error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
  --> $DIR/borrowck-loan-blocks-mut-uniq.rs:20:12
   |
LL |       borrow(&*v,
   |       -      --- immutable borrow occurs here
   |  _____|
   | |
LL | |            |w| { //~ ERROR cannot borrow `v` as mutable
   | |            ^^^ mutable borrow occurs here
LL | |             v = box 4;
   | |             - second borrow occurs due to use of `v` in closure
LL | |             assert_eq!(*v, 3);
LL | |             assert_eq!(*w, 4);
LL | |         })
   | |__________- borrow later used here

error: aborting due to previous error

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