };
   }
 }
@@ -985,6 +1012,16 @@ abstract class TextInputClient {
   /// formatting.
   void updateEditingValue(TextEditingValue value);
 
+  /// Requests that this client update its editing state by applying the deltas
+  /// received from the engine.
+  ///
+  /// The list of [TextEditingDelta]'s are treated as changes that will be applied
+  /// to the client's editing state. A change is any mutation to the raw text
+  /// value, or any updates to the selection and/or composing region.
+  ///
+  /// {@macro flutter.services.TextEditingDelta.optIn}
+  void updateEditingValueWithDeltas(List<TextEditingDelta> textEditingDeltas);
+
   /// Requests that this client perform the given action.
   void performAction(TextInputAction action);
 
@@ -1476,6 +1513,18 @@ class TextInput {
       case 'TextInputClient.updateEditingState':
         _currentConnection!._client.updateEditingValue(TextEditingValue.fromJSON(args[1] as Map<String, dynamic>));
         break;
+      case 'TextInputClient.updateEditingStateWithDeltas':
+        final List<TextEditingDelta> deltas = <TextEditingDelta>[];
+
+        final Map<String, dynamic> encoded = args[1] as Map<String, dynamic>;
+
+        for (final dynamic encodedDelta in encoded['deltas']) {
+          final TextEditingDelta delta = TextEditingDelta.fromJSON(encodedDelta as Map<String, dynamic>);
+          deltas.add(delta);
+        }
+
+        _currentConnection!._client.updateEditingValueWithDeltas(deltas);
+        break;
       case 'TextInputClient.performAction':
         _currentConnection!._client.performAction(_toTextInputAction(args[1] as String));
         break;

packages/flutter/lib/src/widgets/editable_text.dart

@@ -1795,6 +1795,15 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   @override
   TextEditingValue get currentTextEditingValue => _value;
 
+  @override
+  void updateEditingValueWithDeltas(List<TextEditingDelta> textEditingDeltas) {
+    TextEditingValue value = _value;
+    for (final TextEditingDelta delta in textEditingDeltas) {
+      value = delta.apply(value);
+    }
+    updateEditingValue(value);
+  }
+
   @override
   void updateEditingValue(TextEditingValue value) {
     // This method handles text editing state updates from the platform text

packages/flutter/test/services/autofill_test.dart

@@ -106,6 +106,19 @@ class FakeAutofillClient implements TextInputClient, AutofillClient {
     latestMethodCall = 'updateEditingValue';
   }
 
+  @override
+  void updateEditingValueWithDeltas(List<TextEditingDelta> textEditingDeltas) {
+    TextEditingValue newEditingValue = currentTextEditingValue;
+
+    for (final TextEditingDelta delta in textEditingDeltas) {
+      newEditingValue = delta.apply(newEditingValue);
+    }
+
+    currentTextEditingValue = newEditingValue;
+
+    latestMethodCall = 'updateEditingValueWithDeltas';
+  }
+
   @override
   AutofillScope? currentAutofillScope;
 

