error[E0277]: `NoSync` cannot be shared between threads safely
  --> $DIR/mutable-enum-indirect.rs:17:5
   |
LL | fn bar<T: Sync>(_: T) {}
   |    ---    ---- required by this bound in `bar`
...
LL |     bar(&x);
   |     ^^^ `NoSync` cannot be shared between threads safely
   |
   = help: within `&Foo`, the trait `std::marker::Sync` is not implemented for `NoSync`
   = note: required because it appears within the type `Foo`
   = note: required because it appears within the type `&Foo`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.