Implement new flatten specification.

tests/compiler/dart2js/flatten_test.dart

+// Copyright (c) 2013, 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.
+
+library subtype_test;
+
+import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
+import 'type_test_helper.dart';
+import 'package:compiler/src/dart_types.dart';
+import "package:compiler/src/elements/elements.dart"
+       show Element, ClassElement;
+
+void main() {
+  asyncTest(() => TypeEnvironment.create(r"""
+      abstract class F<T> implements Future<T> {}
+      abstract class G<T> implements Future<G<T>> {}
+      abstract class H<T> implements Future<H<H<T>>> {}
+      """).then((env) {
+
+    void check(DartType T, DartType expectedFlattenedType) {
+      DartType flattenedType = env.flatten(T);
+      Expect.equals(expectedFlattenedType, flattenedType,
+                    "Unexpected flattening of '$T' = '$flattenedType',"
+                    "expected '$expectedFlattenedType'.");
+    }
+
+    ClassElement Future_ = env.getElement('Future');
+    ClassElement F = env.getElement('F');
+    ClassElement G = env.getElement('G');
+    ClassElement H = env.getElement('H');
+    DartType int_ = env['int'];
+    DartType dynamic_ = env['dynamic'];
+    DartType Future_int = instantiate(Future_, [int_]);
+    DartType F_int = instantiate(F, [int_]);
+    DartType G_int = instantiate(G, [int_]);
+    DartType H_int = instantiate(H, [int_]);
+    DartType H_H_int = instantiate(H, [H_int]);
+
+    // flatten(int) = int
+    check(int_, int_);
+
+    // flatten(Future) = dynamic
+    check(Future_.rawType, dynamic_);
+
+    // flatten(Future<int>) = int
+    check(Future_int, int_);
+
+    // flatten(Future<Future<int>>) = int
+    check(instantiate(Future_, [Future_int]), int_);
+
+    // flatten(F) = dynamic
+    check(F.rawType, dynamic_);
+
+    // flatten(F<int>) = int
+    check(F_int, int_);
+
+    // flatten(F<Future<int>>) = Future<int>
+    check(instantiate(F, [Future_int]), Future_int);
+
+    // flatten(G) = G
+    check(G.rawType, G.rawType);
+
+    // flatten(G<int>) = G<int>
+    check(G_int, G_int);
+
+    // flatten(H) = H<H>
+    check(H.rawType, instantiate(H, [H.rawType]));
+
+    // flatten(H<int>) = H<H<int>>
+    check(H_int, H_H_int);
+
+    // flatten(Future<F<int>>) = int
+    check(instantiate(Future_, [F_int]), int_);
+
+    // flatten(Future<G<int>>) = int
+    check(instantiate(Future_, [G_int]), G_int);
+
+    // flatten(Future<H<int>>) = int
+    check(instantiate(Future_, [H_int]), H_H_int);
+  }));
+}