error[E0594]: cannot assign to `n`, as it is not declared as mutable
  --> $DIR/unboxed-closures-mutate-upvar.rs:15:9
   |
LL |     let n = 0;
   |         - help: consider changing this to be mutable: `mut n`
LL |     let mut f = to_fn_mut(|| {
LL |         n += 1;
   |         ^^^^^^ cannot assign

error[E0594]: cannot assign to `n`, as it is not declared as mutable
  --> $DIR/unboxed-closures-mutate-upvar.rs:32:9
   |
LL |     let n = 0;
   |         - help: consider changing this to be mutable: `mut n`
...
LL |         n += 1;
   |         ^^^^^^ cannot assign

error[E0594]: cannot assign to `n`, as it is not declared as mutable
  --> $DIR/unboxed-closures-mutate-upvar.rs:46:9
   |
LL |     let n = 0;
   |         - help: consider changing this to be mutable: `mut n`
LL |     let mut f = to_fn(move || {
LL |         n += 1;
   |         ^^^^^^ cannot assign

error[E0594]: cannot assign to `n`, as it is a captured variable in a `Fn` closure
  --> $DIR/unboxed-closures-mutate-upvar.rs:53:9
   |
LL | fn to_fn<A:std::marker::Tuple,F:Fn<A>>(f: F) -> F { f }
   |                                           - change this to accept `FnMut` instead of `Fn`
...
LL |     let mut f = to_fn(move || {
   |                 ----- ------- in this closure
   |                 |
   |                 expects `Fn` instead of `FnMut`
LL |         n += 1;
   |         ^^^^^^ cannot assign

error: aborting due to 4 previous errors

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