error[E0282]: type annotations needed --> $DIR/unconstrained-none.rs:4:5 | LL | None; | ^^^^ cannot infer type of the type parameter `T` declared on the enum `Option` | help: consider specifying the generic argument | LL | None::; | +++++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0282`.