Allow live reloading of built-in scripts

editor/plugins/script_editor_plugin.cpp

@@ -1079,8 +1079,12 @@ void ScriptEditor::_mark_built_in_scripts_as_saved(const String &p_parent_path)
 		}
 
 		Ref<Script> scr = edited_res;
-		if (scr.is_valid() && scr->is_tool()) {
+		if (scr.is_valid()) {
-			scr->reload(true);
+			trigger_live_script_reload(scr->get_path());
+
+			if (scr->is_tool()) {
+				scr->reload(true);
+			}
 		}
 	}
 }

modules/gdscript/gdscript.cpp

@@ -53,6 +53,7 @@
 #include "core/io/file_access_encrypted.h"
 #include "core/os/os.h"
 
+#include "scene/resources/packed_scene.h"
 #include "scene/scene_string_names.h"
 
 #ifdef TOOLS_ENABLED
@@ -2492,7 +2493,7 @@ void GDScriptLanguage::reload_scripts(const Array &p_scripts, bool p_soft_reload
 		SelfList<GDScript> *elem = script_list.first();
 		while (elem) {
 			// Scripts will reload all subclasses, so only reload root scripts.
-			if (elem->self()->is_root_script() && elem->self()->get_path().is_resource_file()) {
+			if (elem->self()->is_root_script() && !elem->self()->get_path().is_empty()) {
 				scripts.push_back(Ref<GDScript>(elem->self())); //cast to gdscript to avoid being erased by accident
 			}
 			elem = elem->next();
@@ -2560,7 +2561,19 @@ void GDScriptLanguage::reload_scripts(const Array &p_scripts, bool p_soft_reload
 	for (KeyValue<Ref<GDScript>, HashMap<ObjectID, List<Pair<StringName, Variant>>>> &E : to_reload) {
 		Ref<GDScript> scr = E.key;
 		print_verbose("GDScript: Reloading: " + scr->get_path());
-		scr->load_source_code(scr->get_path());
+		if (scr->is_built_in()) {
+			// TODO: It would be nice to do it more efficiently than loading the whole scene again.
+			Ref<PackedScene> scene = ResourceLoader::load(scr->get_path().get_slice("::", 0), "", ResourceFormatLoader::CACHE_MODE_IGNORE_DEEP);
+			ERR_CONTINUE(scene.is_null());
+
+			Ref<SceneState> state = scene->get_state();
+			Ref<GDScript> fresh = state->get_sub_resource(scr->get_path());
+			ERR_CONTINUE(fresh.is_null());
+
+			scr->set_source_code(fresh->get_source_code());
+		} else {
+			scr->load_source_code(scr->get_path());
+		}
 		scr->reload(p_soft_reload);
 
 		//restore state if saved

scene/resources/packed_scene.cpp

@@ -1880,6 +1880,16 @@ Vector<NodePath> SceneState::get_editable_instances() const {
 	return editable_instances;
 }
 
+Ref<Resource> SceneState::get_sub_resource(const String &p_path) {
+	for (const Variant &v : variants) {
+		const Ref<Resource> &res = v;
+		if (res.is_valid() && res->get_path() == p_path) {
+			return res;
+		}
+	}
+	return Ref<Resource>();
+}
+
 //add
 
 int SceneState::add_name(const StringName &p_name) {

scene/resources/packed_scene.h

@@ -195,6 +195,7 @@ public:
 	bool has_connection(const NodePath &p_node_from, const StringName &p_signal, const NodePath &p_node_to, const StringName &p_method, bool p_no_inheritance = false);
 
 	Vector<NodePath> get_editable_instances() const;
+	Ref<Resource> get_sub_resource(const String &p_path);
 
 	//build API