pub fn main() {
    struct I {}
    impl std::iter::Iterator for I {
        type Item = u8;
        fn next(&mut self) -> Option<Self::Item> {
            Some(0)
        }
    }
    struct S {}
    impl std::iter::IntoIterator for S {
        type Item = u8;
        type IntoIter = I;
        fn into_iter(self) -> Self::IntoIter {
            unimplemented!()
        }
    }
    fn f<T:IntoIterator>(x:T) { }
    f(S {});
    f(I {});
}