Report HintCode.MISSING_RETURN for async functions with return type that matters.

pkg/analyzer/test/generated/hint_code_test.dart

 // Copyright (c) 2016, 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 analyzer.test.generated.hint_code_test;
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/parser.dart';
@@ skipping 150 matching lines @@
 m() {
   var i = '';
   n(i);
 }
 n(int i) {}''');
     await computeAnalysisResult(source);
     assertErrors(source, [HintCode.ARGUMENT_TYPE_NOT_ASSIGNABLE]);
     verify([source]);
   }
 
+  test_async_future_object_without_return() async {
+    Source source = addSource('''
+import 'dart:async';
+Future<Object> f() async {}
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source, [HintCode.MISSING_RETURN]);
+    verify([source]);
+  }
+
   test_canBeNullAfterNullAware_false_methodInvocation() async {
     Source source = addSource(r'''
 m(x) {
   x?.a()?.b();
 }
 ''');
     await computeAnalysisResult(source);
     assertNoErrors(source);
     verify([source]);
   }
@@ skipping 3852 matching lines @@
   n() {
     var a = m(), b = m();
   }
 }''');
     await computeAnalysisResult(source);
     assertErrors(
         source, [HintCode.USE_OF_VOID_RESULT, HintCode.USE_OF_VOID_RESULT]);
     verify([source]);
   }
 }