error[E0282]: type annotations needed for `Option<_>`
  --> $DIR/issue-42234-unknown-receiver-type.rs:7:7
   |
LL |     let x: Option<_> = None;
   |         - consider giving `x` the explicit type `Option<_>`, where the type parameter `T` is specified
LL |     x.unwrap().method_that_could_exist_on_some_type();
   |       ^^^^^^ cannot infer type for type parameter `T`
   |
   = note: type must be known at this point

error[E0282]: type annotations needed
  --> $DIR/issue-42234-unknown-receiver-type.rs:13:10
   |
LL |         .sum::<_>()
   |          ^^^ cannot infer type
   |
   = note: type must be known at this point

error: aborting due to 2 previous errors

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