error[E0387]: cannot assign to data in a captured outer variable in an `Fn` closure
  --> $DIR/unboxed-closures-mutated-upvar-from-fn-closure.rs:14:9
   |
LL |         counter += 1;
   |         ^^^^^^^^^^^^
   |
help: consider changing this closure to take self by mutable reference
  --> $DIR/unboxed-closures-mutated-upvar-from-fn-closure.rs:13:10
   |
LL |       call(|| {
   |  __________^
LL | |         counter += 1;
LL | |
LL | |
LL | |     });
   | |_____^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0387`.