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::<T>;
   |         +++++

error: aborting due to 1 previous error

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