“Error CS8107: Feature ‘(…)’ is not available in C# 7.0. Please use language version 7.3 or greater” in Azure DevOps build

During work with our latest project, where we’re using Azure DevOps for CI/CD, I encountered this error while trying to build project which used enum as generic type parameter (C# 7.3 feature). I’ve discovered that is quite common issue, without short and simple explanation, so decided to write a quick blog post on how I dealt with it.

I was really confused – build on my local machine worked fine. I was using .NET Framework 4.7 with Visual Studio 2019. I’ve looked into the documentation provided by Microsoft and found a table presented below:

It made me even more confused. According to this, my build should success – all versions of .NET Framework uses C# 7.3 by default. So why my Azure DevOps build pipeline failed?

As I found out here – Azure DevOps build .Net Core error CS8107 – explanation is simple: Azure DevOps agent uses Dotnet CLI for build process. The above table applies for the compiler that is used by Visual Studio. It looks different for Azure DevOps – Dotnet CLI in DevOps by default uses C# 7.0. This is why build succeed on my local machine, but failed in pipeline.

To force usage of C# 7.3 by Azure DevOps, you must specify this explicitly. To do this, create a file Directory.Build.props in your solution root folder and fill it in with following content:

 <Project> <PropertyGroup> <LangVersion>7.3</LangVersion> </PropertyGroup> </Project> 

It does not affect your local build in any way – compiler for .NET Framework (and .NET Core 2.x and 3.x) by default uses C# 7.3 – it’s just the information for Azure DevOps to use proper language version.

And that’s it! After adding the file, the build pipeline finished successfully

Sources

• C# documentation – Configure language version
• Developer Community Visual Studio issue