{"ast_node_type":"other","tokens":[{"end":68,"kind":"keyword","start":0,"text":"impl_generics.params.insert(pointee_param_idx"}]}
    impl_generics.params.insert(pointee_param_idx + 1, extra_param);
    let extra_param = cx.typaram(span, Ident::new(sym::__S, span), self_bounds, None);