fix: Check for removing state while adding a child

[ufrshubham]

Description

Adding a child component to a parent which is in removing state, caused the lifecycle processing to go into a cyclic dependency when the parent is re-added. It happens because, while processing the lifecycle events, child's add event causes itself and the parent to get added to the blocked list. As a result of this, when the parent's add event is processed next, it gets skipped due to being in the blocked list.

This PR makes sure that the child does not get enqueued when parent is about to be removed.

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

NA

[denisgl7]

Thanks!

[spydon]

Can you describe in the PR description what the PR solves?

What happens when enqueeing an add when the parent is removing? Shouldn't it be reconciled at mounting still? 🤔

[ufrshubham]

What happens when enqueeing an add when the parent is removing? Shouldn't it be reconciled at mounting still? 🤔

Due to the sequence of the queue, the child's handleLifecycleEventAdd caused itself and its parent, both to get added to the blocked set here

flame/packages/flame/lib/src/components/core/component_tree_root.dart

Lines 109 to 110 in 892052b

	_blocked.add(identityHashCode(child));
	_blocked.add(identityHashCode(parent));

So in the next iteration when the parent's re-add event was encountered, it was getting skipped here:

flame/packages/flame/lib/src/components/core/component_tree_root.dart

Lines 85 to 88 in 892052b

	if (_blocked.contains(identityHashCode(child)) ||
	_blocked.contains(identityHashCode(parent))) {
	continue;
	}

[spydon]

Lgtm!

[ufrshubham]

Posting the MRE just in case anyone is interested:

class RemoveAddGame extends FlameGame with HasKeyboardHandlerComponents {
  final RectangleComponent rectangle = RectangleComponent(
    size: Vector2.all(100),
    position: Vector2.all(100),
  );

  @override
  Future<void> onLoad() async {
    await add(rectangle);
  }

  @override
  KeyEventResult onKeyEvent(
    KeyEvent event,
    Set<LogicalKeyboardKey> keysPressed,
  ) {
    if (event is! KeyDownEvent) {
      return KeyEventResult.handled;
    }

    if (event.logicalKey == LogicalKeyboardKey.keyA) {
      add(rectangle);
    } else if (event.logicalKey == LogicalKeyboardKey.keyR) {
      rectangle.removeFromParent();
    }

    rectangle.add(Component());

    return super.onKeyEvent(event, keysPressed);
  }
}