error: constant of non-structural type `Vec<()>` in a pattern
  --> $DIR/implicit-const-deref.rs:15:9
   |
LL | const EMPTY: Vec<()> = Vec::new();
   | -------------------- constant defined here
...
LL |         EMPTY => {}
   |         ^^^^^ constant of non-structural type
  --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
   |
   = note: `Vec<()>` must be annotated with `#[derive(PartialEq)]` to be usable in patterns
   |
   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details

error: aborting due to 1 previous error