error[E0594]: cannot assign to `x`, as it is a captured variable in a `Fn` closure
  --> $DIR/wrong-closure-arg-suggestion-125325.rs:23:21
   |
LL |     fn assoc_func(&self, _f: impl Fn()) -> usize {
   |                              --------- change this to accept `FnMut` instead of `Fn`
...
LL |     s.assoc_func(|| x = ());
   |       --------------^^^^^^-
   |       |          |  |
   |       |          |  cannot assign
   |       |          in this closure
   |       expects `Fn` instead of `FnMut`

error[E0594]: cannot assign to `x`, as it is a captured variable in a `Fn` closure
  --> $DIR/wrong-closure-arg-suggestion-125325.rs:25:13
   |
LL | fn func(_f: impl Fn()) -> usize {
   |             --------- change this to accept `FnMut` instead of `Fn`
...
LL |     func(|| x = ())
   |     ---- -- ^^^^^^ cannot assign
   |     |    |
   |     |    in this closure
   |     expects `Fn` instead of `FnMut`

error: aborting due to 2 previous errors

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