Update type variable cases in the regression_49396_test

The definition of flatten was adjusted in
dart-lang/language#2696
such that it better preserves the type information when the type of `e`
in `await e` is a type variable. This CL changes the test to expect
the behavior of the newly specified flatten.

The test has been renamed to 'await_flatten_test.dart'.

Change-Id: Iaf67a53cd3cd181bcb3eb6e85beca7cc1af4d34a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/274682
Commit-Queue: Erik Ernst <[email protected]>
Reviewed-by: Lasse Nielsen <[email protected]>

Author: eernstg

tests/language/async/await_flatten_test.dart

@@ -0,0 +1,247 @@
+// Copyright (c) 2022, 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.
+
+import 'dart:async';
+import 'package:expect/expect.dart';
+import '../static_type_helper.dart';
+
+// Testing the behavior of flatten (cf. SDK issue #49396).
+
+class A {}
+
+abstract class B<X> extends A implements Future<X> {
+  Future<X> get fut;
+  asStream() => fut.asStream();
+  catchError(error, {test}) => fut.catchError(error, test: test);
+  then<R>(onValue, {onError}) => fut.then(onValue, onError: onError);
+  timeout(timeLimit, {onTimeout}) =>
+      fut.timeout(timeLimit, onTimeout: onTimeout);
+  whenComplete(action) => fut.whenComplete(action);
+}
+
+class C extends B<Object?> {
+  final Future<Object?> fut = Future.value(CompletelyUnrelated());
+}
+
+class CompletelyUnrelated {}
+
+class C1 extends A {}
+
+class C2 extends B<C1> {
+  final Future<C1> fut = Future.value(C1());
+}
+
+void main() async {
+  final Object o = Future<Object?>.value();
+  var o2 = await o; // Remains a future.
+  o2.expectStaticType<Exactly<Object>>();
+  Expect.type<Future<Object?>>(o2);
+  Expect.identical(o, o2);
+
+  final FutureOr<Object> x = Future<Object?>.value();
+  var x2 = await x; // Remains a future.
+  x2.expectStaticType<Exactly<Object>>();
+  Expect.type<Future<Object?>>(x2);
+  Expect.identical(x, x2);
+
+  final FutureOr<Future<int>> y = Future<int>.value(1);
+  var y2 = await y; // Remains a `Future<int>`.
+  y2.expectStaticType<Exactly<Future<int>>>();
+  Expect.type<Future<int>>(y2);
+  Expect.identical(y, y2);
+
+  A a = C();
+  var a2 = await a; // Remains a `C` and a `Future<Object?>`.
+  a2.expectStaticType<Exactly<A>>();
+  Expect.type<C>(a2);
+  Expect.identical(a, a2);
+
+  // Type variable; called with `X == Object`.
+  Future<void> f1<X extends Object>(X x) async {
+    var x2 = await x; // Remains a `Future<Object?>`.
+    x2.expectStaticType<Exactly<X>>();
+    Expect.type<Future<Object?>>(x2);
+    Expect.identical(x, x2);
+  }
+
+  await f1<Object>(Future<Object?>.value(null));
+
+  // Type variable; called with `X == A`.
+  Future<void> f2<X extends A>(X x) async {
+    var x2 = await x; // The future is awaited.
+    x2.expectStaticType<Exactly<X>>();
+    Expect.type<C1>(x2);
+    Expect.notType<C2>(x2);
+    Expect.notIdentical(x, x2);
+  }
+
+  await f2<A>(C2());
+
+  // Type variable; called with `X == C2`.
+  Future<void> f3<X extends A>(X x) async {
+    var x2 = await x; // Remains a `C2` and a `Future<C1>`.
+    x2.expectStaticType<Exactly<X>>();
+    Expect.type<C2>(x2);
+    Expect.identical(x, x2);
+  }
+
+  await f3<C2>(C2());
+
+  // Type variable; value of `X` makes no difference.
+  Future<void> f4<X extends Future<A>>(X x) async {
+    var x2 = await x; // The future is awaited.
+    x2.expectStaticType<Exactly<A>>();
+    Expect.type<C1>(x2);
+    Expect.notType<C2>(x2);
+    Expect.notIdentical(x, x2);
+  }
+
+  await f4<Future<A>>(C2());
+  await f4<C2>(C2());
+
+  // Type variable; value of `X` makes no difference.
+  Future<void> f5<X extends FutureOr<A>>(X x) async {
+    var x2 = await x; // The future is awaited.
+    x2.expectStaticType<Exactly<A>>();
+    Expect.type<C1>(x2);
+    Expect.notType<C2>(x2);
