error[E0594]: cannot assign to captured outer variable in an `FnMut` closure
  --> $DIR/issue-46023.rs:18:9
   |
LL |     let x = 0;
   |         - help: consider making `x` mutable: `mut x`
...
LL |         x = 1;
   |         ^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0594`.