error[E0277]: `F` cannot be shared between threads safely
  --> $DIR/closure-bounds-subtype.rs:13:5
   |
LL | fn take_const_owned<F>(_: F) where F: FnOnce() + Sync + Send {
   | ------------------------------------------------------------ required by `take_const_owned`
...
LL |     take_const_owned(f);
   |     ^^^^^^^^^^^^^^^^ `F` cannot be shared between threads safely
   |
   = help: the trait `std::marker::Sync` is not implemented for `F`
   = help: consider adding a `where F: std::marker::Sync` bound

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.