How to create a multi-targeting nuget package from multiple projects

Question

I have a bunch of helper classes for web applications that we want to use across .NET Framework applications, Standard assemblies and .NET Core applications.

I'd like to build these as a Nuget package that can be installed anywhere, and brings across the correct references for the consuming application's target framework.

I've tried the following in the nuspec file:

<files>
    <file src="**.dll" target="lib" />
    <file src="..\Utils.Web.Core\bin\Release\*.dll" target="lib\netcoreapp2.1" />
    <file src="..\Utils.Web.Fx\bin\Release\*.dll" target="lib\net461" />
</files>

<references>
    <group targetFramework="netstandard2.0">
        <reference file="Utils.Web.dll" />
    </group>
    <group targetFramework="net461">
        <reference file="Utils.Web.Fx.dll" />
        <reference file="Utils.Web.dll" />
    </group>
    <group targetFramework="netcore45">
        <reference file="Utils.Web.Core.dll" />
        <reference file="Utils.Web.dll" />
    </group>-->
</references>

What I think this should do is copy the right dlls to the right target .lib folders and reference those assemblies. However the nupkg at the end does not contain any .lib folder.

Is what I am trying to do possible, and what am I missing?

Answer 1

grouping the references can not be intermixed with file list, please look at the schema definition of nuget spec file,

.nuspec reference - Explicit assembly reference

The group format cannot be intermixed with a flat list.

I could be able to create and use nuget pacakge using the below spec,

<package xmlns="http://schemas.microsoft.com/packaging/2010/07/nuspec.xsd">
  <metadata>
    <id>package_id</id>
    <!-- other metadata element -->
    <references>
        <group targetFramework="net461">
            <reference file="Utils.Web.dll" />
            <reference file="Utils.Web.Fx.dll" />
        </group>
        <group targetFramework="netcoreapp2">
            <reference file="Utils.Web.dll" />
            <reference file="Utils.Web.Core.dll" />
        </group>
    </references>
  </metadata>
  <files>
    <file src="bin\Debug\netcoreapp2\Utils.Web.Core.dll" target="lib" />
    <file src="bin\Debug\net461\Utils.Web.Fx.dll" target="lib" />
    <file src="bin\Debug\Utils.Web.dll" target="lib" />
  </files>
</package>

consider using either target attribute of file element or **group them explicitly using references **.