{"ast_node_type":"function","tokens":[{"end":57,"kind":"keyword","start":0,"text":"pub"}]}
    pub fn const_at(&self, i: usize) -> ty::Const<'tcx> {
    #[track_caller]
        self[i].as_const().unwrap_or_else(|| bug!("expected const for param #{} in {:?}", i, self))