Show topologySpreadConstraints in Describe command

Currently describe command does not show `topologySpreadConstraints`
field. This PR adds support for showing topologySpreadConstraints in
describe command.For simplicity, if this field is not set, it will not show
(unlike to other core fields whose are shown as `<none>` even if they are null).

staging/src/k8s.io/kubectl/pkg/describe/describe.go

@@ -840,6 +840,7 @@ func describePod(pod *corev1.Pod, events *corev1.EventList) (string, error) {
 		}
 		printLabelsMultiline(w, "Node-Selectors", pod.Spec.NodeSelector)
 		printPodTolerationsMultiline(w, "Tolerations", pod.Spec.Tolerations)
+		describeTopologySpreadConstraints(pod.Spec.TopologySpreadConstraints, w, "")
 		if events != nil {
 			DescribeEvents(events, w)
 		}
@@ -865,6 +866,32 @@ func describePodIPs(pod *corev1.Pod, w PrefixWriter, space string) {
 	}
 }
 
+func describeTopologySpreadConstraints(tscs []corev1.TopologySpreadConstraint, w PrefixWriter, space string) {
+	if len(tscs) == 0 {
+		return
+	}
+
+	sort.Slice(tscs, func(i, j int) bool {
+		return tscs[i].TopologyKey < tscs[j].TopologyKey
+	})
+
+	w.Write(LEVEL_0, "%sTopology Spread Constraints:\t", space)
+	for i, tsc := range tscs {
+		if i != 0 {
+			w.Write(LEVEL_0, "%s", space)
+			w.Write(LEVEL_0, "%s", "\t")
+		}
+
+		w.Write(LEVEL_0, "%s:", tsc.TopologyKey)
+		w.Write(LEVEL_0, "%v", tsc.WhenUnsatisfiable)
+		w.Write(LEVEL_0, " when max skew %d is exceeded", tsc.MaxSkew)
+		if tsc.LabelSelector != nil {
+			w.Write(LEVEL_0, " for selector %s", metav1.FormatLabelSelector(tsc.LabelSelector))
+		}
+		w.Write(LEVEL_0, "\n")
+	}
+}
+
 func describeVolumes(volumes []corev1.Volume, w PrefixWriter, space string) {
 	if len(volumes) == 0 {
 		w.Write(LEVEL_0, "%sVolumes:\t<none>\n", space)
@@ -2110,6 +2137,7 @@ func DescribePodTemplate(template *corev1.PodTemplateSpec, w PrefixWriter) {
 	}
 	describeContainers("Containers", template.Spec.Containers, nil, nil, w, "  ")
 	describeVolumes(template.Spec.Volumes, w, "  ")
+	describeTopologySpreadConstraints(template.Spec.TopologySpreadConstraints, w, "  ")
 	if len(template.Spec.PriorityClassName) > 0 {
 		w.Write(LEVEL_1, "Priority Class Name:\t%s\n", template.Spec.PriorityClassName)
 	}

staging/src/k8s.io/kubectl/pkg/describe/describe_test.go

@@ -211,6 +211,40 @@ func TestDescribePodTolerations(t *testing.T) {
 	}
 }
 
+func TestDescribeTopologySpreadConstraints(t *testing.T) {
+	fake := fake.NewSimpleClientset(&corev1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "bar",
+			Namespace: "foo",
+		},
+		Spec: corev1.PodSpec{
+			TopologySpreadConstraints: []corev1.TopologySpreadConstraint{
+				{
+					MaxSkew:           3,
+					TopologyKey:       "topology.kubernetes.io/test1",
+					WhenUnsatisfiable: "DoNotSchedule",
+					LabelSelector:     &metav1.LabelSelector{MatchLabels: map[string]string{"key1": "val1", "key2": "val2"}},
+				},
+				{
+					MaxSkew:           1,
+					TopologyKey:       "topology.kubernetes.io/test2",
+					WhenUnsatisfiable: "ScheduleAnyway",
+				},
+			},
+		},
+	})
+	c := &describeClient{T: t, Namespace: "foo", Interface: fake}
+	d := PodDescriber{c}
+	out, err := d.Describe("foo", "bar", DescriberSettings{})
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !strings.Contains(out, "topology.kubernetes.io/test1:DoNotSchedule when max skew 3 is exceeded for selector key1=val1,key2=val2\n") ||
+		!strings.Contains(out, "topology.kubernetes.io/test2:ScheduleAnyway when max skew 1 is exceeded\n") {
+		t.Errorf("unexpected out:\n%s", out)
+	}
+}
+
 func TestDescribeSecret(t *testing.T) {
 	fake := fake.NewSimpleClientset(&corev1.Secret{
 		ObjectMeta: metav1.ObjectMeta{