Undo/redo (#96968)

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

@@ -205,6 +205,8 @@ class DefaultTextEditingShortcuts extends Shortcuts {
     const SingleActivator(LogicalKeyboardKey.keyC, control: true): CopySelectionTextIntent.copy,
     const SingleActivator(LogicalKeyboardKey.keyV, control: true): const PasteTextIntent(SelectionChangedCause.keyboard),
     const SingleActivator(LogicalKeyboardKey.keyA, control: true): const SelectAllTextIntent(SelectionChangedCause.keyboard),
+    const SingleActivator(LogicalKeyboardKey.keyZ, control: true): const UndoTextIntent(SelectionChangedCause.keyboard),
+    const SingleActivator(LogicalKeyboardKey.keyZ, shift: true, control: true): const RedoTextIntent(SelectionChangedCause.keyboard),
   };
 
   // The following key combinations have no effect on text editing on this
@@ -215,6 +217,7 @@ class DefaultTextEditingShortcuts extends Shortcuts {
   //   * Meta + C
   //   * Meta + V
   //   * Meta + A
+  //   * Meta + shift? + Z
   //   * Meta + shift? + arrow down
   //   * Meta + shift? + arrow left
   //   * Meta + shift? + arrow right
@@ -235,6 +238,7 @@ class DefaultTextEditingShortcuts extends Shortcuts {
   //   * Meta + C
   //   * Meta + V
   //   * Meta + A
+  //   * Meta + shift? + Z
   //   * Meta + shift? + arrow down
   //   * Meta + shift? + arrow left
   //   * Meta + shift? + arrow right
@@ -259,6 +263,7 @@ class DefaultTextEditingShortcuts extends Shortcuts {
     //   * Meta + C
     //   * Meta + V
     //   * Meta + A
+    //   * Meta + shift? + Z
     //   * Meta + shift? + arrow down
     //   * Meta + shift? + arrow left
     //   * Meta + shift? + arrow right
@@ -319,12 +324,15 @@ class DefaultTextEditingShortcuts extends Shortcuts {
     const SingleActivator(LogicalKeyboardKey.keyC, meta: true): CopySelectionTextIntent.copy,
     const SingleActivator(LogicalKeyboardKey.keyV, meta: true): const PasteTextIntent(SelectionChangedCause.keyboard),
     const SingleActivator(LogicalKeyboardKey.keyA, meta: true): const SelectAllTextIntent(SelectionChangedCause.keyboard),
+    const SingleActivator(LogicalKeyboardKey.keyZ, meta: true): const UndoTextIntent(SelectionChangedCause.keyboard),
+    const SingleActivator(LogicalKeyboardKey.keyZ, shift: true, meta: true): const RedoTextIntent(SelectionChangedCause.keyboard),
     // The following key combinations have no effect on text editing on this
     // platform:
     //   * End
     //   * Home
     //   * Control + shift? + end
     //   * Control + shift? + home
+    //   * Control + shift? + Z
   };
 
   // The following key combinations have no effect on text editing on this

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

@@ -30,6 +30,7 @@ import 'scroll_configuration.dart';
 import 'scroll_controller.dart';
 import 'scroll_physics.dart';
 import 'scrollable.dart';
+import 'shortcuts.dart';
 import 'text.dart';
 import 'text_editing_intents.dart';
 import 'text_selection.dart';
@@ -3138,6 +3139,11 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       cursor: widget.mouseCursor ?? SystemMouseCursors.text,
       child: Actions(
         actions: _actions,
+        child: _TextEditingHistory(
+          controller: widget.controller,
+          onTriggered: (TextEditingValue value) {
+            userUpdateTextEditingValue(value, SelectionChangedCause.keyboard);
+          },
           child: Focus(
             focusNode: widget.focusNode,
             includeSemantics: false,
@@ -3226,6 +3232,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
             ),
           ),
         ),
+      ),
     );
   }
 
