error[E0277]: the size for values of type `str` cannot be known at compilation time
  --> $DIR/union-unsized.rs:2:8
   |
LL |     a: str,
   |        ^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `str`
   = note: no field of a union may have a dynamically sized type
   = help: change the field's type to have a statically known size
help: borrowed types always have a statically known size
   |
LL |     a: &str,
   |        +
help: the `Box` type always has a statically known size and allocates its contents in the heap
   |
LL |     a: Box<str>,
   |        ++++   +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/union-unsized.rs:2:5
   |
LL |     a: str,
   |     ^^^^^^
   |
   = 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<str>,
   |        +++++++++++++++++++++++   +

error[E0277]: the size for values of type `str` cannot be known at compilation time
  --> $DIR/union-unsized.rs:11:8
   |
LL |     b: str,
   |        ^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `str`
   = note: no field of a union may have a dynamically sized type
   = help: change the field's type to have a statically known size
help: borrowed types always have a statically known size
   |
LL |     b: &str,
   |        +
help: the `Box` type always has a statically known size and allocates its contents in the heap
   |
LL |     b: Box<str>,
   |        ++++   +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> $DIR/union-unsized.rs:11:5
   |
LL |     b: str,
   |     ^^^^^^
   |
   = 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 |     b: std::mem::ManuallyDrop<str>,
   |        +++++++++++++++++++++++   +

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0277, E0740.
For more information about an error, try `rustc --explain E0277`.