{"ast_node_type":"variable","tokens":[{"end":30,"kind":"keyword","start":0,"text":"let"}]}
            let parent_subst =
            let parent_len = generics(self.db, def).parent_generics().map_or(0, |g| g.len_self());
                Substitution::from_iter(Interner, subst.iter(Interner).take(parent_len));