syntax_data: {"ast_node_type":"variable","tokens":[{"end":86,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let ty::FnPtr(sig_tys, _) = coroutine_captures_by_ref_ty.kind() else {
context_before:             ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
context_after:                     panic!();