error: tail calls can only be performed with function definitions or pointers
  --> $DIR/callee_is_weird.rs:7:12
   |
LL |     become std::sync::Exclusive::new(f)()
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: callee has type `Exclusive<fn() {f}>`

error: tail calls can only be performed with function definitions or pointers
  --> $DIR/callee_is_weird.rs:11:12
   |
LL |     become (&mut &std::sync::Exclusive::new(f))()
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: callee has type `&Exclusive<fn() {f}>`

error: tail calls can only be performed with function definitions or pointers
  --> $DIR/callee_is_weird.rs:22:12
   |
LL |     become J();
   |            ^^^
   |
   = note: callee has type `J`

error: aborting due to 3 previous errors