error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
  --> $DIR/borrowck-loan-blocks-mut-uniq.rs:10:12
   |
LL |     borrow(&*v,
   |     ------ --- immutable borrow occurs here
   |     |
   |     immutable borrow later used by call
LL |            |w| {
   |            ^^^ mutable borrow occurs here
LL |             v = Box::new(4);
   |             - second borrow occurs due to use of `v` in closure

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0502`.