LRN Quick Tip: How to Test out C# 7 Features with Roslyn

As of November, people outside of the Roslyn team have been able to build and dogfood changes they make to the compiler and language services. Now that the various feature branches have caught up, we can start playing around with some of the proposed features for C#.

If you’d just like to learn about the features, I’ve put up a few videos on binary literals, digit separators and local functions.

I’ve also prepared a video on How to Test out C# 7 Features with Roslyn

The current branches available on GitHub are:

features/Annotated Types
features/Nullable Reference Types
features/constVar
features/local-functions
features/multi-Var
features/openGenericNameInNameof
features/patterns
features/privateprotected
features/ref-returns
features/tuples

The /future branch is where all these features end up once they’re close to complete and ready to be reviewed for more feedback. Today (Feburary 9, 2015) it’s home to binary literals, digit separators and local functions.

Today we’re going to look at the steps necessary to get the /future branch to build and let us test out the new features.

Cloning and Building Roslyn

The first steps are identical to those found on Roslyn’s “Building Debugging and Testing on Windows” guideline.

1. Clone https://github.com/dotnet/roslyn
2. Check out the /features branch
3. Run the “Developer Command Prompt for VS2015” from your start menu.
4. Navigate to the directory of your Git clone.
5. Run Restore.cmd in the command prompt to restore NuGet packages. (Note: This sometimes takes up to 30 minutes to complete and may appear to be frozen when it’s not)
6. Build on the command line before opening in Visual Studio. Run msbuild /v:m /m Roslyn.sln
7. Open Roslyn.sln

Enabling C# 7 Features in Visual Studio

1. Navigate to CSharpParseOptions.cs and find IsFeatureEnabled()
2. Force it to return true to enable all available features
   
3. In the Solution Explorer, set the VisualStudioSetup project as the startup project and press F5 to run.
4. A new instance of Visual Studio will open with the C# 7 features available for use within VS.

Note: Although there will be no error squiggles in the editors, you won’t be able to perform full-builds until you deploy your changes to the out-of-process compiler.

Enabling C# 7 Features in Out-of-process compiler

To enable full builds within your experimental Visual Studio:

1. Make the above changes.
2. Deploy them to the CompilerExtension project.

There you have it, you can test out local functions, binary literals and digit separators. You can also use a similar approach to try out some of the other feature branches.