Updating node properties in multi-scene inheritance

[keptsecret]

Opening as a draft to write down the different problems I'm finding about this issue.

This issue affects both opened and closed scenes. Making changes in a level 1 scene before opening a previously closed level 3 scene does not affect the same changes.
As far as I can tell this is happening in two places:

1. EditorData::_find_updated_instances is only checking the immediate scene it inherits from
2. When packing a scene to instantiate, SceneState::_parse_node is overwriting default values from the inherited scene with its own previous values, but only if the inheritance is more than one level.
   • For some reason, PropertyUtils::get_property_default_value is unable to find the value from the scene it inherits from, possibly due to construction of states_stack. This means one level inheritance is working fine because the following block tells it to not update the property when being instantiated (whether it's intended or not, I don't know).

godot/scene/resources/packed_scene.cpp

Lines 554 to 560 in 396def9

	if (!pinned_props.has(name)) {
	bool is_valid_default = false;
	Variant default_value = PropertyUtils::get_property_default_value(p_node, name, &is_valid_default, &states_stack, true);
	if (is_valid_default && !PropertyUtils::is_property_value_different(value, default_value)) {
	continue;
	}
	}

Current commit has a fix for 1) but only works if all inherited scenes are open. I haven't found a way to traverse back the inheritance tree that works with checking modified time. This was the attempt at going back the inheritance tree. Since SceneState that the node scene saves is unique and the modified time value is pulled from the scene file when instantiating a node from the SceneState, checking modified time didn't work.

bool EditorData::_find_updated_instances(Node *p_root, Node *p_node, Set<String> &checked_paths) {
	Ref<SceneState> ss;

	if (p_node == p_root) {
		ss = p_node->get_scene_inherited_state();
	} else if (!p_node->get_scene_file_path().is_empty()) {
		ss = p_node->get_scene_instance_state();
	}

	if (ss.is_valid()) {
		String path = ss->get_path();

		if (!checked_paths.has(path)) {
			uint64_t modified_time = FileAccess::get_modified_time(path);
			if (modified_time != ss->get_last_modified_time()) {
				return true; //external scene changed
			}

			checked_paths.insert(path);
		}

		Node *p = ss->instantiate(SceneState::GEN_EDIT_STATE_MAIN);
		bool found = _find_updated_instances(p, p, checked_paths);
		memdelete(p);
		if (found) {
			return true;
		}
	}

	for (int i = 0; i < p_node->get_child_count(); i++) {
		bool found = _find_updated_instances(p_root, p_node->get_child(i), checked_paths);
		if (found) {
			return true;
		}
	}

	return false;
}

Working on a fix for #60846

[keptsecret]

Crucially, current commit version doesn't update level 3 scene properly if level 2 scene is opened before it. Caused by how the modified time field in SceneStates are updated when instantiated, which will not trigger update when opened after.

[Rindbee]

Due to #57606, get_base_scene_state() gets the latest version of base scene state.