error[E0204]: the trait `Copy` cannot be implemented for this type --> $DIR/union-copy.rs:12:15 | LL | a: std::mem::ManuallyDrop | --------------------------------- this field does not implement `Copy` ... LL | impl Copy for W {} | ^ | note: the `Copy` impl for `ManuallyDrop` requires that `String: Copy` --> $DIR/union-copy.rs:8:8 | LL | a: std::mem::ManuallyDrop | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0204`.