+    Expect.notIdentical(x, x2);
+  }
+
+  await f5<A>(C2());
+  await f5<Future<A>>(C2());
+  await f5<Future<C1>>(C2());
+  await f5<C2>(C2());
+
+  // Promoted type variable; called with `X == Object`.
+  Future<void> g1<X>(X x) async {
+    if (x is Object) {
+      var x2 = await x; // Remains a `Future<Object?>`.
+      x2.expectStaticType<Exactly<X>>();
+      Expect.type<Future<Object?>>(x2);
+      Expect.identical(x, x2);
+    }
+  }
+
+  await g1<Object>(Future<Object?>.value(null));
+
+  // Promoted type variable; called with `X == Object?`.
+  Future<void> g2<X>(X x) async {
+    if (x is Object) {
+      var x2 = await x; // The future is awaited.
+      x2.expectStaticType<Exactly<X>>();
+      Expect.isNull(x2);
+    }
+  }
+
+  await g2<Object?>(Future<Object?>.value(null));
+
+  // Promoted type variable; called with `X == A`.
+  Future<void> g3<X>(X x) async {
+    if (x is A) {
+      var x2 = await x; // The future is awaited.
+      x2.expectStaticType<Exactly<X>>();
+      Expect.type<C1>(x2);
+      Expect.notType<C2>(x2);
+      Expect.notIdentical(x, x2);
+    }
+  }
+
+  await g3<A>(C2());
+
+  // Promoted type variable; called with `X == C2`.
+  Future<void> g4<X>(X x) async {
+    if (x is A) {
+      var x2 = await x; // Remains a `C2` and a `Future<C1>`.
+      x2.expectStaticType<Exactly<X>>();
+      Expect.type<C2>(x2);
+      Expect.identical(x, x2);
+    }
+  }
+
+  await g4<C2>(C2());
+
+  // Promoted type variable; the value of `X` does not matter.
+  Future<void> g5<X>(X x) async {
+    if (x is Future<A>) {
+      var x2 = await x; // The future is awaited.
+      x2.expectStaticType<Exactly<A>>();
+      Expect.type<C1>(x2);
+      Expect.notType<C2>(x2);
+      Expect.notIdentical(x, x2);
+    }
+  }
+
+  await g5<A>(C2());
+  await g5<C2>(C2());
+  await g5<Future<A>>(C2());
+
+  // Promoted type variable; the value of `X` does not matter.
+  Future<void> g6<X>(X x) async {
+    if (X is FutureOr<A>) {
+      var x2 = await x; // The future is awaited.
+      x2.expectStaticType<Exactly<A>>();
+      Expect.type<C1>(x2);
+      Expect.notType<C2>(x2);
+      Expect.notIdentical(x, x2);
+    }
+  }
+
+  await g6<A>(C2());
+  await g6<C2>(C2());
+  await g6<Future<A>>(C2());
+  await g6<Future<C1>>(C2());
+
+  // Promoted type variable; values of type variables makes no difference.
+  Future<void> g7<X, Y extends Future<int>>(X x) async {
+    if (x is Future<int> && x is Y) {
+      // The promoted type of `x` is `X & Y`.
+      var x2 = await x; // The future is awaited.
+      x2.expectStaticType<Exactly<int>>();
+      Expect.equals(1, x2);
+    }
+  }
+
+  await g7<Object?, Object?>(Future<int>.value(1));
+
+  // S? bounded type: called with `X == Null`.
+  Future<void> h1<X extends Future<A>?>(X x) {
+    var x2 = await x; // Remains null.
+    x2.expectStaticType<Exactly<A?>>();
+    Expect.identical(null, x2);
+  }
+
+  await h1<Null>(null);
+
+  // S? bounded type: called with `X == Future<A>`.
+  Future<void> h2<X extends Future<A>?>(X x) {
+    var x2 = await x; // The future is awaited.
+    x2.expectStaticType<Exactly<A?>>();
+    Expect.type<C1>(x2);
+    Expect.notType<C2>(x2);
+    Expect.notIdentical(x, x2);
+  }
+
+  await h2<Future<A>>(C2());
+
+  // S? bounded type: called with `X == Null`.
+  Future<void> h3<X extends FutureOr<A>?>(X x) {
+    var x2 = await x; // Remains null.
+    x2.expectStaticType<Exactly<A?>>();
+    Expect.identical(null, x2);
+  }
+
+  await h3<Null>(null);
+
+  // S? bounded type: called with `X == FutureOr<A>`.
+  Future<void> h4<X extends FutureOr<A>?>(X x) {
+    var x2 = await x; // The future is awaited.
+    x2.expectStaticType<Exactly<A?>>();
+    Expect.type<C1>(x2);
+    Expect.notType<C2>(x2);
+    Expect.notIdentical(x, x2);
+  }
+
+  await h4<FutureOr<A>>(C2());
+}