src/test/ui/consts/const-eval/feature-gate-const_fn_union.stderr

error[E0658]: unions in const fn are unstable (see issue #51909)
  --> $DIR/feature-gate-const_fn_union.rs:11:5
   |
LL |     Foo { u }.i
   |     ^^^^^^^^^^^
   |
   = help: add #![feature(const_fn_union)] to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.