error[E0716]: temporary value dropped while borrowed
  --> $DIR/union_promotion.rs:8:29
   |
LL |       let x: &'static bool = &unsafe {
   |  ____________-------------____^
   | |            |
   | |            type annotation requires that borrow lasts for `'static`
LL | |         Foo { a: &1 }.b == Foo { a: &2 }.b
LL | |     };
   | |_____^ creates a temporary value which is freed while still in use
LL |   }
   |   - temporary value is freed at the end of this statement

error: aborting due to previous error

For more information about this error, try `rustc --explain E0716`.