Merge pull request #60021 from nikhita/sample-controller-subresources

Automatic merge from submit-queue (batch tested with PRs 60102, 59970, 60021, 62011, 62080). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

sample-controller: add status subresource support

Builds on top of https://github.com/kubernetes/kubernetes/pull/55168.

**DO NOT MERGE** until https://github.com/kubernetes/kubernetes/pull/55168 is merged. Adding a hold.
/hold

Update: It is now merged! 🎉

This PR:

- Adds an example to show how to use the `/status` subresource with custom resources.
- Generates `UpdateStatus` for the `Foo` resource.
- Updates the comment in the controller to mention that `UpdateStatus` can now be used. Note: this is not enabled by default because subresources require the feature gate to be enabled and are not on by default.
- Updates the README to add feature gate information and examples for `CustomResourceSubresources`.
- Updates the README to remove feature gate information for CRD validation since the current example uses `apps/v1` deployments (and thus requires v1.9 anyway).

**Release note**:

```release-note
NONE
```

/assign sttts munnerz

Kubernetes-commit: 7bde13f191f0791a87fe5e2575feb3d4849de536

vendor/k8s.io/apimachinery/pkg/runtime/converter.go

@@ -411,8 +411,7 @@ func (c *unstructuredConverter) ToUnstructured(obj interface{}) (map[string]inte
 	var u map[string]interface{}
 	var err error
 	if unstr, ok := obj.(Unstructured); ok {
-		// UnstructuredContent() mutates the object so we need to make a copy first
-		u = unstr.DeepCopyObject().(Unstructured).UnstructuredContent()
+		u = unstr.UnstructuredContent()
 	} else {
 		t := reflect.TypeOf(obj)
 		value := reflect.ValueOf(obj)
@@ -449,12 +448,20 @@ func DeepCopyJSON(x map[string]interface{}) map[string]interface{} {
 func DeepCopyJSONValue(x interface{}) interface{} {
 	switch x := x.(type) {
 	case map[string]interface{}:
+		if x == nil {
+			// Typed nil - an interface{} that contains a type map[string]interface{} with a value of nil
+			return x
+		}
 		clone := make(map[string]interface{}, len(x))
 		for k, v := range x {
 			clone[k] = DeepCopyJSONValue(v)
 		}
 		return clone
 	case []interface{}:
+		if x == nil {
+			// Typed nil - an interface{} that contains a type []interface{} with a value of nil
+			return x
+		}
 		clone := make([]interface{}, len(x))
 		for i, v := range x {
 			clone[i] = DeepCopyJSONValue(v)

vendor/k8s.io/apimachinery/pkg/runtime/interfaces.go

@@ -234,9 +234,9 @@ type Object interface {
 // to JSON allowed.
 type Unstructured interface {
 	Object
-	// UnstructuredContent returns a non-nil, mutable map of the contents of this object. Values may be
+	// UnstructuredContent returns a non-nil map with this object's contents. Values may be
 	// []interface{}, map[string]interface{}, or any primitive type. Contents are typically serialized to
-	// and from JSON.
+	// and from JSON. SetUnstructuredContent should be used to mutate the contents.
 	UnstructuredContent() map[string]interface{}
 	// SetUnstructuredContent updates the object content to match the provided map.
 	SetUnstructuredContent(map[string]interface{})