@@ -4154,3 +4161,256 @@ class _CopySelectionAction extends ContextAction<CopySelectionTextIntent> {
   @override
   bool get isActionEnabled => state._value.selection.isValid && !state._value.selection.isCollapsed;
 }
+
+/// A void function that takes a [TextEditingValue].
+@visibleForTesting
+typedef TextEditingValueCallback = void Function(TextEditingValue value);
+
+/// Provides undo/redo capabilities for text editing.
+///
+/// Listens to [controller] as a [ValueNotifier] and saves relevant values for
+/// undoing/redoing. The cadence at which values are saved is a best
+/// approximation of the native behaviors of a hardware keyboard on Flutter's
+/// desktop platforms, as there are subtle differences between each of these
+/// platforms.
+///
+/// Listens to keyboard undo/redo shortcuts and calls [onTriggered] when a
+/// shortcut is triggered that would affect the state of the [controller].
+class _TextEditingHistory extends StatefulWidget {
+  /// Creates an instance of [_TextEditingHistory].
+  const _TextEditingHistory({
+    Key? key,
+    required this.child,
+    required this.controller,
+    required this.onTriggered,
+  }) : super(key: key);
+
+  /// The child widget of [_TextEditingHistory].
+  final Widget child;
+
+  /// The [TextEditingController] to save the state of over time.
+  final TextEditingController controller;
+
+  /// Called when an undo or redo causes a state change.
+  ///
+  /// If the state would still be the same before and after the undo/redo, this
+  /// will not be called. For example, receiving a redo when there is nothing
+  /// to redo will not call this method.
+  ///
+  /// It is also not called when the controller is changed for reasons other
+  /// than undo/redo.
+  final TextEditingValueCallback onTriggered;
+
+  @override
+  State<_TextEditingHistory> createState() => _TextEditingHistoryState();
+}
+
+class _TextEditingHistoryState extends State<_TextEditingHistory> {
+  final _UndoStack<TextEditingValue> _stack = _UndoStack<TextEditingValue>();
+  late final _Throttled<TextEditingValue> _throttledPush;
+  Timer? _throttleTimer;
+
+  // This duration was chosen as a best fit for the behavior of Mac, Linux,
+  // and Windows undo/redo state save durations, but it is not perfect for any
+  // of them.
+  static const Duration _kThrottleDuration = Duration(milliseconds: 500);
+
+  void _undo(UndoTextIntent intent) {
+    _update(_stack.undo());
+  }
+
+  void _redo(RedoTextIntent intent) {
+    _update(_stack.redo());
+  }
+
+  void _update(TextEditingValue? nextValue) {
+    if (nextValue == null) {
+      return;
+    }
+    if (nextValue.text == widget.controller.text) {
+      return;
+    }
+    widget.onTriggered(widget.controller.value.copyWith(
+      text: nextValue.text,
+      selection: nextValue.selection,
+    ));
+  }
+
+  void _push() {
+    if (widget.controller.value == TextEditingValue.empty) {
+      return;
+    }
+
+    _throttleTimer = _throttledPush(widget.controller.value);
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    _throttledPush = _throttle<TextEditingValue>(
+      duration: _kThrottleDuration,
+      function: _stack.push,
+    );
+    _push();
+    widget.controller.addListener(_push);
+  }
+
+  @override
+  void didUpdateWidget(_TextEditingHistory oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (widget.controller != oldWidget.controller) {
+      _stack.clear();
+      oldWidget.controller.removeListener(_push);
+      widget.controller.addListener(_push);
+    }
+  }
+
+  @override
+  void dispose() {
+    widget.controller.removeListener(_push);
+    _throttleTimer?.cancel();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Actions(
+      actions: <Type, Action<Intent>> {
+        UndoTextIntent: Action<UndoTextIntent>.overridable(context: context, defaultAction: CallbackAction<UndoTextIntent>(onInvoke: _undo)),
+        RedoTextIntent: Action<RedoTextIntent>.overridable(context: context, defaultAction: CallbackAction<RedoTextIntent>(onInvoke: _redo)),
+      },
+      child: widget.child,
+    );
+  }
+}
+
+/// A data structure representing a chronological list of states that can be
+/// undone and redone.
+class _UndoStack<T> {
+  /// Creates an instance of [_UndoStack].
+  _UndoStack();
+
+  final List<T> _list = <T>[];
+
+  // The index of the current value, or null if the list is emtpy.
+  late int _index;
+
+  /// Returns the current value of the stack.
+  T? get currentValue => _list.isEmpty ? null : _list[_index];
+
+  /// Add a new state change to the stack.
+  ///
+  /// Pushing identical objects will not create multiple entries.
+  void push(T value) {
+    if (_list.isEmpty) {
+      _index = 0;
+      _list.add(value);
+      return;
+    }
+
+    assert(_index < _list.length && _index >= 0);
+
+    if (value == currentValue) {
+      return;
+    }
+
+    // If anything has been undone in this stack, remove those irrelevant states
+    // before adding the new one.
+    if (_index != null && _index != _list.length - 1) {
+      _list.removeRange(_index + 1, _list.length);
+    }
+    _list.add(value);
+    _index = _list.length - 1;
+  }
+
+  /// Returns the current value after an undo operation.
+  ///
+  /// An undo operation moves the current value to the previously pushed value,
+  /// if any.
+  ///
+  /// Iff the stack is completely empty, then returns null.
+  T? undo() {
+    if (_list.isEmpty) {
+      return null;
+    }
+
+    assert(_index < _list.length && _index >= 0);
+
+    if (_index != 0) {
+      _index = _index - 1;
+    }
+
+    return currentValue;
+  }
+
+  /// Returns the current value after a redo operation.
+  ///
+  /// A redo operation moves the current value to the value that was last
+  /// undone, if any.
+  ///
+  /// Iff the stack is completely empty, then returns null.
+  T? redo() {
+    if (_list.isEmpty) {
+      return null;
+    }
+
+    assert(_index < _list.length && _index >= 0);
+
+    if (_index < _list.length - 1) {
+      _index = _index + 1;
+    }
+
+    return currentValue;
+  }
+
+  /// Remove everything from the stack.
+  void clear() {
+    _list.clear();
+    _index = -1;
+  }
+
+  @override
+  String toString() {
+    return '_UndoStack $_list';
+  }
+}
+
+/// A function that can be throttled with the throttle function.
+typedef _Throttleable<T> = void Function(T currentArg);
+
+/// A function that has been throttled by [_throttle].
+typedef _Throttled<T> = Timer Function(T currentArg);
+
+/// Returns a _Throttled that will call through to the given function only a
+/// maximum of once per duration.
+///
+/// Only works for functions that take exactly one argument and return void.
+_Throttled<T> _throttle<T>({
+  required Duration duration,
+  required _Throttleable<T> function,
+  // If true, calls at the start of the timer.
+  bool leadingEdge = false,
+}) {
+  Timer? timer;
+  bool calledDuringTimer = false;
+  late T arg;
+
+  return (T currentArg) {
+    arg = currentArg;
+    if (timer != null) {
+      calledDuringTimer = true;
+      return timer!;
+    }
+    if (leadingEdge) {
+      function(arg);
+    }
+    calledDuringTimer = false;
+    timer = Timer(duration, () {
+      if (!leadingEdge || calledDuringTimer) {
+        function(arg);
+      }
+      timer = null;
+    });
+    return timer!;
+  };
+}

