error[E0369]: cannot add `{integer}` to `Box<isize>`
  --> $DIR/issue-14915.rs:6:22
   |
LL |     println!("{}", x + 1);
   |                    - ^ - {integer}
   |                    |
   |                    Box<isize>

error: aborting due to previous error

For more information about this error, try `rustc --explain E0369`.