error[E0373]: closure may outlive the current function, but it borrows `x`, which is owned by the current function
  --> $DIR/async-borrowck-escaping-closure-error.rs:5:15
   |
LL |     Box::new((async || x)())
   |               ^^^^^^^^ - `x` is borrowed here
   |               |
   |               may outlive borrowed value `x`
   |
note: closure is returned here
  --> $DIR/async-borrowck-escaping-closure-error.rs:5:5
   |
LL |     Box::new((async || x)())
   |     ^^^^^^^^^^^^^^^^^^^^^^^^
help: to force the closure to take ownership of `x` (and any other referenced variables), use the `move` keyword
   |
LL |     Box::new((async move || x)())
   |                     ++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0373`.