error[E0072]: recursive types `Foo` and `Bar` have infinite size
  --> $DIR/recursive-type-field.rs:3:1
   |
LL | struct Foo<'a> {
   | ^^^^^^^^^^^^^^
LL |     bar: Bar<'a>,
   |          ------- recursive without indirection
...
LL | struct Bar<'a> {
   | ^^^^^^^^^^^^^^
LL |     y: (Foo<'a>, Foo<'a>),
   |         -------  ------- recursive without indirection
   |         |
   |         recursive without indirection
   |
help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle
   |
LL ~     bar: Box<Bar<'a>>,
LL |     b: Rc<Bar<'a>>,
 ...
LL | struct Bar<'a> {
LL ~     y: (Box<Foo<'a>>, Box<Foo<'a>>),
   |

error: aborting due to previous error

For more information about this error, try `rustc --explain E0072`.