Add `undoStackModifier` to `UndoHistory` (#138674)

This change adds a feature to `UndoHistory` that allows the user to modify the value being pushed onto the undo stack.

This is used by the framework to ignore the composing region when pushing history entries to the Undo stack on Android. This is so an undo does not trigger an input connection restart by the Android TextInputPlugin, which occurs when the framework changes the composing region. This is also the native platform behavior observed in Google Keep app on Android, where doing an undo during composing reverts to the previous state but with composing inactive and a subsequent redo does not bring back the composing region.

Fixes #130881
Partial fix for #134398

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

@@ -4823,6 +4823,13 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
                 return oldValue.text != newValue.text || oldValue.composing != newValue.composing;
               },
+              undoStackModifier: (TextEditingValue value) {
+                // On Android we should discard the composing region when pushing
+                // a new entry to the undo stack. This prevents the TextInputPlugin
+                // from restarting the input on every undo/redo when the composing
+                // region is changed by the framework.
+                return defaultTargetPlatform == TargetPlatform.android ? value.copyWith(composing: TextRange.empty) : value;
+              },
               focusNode: widget.focusNode,
               controller: widget.undoController,
               child: Focus(

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

@@ -32,6 +32,7 @@ class UndoHistory<T> extends StatefulWidget {
     required this.value,
     required this.onTriggered,
     required this.focusNode,
+    this.undoStackModifier,
     this.controller,
     required this.child,
   });
@@ -43,6 +44,14 @@ class UndoHistory<T> extends StatefulWidget {
   /// the undo stack.
   final bool Function(T? oldValue, T newValue)? shouldChangeUndoStack;
 
+  /// Called right before a new entry is pushed to the undo stack.
+  ///
+  /// The value returned from this method will be pushed to the stack instead
+  /// of the original value.
+  ///
+  /// If null then the original value will always be pushed to the stack.
+  final T Function(T value)? undoStackModifier;
+
   /// 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
@@ -178,9 +187,14 @@ class UndoHistoryState<T> extends State<UndoHistory<T>> with UndoManagerClient {
       return;
     }
 
-    _lastValue = widget.value.value;
+    final T nextValue = widget.undoStackModifier?.call(widget.value.value) ?? widget.value.value;
+    if (nextValue == _lastValue) {
+      return;
+    }
+
+    _lastValue = nextValue;
 
-    _throttleTimer = _throttledPush(widget.value.value);
+    _throttleTimer = _throttledPush(nextValue);
   }
 
   void _handleFocus() {

packages/flutter/test/widgets/editable_text_test.dart

@@ -13127,6 +13127,13 @@ void main() {
     Future<void> sendUndo(WidgetTester tester) => sendUndoRedo(tester);
     Future<void> sendRedo(WidgetTester tester) => sendUndoRedo(tester, true);
 
+    TextEditingValue emptyComposingOnAndroid(TextEditingValue value) {
+      if (defaultTargetPlatform == TargetPlatform.android) {
+        return value.copyWith(composing: TextRange.empty);
+      }
+      return value;
+    }
+
     Widget boilerplate() {
       return MaterialApp(
         home: EditableText(
@@ -13330,14 +13337,14 @@ void main() {
 
       // Undo first insertion.
       await sendUndo(tester);
-      expect(controller.value, composingStep2);
+      expect(controller.value, emptyComposingOnAndroid(composingStep2));
 
       // Waiting for the throttling between undos should have no effect.
       await tester.pump(const Duration(milliseconds: 500));
 
       // Undo second insertion.
       await sendUndo(tester);
-      expect(controller.value, composingStep1);
+      expect(controller.value, emptyComposingOnAndroid(composingStep1));
 
     // On web, these keyboard shortcuts are handled by the browser.
     }, variant: TargetPlatformVariant.only(TargetPlatform.android), skip: kIsWeb); // [intended]
@@ -13899,7 +13906,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 nihao',
-          composing: TextRange(start: 2, end: 7),
           selection: TextSelection.collapsed(offset: 7),
         ),
       );
@@ -13909,7 +13915,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 ni',
-          composing: TextRange(start: 2, end: 4),
           selection: TextSelection.collapsed(offset: 4),
         ),
       );
@@ -13927,7 +13932,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 ni',
-          composing: TextRange(start: 2, end: 4),
           selection: TextSelection.collapsed(offset: 4),
         ),
       );
@@ -13936,7 +13940,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 nihao',
-          composing: TextRange(start: 2, end: 7),
           selection: TextSelection.collapsed(offset: 7),
         ),
       );
@@ -13962,7 +13965,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 nihao',
-          composing: TextRange(start: 2, end: 7),
           selection: TextSelection.collapsed(offset: 7),
         ),
       );
@@ -13971,7 +13973,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 ni',
-          composing: TextRange(start: 2, end: 4),
           selection: TextSelection.collapsed(offset: 4),
         ),
       );
@@ -14011,7 +14012,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 ni',
-          composing: TextRange(start: 2, end: 4),
           selection: TextSelection.collapsed(offset: 4),
         ),
       );
@@ -14020,7 +14020,6 @@ void main() {
         controller.value,
         const TextEditingValue(
           text: '1 nihao',
-          composing: TextRange(start: 2, end: 7),
           selection: TextSelection.collapsed(offset: 7),
         ),
       );
@@ -14138,10 +14137,12 @@ void main() {
         case TargetPlatform.android:
           expect(
             controller.value,
-            const TextEditingValue(
-              text: '1 2 ni',
-              composing: TextRange(start: 4, end: 6),
-              selection: TextSelection.collapsed(offset: 6),
+            emptyComposingOnAndroid(
+              const TextEditingValue(
+                text: '1 2 ni',
+                composing: TextRange(start: 4, end: 6),
+                selection: TextSelection.collapsed(offset: 6),
+              ),
             ),
           );
         // Composing changes are ignored on all other platforms.
@@ -14195,10 +14196,12 @@ void main() {
         case TargetPlatform.android:
           expect(
             controller.value,
-            const TextEditingValue(
-              text: '1 2 ni',
-              composing: TextRange(start: 4, end: 6),
-              selection: TextSelection.collapsed(offset: 6),
+            emptyComposingOnAndroid(
+              const TextEditingValue(
+                text: '1 2 ni',
+                composing: TextRange(start: 4, end: 6),
+                selection: TextSelection.collapsed(offset: 6),
+              ),
             ),
           );
         // Composing changes are ignored on all other platforms.