rust/src/test/ui/inference/cannot-infer-closure.stderr

error[E0282]: type annotations needed for the closure
  --> $DIR/cannot-infer-closure.rs:3:9
   |
LL |     let x = |a: (), b: ()| {
   |         - consider giving `x` a boxed closure type like `Box<Fn((), ()) -> std::result::Result<(), _>>`
LL |         Err(a)?;
   |         ^^^^^^^ cannot infer type

error: aborting due to previous error

For more information about this error, try `rustc --explain E0282`.