$ cargo doc

error[E0392]: parameter `T` is never used
 --> src/main.rs:4:18
  |
4 | struct MyPhantom<T>;
  |                  ^ unused parameter
  |
  = help: consider removing `T`, referring to it in a field, or using a marker such as `std::marker::PhantomData`
  = help: if you intended `T` to be a const parameter, use `const T: usize` instead