pkg/front_end/testcases/inference/future_union_downwards.dart

// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
// @dart=2.9
/*@testedFeatures=inference*/
library test;

import 'dart:async';

class MyFuture<T> implements Future<T> {
  MyFuture() {}
  MyFuture.value([x]) {}
  dynamic noSuchMethod(invocation) => null;
  MyFuture<S> then<S>(FutureOr<S> f(T x), {Function onError}) => null;
}

MyFuture f;
// Instantiates Future<int>
Future<int> t1 = f. /*@ typeArgs=int* */ /*@target=MyFuture.then*/ then(
    /*@ returnType=Future<int*>* */ (/*@ type=dynamic */ _) =>
        new /*@ typeArgs=int* */ Future.value('hi'));

// Instantiates List<int>
Future<List<int>> t2 =
    f. /*@ typeArgs=List<int*>* */ /*@target=MyFuture.then*/ then(
        /*@ returnType=List<int*>* */ (/*@ type=dynamic */ _) => /*@ typeArgs=int* */ [
              3
            ]);
Future<List<int>> g2() async {
  return /*@ typeArgs=int* */ [3];
}

Future<List<int>> g3() async {
  return new /*@ typeArgs=List<int*>* */ Future.value(
      /*@ typeArgs=int* */ [3]);
}

main() {}