warning: unused `offset_of` call that must be used
  --> $DIR/offset-of-must-use.rs:6:5
   |
LL |     core::mem::offset_of!((String,), 0);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the `offset_of` call produces a value
   |
note: the lint level is defined here
  --> $DIR/offset-of-must-use.rs:3:9
   |
LL | #![warn(unused)]
   |         ^^^^^^
   = note: `#[warn(unused_must_use)]` implied by `#[warn(unused)]`
   = note: this warning originates in the macro `core::mem::offset_of` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: 1 warning emitted