{"ast_node_type":"variable","tokens":[{"end":68,"kind":"keyword","start":0,"text":"let"}]}
        let mut it = substs.iter().skip(parent_substs_len).cloned();
        let parent_substs_len = parent_substs.as_ref().map_or(0, |s| s.len(Interner));
        let builder = TyBuilder::subst_for_def(self.db, generic_def, parent_substs);