Exclude target framework from NuGet package - .net-core

Question

How can i exclude specific target framework from nuspec (NuGet package) generation?
This is my csproj:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFrameworks>netstandard2.0;net5.0;net5.0-windows</TargetFrameworks>
<IsPackable>true</IsPackable>
</PropertyGroup>
<PropertyGroup Condition="'$(TargetFramework)' == 'net5.0-windows'">
<IsPackable>false</IsPackable>
</PropertyGroup>
</Project>
dotnet pack command generates NuGet package that contains all target frameworks not only netstandard2.0 and net5.0
Generated nuspec:
<?xml version="1.0" encoding="utf-8"?>
<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
<metadata>
<id>ExampleLibrary</id>
<version>1.0.0</version>
<authors>ExampleLibrary</authors>
<description>Package Description</description>
<dependencies>
<group targetFramework="net5.0" />
<group targetFramework="net5.0-windows7.0" />
<group targetFramework=".NETStandard2.0" />
</dependencies>
</metadata>
</package>

Answer 1

<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFrameworks>netstandard2.0;net5.0;net5.0-windows7.0</TargetFrameworks>
<IsPackable>true</IsPackable>
<GenerateNuspecDependsOn>$(GenerateNuspecDependsOn);_ExcludeTargetFramework;_ExcludeTargetFrameworkDependency</GenerateNuspecDependsOn>
</PropertyGroup>
<Target Name="_ExcludeTargetFramework" AfterTargets="_GetTargetFrameworksOutput" BeforeTargets="_WalkEachTargetPerFramework">
<ItemGroup>
<_TargetFrameworks Remove="net5.0-windows7.0" />
</ItemGroup>
</Target>
<Target Name="_ExcludeTargetFrameworkDependency" AfterTargets="_WalkEachTargetPerFramework" BeforeTargets="GenerateNuspec">
<ItemGroup>
<_FrameworksWithSuppressedDependencies Include="net5.0-windows7.0" />
</ItemGroup>
</Target>
</Project>
<?xml version="1.0" encoding="utf-8"?>
<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
<metadata>
<id>ExampleLibrary</id>
<version>1.0.0</version>
<authors>ExampleLibrary</authors>
<description>Package Description</description>
<dependencies>
<group targetFramework="net5.0" />
<group targetFramework=".NETStandard2.0" />
</dependencies>
</metadata>
</package>

Answer 2

Remove all the dependencies (including TargetFramework)
In case you want to remove all dependencies (ie all target frameworks), the above solution won't work. Build will fail with the following error:
error MSB4044: The "ResolvePackageAssets" task was not given a value for the required parameter "TargetFramework".
Easy way
In case you just want to remove all dependencies, you can use the SuppressDependenciesWhenPacking property.
<PropertyGroup>
<SuppressDependenciesWhenPacking>true</SuppressDependenciesWhenPacking>
</PropertyGroup>
Full control of Nuspec
Otherwise, if you want to have a full control on the content of Nuspec after a first pass of generation, you can use a variation of this:
<?xml version="1.0" encoding="utf-8"?>
<Project>
<UsingTask
TaskName="RemoveDependencies"
TaskFactory="CodeTaskFactory"
AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll" >
<ParameterGroup>
<Nuspec ParameterType="System.String" Required="true"/>
</ParameterGroup>
<Task>
<Reference Include="System.Xml"/>
<Reference Include="System.Xml.Linq"/>
<Using Namespace="System"/>
<Using Namespace="System.IO"/>
<Using Namespace="System.Xml.Linq"/>
<Code Type="Fragment" Language="cs">
<!-- Modify XML of the NuSpec -->
<![CDATA[
XElement doc = XElement.Load(Nuspec);
var dependenciesElement = doc.Descendants(XName.Get("dependencies", "http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd")).FirstOrDefault();
if (dependenciesElement != null)
{
dependenciesElement.Remove();
}
using (var textWriter = File.CreateText(Nuspec))
{
doc.Save(textWriter);
}]]>
</Code>
</Task>
</UsingTask>
<!-- From https://stackoverflow.com/questions/53762903/how-to-inject-a-custom-dependency-in-an-msbuild-nuget-pack-generated-nuspec -->
<!-- Disable nupkg generation before running pack -->
<Target Name="__DisablePacking" BeforeTargets="GenerateNuspec" Condition="$(NuspecFile) == '' And $(IsPackable) != 'false'">
<PropertyGroup>
<ContinuePackingAfterGeneratingNuspec>false</ContinuePackingAfterGeneratingNuspec>
</PropertyGroup>
</Target>
<!-- Remove .Net Standard 2.0 dependency as it's a native package -->
<!-- Modify the generated nuspec file and rerun the pack target -->
<Target Name="__ExcludeTargetFrameworkDependency" AfterTargets="Pack" Condition="$(NuspecFile) == '' And $(IsPackable) != 'false'">
<!-- Get the nuspec file name -->
<PropertyGroup>
<_NugetPackOutputAsProperty>#(NuGetPackOutput)</_NugetPackOutputAsProperty>
</PropertyGroup>
<ItemGroup>
<_NugetPackOutputAsItem Remove="#(_NugetPackOutputAsItem)"/>
<_NugetPackOutputAsItem Include="$(_NugetPackOutputAsProperty.Split(';'))" />
</ItemGroup>
<PropertyGroup>
<__NuspecFileName>%(_NugetPackOutputAsItem.Identity)</__NuspecFileName>
</PropertyGroup>
<Message Importance="High" Text="Remove Dependencies from $(__NuspecFileName)" />
<RemoveDependencies Nuspec="$(__NuspecFileName)" />
<!-- Invoke the Pack target again with packing enabled -->
<PropertyGroup>
<ContinuePackingAfterGeneratingNuspec>true</ContinuePackingAfterGeneratingNuspec>
</PropertyGroup>
<MsBuild
Projects="$(MSBuildProjectFullPath)"
Targets="Pack"
Properties="NuspecFile=$(__NuspecFileName);NoPackageAnalysis=true">
</MsBuild>
</Target>
</Project>
Notes:
GenerateNuspec target is doing both generation and packing. To disable packing after nuspec generation, we can use the ContinuePackingAfterGeneratingNuspec property.
Pack target is invoked twice (once by the user) and the second time with the system after first pack.
__ExcludeTargetFrameworkDependency rely on the Nuspec File value to be empty to execute on the first pack and to not execute on the second run. It obviously won't work if a Nuspec file is provided for the first run (with NuspecFile property).
Note the usage of And $(IsPackable) != 'false' to avoid invoking the target on test projects.
All NuGet targets like GenerateNuspec are located in C:\Program Files\dotnet\sdk\6.0.308\Sdks\NuGet.Build.Tasks.Pack\build\NuGet.Build.Tasks.Pack.targets
All NuGet tasks for .NET 6, like PackTask, are located in C:\Program Files\dotnet\sdk\6.0.308\Sdks\NuGet.Build.Tasks.Pack\Desktop\NuGet.Build.Tasks.Pack.dll