fix: undo failed in a nested list in a special case

lib/src/core/document/node.dart

@@ -1,6 +1,7 @@
 import 'dart:collection';
 
 import 'package:appflowy_editor/appflowy_editor.dart';
+import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:nanoid/non_secure.dart';
 
@@ -144,6 +145,7 @@
 
     Log.editor.debug('insert Node $entry at path ${path + [index]}}');
 
+    entry._resetRelationshipIfNeeded();
     entry.parent = this;
 
     _cacheChildren = null;
@@ -189,9 +191,9 @@
   }
 
   @override
-  void unlink() {
+  bool unlink() {
     if (parent == null) {
-      return;
+      return false;
     }
     Log.editor.debug('delete Node $this from path $path');
     super.unlink();
@@ -200,6 +202,17 @@
 
     parent?.notifyListeners();
     parent = null;
+    return true;
+  }
+
+  // reset the relationship of the node before inserting it to another node
+  //  to ensure it is not in the tree
+  // otherwise, it will throw a state error
+  //  'Bad state: LinkedNode is already in a LinkedList'
+  void _resetRelationshipIfNeeded() {
+    if (parent != null || list != null) {
+      unlink();
+    }
   }
 
   @override
@@ -266,6 +279,30 @@
     final index = parent.children.indexOf(this);
     return parent._computePath([index, ...previous]);
   }
+
+  /// check the integrity of the document (for DEBUG only)
+  void checkDocumentIntegrity() {
+    // skip the root node
+    if (path.isNotEmpty) {
+      // if node is rendered in the tree, its parent should not be null
+      final errorMessage =
+          '''Please submit an issue to https://github.com/AppFlowy-IO/appflowy-editor/issues if you see this error!
+          node = ${toJson()}''';
+      assert(
+        parent != null,
+        errorMessage,
+      );
+      // also, its parent should contain this node
+      assert(
+        parent!.children.where((element) => element.id == id).length == 1,
+        errorMessage,
+      );
+    }
+
+    for (final child in children) {
+      child.checkDocumentIntegrity();
+    }
+  }
 }
 
 @Deprecated('Use Paragraph instead')

lib/src/editor_state.dart

@@ -211,6 +211,7 @@
   }
 
   Timer? _debouncedSealHistoryItemTimer;
+  final bool _enableCheckIntegrity = false;
 
   /// Apply the transaction to the state.
   ///
@@ -231,6 +232,11 @@
       return;
     }
 
+    // it's a time consuming task, only enable it if necessary.
+    if (_enableCheckIntegrity) {
+      document.root.checkDocumentIntegrity();
+    }
+
     final completer = Completer<void>();
 
     // broadcast to other users here, before applying the transaction

test/new/service/shortcuts/command_shortcut_events/undo_redo_command_test.dart

@@ -114,6 +114,84 @@ void main() async {
 
       await editor.dispose();
     });
+
+    // Before
+    // Welcome to AppFlowy 0| <- cursor here
+    //  Welcome to AppFlowy 0 - 1
+    //
+    // press enter key at the cursor position
+    // and then, press tab key to indent the empty line
+    // After
+    // Welcome to AppFlowy 0
+    //  | <- cursor here
+    //    Welcome to AppFlowy 0 - 1
+    //
+    // execute undo command twice
+    //
+    // then it should be like this
+    // Welcome to AppFlowy 0| <- cursor here
+    //  Welcome to AppFlowy 0 - 1
+    //
+    // after that, execute redo command twice
+    //
+    // Welcome to AppFlowy 0
+    //  | <- cursor here
+    //    Welcome to AppFlowy 0 - 1
+    testWidgets('Undo the nested list', (tester) async {
+      const text0 = 'Welcome to AppFlowy 0';
+      const text01 = 'Welcome to AppFlowy 0 - 1';
+
+      // Welcome to AppFlowy 0
+      // |Welcome to AppFlowy 0 - 1
+      final editor = tester.editor
+        ..addParagraph(initialText: text0)
+        ..addParagraph(initialText: text01);
+
+      await editor.startTesting();
+      await editor.updateSelection(
+        Selection.collapsed(Position(path: [1], offset: 0)),
+      );
+      await editor.pressKey(key: LogicalKeyboardKey.tab);
+
+      // Welcome to AppFlowy 0|
+      //  Welcome to AppFlowy 0 - 1
+      await editor.updateSelection(
+        Selection.collapsed(Position(path: [0], offset: text0.length)),
+      );
+      await editor.pressKey(character: '\n');
+      await editor.pressKey(key: LogicalKeyboardKey.tab);
+      await tester.pumpAndSettle();
+
+      expect(editor.nodeAtPath([0])!.delta!.toPlainText(), text0);
+      expect(editor.nodeAtPath([0, 0])!.delta!.toPlainText(), isEmpty);
+      expect(editor.nodeAtPath([0, 0, 0])!.delta!.toPlainText(), text01);
+
+      // first undo
+      await _pressUndoCommand(editor);
+      expect(editor.nodeAtPath([0])!.delta!.toPlainText(), text0);
+      expect(editor.nodeAtPath([1])!.delta!.toPlainText(), isEmpty);
+      expect(editor.nodeAtPath([1, 0])!.delta!.toPlainText(), text01);
+
+      // second undo
+      await _pressUndoCommand(editor);
+      expect(editor.nodeAtPath([0])!.delta!.toPlainText(), text0);
+      expect(editor.nodeAtPath([0, 0])!.delta!.toPlainText(), text01);
+
+      // first redo
+      await _pressRedoCommand(editor);
+      expect(editor.nodeAtPath([0])!.delta!.toPlainText(), text0);
+      expect(editor.nodeAtPath([0])!.children, isEmpty);
+      expect(editor.nodeAtPath([1])!.delta!.toPlainText(), isEmpty);
+      expect(editor.nodeAtPath([1, 0])!.delta!.toPlainText(), text01);
+
+      // second redo
+      await _pressRedoCommand(editor);
+      expect(editor.nodeAtPath([0])!.delta!.toPlainText(), text0);
+      expect(editor.nodeAtPath([1])!.delta!.toPlainText(), isEmpty);
+      expect(editor.nodeAtPath([1, 0])!.delta!.toPlainText(), text01);
+
+      await editor.dispose();
+    });
   });
 }