{"ast_node_type":"variable","tokens":[{"end":87,"kind":"keyword","start":0,"text":"//"}]}
            // "let &x = &dyn SomeTrait" or "let box x = Box<dyn SomeTrait>", an error.
            // This is "x = dyn SomeTrait" being reduced from
            let type_str = self.ty_to_string(expected);