error[E0597]: `books` does not live long enough
  --> $DIR/borrowck-escaping-closure-error-2.rs:11:17
   |
LL |     Box::new(|| books.push(4))
   |     ------------^^^^^---------
   |     |        |  |
   |     |        |  borrowed value does not live long enough
   |     |        value captured here
   |     borrow later used here
LL |
LL | }
   | - `books` dropped here while still borrowed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0597`.