warning: method `foo` is never used
  --> $DIR/raw-fat-ptr.rs:35:16
   |
LL | trait Foo { fn foo(&self) -> usize; }
   |       ---      ^^^
   |       |
   |       method in this trait
   |
   = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: 1 warning emitted