Pulp

The serializer does the correct thing, because the serializer does not use Repository.latest_version()

(pulp) [vagrant@pulp3-source-fedora31 pulp_rpm]$ http :24817${TARGET_REPO}versions/
HTTP/1.1 200 OK
Allow: GET, HEAD, OPTIONS
Connection: close
Content-Length: 283
Content-Type: application/json
Date: Wed, 12 Feb 2020 18:40:06 GMT
Server: gunicorn/20.0.4
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "count": 1,
    "next": null,
    "previous": null,
    "results": [
        {
            "base_version": null,
            "content_summary": {
                "added": {},
                "present": {},
                "removed": {}
            },
            "number": 0,
            "pulp_created": "2020-02-11T21:52:54.154568Z",
            "pulp_href": "/pulp/api/v3/repositories/rpm/rpm/8df090fe-a51e-4d23-acc4-e140e6294e02/versions/0/"
        }
    ]
}

(pulp) [vagrant@pulp3-source-fedora31 pulp_rpm]$ http :24817${TARGET_REPO}
HTTP/1.1 200 OK
Allow: GET, PUT, PATCH, DELETE, HEAD, OPTIONS
Connection: close
Content-Length: 377
Content-Type: application/json
Date: Wed, 12 Feb 2020 18:40:17 GMT
Server: gunicorn/20.0.4
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "description": null,
    "latest_version_href": "/pulp/api/v3/repositories/rpm/rpm/8df090fe-a51e-4d23-acc4-e140e6294e02/versions/0/",
    "name": "targetrepo",
    "pulp_created": "2020-02-11T21:52:54.152669Z",
    "pulp_href": "/pulp/api/v3/repositories/rpm/rpm/8df090fe-a51e-4d23-acc4-e140e6294e02/",
    "versions_href": "/pulp/api/v3/repositories/rpm/rpm/8df090fe-a51e-4d23-acc4-e140e6294e02/versions/"
}

However, underneath the hood, Pulp and plugin writers might have a problem, because if the "latest version" was deleted, Repository.latest_version() will return "None" instead of the one prior to the deleted one.

In [1]: RpmRepository.objects.all()[1].latest_version()    

In [2]: RepositoryVersion.objects.filter(repository=RpmRepository.objects.all()[1])                                    
Out[2]: <QuerySet [<Repository: targetrepo; Version: 0>]>

In [3]: RpmRepository.objects.all()[1].last_version        
Out[3]: 1

So what the JSON API returns and what the internal APIs return do not match up.

Anything that uses the internal APIs to find the latest version, like copy (what I'm working on) or probably distributions (though I haven't tested it) will run into this issue.