error: to use a constant of type `B` in a pattern, `B` must be annotated with `#[derive(PartialEq, Eq)]`
  --> $DIR/match-nonempty-array-forbidden-without-eq.rs:16:9
   |
LL |         FOO => { }
   |         ^^^
   |
   = note: the traits must be derived, manual `impl`s are not sufficient
   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details

error: aborting due to previous error