error: unreachable pattern
  --> $DIR/slice-pattern-const-3.rs:28:9
   |
LL |         FOO => (), //~ ERROR unreachable pattern
   |         ^^^
   |
note: lint level defined here
  --> $DIR/slice-pattern-const-3.rs:1:9
   |
LL | #![deny(unreachable_patterns)]
   |         ^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error