Make Completer.complete handle a Future with a misbehaving "then" call.

tests/lib/async/future_test.dart

 // Copyright (c) 2012, 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 future_test;
 
 import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 
@@ skipping 858 matching lines @@
           });
 
   }, onError: (int index, s) {
     Expect.isTrue(index == 0 || index == 2, "$index");
     Expect.isFalse(uncaughts[index]);
     uncaughts[index] = true;
     asyncEnd();
   });
 }
 
+void testBadFuture() {
+  var bad = new BadFuture();
+  // Completing with bad future (then call throws) puts error in result.
+  asyncStart();
+  Completer completer = new Completer();
+  completer.complete(bad);
+  completer.future.then((_) { fail("unreachable"); },
+                        onError: (e, s) {
+                          Expect.isTrue(completer.isCompleted);
+                          asyncEnd();
+                        });
+
+  asyncStart();
+  var f = new Future.value().then((_) => bad);
+  f.then((_) { fail("unreachable"); },
+         onError: (e, s) {
+           asyncEnd();
+         });
+}
+
 main() {
   asyncStart();
 
   testValue();
   testSync();
   testNeverComplete();
 
   testComplete();
   testCompleteWithSuccessHandlerBeforeComplete();
   testCompleteWithSuccessHandlerAfterComplete();
@@ skipping 39 matching lines @@
 
   testChainedFutureValue();
   testChainedFutureValueDelay();
   testChainedFutureError();
 
   testSyncFuture_i13368();
 
   testWaitCleanUp();
   testWaitCleanUpError();
 
+  testBadFuture();
+
   asyncEnd();
 }
 
 /// A Future that isn't recognizable as a _Future.
 class CustomFuture<T> implements Future<T> {
   Future _realFuture;
   CustomFuture(this._realFuture);
   Future then(action(result), {Function onError}) =>
       _realFuture.then(action, onError: onError);
   Future catchError(Function onError, {bool test(e)}) =>
       _realFuture.catchError(onError, test: test);
   Future whenComplete(action()) => _realFuture.whenComplete(action);
   Future timeout(Duration timeLimit, {void onTimeout()}) =>
       _realFuture.timeout(timeLimit, onTimeout: onTimeout);
   Stream asStream() => _realFuture.asStream();
   String toString() => "CustomFuture@${_realFuture.hashCode}";
   int get hashCode => _realFuture.hashCode;
 }
+
+class BadFuture<T> implements Future<T> {
+  Future then(action(result)) {
+    throw "then GOTCHA!";
+  }
+  Future catchError(Function onError) {
+    throw "catch GOTCHA!";
+  }
+  Future whenComplete(action()) {
+    throw "finally GOTCHA!";
+  }
+}