error[E0517]: attribute should be applied to a struct or union
  --> $DIR/ice-const-prop-unions-known-panics-lint-123710.rs:6:8
   |
LL |   #[repr(packed)]
   |          ^^^^^^
...
LL | / enum E {
LL | |     A,
LL | |     B,
LL | |     C,
LL | | }
   | |_- not a struct or union

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/ice-const-prop-unions-known-panics-lint-123710.rs:18:9
   |
LL |         e: E,
   |         ^^^^
   |
   = 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 |         e: std::mem::ManuallyDrop<E>,
   |            +++++++++++++++++++++++ +

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0517, E0740.
For more information about an error, try `rustc --explain E0517`.