Bug 32712 - Incorrect compile error CS4016 when for async function that returns Task<Task>
Summary: Incorrect compile error CS4016 when for async function that returns Task<Task>
Alias: None
Product: Compilers
Classification: Mono
Component: C# ()
Version: 4.0.0
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: ---
Assignee: Marek Safar
Depends on:
Reported: 2015-08-03 11:25 UTC by jesse.attas
Modified: 2015-08-04 07:02 UTC (History)
1 user (show)

Is this bug a regression?: ---
Last known good build:

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Description jesse.attas 2015-08-03 11:25:45 UTC
The code snippet below compiles fine in a VS WPF application but generates a compiler error in Xamarin.iOS and Xamarin.Android.

Error CS4016: `AsyncTest.ViewController.ReturnsTaskOfTaskAsync()': The return expression type of async method must be `System.Threading.Tasks.Task' rather than `Task<System.Threading.Tasks.Task>' (CS4016) (AsyncTest)

Code Snippet:
        public async Task ReturnsTaskAsync(Task task)
            await task;

        public async Task<Task> ReturnsTaskOfTaskAsync()
            var t1 = Task.FromResult(ReturnsTaskAsync(null));
            await t1;
            var t2 = Task.FromResult(ReturnsTaskAsync(null));
            return t2;

Tools versions:
Xamarin Studio
Version 5.9.4 (build 5)
Installation UUID: 53fef2ac-96fd-4c07-9e93-cd87aad8d83c
	Mono 4.0.2 ((detached/c99aa0c)
	GTK+ 2.24.23 (Raleigh theme)

	Package version: 400020005

Version: (Business Edition)
Android SDK: /Users/JA/Library/Developer/Xamarin/android-sdk-macosx
	Supported Android versions:
		2.3   (API level 10)
		4.0.3 (API level 15)
		4.2   (API level 17)
		4.4   (API level 19)
		5.0   (API level 21)
Java SDK: /usr
java version "1.7.0_76"
Java(TM) SE Runtime Environment (build 1.7.0_76-b13)
Java HotSpot(TM) 64-Bit Server VM (build 24.76-b04, mixed mode)

Xamarin Android Player
Version: Unknown version
Location: /Applications/Xamarin Android Player.app

Apple Developer Tools
Xcode 6.4 (7720)
Build 6E35b

Version: (Business Edition)
Hash: 8b265d6
Branch: master
Build date: 2015-06-30 15:19:13-0400

Not Installed

Build Information
Release ID: 509040005
Git revision: 8010a90f6e246b32364e3fb46ef2c9d1be9c9a2b
Build date: 2015-06-08 16:52:06-04
Xamarin addins: 7e93e9c3503f28770f23ce1b7eafd829919f18e8

Operating System
Mac OS X 10.10.4
Comment 1 Marek Safar 2015-08-04 07:02:28 UTC
Fixed in master and Mono 4.2