error: unnecessary allocation, use `&` instead
  --> $DIR/unused-allocation.rs:5:9
   |
LL |     _ = (box [1]).len();
   |         ^^^^^^^^^
   |
note: the lint level is defined here
  --> $DIR/unused-allocation.rs:2:9
   |
LL | #![deny(unused_allocation)]
   |         ^^^^^^^^^^^^^^^^^

error: unnecessary allocation, use `&` instead
  --> $DIR/unused-allocation.rs:6:9
   |
LL |     _ = Box::new([1]).len();
   |         ^^^^^^^^^^^^^

error: aborting due to 2 previous errors