{"ast_node_type":"other","tokens":[{"end":1,"kind":"keyword","start":0,"text":"{"}]}
{
    F: for<'a, 'tcx> FnOnce(&ImplicitCtxt<'a, 'tcx>) -> R,
    with_context_opt(|opt_context| f(opt_context.expect("no ImplicitCtxt stored in tls")))