syntax_data: {"ast_node_type":"function","tokens":[{"end":52,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
context_after:         if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) = *t.kind() {