Avoid returning nil responseKind in v1beta1 aggregated discovery

Kubernetes-commit: 1876ddf71497bad349f7c4df24c2e22356d3bad9

Author: liggitt

discovery/aggregated_discovery.go

@@ -111,6 +111,8 @@ func convertAPIGroup(g apidiscovery.APIGroupDiscovery) (
 	return group, gvResources, failedGVs
 }
 
+var emptyKind = metav1.GroupVersionKind{}
+
 // convertAPIResource tranforms a APIResourceDiscovery to an APIResource. We are
 // resilient to missing GVK, since this resource might be the parent resource
 // for a subresource. If the parent is missing a GVK, it is not returned in
@@ -125,7 +127,7 @@ func convertAPIResource(in apidiscovery.APIResourceDiscovery) (metav1.APIResourc
 		Categories:   in.Categories,
 	}
 	var err error
-	if in.ResponseKind != nil {
+	if in.ResponseKind != nil && (*in.ResponseKind) != emptyKind {
 		result.Group = in.ResponseKind.Group
 		result.Version = in.ResponseKind.Version
 		result.Kind = in.ResponseKind.Kind
@@ -140,7 +142,7 @@ func convertAPIResource(in apidiscovery.APIResourceDiscovery) (metav1.APIResourc
 // convertAPISubresource tranforms a APISubresourceDiscovery to an APIResource.
 func convertAPISubresource(parent metav1.APIResource, in apidiscovery.APISubresourceDiscovery) (metav1.APIResource, error) {
 	result := metav1.APIResource{}
-	if in.ResponseKind == nil {
+	if in.ResponseKind == nil || (*in.ResponseKind) == emptyKind {
 		return result, fmt.Errorf("subresource %s/%s missing GVK", parent.Name, in.Subresource)
 	}
 	result.Name = fmt.Sprintf("%s/%s", parent.Name, in.Subresource)

discovery/aggregated_discovery_test.go

@@ -610,6 +610,76 @@ func TestSplitGroupsAndResources(t *testing.T) {
 			},
 			expectedFailedGVs: map[schema.GroupVersion]error{},
 		},
+		{
+			name: "Aggregated discovery with single subresource and parent empty GVK",
+			agg: apidiscovery.APIGroupDiscoveryList{
+				Items: []apidiscovery.APIGroupDiscovery{
+					{
+						ObjectMeta: metav1.ObjectMeta{
+							Name: "external.metrics.k8s.io",
+						},
+						Versions: []apidiscovery.APIVersionDiscovery{
+							{
+								Version: "v1beta1",
+								Resources: []apidiscovery.APIResourceDiscovery{
+									{
+										// resilient to empty GVK for parent
+										Resource:         "*",
+										Scope:            apidiscovery.ScopeNamespace,
+										SingularResource: "",
+										ResponseKind:     &metav1.GroupVersionKind{},
+										Subresources: []apidiscovery.APISubresourceDiscovery{
+											{
+												Subresource: "other-external-metric",
+												ResponseKind: &metav1.GroupVersionKind{
+													Kind: "MetricValueList",
+												},
+												Verbs: []string{"get"},
+											},
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expectedGroups: metav1.APIGroupList{
+				Groups: []metav1.APIGroup{
+					{
+						Name: "external.metrics.k8s.io",
+						Versions: []metav1.GroupVersionForDiscovery{
+							{
+								GroupVersion: "external.metrics.k8s.io/v1beta1",
+								Version:      "v1beta1",
+							},
+						},
+						PreferredVersion: metav1.GroupVersionForDiscovery{
+							GroupVersion: "external.metrics.k8s.io/v1beta1",
+							Version:      "v1beta1",
+						},
+					},
+				},
+			},
+			expectedGVResources: map[schema.GroupVersion]*metav1.APIResourceList{
+				{Group: "external.metrics.k8s.io", Version: "v1beta1"}: {
+					GroupVersion: "external.metrics.k8s.io/v1beta1",
+					APIResources: []metav1.APIResource{
+						// Since parent GVK was nil, it is NOT returned--only the subresource.
+						{
+							Name:         "*/other-external-metric",
+							SingularName: "",
+							Namespaced:   true,
+							Group:        "",
+							Version:      "",
+							Kind:         "MetricValueList",
+							Verbs:        []string{"get"},
+						},
+					},
+				},
+			},
+			expectedFailedGVs: map[schema.GroupVersion]error{},
+		},
 		{
 			name: "Aggregated discovery with multiple subresources",
 			agg: apidiscovery.APIGroupDiscoveryList{