error[E0728]: `await` is only allowed inside `async` functions and blocks
  --> $DIR/issue-51719.rs:8:24
   |
LL |     let _gen = || foo().await;
   |                --      ^^^^^^ only allowed inside `async` functions and blocks
   |                |
   |                this is not `async`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0728`.