error[E0308]: mismatched types
  --> $DIR/issue-5358-1.rs:16:9
   |
LL |         Either::Right(_) => {}
   |         ^^^^^^^^^^^^^^^^ expected struct `S`, found enum `Either`
   |
   = note: expected type `S`
              found type `Either<_, _>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.