| error[E0308]: mismatched types | 
 |   --> $DIR/def-path.rs:7:9 | 
 |    | | 
 | LL |     let x = async || {}; | 
 |    |                      -- the expected `async` closure body | 
 | LL | | 
 | LL |     let () = x(); | 
 |    |         ^^   --- this expression has type `{static main::{closure#0}::{closure#0}<?17t> upvar_tys=?16t resume_ty=ResumeTy yield_ty=() return_ty=() witness=?5t}` | 
 |    |         | | 
 |    |         expected `async` closure body, found `()` | 
 |    | | 
 |    = note: expected `async` closure body `{static main::{closure#0}::{closure#0}<?17t> upvar_tys=?16t resume_ty=ResumeTy yield_ty=() return_ty=() witness=?5t}` | 
 |                          found unit type `()` | 
 |  | 
 | error: aborting due to 1 previous error | 
 |  | 
 | For more information about this error, try `rustc --explain E0308`. |