Visual Studio 2017 publish ASP.NET Core app with C# 7.2

Question

I have a Asp.Net MVC Core website that's using public static async Task Main(). For that to work I've set the language version to C# 7.2 (in the properties -> build -> advanced dialog, double checked in the csproj) for both Debug and Release build configurations.

App builds and starts fine in both Debug and Release mode.

Now, I'm trying to publish it to an Azure Website directly from Visual Studio 2017 15.5.2 (with WebDeploy) and I get this:

Program.cs(17,29): Error CS8107: Feature 'async main' is not available in C# 7.0. Please use language version 7.1 or greater. CSC(0,0): Error CS5001: Program does not contain a static 'Main' method suitable for an entry point

In the output window I see it's running C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\Roslyn\csc.exe with some flags, probably one of them is wrong?

Anyone know if this is a known issue or I'm doing something wrong?

user1336 · Accepted Answer · 2018-01-10 10:31:02Z

3

This appears to be a bug in Visual Studio. Adding this line to main property group in the .csproj file resolved the issue for me:

<LangVersion>latest</LangVersion>

The issue was also reported here in the ASP.NET Home repository.

edited Jan 10, 2018 at 10:31

answered Jan 10, 2018 at 9:41

user1336

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Chris Pratt · Accepted Answer · 2017-12-29 20:04:25Z

2

Not an answer, per se, but for what it's worth async Main is just syntactic sugar. Behind the scenes Roslyn just adds the standard void Main wrapper construction:

static void Main(object[] args)
{
    MainAsync(args).GetAwaiter().GetResult();
}

static async Task MainAsync(object[] args)
{
    // your code
}

It's probably not worth your time trying to get the server on the same page C# version-wise, just to save literally three lines of code.

answered Dec 29, 2017 at 20:04

community wiki

Chris Pratt

1 Comment

adrian h. Over a year ago

Yea i reverted back to this in the meantime as i can't find the source of the issue

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