error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/field_checks.rs:24:5
   |
LL |     a: String,
   |     ^^^^^^^^^
   |
   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
help: wrap the field type in `ManuallyDrop<...>`
   |
LL |     a: std::mem::ManuallyDrop<String>,
   |        +++++++++++++++++++++++      +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/field_checks.rs:28:5
   |
LL |     a: std::cell::RefCell<i32>,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
help: wrap the field type in `ManuallyDrop<...>`
   |
LL |     a: std::mem::ManuallyDrop<std::cell::RefCell<i32>>,
   |        +++++++++++++++++++++++                       +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/field_checks.rs:32:5
   |
LL |     a: T,
   |     ^^^^
   |
   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
help: wrap the field type in `ManuallyDrop<...>`
   |
LL |     a: std::mem::ManuallyDrop<T>,
   |        +++++++++++++++++++++++ +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/field_checks.rs:44:5
   |
LL |     nest: U5,
   |     ^^^^^^^^
   |
   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
help: wrap the field type in `ManuallyDrop<...>`
   |
LL |     nest: std::mem::ManuallyDrop<U5>,
   |           +++++++++++++++++++++++  +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/field_checks.rs:48:5
   |
LL |     nest: [U5; 0],
   |     ^^^^^^^^^^^^^
   |
   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
help: wrap the field type in `ManuallyDrop<...>`
   |
LL |     nest: std::mem::ManuallyDrop<[U5; 0]>,
   |           +++++++++++++++++++++++       +

error: aborting due to 5 previous errors

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