error[E0392]: parameter `T` is never used --> $DIR/issue-17904-2.rs:4:12 | LL | struct Foo where T: Copy; //~ ERROR parameter `T` is never used | ^ unused type parameter | = help: consider removing `T` or using a marker such as `std::marker::PhantomData` error: aborting due to previous error For more information about this error, try `rustc --explain E0392`.