Conditional project references fail when targeting multiple TFMs

Reproduction steps:

1. Create 3 projects, LibA, LibB & LibC (netstandard1.1)
2. Reference LibA from LibB and LibB from LibC
3. Add a class in LibA and reference it in LibC
4. Confirm successful build
5. Make LibC target another TFM (netcoreapp1.1)
6. Add a project reference to LibA, conditional to the second TFM
7. Run dotnet build or build in VS2017
8. Build fails for first TFM (netstandard1.1)

The following error message is provided: Cannot find project info for ‘X:\LibA\LibA.csproj’. This can indicate a missing project reference. LibC C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\Sdks\Microsoft.NET.Sdk\build\Microsoft.NET.Sdk.targets 92

This is LibC.csproj:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>    
    <TargetFrameworks>netstandard1.1;netcoreapp1.1</TargetFrameworks>
  </PropertyGroup>
  <ItemGroup>
    <ProjectReference Include="..\LibB\LibB.csproj" />
  </ItemGroup>
  <ItemGroup Condition=" '$(TargetFramework)' == 'netcoreapp1.1'">
    <ProjectReference Include="..\LibA\LibA.csproj" />
  </ItemGroup>
</Project>

Removing the conditional TFM, e.g. letting LibC only target netstandard1.1 again will result in a successful build even if the conditional reference remains.

[dsplaisted]

@sfoslund Would you be able to take a look at this? Nick’s comment describes the issue.

[nguerrera]

I haven’t worked on this project for a long time, so I’m not aware of any updates. Adding @marcpopMSFT @dsplaisted