don't migrate storage version if CRD has one storage

apiextensions/storageversion/migrator.go

@@ -68,6 +68,11 @@ func (m *Migrator) Migrate(ctx context.Context, gr schema.GroupResource) error {
 		return fmt.Errorf("unable to determine storage version for %s", gr)
 	}
 
+	// don't migrate storage version if CRD has a single valid storage in its status
+	if len(crd.Status.StoredVersions) == 1 && crd.Status.StoredVersions[0] == version {
+		return nil
+	}
+
 	if err := m.migrateResources(ctx, gr.WithVersion(version)); err != nil {
 		return err
 	}

apiextensions/storageversion/migrator_test.go

@@ -63,6 +63,21 @@ var (
 			},
 		},
 	}
+
+	singleVersionFakeCRD = &apix.CustomResourceDefinition{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: fakeGR.String(),
+		},
+		Spec: apix.CustomResourceDefinitionSpec{
+			Group: fakeGK.Group,
+			Versions: []apix.CustomResourceDefinitionVersion{
+				{Name: "v1", Served: true, Storage: true},
+			},
+		},
+		Status: apix.CustomResourceDefinitionStatus{
+			StoredVersions: []string{"v1"},
+		},
+	}
 )
 
 func TestMigrate(t *testing.T) {
@@ -88,6 +103,22 @@ func TestMigrate(t *testing.T) {
 	)
 }
 
+func TestMigrate_SingleStoredVersion(t *testing.T) {
+	// setup
+	dclient := dynamicFake.NewSimpleDynamicClient(runtime.NewScheme())
+	cclient := apixFake.NewSimpleClientset(singleVersionFakeCRD)
+	m := NewMigrator(dclient, cclient)
+
+	if err := m.Migrate(context.Background(), fakeGR); err != nil {
+		t.Fatal("Migrate() =", err)
+	}
+
+	assertPatches(t, cclient.Actions(),
+		// patch resource definition dropping non-storage version
+		crdStorageVersionPatch(singleVersionFakeCRD.Name, "v1"),
+	)
+}
+
 // func TestMigrate_Paging(t *testing.T) {
 // 	t.Skip("client-go lacks testing pagination " +
 // 		"since list options aren't captured in actions")