🐛 fake client: fix SSA after List with non-list kind

pkg/client/client_test.go

@@ -2516,6 +2516,43 @@ U5wwSivyi7vmegHKmblOzNVKA5qPO8zWzqBC
 				Expect(hasDep).To(BeTrue())
 			})
 
+			It("should fetch unstructured collection of objects when setting a non-list kind", func(ctx SpecContext) {
+				// While it is not ideal to omit the List suffix it can easily happen.
+				// As the client is using TrimSuffix(gvk.Kind,"List") this also works.
+				// As it works it is part of our API and we should test it accordingly.
+				By("create an initial object")
+				_, err := clientset.AppsV1().Deployments(ns).Create(ctx, dep, metav1.CreateOptions{})
+				Expect(err).NotTo(HaveOccurred())
+
+				cl, err := client.New(cfg, client.Options{})
+				Expect(err).NotTo(HaveOccurred())
+
+				By("listing all objects of that type in the cluster")
+				deps := &unstructured.UnstructuredList{}
+				deps.SetGroupVersionKind(schema.GroupVersionKind{
+					Group:   "apps",
+					Kind:    "Deployment",
+					Version: "v1",
+				})
+				err = cl.List(ctx, deps)
+				Expect(err).NotTo(HaveOccurred())
+
+				Expect(deps.Items).NotTo(BeEmpty())
+				hasDep := false
+				for _, item := range deps.Items {
+					Expect(item.GroupVersionKind()).To(Equal(schema.GroupVersionKind{
+						Group:   "apps",
+						Kind:    "Deployment",
+						Version: "v1",
+					}))
+					if item.GetName() == dep.Name && item.GetNamespace() == dep.Namespace {
+						hasDep = true
+						break
+					}
+				}
+				Expect(hasDep).To(BeTrue())
+			})
+
 			It("should fetch unstructured collection of objects, even if scheme is empty", func(ctx SpecContext) {
 				By("create an initial object")
 				_, err := clientset.AppsV1().Deployments(ns).Create(ctx, dep, metav1.CreateOptions{})

pkg/client/fake/client.go

@@ -1701,6 +1701,12 @@ func (c *fakeClient) addToSchemeIfUnknownAndUnstructuredOrPartial(obj runtime.Ob
 		return err
 	}
 
+	if isUnstructuredList || isPartialList {
+		if !strings.HasSuffix(gvk.Kind, "List") {
+			gvk.Kind += "List"
+		}
+	}
+
 	if !c.scheme.Recognizes(gvk) {
 		c.scheme.AddKnownTypeWithName(gvk, obj)
 	}

pkg/client/fake/client_test.go

@@ -2939,6 +2939,40 @@ var _ = Describe("Fake client", func() {
 		Expect(result.Object["spec"]).To(Equal(map[string]any{"other": "data"}))
 	})
 
+	It("supports server-side apply of a custom resource via Apply method after List with a non-list kind", func(ctx SpecContext) {
+		cl := NewClientBuilder().Build()
+
+		// Previously this List call lead to addToSchemeIfUnknownAndUnstructuredOrPartial adding FakeResource as UnstructuredList to the scheme.
+		// This broke the subsequent SSA call as it was trying to create a new FakeResource object as an UnstructuredList.
+		// After a fix this List call leads to addToSchemeIfUnknownAndUnstructuredOrPartial adding FakeResourceList as UnstructuredList to the
+		// scheme even if the UnstructuredList here is missing the List suffix.
+		objList := &unstructured.UnstructuredList{}
+		objList.SetAPIVersion("custom/v1")
+		objList.SetKind("FakeResource")
+		Expect(cl.List(ctx, objList)).To(Succeed())
+
+		obj := &unstructured.Unstructured{}
+		obj.SetAPIVersion("custom/v1")
+		obj.SetKind("FakeResource")
+		obj.SetName("foo")
+		result := obj.DeepCopy()
+
+		Expect(unstructured.SetNestedField(obj.Object, map[string]any{"some": "data"}, "spec")).To(Succeed())
+
+		applyConfig := client.ApplyConfigurationFromUnstructured(obj)
+		Expect(cl.Apply(ctx, applyConfig, &client.ApplyOptions{FieldManager: "test-manager"})).To(Succeed())
+
+		Expect(cl.Get(ctx, client.ObjectKeyFromObject(result), result)).To(Succeed())
+		Expect(result.Object["spec"]).To(Equal(map[string]any{"some": "data"}))
+
+		Expect(unstructured.SetNestedField(obj.Object, map[string]any{"other": "data"}, "spec")).To(Succeed())
+		applyConfig2 := client.ApplyConfigurationFromUnstructured(obj)
+		Expect(cl.Apply(ctx, applyConfig2, &client.ApplyOptions{FieldManager: "test-manager"})).To(Succeed())
+
+		Expect(cl.Get(ctx, client.ObjectKeyFromObject(result), result)).To(Succeed())
+		Expect(result.Object["spec"]).To(Equal(map[string]any{"other": "data"}))
+	})
+
 	It("sets the fieldManager in create, patch and update", func(ctx SpecContext) {
 		owner := "test-owner"
 		cl := client.WithFieldOwner(