error: unconstrained generic constant
  --> $DIR/unify-op-with-fn-call.rs:28:12
   |
LL |     bar2::<{ std::ops::Add::add(N, N) }>();
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: try adding a `where` bound using this expression: `where [(); { std::ops::Add::add(N, N) }]:`

error: aborting due to previous error