Target which adds ProjectReference or PackageReference on a condition

[oruchreis]

Hi,
I'm trying to add ProjectReference or PackageReference on a condition with a target. I have csproj files including these:

<CustomReference Include="Package1" />
<CustomReference Include="Package2" />

The condition property is set in Directory.Build.props:

<PropertyGroup>
  <UseLocalNuGetProjects Condition="'$(UseLocalNuGetProjects)' == ''">true</UseLocalNuGetProjects>

And the target is implemented in Directory.Build.targets :

<Project>
  <Target Name="ResolveCustomeReferences"  BeforeTargets="BeforeBuild;ResolveReferences">
    <ItemGroup Condition="'@(CustomReference.Identity)' != ''">
      <MSBuild Projects="$(MSBuildThisFileDirectory)Libraries/%(CustomReference.Identity)/%(CustomReference.Identity).csproj" 
               Targets="Restore;Build" Condition="'$(UseLocalNuGetProjects)' == 'true'" />
      <ProjectReference Include="$(MSBuildThisFileDirectory)Libraries/%(CustomReference.Identity)/%(CustomReference.Identity).csproj"
                        Condition="'$(UseLocalNuGetProjects)' == 'true'" IncludeAssets="all" />      
      <PackageReference Include="@(CustomReference)"
                        Condition="'$(UseLocalNuGetProjects)' != 'true'" /><!-- I have also Directory.Packages.props so I don't need version in PackageReference in the target. -->
    </ItemGroup>
  </Target>
</Project>

I have 2 problem with this approach:

1. The build is working if the project doesn't use transitive nuget packages in the referenced project with ProjectReference. If the project uses nuget packages included in the referenced project with ProjectReference, then build fails. Normally, if we set ProjectReference statically in the csproj, we can use transitive nuget packages in that reference, but I couldn't overcome the unresolved nuget package errors with above dynamically added ProjectReference.
2. The intellisense and solution explorer doesn't see the ProjectReference nor PackageReference according to UseLocalNuGetProjects property.

How can I solve these two problems?

By the way I've tried many targets in BeforeTargets like ResolveProjectReferencesDesignTime2, CompileDesignTime, ResolveProjectReferences, ResolvePackageDependencies, Compile, etc, but no luck.

Best Regards.

[vst121]

Hi,

Both issues stem from the fact that ProjectReference and PackageReference items need to be evaluated at project evaluation time, not inside a target. When you add them dynamically inside a target:

• Transitive NuGet references won’t flow correctly because MSBuild resolves NuGet package graphs during evaluation, before any target runs. That’s why your dynamically added ProjectReference doesn’t see the referenced project’s packages.
• IntelliSense / Solution Explorer doesn’t see them because those editors read the project items from the evaluated .csproj, and targets aren’t executed in design-time evaluation.

Solution:

• Move your conditional ProjectReference / PackageReference into ItemGroups with conditions directly in your .csproj or
  Directory.Build.props, instead of adding them inside a target. Example:

<ItemGroup Condition="'$(UseLocalNuGetProjects)' == 'true'">
  <ProjectReference Include="Libraries\Package1\Package1.csproj" />
  <ProjectReference Include="Libraries\Package2\Package2.csproj" />
</ItemGroup>

<ItemGroup Condition="'$(UseLocalNuGetProjects)' != 'true'">
  <PackageReference Include="Package1" />
  <PackageReference Include="Package2" />
</ItemGroup>

• If you need the list to be dynamic, you can use an ItemGroup in Directory.Build.props with items, then transform them into ProjectReference / PackageReference in another static ItemGroup using MSBuild item metadata and Condition.

This way, NuGet and the IDE can resolve dependencies at evaluation time, and transitive packages will flow correctly.