Condition on "PropertyGroup" in Directory.build.props not working

Question

I've created a Directory.build.props file so I can set the C# language version in there. But I also have Visual Basic Projects, so i wanted to limit the setting to C# projects.

<Project>
    <PropertyGroup Condition="'$(ProjectExt)'=='.csproj'">
        <LangVersion>7.2</LangVersion>   
    </PropertyGroup>
</Project>

But my project is not loading it / the UI is not displaying the language version 7.2. I've tried to apply the same condition inside the csproj file, also not working.

<PropertyGroup>
    <LangVersion Condition="'$(ProjectExt)'=='.csproj'">7.2</LangVersion>
</PropertyGroup>

However, this will work:

<Target Name="PostBuild" AfterTargets="PostBuildEvent">
    <Message Text="Condition working" Importance="high" Condition="'$(ProjectExt)'=='.csproj'"/>
</Target>

The build will output my message

Why is the condition not working on my LanguageVersion? Any Clues?

Answer 1

You will need to use a property to condition on that is available very early in the build. In your case, you should condition on MSBuildProjectExtension:

<PropertyGroup>
  <LangVersion Condition="'$(MSBuildProjectExtension)'=='.csproj'">7.2</LangVersion>
</PropertyGroup>

See MSBuild reserved and well-known properties for the complete set of available properties.

ProjectExt is only defined late in the build definition and is therefore not available in Directory.Build.props, which is imported very early into the project.