src/test/ui/closures/closure-immutable-outer-variable.stderr

   1 error[E0594]: cannot assign to `y`, as it is not declared as mutable
   2   --> $DIR/closure-immutable-outer-variable.rs:11:26
   3    |
   4 LL |     let y = true;
   5    |         - help: consider changing this to be mutable: `mut y`
   6 LL |     foo(Box::new(move || y = !y) as Box<_>);
   7    |                          ^^^^^^ cannot assign
   8
   9 error: aborting due to previous error
  10
  11 For more information about this error, try `rustc --explain E0594`.