error: Output port index is unused. (Is the port on the correct side?)
 --> tests/compile-fail/surface_port_unused_both_parens.rs:6:32
  |
6 |         dst = (for_each(drop))[0];
  |                                ^

error: Input port index is unused. (Is the port on the correct side?)
 --> tests/compile-fail/surface_port_unused_both_parens.rs:5:16
  |
5 |         src = [0](source_iter(0..10));
  |                ^