error: to use a constant of type `Cow<'_, str>` in a pattern, `Cow<'_, str>` must be annotated with `#[derive(PartialEq)]`
  --> $DIR/issue-89088.rs:16:9
   |
LL |         FOO => todo!(),
   |         ^^^
   |
   = note: the traits must be derived, manual `impl`s are not sufficient
   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details

error: aborting due to 1 previous error