Declaratively validate RC...Replicas optionality

The existing test run both declarative and manual validation and it
still passes.

Author: thockin

pkg/apis/core/v1/zz_generated.validations.go

@@ -6191,10 +6191,10 @@ func ValidateReplicationControllerSpec(spec, oldSpec *core.ReplicationController
 	allErrs := field.ErrorList{}
 	allErrs = append(allErrs, ValidateNonnegativeField(int64(spec.MinReadySeconds), fldPath.Child("minReadySeconds"))...)
 	allErrs = append(allErrs, ValidateNonEmptySelector(spec.Selector, fldPath.Child("selector"))...)
-	if spec.Replicas == nil {
-		allErrs = append(allErrs, field.Required(fldPath.Child("replicas"), ""))
-	} else {
-		if !utilfeature.DefaultFeatureGate.Enabled(features.DeclarativeValidation) {
+	if !utilfeature.DefaultFeatureGate.Enabled(features.DeclarativeValidation) {
+		if spec.Replicas == nil {
+			allErrs = append(allErrs, field.Required(fldPath.Child("replicas"), ""))
+		} else {
 			allErrs = append(allErrs, ValidateNonnegativeField(int64(*spec.Replicas), fldPath.Child("replicas"))...)
 		}
 	}

pkg/apis/core/validation/validation.go

@@ -5101,7 +5101,9 @@ type ReplicationControllerSpec struct {
 	// Defaults to 1.
 	// More info: https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller#what-is-a-replicationcontroller
 	// +optional
+	// +k8s:optional
 	// +default=1
+	// FIXME: should we convert to +k8s:default ?
 	// +k8s:minimum=0
 	Replicas *int32 `json:"replicas,omitempty" protobuf:"varint,1,opt,name=replicas"`