error: this pattern takes a reference on something that is being de-referenced
  --> $DIR/needless_borrowed_ref.rs:7:34
   |
LL |     let _ = v.iter_mut().filter(|&ref a| a.is_empty());
   |                                  ^^^^^^ help: try removing the `&ref` part and just keep: `a`
   |
   = note: `-D clippy::needless-borrowed-reference` implied by `-D warnings`

error: aborting due to previous error

