Let RenderEditable.delete directly delete from the controller text. (#82215)

packages/flutter/lib/src/rendering/editable.dart

@@ -1011,9 +1011,9 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     return _getTextPositionVertical(offset, verticalOffset);
   }
 
-  // Deletes the current uncollapsed selection.
+  // Deletes the text within `selection` if it's non-empty.
   void _deleteSelection(TextSelection selection, SelectionChangedCause cause) {
-    assert(selection.isCollapsed == false);
+    assert(!selection.isCollapsed);
 
     if (_readOnly || !selection.isValid || selection.isCollapsed) {
       return;
@@ -1023,7 +1023,6 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     final String textBefore = selection.textBefore(text);
     final String textAfter = selection.textAfter(text);
     final int cursorPosition = math.min(selection.start, selection.end);
-
     final TextSelection newSelection = TextSelection.collapsed(offset: cursorPosition);
     _setTextEditingValue(
       TextEditingValue(text: textBefore + textAfter, selection: newSelection),
@@ -1031,6 +1030,48 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     );
   }
 
+  // Deletes the current non-empty selection.
+  //
+  // Operates on the text/selection contained in textSelectionDelegate, and does
+  // not depend on `RenderEditable.selection`.
+  //
+  // If the selection is currently non-empty, this method deletes the selected
+  // text and returns true. Otherwise this method does nothing and returns
+  // false.
+  bool _deleteNonEmptySelection(SelectionChangedCause cause) {
+    // TODO(LongCatIsLooong): remove this method from `RenderEditable`
+    // https://github.com/flutter/flutter/issues/80226.
+    assert(!readOnly);
+    final TextEditingValue controllerValue = textSelectionDelegate.textEditingValue;
+    final TextSelection selection = controllerValue.selection;
+    assert(selection.isValid);
+
+    if (selection.isCollapsed) {
+      return false;
+    }
+
+    final String textBefore = selection.textBefore(controllerValue.text);
+    final String textAfter = selection.textAfter(controllerValue.text);
+    final TextSelection newSelection = TextSelection.collapsed(offset: selection.start);
+    final TextRange composing = controllerValue.composing;
+    final TextRange newComposingRange = !composing.isValid || composing.isCollapsed
+      ? TextRange.empty
+      : TextRange(
+        start: composing.start - (composing.start - selection.start).clamp(0, selection.end - selection.start),
+        end: composing.end - (composing.end - selection.start).clamp(0, selection.end - selection.start),
+      );
+
+    _setTextEditingValue(
+      TextEditingValue(
+        text: textBefore + textAfter,
+        selection: newSelection,
+        composing: newComposingRange,
+      ),
+      cause,
+    );
+    return true;
+  }
+
   // Deletes the from the current collapsed selection to the start of the field.
   //
   // The given SelectionChangedCause indicates the cause of this change and
@@ -1089,12 +1130,15 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     );
   }
 
-  /// Deletes backwards from the current selection.
+  /// Deletes backwards from the selection in [textSelectionDelegate].
   ///
-  /// If the [selection] is collapsed, deletes a single character before the
+  /// This method operates on the text/selection contained in
+  /// [textSelectionDelegate], and does not depend on [selection].
+  ///
+  /// If the selection is collapsed, deletes a single character before the
   /// cursor.
   ///
-  /// If the [selection] is not collapsed, deletes the selection.
+  /// If the selection is not collapsed, deletes the selection.
   ///
   /// {@template flutter.rendering.RenderEditable.cause}
   /// The given [SelectionChangedCause] indicates the cause of this change and
@@ -1105,29 +1149,45 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
   ///
   ///   * [deleteForward], which is same but in the opposite direction.
   void delete(SelectionChangedCause cause) {
-    assert(_selection != null);
+    // `delete` does not depend on the text layout, and the boundary analysis is
+    // done using the `previousCharacter` method instead of ICU, we can keep
+    // deleting without having to layout the text. For this reason, we can
+    // directly delete the character before the caret in the controller.
+    //
+    // TODO(LongCatIsLooong): remove this method from RenderEditable.
+    // https://github.com/flutter/flutter/issues/80226.
+    final TextEditingValue controllerValue = textSelectionDelegate.textEditingValue;
+    final TextSelection selection = controllerValue.selection;
 
