error[E0740]: unions may not contain fields that need dropping
  --> $DIR/issue-41073.rs:4:5
   |
LL |     a: A,
   |     ^^^^
   |
note: `std::mem::ManuallyDrop` can be used to wrap the type
  --> $DIR/issue-41073.rs:4:5
   |
LL |     a: A,
   |     ^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0740`.