TeamCity NuGet package build for different .NET Frameworks

I've been doing updates to .NET Framework targeted versions of projects updating to latest .NET (4.6.2).

Some of these projects are NuGet packages, built in TeamCity 9.0.2.

I've use the steps in this guide to create multiple build configurations for different .NET Framework version as some of the projects I haven't updated to 4.6.2 reference the NuGet packages. So I am trying to get TeamCity to use these build configurations to output the various Net40, Net45, Net46 and Net462 versions so that I have full compatibility without forcing the need to upgrade all projects that use the NuGet when updating the packages.

I really can't figure out how to do this in TeamCity. I am fairly sure that this should be done in the "Build Steps" configuration, but so far I've not managed to get this to work.

So one thing I've tried, which I think I need to do but am not sure is duplicate the first build step and set the Configuration to Release-Net46. I think this is necessary otherwise this version of the assembly wouldn't be built (please correct me if I'm wrong about that!)

The second thing I've tried is to duplicate the NuGet Pack step and in Properties set Configuration=Release-Net46 but all that did was replace the Net462 version with Net46 and not include both in the artifacts like I'd hoped.

I also tried in the Properties of NuGet Pack to have multiple Configuration elements like Configuration=Release;Configuration=Release-Net46 or Configuration=Release,Release-Net46 but both of those resulted in the build failing altogether so clearly that's not the answer.

I think there must be a way to get this NuGet Pack build step to pick up the output from the other build configurations and output all available versions of the assembly to the artifacts.

Is that possible? I had thought about creating separate projects for each build configuration in TeamCity but I'm unsure if that's the correct way or it that would cause issues with the package feed and it would seem untidy to duplicate the project four times for each .NET Framework version.

Ok I ended up solving this through trial and error and learning about NuSpec. Note, I didn't find a way to do this using purely TeamCity settings but this is equally good.

I was correct that you need extra build steps to build the assemblies in the solution/project level build configurations and point each Configuration at Release-NetX.

EDIT I've found it's actually best in the above to point the NetX build steps at the .csproj rather than the .sln. That way you don't need the build configurations at a solution level, as long as they exist in the .csproj then it will all build fine.

Once this is done, TC will then be building all versions into their respective bin\Release-NetX directories.

Next was to add a .nuspec file to the root directory of the solution project to build the NuGet for.

<?xml version="1.0"?>
<package xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <metadata xmlns="http://schemas.microsoft.com/packaging/2010/07/nuspec.xsd">
    <id>Foo.Bar.Package</id>
    <version>1.0.23</version>
    <authors>FooBar Industries</authors>
    <requireLicenseAcceptance>false</requireLicenseAcceptance>
    <description>FooBar Industries package</description>
  </metadata>
  <files>
    <file src="bin\Release\*.dll" target="lib\net462" />
    <file src="bin\Release-Net46\*.dll" target="lib\net46" />
    <file src="bin\Release-Net45\*.dll" target="lib\net45" />
    <file src="bin\Release-Net4\*.dll" target="lib\net40" />
  </files>
</package>

Next is to alter the NuGet Pack TeamCity Build Step and in Specification files section and point this to your .nuspec file. There's a checkbox for Prefer project files to .nuspec. It worked for my just by unchecking this and I didn't even need to point to .nuspec file.