{"ast_node_type":"variable","tokens":[{"end":49,"kind":"keyword","start":0,"text":"let"}]}
        let mut first_tt = self.token_tree.len();
    fn subtree(&mut self, idx: usize, subtree: tt::iter::TtIter<'a, S>) {
        let n_tt = subtree.clone().count(); // FIXME: `count()` walks over the entire iterator.