godot/modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators/Godot.SourceGenerators.props

<Project>
  <ItemGroup>
    <!-- $(GodotProjectDir) is defined by Godot.NET.Sdk -->
    <CompilerVisibleProperty Include="GodotProjectDir" />
    <CompilerVisibleProperty Include="GodotSourceGenerators" />
    <CompilerVisibleProperty Include="IsGodotToolsProject" />
  </ItemGroup>
</Project>