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Feature ‘default literal’ is not available in C# 7.0.

On one of my projects we are ‘default literals’, one of the features introduced in C#7.1.  To be able to use this, you have to change your project properties to point to the latest minor version(more information here: Unfortunately on the build server it didn’t work as expected, but got the following error in our build logs:

error CS8107: Feature ‘default literal’ is not available in C# 7.0. Please use language version 7.1 or greater.

The strange this was that on the same build server,  another build using the same feature did succeed. So it couldn’t be linked to the possibility that C# 7.1 was not installed on the build server.

Then I got some inspiration, maybe it was related to the Build Configuration. And indeed when I switched from Debug to Release the problem appeared in my Visual Studio as well:


When enabling C# 7.1 for this project, a <langversion> is introduced in the csproj file:


The problem was that this line was set inside a conditional propertygroup:

<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">



By moving the <langversion> to another propertygroup(without a conditional) the problem was solved.

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