{"ast_node_type":"variable","tokens":[{"end":61,"kind":"keyword","start":0,"text":"let"}]}
    let s_ty = cx.ty_ident(span, Ident::new(sym::__S, span));
    // example, instead of `MyType<'a, T>`, it will be `MyType<'a, __S>`.
    let mut alt_self_params = self_params;