GDScript: Initialize static variables with defaults in-editor

When the script is not marked as `@tool` the static constructor is not
called and thus the variables contain `null` by default. But since some
validated operations requires a valid value, this would cause a crash.

This commit solves this by initializing the static variables with a
default value based on their types in the editor, when they are not
marked as `@tool`, so if some `@tool` script access them, they will have
a valid typed value, avoiding the crash.

modules/gdscript/gdscript.cpp

@@ -678,6 +678,27 @@ Error GDScript::_static_init() {
 
 #ifdef TOOLS_ENABLED
 
+void GDScript::_static_default_init() {
+	for (const KeyValue<StringName, MemberInfo> &E : static_variables_indices) {
+		const GDScriptDataType &type = E.value.data_type;
+		// Only initialize builtin types, which are not expected to be `null`.
+		if (!type.has_type || type.kind != GDScriptDataType::BUILTIN) {
+			continue;
+		}
+		if (type.builtin_type == Variant::ARRAY && type.has_container_element_type(0)) {
+			Array default_value;
+			const GDScriptDataType &element_type = type.get_container_element_type(0);
+			default_value.set_typed(element_type.builtin_type, element_type.native_type, element_type.script_type);
+			static_variables.write[E.value.index] = default_value;
+		} else {
+			Variant default_value;
+			Callable::CallError err;
+			Variant::construct(type.builtin_type, default_value, nullptr, 0, err);
+			static_variables.write[E.value.index] = default_value;
+		}
+	}
+}
+
 void GDScript::_save_old_static_data() {
 	old_static_variables_indices = static_variables_indices;
 	old_static_variables = static_variables;
@@ -841,6 +862,9 @@ Error GDScript::reload(bool p_keep_state) {
 #ifdef TOOLS_ENABLED
 	if (can_run && p_keep_state) {
 		_restore_old_static_data();
+	} else if (!can_run) {
+		// Initialize static variables with sane default values even if the constructor isn't called.
+		_static_default_init();
 	}
 #endif
 

modules/gdscript/gdscript.h

@@ -169,6 +169,9 @@ private:
 	GDScriptFunction *static_initializer = nullptr;
 
 	Error _static_init();
+#ifdef TOOLS_ENABLED
+	void _static_default_init(); // Initialize static variables with default values based on their types.
+#endif
 
 	int subclass_count = 0;
 	RBSet<Object *> instances;