error: this let-binding has unit value
  --> $DIR/ice-8821.rs:7:5
   |
LL |     let _: () = FN();
   |     ^^^^^^^^^^^^^^^^^ help: omit the `let` binding: `FN();`
   |
   = note: `-D clippy::let-unit-value` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::let_unit_value)]`

error: aborting due to previous error