Extend Cluster builtin to include metadata

This ptach extends the cluster builtins to include the labels and
annotations set on the Cluster, if any. This can be used by the runtime
extensions or JSON patches to set metadata based info.

Author: srm09

docs/book/src/tasks/experimental-features/cluster-class/write-clusterclass.md

@@ -608,7 +608,7 @@ spec:
 
 In addition to variables specified in the ClusterClass, the following builtin variables can be 
 referenced in patches:
-- `builtin.cluster.{name,namespace,uid}`
+- `builtin.cluster.{name,namespace,uid,metadata.labels,metadata.annotations}`
 - `builtin.cluster.topology.{version,class}`
 - `builtin.cluster.network.{serviceDomain,services,pods,ipFamily}`
     - Note: ipFamily is deprecated and will be removed in a future release. see https://github.com/kubernetes-sigs/cluster-api/issues/7521.

exp/runtime/hooks/api/v1alpha1/topologymutation_variable_types.go

@@ -55,6 +55,10 @@ type ClusterBuiltins struct {
 	// +optional
 	UID types.UID `json:"uid,omitempty"`
 
+	// metadata is the metadata set on the Cluster object.
+	// +optional
+	Metadata *clusterv1.ObjectMeta `json:"metadata,omitempty"`
+
 	// topology represents the cluster topology variables.
 	// +optional
 	Topology *ClusterTopologyBuiltins `json:"topology,omitempty"`

exp/runtime/hooks/api/v1alpha1/zz_generated.deepcopy.go

@@ -1078,9 +1078,11 @@ func setupTestObjects() (*scope.ClusterBlueprint, *scope.ClusterState) {
 			Kind:       "Cluster",
 		},
 		ObjectMeta: metav1.ObjectMeta{
-			Name:      "cluster1",
-			Namespace: metav1.NamespaceDefault,
-			UID:       uuid.NewUUID(),
+			Name:        "cluster1",
+			Namespace:   metav1.NamespaceDefault,
+			UID:         uuid.NewUUID(),
+			Labels:      map[string]string{"foo": "bar"},
+			Annotations: map[string]string{"fizz": "buzz"},
 		},
 		Spec: clusterv1.ClusterSpec{
 			Paused: false,

exp/runtime/hooks/api/v1alpha1/zz_generated.openapi.go

@@ -60,6 +60,12 @@ func Global(clusterTopology *clusterv1.Topology, cluster *clusterv1.Cluster, pat
 			},
 		},
 	}
+	if cluster.Labels != nil || cluster.Annotations != nil {
+		builtin.Cluster.Metadata = &clusterv1.ObjectMeta{
+			Labels:      cluster.Labels,
+			Annotations: cluster.Annotations,
+		}
+	}
 	if cluster.Spec.ClusterNetwork != nil {
 		clusterNetworkIPFamily, _ := cluster.GetIPFamily()
 		builtin.Cluster.Network = &runtimehooksv1.ClusterNetworkBuiltins{

internal/controllers/topology/cluster/patches/engine_test.go

@@ -66,9 +66,11 @@ func TestGlobal(t *testing.T) {
 			},
 			cluster: &clusterv1.Cluster{
 				ObjectMeta: metav1.ObjectMeta{
-					Name:      "cluster1",
-					Namespace: metav1.NamespaceDefault,
-					UID:       types.UID(clusterUID),
+					Name:        "cluster1",
+					Namespace:   metav1.NamespaceDefault,
+					UID:         types.UID(clusterUID),
+					Labels:      map[string]string{"foo": "bar"},
+					Annotations: map[string]string{"fizz": "buzz"},
 				},
 				Spec: clusterv1.ClusterSpec{
 					Topology: &clusterv1.Topology{
@@ -102,6 +104,7 @@ func TestGlobal(t *testing.T) {
 						"name": "cluster1",
   						"namespace": "default",
 						"uid": "8a35f406-6b9b-4b78-8c93-a7f878d90623",
+						"metadata": {"labels":{"foo":"bar"}, "annotations":{"fizz":"buzz"}},
  						 "topology":{
   						  	"version": "v1.21.1",
  						   	"class": "clusterClass1"

internal/controllers/topology/cluster/patches/variables/variables.go

@@ -472,6 +472,8 @@ var builtinVariables = sets.Set[string]{}.Insert(
 	"builtin.cluster.name",
 	"builtin.cluster.namespace",
 	"builtin.cluster.uid",
+	"builtin.cluster.metadata.labels",
+	"builtin.cluster.metadata.annotations",
 
 	// ClusterTopology builtins.
 	"builtin.cluster.topology",