packages/flutter/test/services/text_editing_delta_test.dart

@@ -0,0 +1,217 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:convert' show jsonDecode;
+
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('TextEditingDeltaInsertion', () {
+    test('Verify creation of insertion delta when inserting at a collapsed selection.', () {
+      const String jsonInsertionDelta = '{'
+          '"oldText": "",'
+          ' "deltaText": "let there be text",'
+          ' "deltaStart": 0,'
+          ' "deltaEnd": 0,'
+          ' "selectionBase": 17,'
+          ' "selectionExtent": 17,'
+          ' "selectionAffinity" : "TextAffinity.downstream" ,'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": -1,'
+          ' "composingExtent": -1}';
+      final TextEditingDeltaInsertion delta = TextEditingDelta.fromJSON(jsonDecode(jsonInsertionDelta) as Map<String, dynamic>) as TextEditingDeltaInsertion;
+      const TextRange expectedComposing = TextRange.empty;
+      const int expectedInsertionOffset = 0;
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 17);
+
+      expect(delta.oldText, '');
+      expect(delta.textInserted, 'let there be text');
+      expect(delta.insertionOffset, expectedInsertionOffset);
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+
+    test('Verify creation of insertion delta when inserting at end of composing region.', () {
+      const String jsonInsertionDelta = '{'
+          '"oldText": "hello worl",'
+          ' "deltaText": "world",'
+          ' "deltaStart": 6,'
+          ' "deltaEnd": 10,'
+          ' "selectionBase": 11,'
+          ' "selectionExtent": 11,'
+          ' "selectionAffinity" : "TextAffinity.downstream",'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": 6,'
+          ' "composingExtent": 11}';
+
+      final TextEditingDeltaInsertion delta = TextEditingDelta.fromJSON(jsonDecode(jsonInsertionDelta) as Map<String, dynamic>) as TextEditingDeltaInsertion;
+      const TextRange expectedComposing = TextRange(start: 6, end: 11);
+      const int expectedInsertionOffset = 10;
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 11);
+
+      expect(delta.oldText, 'hello worl');
+      expect(delta.textInserted, 'd');
+      expect(delta.insertionOffset, expectedInsertionOffset);
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+  });
+
+  group('TextEditingDeltaDeletion', () {
+    test('Verify creation of deletion delta when deleting.', () {
+      const String jsonDeletionDelta = '{'
+          '"oldText": "let there be text.",'
+          ' "deltaText": "",'
+          ' "deltaStart": 1,'
+          ' "deltaEnd": 2,'
+          ' "selectionBase": 1,'
+          ' "selectionExtent": 1,'
+          ' "selectionAffinity" : "TextAffinity.downstream" ,'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": -1,'
+          ' "composingExtent": -1}';
+
+      final TextEditingDeltaDeletion delta = TextEditingDelta.fromJSON(jsonDecode(jsonDeletionDelta) as Map<String, dynamic>) as TextEditingDeltaDeletion;
+      const TextRange expectedComposing = TextRange.empty;
+      const TextRange expectedDeletedRange = TextRange(start: 1, end: 2);
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 1);
+
+      expect(delta.oldText, 'let there be text.');
+      expect(delta.textDeleted, 'e');
+      expect(delta.deletedRange, expectedDeletedRange);
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+
+    test('Verify creation of deletion delta when deleting at end of composing region.', () {
+      const String jsonDeletionDelta = '{'
+          '"oldText": "hello world",'
+          ' "deltaText": "worl",'
+          ' "deltaStart": 6,'
+          ' "deltaEnd": 11,'
+          ' "selectionBase": 10,'
+          ' "selectionExtent": 10,'
+          ' "selectionAffinity" : "TextAffinity.downstream",'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": 6,'
+          ' "composingExtent": 10}';
+
+      final TextEditingDeltaDeletion delta = TextEditingDelta.fromJSON(jsonDecode(jsonDeletionDelta) as Map<String, dynamic>) as TextEditingDeltaDeletion;
+      const TextRange expectedComposing = TextRange(start: 6, end: 10);
+      const TextRange expectedDeletedRange = TextRange(start: 10, end: 11);
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 10);
+
+      expect(delta.oldText, 'hello world');
+      expect(delta.textDeleted, 'd');
+      expect(delta.deletedRange, expectedDeletedRange);
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+  });
+
+  group('TextEditingDeltaReplacement', () {
+    test('Verify creation of replacement delta when replacing with longer.', () {
+      const String jsonReplacementDelta = '{'
+          '"oldText": "hello worfi",'
+          ' "deltaText": "working",'
+          ' "deltaStart": 6,'
+          ' "deltaEnd": 11,'
+          ' "selectionBase": 13,'
+          ' "selectionExtent": 13,'
