Add ability to export Node pointers as NodePaths

This PR implements:
* A new hint: PROPERTY_HINT_NODE_TYPE for variant type OBJECT, which can take specific node types as hint string.
* The editor will show it as a node path, but will set it as a pointer to a node from the current scene if you select a path.
* When scene is saved, the node path is saved, then restored as a pointer.

NOTE: This is a proof of concept and this approach will most likely not work. The reason if that, if the node referenced is deleted, then when trying to edit this the node will become invalid.

Potential workarounds: Since this uses the Variant API, it should obtain the pointer from the Variant object ID. Yet, this would either only really work in GDScript or it would need to be implemented with workarounds in every language.
Alternative ways to make this work: Nodes could export an additional property with a node path (like for which_node, it could be which_node_path).
Another alternative: Path editing could happen as a hidden metadata (ignoring the pointer).

1 files changed, 15 insertions, 6 deletions

diff --git a/editor/editor_inspector.cpp b/editor/editor_inspector.cpp
index 0f31e3e7bb..2bf0cd2f20 100644
--- a/editor/editor_inspector.cpp
+++ b/editor/editor_inspector.cpp
@@ -406,7 +406,7 @@ Object *EditorProperty::get_edited_object() {
 	return object;
 }
 
-StringName EditorProperty::get_edited_property() {
+StringName EditorProperty::get_edited_property() const {
 	return property;
 }
 
@@ -437,16 +437,20 @@ Variant EditorPropertyRevert::get_property_revert_value(Object *p_object, const
 	return PropertyUtils::get_property_default_value(p_object, p_property, r_is_valid);
 }
 
-bool EditorPropertyRevert::can_property_revert(Object *p_object, const StringName &p_property) {
+bool EditorPropertyRevert::can_property_revert(Object *p_object, const StringName &p_property, const Variant *p_custom_current_value) {
 	bool is_valid_revert = false;
 	Variant revert_value = EditorPropertyRevert::get_property_revert_value(p_object, p_property, &is_valid_revert);
 	if (!is_valid_revert) {
 		return false;
 	}
-	Variant current_value = p_object->get(p_property);
+	Variant current_value = p_custom_current_value ? *p_custom_current_value : p_object->get(p_property);
 	return PropertyUtils::is_property_value_different(current_value, revert_value);
 }
 
+StringName EditorProperty::_get_revert_property() const {
+	return property;
+}
+
 void EditorProperty::update_revert_and_pin_status() {
 	if (property == StringName()) {
 		return; //no property, so nothing to do
@@ -458,7 +462,8 @@ void EditorProperty::update_revert_and_pin_status() {
 		CRASH_COND(!node);
 		new_pinned = node->is_property_pinned(property);
 	}
-	bool new_can_revert = EditorPropertyRevert::can_property_revert(object, property) && !is_read_only();
+	Variant current = object->get(_get_revert_property());
+	bool new_can_revert = EditorPropertyRevert::can_property_revert(object, property, &current) && !is_read_only();
 
 	if (new_can_revert != can_revert || new_pinned != pinned) {
 		can_revert = new_can_revert;
@@ -717,11 +722,15 @@ void EditorProperty::set_bottom_editor(Control *p_control) {
 	bottom_editor = p_control;
 }
 
+Variant EditorProperty::_get_cache_value(const StringName &p_prop, bool &r_valid) const {
+	return object->get(p_prop, &r_valid);
+}
+
 bool EditorProperty::is_cache_valid() const {
 	if (object) {
 		for (const KeyValue<StringName, Variant> &E : cache) {
 			bool valid;
-			Variant value = object->get(E.key, &valid);
+			Variant value = _get_cache_value(E.key, valid);
 			if (!valid || value != E.value) {
 				return false;
 			}
@@ -733,7 +742,7 @@ void EditorProperty::update_cache() {
 	cache.clear();
 	if (object && property != StringName()) {
 		bool valid;
-		Variant value = object->get(property, &valid);
+		Variant value = _get_cache_value(property, valid);
 		if (valid) {
 			cache[property] = value;
 		}