{"ast_node_type":"variable","tokens":[{"end":59,"kind":"keyword","start":0,"text":"let"}]}
        let index_guess = ExpnIndex::from_u32(index_guess);
        debug_assert_eq!(ExpnId::from_hash(hash), None);
        let old_hash = self.root.expn_hashes.get(self, index_guess).map(|lazy| lazy.decode(self));