-    if (_readOnly || !_selection!.isValid) {
+    if (!selection.isValid || readOnly || _deleteNonEmptySelection(cause)) {
       return;
     }
 
-    if (!_selection!.isCollapsed) {
-      return _deleteSelection(_selection!, cause);
-    }
-
-    final String text = textSelectionDelegate.textEditingValue.text;
-    String textBefore = _selection!.textBefore(text);
+    assert(selection.isCollapsed);
+    final String textBefore = selection.textBefore(controllerValue.text);
     if (textBefore.isEmpty) {
       return;
     }
 
-    final int characterBoundary = previousCharacter(textBefore.length, textBefore);
-    textBefore = textBefore.substring(0, characterBoundary);
+    final String textAfter = selection.textAfter(controllerValue.text);
 
-    final String textAfter = _selection!.textAfter(text);
+    final int characterBoundary = previousCharacter(textBefore.length, textBefore);
     final TextSelection newSelection = TextSelection.collapsed(offset: characterBoundary);
+    final TextRange composing = controllerValue.composing;
+    assert(textBefore.length >= characterBoundary);
+    final TextRange newComposingRange = !composing.isValid || composing.isCollapsed
+      ? TextRange.empty
+      : TextRange(
+        start: composing.start - (composing.start - characterBoundary).clamp(0, textBefore.length - characterBoundary),
+        end: composing.end - (composing.end - characterBoundary).clamp(0, textBefore.length - characterBoundary),
+      );
+
     _setTextEditingValue(
-      TextEditingValue(text: textBefore + textAfter, selection: newSelection),
+      TextEditingValue(
+        text: textBefore.substring(0, characterBoundary) + textAfter,
+        selection: newSelection,
+        composing: newComposingRange,
+      ),
       cause,
     );
   }
@@ -1238,12 +1298,16 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     );
   }
 
-  /// Deletes in the foward direction from the current selection.
+  /// Deletes in the foward direction, from the current selection in
+  /// [textSelectionDelegate].
   ///
-  /// If the [selection] is collapsed, deletes a single character after the
+  /// This method operates on the text/selection contained in
+  /// [textSelectionDelegate], and does not depend on [selection].
+  ///
+  /// If the selection is collapsed, deletes a single character after the
   /// cursor.
   ///
-  /// If the [selection] is not collapsed, deletes the selection.
+  /// If the selection is not collapsed, deletes the selection.
   ///
   /// {@macro flutter.rendering.RenderEditable.cause}
   ///
@@ -1251,29 +1315,36 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
   ///
   ///   * [delete], which is same but in the opposite direction.
   void deleteForward(SelectionChangedCause cause) {
-    assert(_selection != null);
+    // TODO(LongCatIsLooong): remove this method from RenderEditable.
+    // https://github.com/flutter/flutter/issues/80226.
+    final TextEditingValue controllerValue = textSelectionDelegate.textEditingValue;
+    final TextSelection selection = controllerValue.selection;
 
-    if (_readOnly || !_selection!.isValid) {
+    if (!selection.isValid || _readOnly || _deleteNonEmptySelection(cause)) {
       return;
     }
 
-    if (!_selection!.isCollapsed) {
-      return _deleteSelection(_selection!, cause);
-    }
-
-    final String text = textSelectionDelegate.textEditingValue.text;
-    final String textBefore = _selection!.textBefore(text);
-    String textAfter = _selection!.textAfter(text);
-
+    assert(selection.isCollapsed);
+    final String textAfter = selection.textAfter(controllerValue.text);
     if (textAfter.isEmpty) {
       return;
     }
 
