warning: struct is never constructed: `Foo`
  --> $DIR/issue-42479.rs:15:1
   |
LL | struct Foo {
   | ^^^^^^^^^^
   |
   = note: #[warn(dead_code)] on by default

warning: method is never used: `inside`
  --> $DIR/issue-42479.rs:20:5
   |
LL |     fn inside(&self) -> impl Iterator<Item = &i32> {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^