msbuild should pass TFM for classic csproj project to GetReferenceNearestTargetFrameworkTask

[mishra14]

after talking with @rainersigwald, we realized that when msbuild invokes NuGet's GetReferenceNearestTargetFrameworkTask, it does not pass the tfm from a referenced project if it is a classic csproj.

code in question- https://github.com/Microsoft/msbuild/blob/51f53ebf530612beede45d13c535152785e23bdd/src/Tasks/Microsoft.Common.CurrentVersion.targets#L1700-L1713

[rainersigwald]

The core issue here is that $(TargetFramework) doesn't get defined in non-SDK builds. If GetReferenceNearestTargetFrameworkTask can accept full TFMs, I think we could solve this with just an additional

       <TargetFrameworks Condition="'$(TargetFrameworks)' == '' and '$(TargetFramework)' == ''">$(TargetFrameworkMoniker)</TargetFrameworks> 

Do you know if that's the case @mishra14? If we have to massage the long-form TFM to get a short name out of it we'll probably need a NuGet task for that.

[mishra14]

@rainersigwald Do you mean the full moniker like .NETFramework,Version=v4.6?

If so then yes, that will be fine, current code can parse the long names. Also, given that you convert TargetFramework into TargetFrameworks, if you rolled TargetFrameworkMoniker into that as well, then it should work with no NuGet changes.

[rainersigwald]

An attempt at this: #3620. It's stale so closing it but might be a good basis for picking this up again.