Persist NuGet packages empty target frameworks

Context

GitLab's NuGet Repository doesn't persist the target frameworks that don't have any dependencies.

For example, if a package was published with the following metadata:

XML

<dependencies>
    <group targetFramework=".NETStandard1.3">
        <dependency id="System.Net.Http" version="4.3.1" />
        <dependency id="System.Xml.XmlDocument" version="4.3.0" />
        <dependency id="System.Xml.XPath" version="4.3.0" />
        <dependency id="System.Xml.XPath.XmlDocument" version="4.3.0" />
    </group>
    <group targetFramework=".NETFramework4.0" />
    <group targetFramework=".NETFramework4.0-Client" />
    <group targetFramework=".NETFramework4.5" />
    <group targetFramework=".NETCore4.5" />
    <group targetFramework=".NETStandard1.6">
        <dependency id="System.Net.Http" version="4.3.1" />
        <dependency id="System.Xml.XmlDocument" version="4.3.0" />
        <dependency id="System.Xml.XPath" version="4.3.0" />
        <dependency id="System.Xml.XPath.XmlDocument" version="4.3.0" />
        <dependency id="NETStandard.Library" version="1.6.1" />
    </group>
    <group targetFramework=".NETPortable0.0-net45+netcore45+wp8+MonoAndroid+MonoTouch" />
    <group targetFramework=".NETPortable0.0-net45+netcore45+wpa81+wp8+MonoAndroid+MonoTouch" />
    <group targetFramework="Silverlight5.0" />
    <group targetFramework="UAP10.0">
        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="5.2.3" />
        <dependency id="System.Net.Http" version="4.3.2" />
        <dependency id="System.Xml.XPath" version="4.3.0" />
        <dependency id="System.Xml.XPath.XDocument" version="4.3.0" />
        <dependency id="System.Xml.XPath.XmlDocument" version="4.3.0" />
    </group>
    <group targetFramework=".NETStandard2.0">
        <dependency id="System.Net.Http" version="4.3.2" />
        <dependency id="System.Xml.XmlDocument" version="4.3.0" />
        <dependency id="System.Xml.XPath.XmlDocument" version="4.3.0" />
        <dependency id="System.Xml.XPath" version="4.3.0" />
    </group>
</dependencies>

we can see some target frameworks that have no dependencies:

• .NETFramework4.0
• .NETFramework4.0-Client
• .NETFramework4.5
• .NETCore4.5
• .NETPortable0.0-net45+netcore45+wp8+MonoAndroid+MonoTouch
• .NETPortable0.0-net45+netcore45+wpa81+wp8+MonoAndroid+MonoTouch
• Silverlight5.0

Those targets are ignored by GitLab's NuGet Repository, and this leads to the dependency confusion described in Package registry fails to resolve NuGet depende... (#440403).

What does this MR do and why?

The current dependency persistence design isn't ready to host those empty targets, which means it only support persisting dependencies that have name and version, while in the case of empty targets, we don't have any dependencies.

To work around this limitation, we create a dummy dependency for each empty target framework, and then filter them out in the metadata presenter.

References

• Package registry fails to resolve NuGet depende... (#440403) • Moaz Khalifa • 18.7 • Needs attention

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Publish this package to the NuGet Repository:

   dotnet nuget push htmlagilitypack.1.6.5.nupkg --source http://gdk.test:3000/api/v4/projects/<project_id>/packages/nuget/index.json --api-key <PAT>

2. Compare the dependencies we return with nuget.org

   # from gitlab registry
   curl -s -H "Private-Token: <PAT>" "http://gdk.test:3000/api/v4/projects/<project_id>/packages/nuget/metadata/HtmlAgilityPack/1.6.5.json" | jq '.catalogEntry.dependencyGroups'
   
   # from nuget.org
   curl "https://api.nuget.org/v3/catalog0/data/2018.10.15.07.01.06/htmlagilitypack.1.6.5.json" | jq '.dependencyGroups'

   Notice that all target frameworks that have no dependencies are present in the GitLab's endpoint response, the same as in nuget.org's response.

3. Move to master and delete the package, then republish it, and compare the dependencies again. You will notice how the response is different: mainly all target frameworks that have no dependencies are missing from GitLab's response, while present in nuget.org's response.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #440403