Convert Object::cast_to() to the static version

Currently we rely on some undefined behavior when Object->cast_to() gets
called with a Null pointer. This used to work fine with GCC < 6 but
newer versions of GCC remove all codepaths in which the this pointer is
Null. However, the non-static cast_to() was supposed to be null safe.

This patch makes cast_to() Null safe and removes the now redundant Null
checks where they existed.

It is explained in this article: https://www.viva64.com/en/b/0226/

4 files changed, 13 insertions, 14 deletions

diff --git a/scene/resources/packed_scene.cpp b/scene/resources/packed_scene.cpp
index d7ea675a47..3ce44e2c31 100644
--- a/scene/resources/packed_scene.cpp
+++ b/scene/resources/packed_scene.cpp
@@ -151,18 +151,18 @@ Node *SceneState::instance(GenEditState p_edit_state) const {
 			//print_line("created");
 			//node belongs to this scene and must be created
 			Object *obj = ClassDB::instance(snames[n.type]);
-			if (!obj || !obj->cast_to<Node>()) {
+			if (!Object::cast_to<Node>(obj)) {
 				if (obj) {
 					memdelete(obj);
 					obj = NULL;
 				}
 				WARN_PRINT(String("Warning node of type " + snames[n.type].operator String() + " does not exist.").ascii().get_data());
 				if (n.parent >= 0 && n.parent < nc && ret_nodes[n.parent]) {
-					if (ret_nodes[n.parent]->cast_to<Spatial>()) {
+					if (Object::cast_to<Spatial>(ret_nodes[n.parent])) {
 						obj = memnew(Spatial);
-					} else if (ret_nodes[n.parent]->cast_to<Control>()) {
+					} else if (Object::cast_to<Control>(ret_nodes[n.parent])) {
 						obj = memnew(Control);
-					} else if (ret_nodes[n.parent]->cast_to<Node2D>()) {
+					} else if (Object::cast_to<Node2D>(ret_nodes[n.parent])) {
 						obj = memnew(Node2D);
 					}
 				}
@@ -172,7 +172,7 @@ Node *SceneState::instance(GenEditState p_edit_state) const {
 				}
 			}
 
-			node = obj->cast_to<Node>();
+			node = Object::cast_to<Node>(obj);
 
 		} else {
 			print_line("wtf class is disabled for: " + itos(n.type));
@@ -754,7 +754,7 @@ Error SceneState::_parse_connections(Node *p_owner, Node *p_node, Map<StringName
 			// only connections that originate or end into main saved scene are saved
 			// everything else is discarded
 
-			Node *target = c.target->cast_to<Node>();
+			Node *target = Object::cast_to<Node>(c.target);
 
 			if (!target) {
 				continue;
diff --git a/scene/resources/scene_format_text.cpp b/scene/resources/scene_format_text.cpp
index 49cd030a9a..0cccdc4fbf 100644
--- a/scene/resources/scene_format_text.cpp
+++ b/scene/resources/scene_format_text.cpp
@@ -239,7 +239,7 @@ Error ResourceInteractiveLoaderText::poll() {
 				return error;
 			}
 
-			Resource *r = obj->cast_to<Resource>();
+			Resource *r = Object::cast_to<Resource>(obj);
 			if (!r) {
 
 				error_text += "Can't create sub resource of type, because not a resource: " + type;
@@ -305,7 +305,7 @@ Error ResourceInteractiveLoaderText::poll() {
 			return error;
 		}
 
-		Resource *r = obj->cast_to<Resource>();
+		Resource *r = Object::cast_to<Resource>(obj);
 		if (!r) {
 
 			error_text += "Can't create sub resource of type, because not a resource: " + res_type;
diff --git a/scene/resources/shape.cpp b/scene/resources/shape.cpp
index 6be88374e5..d719aa5403 100644
--- a/scene/resources/shape.cpp
+++ b/scene/resources/shape.cpp
@@ -74,7 +74,7 @@ Ref<ArrayMesh> Shape::get_debug_mesh() {
 		arr.resize(Mesh::ARRAY_MAX);
 		arr[Mesh::ARRAY_VERTEX] = array;
 
-		SceneTree *st = OS::get_singleton()->get_main_loop()->cast_to<SceneTree>();
+		SceneTree *st = Object::cast_to<SceneTree>(OS::get_singleton()->get_main_loop());
 
 		debug_mesh_cache->add_surface_from_arrays(Mesh::PRIMITIVE_LINES, arr);
 
diff --git a/scene/resources/theme.cpp b/scene/resources/theme.cpp
index ac1bb105ac..c2c7c37762 100644
--- a/scene/resources/theme.cpp
+++ b/scene/resources/theme.cpp
@@ -1030,14 +1030,13 @@ RES ResourceFormatLoaderTheme::load(const String &p_path, const String &p_origin
 					ERR_FAIL_V(RES());
 				}
 
-				if (res->cast_to<StyleBox>()) {
-
+				if (Object::cast_to<StyleBox>(*res)) {
 					theme->set_stylebox(item, control, res);
-				} else if (res->cast_to<Font>()) {
+				} else if (Object::cast_to<Font>(*res)) {
 					theme->set_font(item, control, res);
-				} else if (res->cast_to<Font>()) {
+				} else if (Object::cast_to<Font>(*res)) {
 					theme->set_font(item, control, res);
-				} else if (res->cast_to<Texture>()) {
+				} else if (Object::cast_to<Texture>(*res)) {
 					theme->set_icon(item, control, res);
 				} else {
 					memdelete(f);