warning: unused variable: `a`
  --> $DIR/attributes-included.rs:17:9
   |
LL |     let a: i32 = "foo";
   |         ^ help: if this is intentional, prefix it with an underscore: `_a`
   |
note: the lint level is defined here
  --> $DIR/attributes-included.rs:4:9
   |
LL | #![warn(unused)]
   |         ^^^^^^
   = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`

warning: 1 warning emitted