error: reference to `Umm` held across a suspend point, but should not be
  --> $DIR/ref.rs:18:13
   |
LL |         let guard = &mut self.u;
   |             ^^^^^
LL |
LL |         other().await;
   |                 ----- the value is held across this suspend point
   |
note: You gotta use Umm's, ya know?
  --> $DIR/ref.rs:18:13
   |
LL |         let guard = &mut self.u;
   |             ^^^^^
help: consider using a block (`{ ... }`) to shrink the value's scope, ending before the suspend point
  --> $DIR/ref.rs:18:13
   |
LL |         let guard = &mut self.u;
   |             ^^^^^
note: the lint level is defined here
  --> $DIR/ref.rs:3:9
   |
LL | #![deny(must_not_suspend)]
   |         ^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error