{"ast_node_type":"other","tokens":[{"end":63,"kind":"keyword","start":0,"text":"//"}]}
    // 7 = 2-letter parameter + ": " + 1-letter variance + ", "
    let generics = GenericArgs::identity_for_item(tcx, def_id);
    let mut ret = String::with_capacity(2 + 7 * variances.len());