NETSDK1100 blocks building on Linux

I have a test project which multi-targets between net472;netcoreapp2.1;netcoreapp3.0. Only when targeting net472 or netcoreapp3.0 does it reference or use any WPF/WinForms types. Nevertheless, I have to set the SDK attribute to Microsoft.NET.Sdk.WindowsDesktop for this to work with netcoreapp3.0 at all, AFAIK.

This blocks the test project from building the netcoreapp2.1 target on linux, which blocks me testing my library on Linux.

How should I proceed?

[natemcmaster]

I ran into this myself with the 3.1 SDK. My workaround was to add this to my csproj file. This is a workaround, of course, so your mileage may vary.

<ItemGroup>
  <KnownFrameworkReference Update="Microsoft.WindowsDesktop.App" IsWindowsOnly="false" />
  <KnownFrameworkReference Update="Microsoft.WindowsDesktop.App.WPF" IsWindowsOnly="false" />
  <KnownFrameworkReference Update="Microsoft.WindowsDesktop.App.WindowsForms" IsWindowsOnly="false" />
</ItemGroup>

[AArnott]

so we don’t want to bloat the SDK for them by including the support by default.

Why must this additional support be built into the SDK at all? Why not have it be a nuget package that can be referenced by UI projects, that includes the SDK tools necessary to build such projects?