warning: method `dummy` is never used
  --> $DIR/macro-self-mutability-7911.rs:8:8
   |
LL | trait FooBar {
   |       ------ method in this trait
LL |     fn dummy(&self) { }
   |        ^^^^^
   |
   = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: 1 warning emitted