{"ast_node_type":"function","tokens":[{"end":77,"kind":"keyword","start":0,"text":"fn"}]}
    fn check_fn(&mut self, def_id: LocalDefId, decl: &'tcx hir::FnDecl<'_>) {
    /// types that have external ABIs, as these still need checked.
        let sig = self.cx.tcx.fn_sig(def_id).instantiate_identity();