✨ Fake client: Allow adding indexes at runtime

The cache allows to add indexes at runtime, however doing so isn't
really testable with the fakeclient, as it didn't have that capability.
Add it.

Author: alvaroaleman

pkg/client/fake/client.go

@@ -84,6 +84,8 @@ type fakeClient struct {
 	// indexes maps each GroupVersionKind (GVK) to the indexes registered for that GVK.
 	// The inner map maps from index name to IndexerFunc.
 	indexes map[schema.GroupVersionKind]map[string]client.IndexerFunc
+	// indexesLock must be held when accessing indexes.
+	indexesLock sync.RWMutex
 }
 
 var _ client.WithWatch = &fakeClient{}
@@ -648,10 +650,11 @@ func (c *fakeClient) filterList(list []runtime.Object, gvk schema.GroupVersionKi
 func (c *fakeClient) filterWithFields(list []runtime.Object, gvk schema.GroupVersionKind, fs fields.Selector) ([]runtime.Object, error) {
 	requiresExact := selector.RequiresExactMatch(fs)
 	if !requiresExact {
-		return nil, fmt.Errorf("field selector %s is not in one of the two supported forms \"key==val\" or \"key=val\"",
-			fs)
+		return nil, fmt.Errorf(`field selector %s is not in one of the two supported forms "key==val" or "key=val"`, fs)
 	}
 
+	c.indexesLock.RLock()
+	defer c.indexesLock.RUnlock()
 	// Field selection is mimicked via indexes, so there's no sane answer this function can give
 	// if there are no indexes registered for the GroupVersionKind of the objects in the list.
 	indexes := c.indexes[gvk]
@@ -1528,3 +1531,37 @@ func applyScale(obj client.Object, scale *autoscalingv1.Scale) error {
 	}
 	return nil
 }
+
+// AddIndex adds an index to a fake client. It will panic if used with a client that is not a fake client.
+// It will error if there is already an index for given object with the same name as field.
+//
+// It can be used to test code that adds indexes to the cache at runtime.
+func AddIndex(c client.Client, obj runtime.Object, field string, extractValue client.IndexerFunc) error {
+	fakeClient, isFakeClient := c.(*fakeClient)
+	if !isFakeClient {
+		panic("AddIndex can only be used with a fake client")
+	}
+	fakeClient.indexesLock.Lock()
+	defer fakeClient.indexesLock.Unlock()
+
+	if fakeClient.indexes == nil {
+		fakeClient.indexes = make(map[schema.GroupVersionKind]map[string]client.IndexerFunc, 1)
+	}
+
+	gvk, err := apiutil.GVKForObject(obj, fakeClient.scheme)
+	if err != nil {
+		return fmt.Errorf("failed to get gvk for %T: %w", obj, err)
+	}
+
+	if fakeClient.indexes[gvk] == nil {
+		fakeClient.indexes[gvk] = make(map[string]client.IndexerFunc, 1)
+	}
+
+	if fakeClient.indexes[gvk][field] != nil {
+		return fmt.Errorf("index %s already exists", field)
+	}
+
+	fakeClient.indexes[gvk][field] = extractValue
+
+	return nil
+}

pkg/client/fake/client_test.go

@@ -1388,6 +1388,47 @@ var _ = Describe("Fake client", func() {
 					Expect(cl.List(context.Background(), list, listOpts)).To(Succeed())
 					Expect(list.Items).To(BeEmpty())
 				})
+
+				It("supports adding an index at runtime", func() {
+					listOpts := &client.ListOptions{
+						FieldSelector: fields.OneTermEqualSelector("metadata.name", "test-deployment-2"),
+					}
+					list := &appsv1.DeploymentList{}
+					err := cl.List(context.Background(), list, listOpts)
+					Expect(err).To(HaveOccurred())
+					Expect(err.Error()).To(ContainSubstring("no index with name metadata.name has been registered"))
+
+					err = AddIndex(cl, &appsv1.Deployment{}, "metadata.name", func(obj client.Object) []string {
+						return []string{obj.GetName()}
+					})
+					Expect(err).To(Succeed())
+
+					Expect(cl.List(context.Background(), list, listOpts)).To(Succeed())
+					Expect(list.Items).To(ConsistOf(*dep2))
+				})
+
+				It("Is not a datarace to add and use indexes in parallel", func() {
+					wg := sync.WaitGroup{}
+					wg.Add(2)
+
+					listOpts := &client.ListOptions{
+						FieldSelector: fields.OneTermEqualSelector("spec.replicas", "2"),
+					}
+					go func() {
+						defer wg.Done()
+						defer GinkgoRecover()
+						Expect(cl.List(context.Background(), &appsv1.DeploymentList{}, listOpts)).To(Succeed())
+					}()
+					go func() {
+						defer wg.Done()
+						defer GinkgoRecover()
+						err := AddIndex(cl, &appsv1.Deployment{}, "metadata.name", func(obj client.Object) []string {
+							return []string{obj.GetName()}
+						})
+						Expect(err).To(Succeed())
+					}()
+					wg.Wait()
+				})
 			})
 		})