Packaging of 'net5.0-windows' broken since 5.9.1.11

[GeertvanHorrik]

Details about Problem

NuGet product used (NuGet.exe | Visual Studio | MSBuild.exe | dotnet.exe): NuGet.exe

Product version:

Worked before? If so, with which NuGet version:

Worked: 5.8.1
Not working: 5.9.1.11

Repro steps and/or sample project

We want to package a NuGet package with only "net5.0-windows". We need this to support our Squirrel installations and updates.

Before 5.9, we could create a package for a project targeting net5.0-windows. After the update, we no longer can package because of this error:

NU1012: Some included files are included under TFMs which are missing a platform version: net5.0-windows
NuGet.Packaging.Core.PackagingException: Some included files are included under TFMs which are missing a platform version: net5.0-windows
   at NuGet.Packaging.PackageBuilder.ValidateFileFrameworks(IEnumerable`1 files)
   at NuGet.Packaging.PackageBuilder.Save(Stream stream)
   at NuGet.Commands.PackCommandRunner.BuildPackage(PackageBuilder builder, String outputPath, Boolean symbolsPackage)
   at NuGet.Commands.PackCommandRunner.BuildFromNuspec(String path)
   at NuGet.CommandLine.PackCommand.ExecuteCommand()
   at NuGet.CommandLine.Command.ExecuteCommandAsync()
   at NuGet.CommandLine.Command.Execute()
   at NuGet.CommandLine.Program.MainCore(String workingDirectory, String[] args)

Our potential workarounds are:

1. Don't update NuGet to 5.9
2. Explicitly set net5.0-windows7.0 as target framework (but why enforce this, it should fallback to this by default?)

Verbose Logs

[erdembayar]

@GeertvanHorrik
Thank you for filing this issue.
I believe that change was part of wider .net 5 sdk change. If you looks at .net 5 sdk design then you'll see net5.0-windowsX.Y as target framework, and X.Y as TPV(TargetPlatformVersion).
@zkat Could be able to add more details here?

Edit: If you're not going to pack via csproj, then you'll need to append the platform version number yourself as mentioned here.

[nkolev92]

This is by design.
The net5.0-platform style target frameworks must have a target platform version.

Change here; NuGet/NuGet.Client#3691