error[E0806]: `y` has 1 parameter but #[foo] requires it to have 0
  --> $DIR/E0806.rs:7:9
   |
LL | fn x();
   | ------- requires 0 parameters
LL |
LL | #[foo]
   | ------ required because of this attribute
LL | fn y(a: u64) -> u64 {
   |         ^^^ expected 0 parameters, found 1

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0806`.
