[Regression] .NET 6 SDK will no longer copy the netstandard facades to the publish directory for net461 apps

cc: @dsplaisted @marcpopMSFT @andschwa @ericstj

Repro Steps

1. Create a new netstandard lib

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
  </PropertyGroup>

</Project>

1. Create a new net461 Console app that references it:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net461</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <ProjectReference Include="..\reproLib\reproLib.csproj" />
  </ItemGroup>

</Project>

1. Publish the project with dotnet publish

Expected Because the net461 project is referencing a netstandard library, tooling should inject all of the netstandard facades onto the publish directory to ensure the application will be able to run as expected. This is what happens with .NET 5.0 and previous sdks.

Actual bin directory does get the facades injected, but the publish directory won’t when you use a 6.0 SDK, which means that if the app tries to run in a machine that only has .NET 461 installed, the app will likely crash at runtime.

Problem

I took a look and the issue here seems to be caused by this change which basically changed the way we calculate the items to be copied to the publish directory and added an additional filter to check if the ResolveCopyLocal item had the Private metadata set to false. When we are injecting the netstandard facades to resolveCopyLocal item, we explicitly set Private to false, which is why they are now all getting excludded from the publish directory. Here is where we set the metadata to false and the explanation of why we do it: https://github.com/dotnet/sdk/blob/203c2ac3eeb99d188d2b439c96f72f93b7b726fd/src/Tasks/Microsoft.NET.Build.Extensions.Tasks/msbuildExtensions/Microsoft/Microsoft.NET.Build.Extensions/Microsoft.NET.Build.Extensions.NETFramework.targets#L91-L109

This regression has a potential of great impact, so we should consider how we can fix it before 6.0 ships, whether the solution is to not set Private item to false or if the solution is instead to change the new filter on the publish items.

[joperezr]

@dsplaisted is there an ETA for when this fix will land? I suppose that before shipping 6.0? If we don’t fix this in time I’m afraid a lot of customers will start hitting this as soon as we ship a VS that contains this SDK

[joperezr]

@andschwa I haven’t fully tested it, but you can try to see if the following target works for your needs:

  <Target Name="InjectNetStandardFacadesToPublishDirectory"
          BeforeTargets="ComputeResolvedFilesToPublishList"
          Condition="'@(_NETStandardLibraryNETFrameworkLib)' != ''">
    <ItemGroup>
      <_ResolvedCopyLocalPublishAssets Include="@(_NETStandardLibraryNETFrameworkLib)" 
                                      Condition="'%(_NETStandardLibraryNETFrameworkLib.FileName)' != 'netfx.force.conflicts'" />
    </ItemGroup>
  </Target>

I’m sure it is not perfect and it depends on internal items and targets so it is fragile and easy to get broken, but it may work while you wait for the final fix to make it to the SDK. From the testing I did, this should be injecting correctly all of the facades that your app requires into your publish directory.