+          ' "selectionAffinity" : "TextAffinity.downstream",'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": 6,'
+          ' "composingExtent": 13}';
+
+      final TextEditingDeltaReplacement delta = TextEditingDelta.fromJSON(jsonDecode(jsonReplacementDelta) as Map<String, dynamic>) as TextEditingDeltaReplacement;
+      const TextRange expectedComposing = TextRange(start: 6, end: 13);
+      const TextRange expectedReplacedRange = TextRange(start: 6, end: 11);
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 13);
+
+      expect(delta.oldText, 'hello worfi');
+      expect(delta.textReplaced, 'worfi');
+      expect(delta.replacementText, 'working');
+      expect(delta.replacedRange, expectedReplacedRange);
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+
+    test('Verify creation of replacement delta when replacing with shorter.', () {
+      const String jsonReplacementDelta = '{'
+          '"oldText": "hello world",'
+          ' "deltaText": "h",'
+          ' "deltaStart": 6,'
+          ' "deltaEnd": 11,'
+          ' "selectionBase": 7,'
+          ' "selectionExtent": 7,'
+          ' "selectionAffinity" : "TextAffinity.downstream",'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": 6,'
+          ' "composingExtent": 7}';
+
+      final TextEditingDeltaReplacement delta = TextEditingDelta.fromJSON(jsonDecode(jsonReplacementDelta) as Map<String, dynamic>) as TextEditingDeltaReplacement;
+      const TextRange expectedComposing = TextRange(start: 6, end: 7);
+      const TextRange expectedReplacedRange = TextRange(start: 6, end: 11);
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 7);
+
+      expect(delta.oldText, 'hello world');
+      expect(delta.textReplaced, 'world');
+      expect(delta.replacementText, 'h');
+      expect(delta.replacedRange, expectedReplacedRange);
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+
+    test('Verify creation of replacement delta when replacing with same.', () {
+      const String jsonReplacementDelta = '{'
+          '"oldText": "hello world",'
+          ' "deltaText": "words",'
+          ' "deltaStart": 6,'
+          ' "deltaEnd": 11,'
+          ' "selectionBase": 11,'
+          ' "selectionExtent": 11,'
+          ' "selectionAffinity" : "TextAffinity.downstream",'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": 6,'
+          ' "composingExtent": 11}';
+
+      final TextEditingDeltaReplacement delta = TextEditingDelta.fromJSON(jsonDecode(jsonReplacementDelta) as Map<String, dynamic>) as TextEditingDeltaReplacement;
+      const TextRange expectedComposing = TextRange(start: 6, end: 11);
+      const TextRange expectedReplacedRange = TextRange(start: 6, end: 11);
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 11);
+
+      expect(delta.oldText, 'hello world');
+      expect(delta.textReplaced, 'world');
+      expect(delta.replacementText, 'words');
+      expect(delta.replacedRange, expectedReplacedRange);
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+  });
+
+  group('TextEditingDeltaNonTextUpdate', () {
+    test('Verify non text update delta created.', () {
+      const String jsonNonTextUpdateDelta = '{'
+          '"oldText": "hello world",'
+          ' "deltaText": "",'
+          ' "deltaStart": -1,'
+          ' "deltaEnd": -1,'
+          ' "selectionBase": 10,'
+          ' "selectionExtent": 10,'
+          ' "selectionAffinity" : "TextAffinity.downstream",'
+          ' "selectionIsDirectional": false,'
+          ' "composingBase": 6,'
+          ' "composingExtent": 11}';
+
+      final TextEditingDeltaNonTextUpdate delta = TextEditingDelta.fromJSON(jsonDecode(jsonNonTextUpdateDelta) as Map<String, dynamic>) as TextEditingDeltaNonTextUpdate;
+      const TextRange expectedComposing = TextRange(start: 6, end: 11);
+      const TextSelection expectedSelection = TextSelection.collapsed(offset: 10);
+
+      expect(delta.oldText, 'hello world');
+      expect(delta.selection, expectedSelection);
+      expect(delta.composing, expectedComposing);
+    });
+  });
+}

packages/flutter/test/services/text_input_test.dart

@@ -119,6 +119,7 @@ void main() {
       expect(configuration.inputType, TextInputType.text);
       expect(configuration.readOnly, false);
       expect(configuration.obscureText, false);
+      expect(configuration.enableDeltaModel, false);
       expect(configuration.autocorrect, true);
       expect(configuration.actionLabel, null);
       expect(configuration.textCapitalization, TextCapitalization.none);
@@ -450,6 +451,11 @@ class FakeTextInputClient implements TextInputClient {
     latestMethodCall = 'updateEditingValue';
   }
 
+  @override
+  void updateEditingValueWithDeltas(List<TextEditingDelta> textEditingDeltas) {
+    latestMethodCall = 'updateEditingValueWithDeltas';
+  }
+
   @override
   void updateFloatingCursor(RawFloatingCursorPoint point) {
     latestMethodCall = 'updateFloatingCursor';