warning[E0507]: cannot move out of borrowed content
  --> $DIR/borrowck-migrate-to-nll.rs:35:17
   |
LL |                 (|| { let bar = foo; bar.take() })();
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot move out of borrowed content
   |
   = warning: This error has been downgraded to a warning for backwards compatibility with previous releases.
           It represents potential unsoundness in your code.
           This warning will become a hard error in the future.