warning: value assigned to `x` is never read
  --> $DIR/issue-11958.rs:8:36
   |
LL |     let _thunk = Box::new(move|| { x = 2; });
   |                                    ^
   |
   = help: maybe it is overwritten before being read?
   = note: `#[warn(unused_assignments)]` on by default

warning: unused variable: `x`
  --> $DIR/issue-11958.rs:8:36
   |
LL |     let _thunk = Box::new(move|| { x = 2; });
   |                                    ^
   |
   = help: did you mean to capture by reference instead?
   = note: `#[warn(unused_variables)]` on by default

warning: 2 warnings emitted