_notification(PREDELETE) crashes when nodes are freed before RollbackSynchronizer

[domsl]

🐛 Description

When closing the game by forcing it closed (I think NOTIFICATION_WM_CLOSE_REQUEST) I get following errors:

E 0:00:04:422   property-pool.gd:53 @ get_subjects(): Attempted to assign an invalid (previously freed?) object instance into a 'TypedArray'.
  <C++ Error>   Method/function failed. Returning: false
  <C++ Source>  core/variant/container_type_validate.h:96 @ _internal_validate_object()
  <Stack Trace> property-pool.gd:53 @ get_subjects()
                rollback-synchronizer.gd:334 @ _notification()

Steps to reproduce

1. I am not sure how to reprodcue this in forrestbrawler, but in my game it is dependet on the position of RollbackSynchronizer in the tree (RBS last position in tree does not trigger bug, in the middle of player scene it does)
2. Run Game
3. Quit Game

Where the errors happens

Probably related to the reverse order

Ideas to fix?

Maybe filtering it with is_instance_valid() before iterating would be enoug?

[elementbound]

Thanks for the report @domsl!

Probably filtering would be suboptimal, since that would mean we don't deregister nodes from the RollbackSimulationServer, NetworkSynchronizationServer, etc.

It seems like one way around the order is instead of checking for NOTIFICATION_PREDELETE to check for the exit tree signal like so:

	if what == NOTIFICATION_EDITOR_PRE_SAVE:
		update_configuration_warnings()
	elif what == NOTIFICATION_EXIT_TREE and root.is_queued_for_deletion():
		for node in _sim_nodes + _state_properties.get_subjects() + _input_properties.get_subjects():
			# ...

This would probably not work with free() though, only with queue_free().