Fix gdscript analyzer error when instantiating EditorPlugins.

Editor code is not instantiable outside of the editor
(https://github.com/godotengine/godot/blob/1d14c054a12dacdc193b589e4afb0ef319ee2aae/core/object/class_db.cpp#L369).
This is fine for editor plugins and the like, but the GDScript analyzer
balks at it, causing F5 runs to fail: godotengine#73525.

Instead, we really just want to know if the type is abstract - so add
a new ClassDB method to check that and nothing else.

Update core/object/class_db.cpp

Apply code review comments

Co-Authored-By: Bryce <[email protected]>

Author: baptr

core/object/class_db.cpp

@@ -671,6 +671,21 @@ bool ClassDB::can_instantiate(const StringName &p_class) {
 	return (!ti->disabled && ti->creation_func != nullptr && !(ti->gdextension && !ti->gdextension->create_instance));
 }
 
+bool ClassDB::is_abstract(const StringName &p_class) {
+	OBJTYPE_RLOCK;
+
+	ClassInfo *ti = classes.getptr(p_class);
+	if (!ti) {
+		if (!ScriptServer::is_global_class(p_class)) {
+			ERR_FAIL_V_MSG(false, "Cannot get class '" + String(p_class) + "'.");
+		}
+		String path = ScriptServer::get_global_class_path(p_class);
+		Ref<Script> scr = ResourceLoader::load(path);
+		return scr.is_valid() && scr->is_valid() && scr->is_abstract();
+	}
+	return ti->creation_func == nullptr && (!ti->gdextension || ti->gdextension->create_instance == nullptr);
+}
+
 bool ClassDB::is_virtual(const StringName &p_class) {
 	OBJTYPE_RLOCK;
 

core/object/class_db.h

@@ -287,6 +287,7 @@ class ClassDB {
 	static bool class_exists(const StringName &p_class);
 	static bool is_parent_class(const StringName &p_class, const StringName &p_inherits);
 	static bool can_instantiate(const StringName &p_class);
+	static bool is_abstract(const StringName &p_class);
 	static bool is_virtual(const StringName &p_class);
 	static Object *instantiate(const StringName &p_class);
 	static Object *instantiate_no_placeholders(const StringName &p_class);

modules/gdscript/gdscript_analyzer.cpp

@@ -5180,7 +5180,7 @@ bool GDScriptAnalyzer::get_function_signature(GDScriptParser::Node *p_source, bo
 		if (!class_exists(base_native)) {
 			push_error(vformat("Native class %s used in script doesn't exist or isn't exposed.", base_native), p_source);
 			return false;
-		} else if (p_is_constructor && !ClassDB::can_instantiate(base_native)) {
+		} else if (p_is_constructor && ClassDB::is_abstract(base_native)) {
 			if (p_base_type.kind == GDScriptParser::DataType::CLASS) {
 				push_error(vformat(R"(Class "%s" cannot be constructed as it is based on abstract native class "%s".)", p_base_type.class_type->fqcn.get_file(), base_native), p_source);
 			} else if (p_base_type.kind == GDScriptParser::DataType::SCRIPT) {