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

@@ -231,6 +231,16 @@ class PasteTextIntent extends Intent {
   final SelectionChangedCause cause;
 }
 
+/// An [Intent] that represents a user interaction that attempts to go back to
+/// the previous editing state.
+class RedoTextIntent extends Intent {
+  /// Creates a [RedoTextIntent].
+  const RedoTextIntent(this.cause);
+
+  /// {@macro flutter.widgets.TextEditingIntents.cause}
+  final SelectionChangedCause cause;
+}
+
 /// An [Intent] that represents a user interaction that attempts to modify the
 /// current [TextEditingValue] in an input field.
 class ReplaceTextIntent extends Intent {
@@ -250,10 +260,20 @@ class ReplaceTextIntent extends Intent {
   final SelectionChangedCause cause;
 }
 
+/// An [Intent] that represents a user interaction that attempts to go back to
+/// the previous editing state.
+class UndoTextIntent extends Intent {
+  /// Creates an [UndoTextIntent].
+  const UndoTextIntent(this.cause);
+
+  /// {@macro flutter.widgets.TextEditingIntents.cause}
+  final SelectionChangedCause cause;
+}
+
 /// An [Intent] that represents a user interaction that attempts to change the
 /// selection in an input field.
 class UpdateSelectionIntent extends Intent {
-  /// Creates a [UpdateSelectionIntent].
+  /// Creates an [UpdateSelectionIntent].
   const UpdateSelectionIntent(this.currentTextEditingValue, this.newSelection, this.cause);
 
   /// The [TextEditingValue] that this [Intent]'s action should perform on.