-    final int deleteCount = nextCharacter(0, textAfter);
-    textAfter = textAfter.substring(deleteCount);
-
+    final String textBefore = selection.textBefore(controllerValue.text);
+    final int characterBoundary = nextCharacter(0, textAfter);
+    final TextRange composing = controllerValue.composing;
+    final TextRange newComposingRange = !composing.isValid || composing.isCollapsed
+      ? TextRange.empty
+      : TextRange(
+        start: composing.start - (composing.start - textBefore.length).clamp(0, characterBoundary),
+        end: composing.end - (composing.end - textBefore.length).clamp(0, characterBoundary),
+      );
     _setTextEditingValue(
-      TextEditingValue(text: textBefore + textAfter, selection: _selection!),
+      TextEditingValue(
+        text: textBefore + textAfter.substring(characterBoundary),
+        selection: selection,
+        composing: newComposingRange,
+      ),
       cause,
     );
   }

packages/flutter/test/rendering/editable_test.dart

@@ -3463,6 +3463,86 @@ void main() {
       });
     });
   });
+
+  group('delete API implementations', () {
+    // Regression test for: https://github.com/flutter/flutter/issues/80226.
+    //
+    // This textSelectionDelegate has different text and selection from the
+    // render editable.
+    final FakeEditableTextState delegate = FakeEditableTextState();
+
+    late RenderEditable editable;
+
+    setUp(() {
+      editable = RenderEditable(
+        text: TextSpan(
+          text: 'A ' * 50,
+        ),
+        startHandleLayerLink: LayerLink(),
+        endHandleLayerLink: LayerLink(),
+        textDirection: TextDirection.ltr,
+        offset: ViewportOffset.fixed(0),
+        textSelectionDelegate: delegate,
+        selection: const TextSelection(baseOffset: 0, extentOffset: 50),
+      );
+
+      delegate.textEditingValue = const TextEditingValue(
+        text: 'BBB',
+        selection: TextSelection.collapsed(offset: 0),
+      );
+    });
+
+    void verifyDoesNotCrashWithInconsistentTextEditingValue(void Function(SelectionChangedCause) method) {
+      editable = RenderEditable(
+        text: TextSpan(
+          text: 'A ' * 50,
+        ),
+        startHandleLayerLink: LayerLink(),
+        endHandleLayerLink: LayerLink(),
+        textDirection: TextDirection.ltr,
+        offset: ViewportOffset.fixed(0),
+        textSelectionDelegate: delegate,
+        selection: const TextSelection(baseOffset: 0, extentOffset: 50),
+      );
+
+      layout(editable, constraints: BoxConstraints.loose(const Size(500.0, 500.0)));
+      dynamic error;
+      try {
+        method(SelectionChangedCause.tap);
+      } catch (e) {
+        error = e;
+      }
+      expect(error, isNull);
+    }
+
+    test('delete is not racy and handles composing region correctly', () {
+      delegate.textEditingValue = const TextEditingValue(
+        text: 'ABCDEF',
+        selection: TextSelection.collapsed(offset: 2),
+        composing: TextRange(start: 1, end: 6),
+      );
+      verifyDoesNotCrashWithInconsistentTextEditingValue(editable.delete);
+      final TextEditingValue textEditingValue = editable.textSelectionDelegate.textEditingValue;
+      expect(textEditingValue.text, 'ACDEF');
+      expect(textEditingValue.selection.isCollapsed, isTrue);
+      expect(textEditingValue.selection.baseOffset, 1);
+      expect(textEditingValue.composing, const TextRange(start: 1, end: 5));
+    });
+
+    test('deleteForward is not racy and handles composing region correctly', () {
+      delegate.textEditingValue = const TextEditingValue(
+        text: 'ABCDEF',
+        selection: TextSelection.collapsed(offset: 2),
+        composing: TextRange(start: 2, end: 6),
+      );
+      verifyDoesNotCrashWithInconsistentTextEditingValue(editable.deleteForward);
+      final TextEditingValue textEditingValue = editable.textSelectionDelegate.textEditingValue;
+      expect(textEditingValue.text, 'ABDEF');
+      expect(textEditingValue.selection.isCollapsed, isTrue);
+      expect(textEditingValue.selection.baseOffset, 2);
+      expect(textEditingValue.composing, const TextRange(start: 2, end: 5));
+    });
+  });
 }
 
 class _TestRenderEditable extends RenderEditable {