anchor.diff:    Future<int> f() async { return new Derived<int>(); } /// 03: ok
     Future<int> x = (() async => new Derived<int>())(); /// 04: runtime error
   
  +  // TODO(vsm): Restore when https://github.com/dart-lang/sdk/issues/25611
  +  // is fixed.
  +  /*
     // flatten(FixedPoint<int>) = FixedPoint<int>
     FixedPoint<int> x = await new FixedPoint<int>(); /// 05: runtime error
     Future<FixedPoint<int>> f() async => new FixedPoint<int>(); /// 06: ok
  
positive.code:   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
  }
  
  class Divergent<T> implements Future<Divergent<Divergent<T>>> {
    noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
  }
  
  
  test() async {
  
negative.code:   Future<Divergent<Divergent<int>>> f() async => new Divergent<int>(); /// 10: ok
    Future<Divergent<Divergent<int>>> f() async { return new Divergent<int>(); } /// 11: ok
    Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())(); /// 12: runtime error
    */
  }
  
  main() {
  