error[E0499]: cannot borrow `f` as mutable more than once at a time
  --> $DIR/borrowck-call-is-borrow-issue-12224.rs:22:16
   |
LL |     f(Box::new(|| {
   |     -          ^^ second mutable borrow occurs here
   |     |
   |     first mutable borrow occurs here
23 |     //~^ ERROR: cannot borrow `f` as mutable more than once
LL |         f((Box::new(|| {})))
   |         - borrow occurs due to use of `f` in closure
LL |     }));
   |       - first borrow ends here

error[E0596]: cannot borrow immutable borrowed content `*f` as mutable
  --> $DIR/borrowck-call-is-borrow-issue-12224.rs:35:5
   |
LL | fn test2<F>(f: &F) where F: FnMut() {
   |                -- use `&mut F` here to make mutable
LL |     (*f)();
   |     ^^^^ cannot borrow as mutable

error[E0596]: cannot borrow `Box` content `*f.f` of immutable binding as mutable
  --> $DIR/borrowck-call-is-borrow-issue-12224.rs:44:5
   |
LL | fn test4(f: &Test) {
   |             ----- use `&mut Test` here to make mutable
LL |     f.f.call_mut(())
   |     ^^^ cannot borrow as mutable

error[E0504]: cannot move `f` into closure because it is borrowed
  --> $DIR/borrowck-call-is-borrow-issue-12224.rs:63:13
   |
LL |     f(Box::new(|a| {
   |     - borrow of `f` occurs here
LL |         foo(f);
   |             ^ move into closure occurs here

error[E0507]: cannot move out of captured outer variable in an `FnMut` closure
  --> $DIR/borrowck-call-is-borrow-issue-12224.rs:63:13
   |
LL |     let mut f = |g: Box<FnMut(isize)>, b: isize| {};
   |         ----- captured outer variable
62 |     f(Box::new(|a| {
LL |         foo(f);
   |             ^ cannot move out of captured outer variable in an `FnMut` closure

error: aborting due to 5 previous errors

You've got a few errors: E0499, E0504, E0507, E0596
If you want more information on an error, try using "rustc --explain E0499"