union Foo { a: str, //~^ ERROR the size for values of type `str` cannot be known at compilation time //~| ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` } enum Bar { Boo = { let _: Option = None; //~ ERROR evaluation of constant value failed 0 }, } union Foo2 {} //~^ ERROR unions cannot have zero fields enum Bar2 { Boo = { let _: Option = None; 0 }, } #[repr(u8, packed)] //~^ ERROR attribute should be applied to a struct or union enum Foo3 { A } enum Bar3 { Boo = { let _: Option = None; 0 }, } fn main() {}