{"ast_node_type":"variable","tokens":[{"end":53,"kind":"keyword","start":0,"text":"let"}]}
            let from = unpack_option_like(tcx, from);
            // `Option<typeof(function)>` to present a clearer error.
            if let (&ty::FnDef(..), SizeSkeleton::Known(size_to, _)) = (from.kind(), sk_to)