Filter out versions without libraries

- Create a get_versions() method in the LibraryListView that filters out
  versions that don't have any libraries from the drop-down menu
- Ensure that the active() manager is unaffected, so the versions are still
valid for the query string, only hidden in the drop-down menu

libraries/tests/test_views.py

@@ -5,21 +5,34 @@ from dateutil.relativedelta import relativedelta
 
 from model_bakery import baker
 
+from versions.models import Version
+
 
 def test_library_list(library_version, tp, url_name="libraries"):
     """GET /libraries/"""
-    last_year = datetime.date.today() - datetime.timedelta(days=365)
+    # Create a version with a library
+    last_year = library_version.version.release_date - datetime.timedelta(days=365)
     v2 = baker.make("versions.Version", name="Version 1.78.0", release_date=last_year)
     lib2 = baker.make(
         "libraries.Library",
         name="sample",
     )
     baker.make("libraries.LibraryVersion", library=lib2, version=v2)
+
+    # Create a version with no libraries
+    v_no_libraries = baker.make(
+        "versions.Version", name="No Libraries", release_date=last_year
+    )
+
+    # Confirm that you know which version is the most recent
+    assert library_version.version == Version.objects.most_recent()
+
     res = tp.get(url_name)
     tp.response_200(res)
     assert "library_list" in res.context
     assert library_version.library in res.context["library_list"]
     assert lib2 not in res.context["library_list"]
+    assert v_no_libraries not in res.context["versions"]
 
 
 def test_library_list_mini(library_version, tp):

libraries/views.py

@@ -3,6 +3,7 @@ import structlog
 
 from dateutil.relativedelta import relativedelta
 from django.http import Http404
+from django.db.models import Count
 from django.shortcuts import get_object_or_404, redirect
 from django.views.generic import DetailView, ListView
 from django.views.generic.edit import FormMixin
@@ -52,7 +53,7 @@ class LibraryList(VersionAlertMixin, ListView):
         else:
             context["version"] = Version.objects.most_recent()
         context["categories"] = self.get_categories(context["version"])
-        context["versions"] = Version.objects.active().order_by("-release_date")
+        context["versions"] = self.get_versions()
         context["library_list"] = self.get_queryset()
         return context
 
@@ -63,6 +64,28 @@ class LibraryList(VersionAlertMixin, ListView):
             .order_by("name")
         )
 
+    def get_versions(self):
+        """
+        Return a queryset of all versions to display in the version dropdown.
+        """
+        versions = Version.objects.active().order_by("-release_date")
+
+        # Annotate each version with the number of libraries it has
+        versions = versions.annotate(
+            library_count=Count("library_version", distinct=True)
+        ).order_by("-release_date")
+
+        # Filter out versions with no libraries
+        versions = versions.filter(library_count__gt=0)
+
+        most_recent_version = Version.objects.most_recent()
+
+        # Confirm the most recent v is in the queryset, even if it has no libraries
+        if most_recent_version not in versions:
+            versions = versions | Version.objects.filter(pk=most_recent_version.pk)
+
+        return versions
+
 
 class LibraryListMini(LibraryList):
     """Flat list version of LibraryList"""