pub fn relate_args_with_variances<I, R>(
relation: &mut R,
ty_def_id: <I as Interner>::DefId,
variances: <I as Interner>::VariancesOf,
a_arg: <I as Interner>::GenericArgs,
b_arg: <I as Interner>::GenericArgs,
fetch_ty_for_diag: bool,
) -> Result<<I as Interner>::GenericArgs, TypeError<I>>where
I: Interner,
R: TypeRelation<I>,