error[E0308]: mismatched types
  --> $DIR/issue-11515.rs:9:33
   |
LL |     let test = box Test { func: closure };
   |                                 ^^^^^^^ expected trait `FnMut`, found trait `Fn`
   |
   = note: expected struct `Box<(dyn FnMut() + 'static)>`
              found struct `Box<(dyn Fn() + 'static)>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.