CC1099: Contract extraction failed: async/iterator issue in async without await

[mgaffigan]

I am getting the error CC1099 on a particular method. I have narrowed the method down to one specific change which will cause the failure. The below sample compiled as a console application with rewriting enabled seems to reliably fail.

Error:

EXEC : error CC1099: Contract extraction failed: async/iterator issue: In method EmptyAsyncTest.Program.Foo, assembly EmptyAsyncTest\EmptyAsyncTest\obj\Debug\EmptyAsyncTest.exe

Code:

using System;
using System.Threading.Tasks;

namespace EmptyAsyncTest
{
    class Program
    {
        static void Main(string[] args)
        {
        }

        async Task Foo()
        {
            if (DateTime.Now.Day == 0 && 1 == 2)
            {
            }
        }
    }
}

The following variations do not trigger the bug:

• Removing async and returning Task.FromResult(false)
• Removing && 1 == 2
• Removing DateTime.Now.Day == 0
• Adding await Task.Delay(1)

Environment:
VS 2015 CTP, Code Contracts 1.9.10714.2, Windows 8.1, Project is .Net 4.5, Only rewriting is enabled
Also repro'd by compiling fe3bf15 and running foxtrot. Same output.

[SergeyTeplyakov]

grabbed.

[sharwell]

@mgaffigan This is a great bug report. Thanks for taking the time to find a simple way to reproduce the problem and explain the variants you tested. 😄

[SergeyTeplyakov]

Investigation results:

1. This bug is only for VS2015
2. Only for async methods without awaits
3. Only for async methods without contracts

I'm running the tests right now for the fix.

[SergeyTeplyakov]

Created PR with a fix: #173.

[mgaffigan]

@SergeyTeplyakov, Thank you for the quick response.

[SergeyTeplyakov]

@mgaffigan You're welcome! And thanks a lot for great bug report!

[takinosaji]

Bug still presented. Got this error on such a code:

public override async Task Meth(Int32 number)
In a function without await.