...
LL | impl Copy for W {}
| ^^^^
+ |
+note: the `Copy` impl for `ManuallyDrop<String>` requires that `String: Copy`
+ --> $DIR/union-copy.rs:8:5
+ |
+LL | a: std::mem::ManuallyDrop<String>
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to previous error