自从切换到VS 2015并使用C＃6 Roslyn功能以来，Visual Studio Online CI的每日构建失败

Question

Since switching from VS 2013 to VS 2015 and using some new C# 6 features, our daily builds in Visual Studio Online have begun failing.

The errors on the build are all pointing to the new auto property feature but I assume all new features will cause this.

An example piece of code that causes a failure is using:

public int MyFavouriteNumber { get; set; } = 7;

instead of

private int _myFavouriteNumber = 7;
public int MyFavouriteNumber 
    { 
        get { return _myFavouriteNumber; } 
        set { _myFavouriteNumber = value; } 
    }

I've had a look around my build configuration, but I can't see anything that relates to C# 6 or Roslyn .

What do I have to change to make my daily builds work again?

Edit

Here's an example error (they're all the same, for auto properties).

Models\\Core\\Bookings\\BookingProduct.cs (29, 0) Invalid token '=' in class, struct, or interface member declaration

Models\\Core\\Bookings\\BookingProduct.cs (29, 0) Invalid token '(' in class, struct, or interface member declaration

And here is the offending line:

public virtual IList<BookingPricingAddon> AddonsPricing { get; set; } = new List<BookingPricingAddon>();

Answer 1

TheLethalCoder 's comments pointed me in the right direction.

The problem was that all of my projects were using Default as the target Language Version, which is fine if you're using VS 2015 , however, my .sln file had the following opening 3 lines:

Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2013
VisualStudioVersion = 12.0.31101.0

Apparently, Visual Studio Online uses this to work out which version of MSBuild to use. (It was using 12 ).

Upgrading my solution to the following:

Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 14
VisualStudioVersion = 14.0.23107.0

allowed Visual Studio Online to see that my IDE was using Roslyn, and therefore used MSBuild 14 .

The easiest way I found to upgrade is to click on the solution in Solution Explorer and then going to File > Save As > Solution File and overwrite your existing solution file, it just upgrades the first 3 lines.

My builds are now successful.

I think the same could be achieved by setting the Language Version on each of your projects. This can be done by going to your .csproj files and navigating to:

Properties > Build > Advanced > Language Version > C# 6.0

A good reference about the Default settings in each IDE can be found here .