SolvedHome Framework assemblies are no longer added to .nuspec when using the new .csproj project system

Moved from #4412 (comment):

In the marvelous world of project.json, specifying a frameworkAssemblies node was enough to tell NuGet to add the corresponding entries in the .nuspec file:

{
  "frameworks": {
    "net451": {
      "frameworkAssemblies": {
        "System.IdentityModel": "4.0.0.0",
        "System.Xml": "4.0.0.0"
      }
    }
  }
}

<?xml version="1.0" encoding="utf-8"?>
<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
  <metadata>
    // ...
    <frameworkAssemblies>
      <frameworkAssembly assemblyName="System.IdentityModel" targetFramework=".NETFramework4.5.1" />
      <frameworkAssembly assemblyName="System.Xml" targetFramework=".NETFramework4.5.1" />
    </frameworkAssemblies>
  </metadata>
</package>

With .csproj, this is no longer true when using Reference:

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

  <ItemGroup>
    <Reference Include="System.IdentityModel" />
    <Reference Include="System.Xml" />
  </ItemGroup>

</Project>

This breaking change has obviously important implications, as framework assemblies are no longer brought transitively, which means that the final user of the package has to reference the framework assemblies in his own app.

Is there any hope of getting this fixed soon? We're ready to merge in .csproj ports on several major NuGet packages with millions of downloads and we're blocked by only this issue. This is incredibly frustrating.

Remember to port to .csproj we had to abandon project.json all together and move our projects over. From the moment we do that, the move itself starts to decay if unmerged. We have to pause all project-related PRs and changes, or make them on both branches and merge all along the way (which users and PRs won't do). To have to hang on merging .csproj formats or indefinitely not release on NuGet are terrible options and they're costing time and frustration. I'm personally up to 6 blocked projects now, and other maintainers at Stack are hitting the same.

Please up the priority on this, it needs a fix very soon.

@NickCraver I am working on this issue, I will update this thread very soon.