1 An `impl Trait` type expands to a recursive type.
3 An `impl Trait` type must be expandable to a concrete type that contains no
4 `impl Trait` types. For example the following example tries to create an
5 `impl Trait` type `T` that is equal to `[T, T]`:
8 fn make_recursive_type() -> impl Sized {
9 [make_recursive_type(), make_recursive_type()]