Deomonstrate GateSet composition

This commit demonstrate how libraries can define and expose Gates and
GateSets, and compose GateSets into new GateSets.  It also defines a small
number of new-style gates, but does not use them yet.

Author: thockin

pkg/features/kube_features.go

@@ -23,6 +23,8 @@ import (
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	clientfeatures "k8s.io/client-go/features"
 	"k8s.io/component-base/featuregate"
+	kubeaggregatorfeatures "k8s.io/kube-aggregator/pkg/features"
+	"k8s.io/utils/feature"
 )
 
 const (
@@ -964,6 +966,31 @@ const (
 	RecursiveReadOnlyMounts featuregate.Feature = "RecursiveReadOnlyMounts"
 )
 
+var (
+	// This is the composed set of gates that standard Kubernetes components
+	// will expose.  It starts with a few critical libs and then we will define
+	// our own below.
+	kubeGates = feature.MergeGateSets(
+		clientfeatures.NewFeatureGates(),
+		kubeaggregatorfeatures.FeatureGates(),
+		apiextensionsfeatures.FeatureGates())
+
+	// owner: @AkihiroSuda
+	// kep: https://kep.k8s.io/3857
+	// alpha: v1.30
+	//
+	// Allows recursive read-only mounts.
+	RecursiveReadOnlyMountsGate = kubeGates.AddOrDie(&feature.Gate{
+		Name: "RecursiveReadOnlyMounts", Default: false, Release: feature.Alpha,
+	})
+)
+
+// KubernetesGates returns the set of feature gates that standard Kubernetes
+// components will expose.
+func KubernetesGates() *feature.GateSet {
+	return kubeGates
+}
+
 func init() {
 	runtime.Must(utilfeature.DefaultMutableFeatureGate.Add(defaultKubernetesFeatureGates))
 

staging/src/k8s.io/apiextensions-apiserver/pkg/features/kube_features.go

@@ -19,6 +19,7 @@ package features
 import (
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/component-base/featuregate"
+	"k8s.io/utils/feature"
 )
 
 const (
@@ -47,6 +48,43 @@ func init() {
 	utilfeature.DefaultMutableFeatureGate.Add(defaultKubernetesFeatureGates)
 }
 
+var (
+	libGates = &feature.GateSet{}
+
+	// Every feature gate should add method here following this template:
+	//
+	// // owner: @username
+	// // alpha: v1.4
+	// MyFeature() bool
+
+	// owner: @alexzielenski
+	// alpha: v1.28
+	//
+	// Ignores errors raised on unchanged fields of Custom Resources
+	// across UPDATE/PATCH requests.
+	CRDValidationRatchetingGate = libGates.AddOrDie(&feature.Gate{
+		Name:    "CRDValidationRatcheting",
+		Default: true,
+		Release: feature.Beta,
+	})
+
+	// owner: @jpbetz
+	// alpha: v1.30
+	//
+	// CustomResourceDefinitions may include SelectableFields to declare which fields
+	// may be used as field selectors.
+	CustomResourceFieldSelectorsGate = libGates.AddOrDie(&feature.Gate{
+		Name:    "CustomResourceFieldSelectors",
+		Default: false,
+		Release: feature.Beta,
+	})
+)
+
+// FeatureGates returns the set of feature gates exposed by this library.
+func FeatureGates() *feature.GateSet {
+	return libGates
+}
+
 // defaultKubernetesFeatureGates consists of all known Kubernetes-specific feature keys.
 // To add a new feature, define a key for it above and add it here. The features will be
 // available throughout Kubernetes binaries.

staging/src/k8s.io/client-go/features/known_features.go

@@ -16,6 +16,10 @@ limitations under the License.
 
 package features
 
+import (
+	"k8s.io/utils/feature"
+)
+
 const (
 	// Every feature gate should add method here following this template:
 	//
@@ -43,6 +47,47 @@ const (
 	InformerResourceVersion Feature = "InformerResourceVersion"
 )
 
+var (
+	libGates = &feature.GateSet{}
+
+	// Every feature gate should add method here following this template:
+	//
+	// // owner: @username
+	// // alpha: v1.4
+	// MyFeature featuregate.Feature = "MyFeature"
+	//
+	// Feature gates should be listed in alphabetical, case-sensitive
+	// (upper before any lower case character) order. This reduces the risk
+	// of code conflicts because changes are more likely to be scattered
+	// across the file.
+
+	// owner: @p0lyn0mial
+	// beta: v1.30
+	//
+	// Allow the client to get a stream of individual items instead of chunking from the server.
+	//
+	// NOTE:
+	//  The feature is disabled in Beta by default because
+	//  it will only be turned on for selected control plane component(s).
+	WatchListClientGate = libGates.AddOrDie(&feature.Gate{
+		Name:    "WatchListClient",
+		Release: feature.Beta,
+	})
+
+	// owner: @nilekhc
+	// alpha: v1.30
+	InformerResourceVersionGate = libGates.AddOrDie(&feature.Gate{
+		Name:    "InformerResourceVersion",
+		Release: feature.Alpha,
+	})
+)
+
+// NewFeatureGates returns the set of feature gates exposed by this library.
+// FIXME: Rename to FeatureGates once old-style function of same name is gone.
+func NewFeatureGates() *feature.GateSet {
+	return libGates
+}
+
 // defaultKubernetesFeatureGates consists of all known Kubernetes-specific feature keys.
 //
 // To add a new feature, define a key for it above and add it here.

staging/src/k8s.io/kube-aggregator/pkg/features/known_features.go

@@ -0,0 +1,25 @@
+package features
+
+import (
+	"k8s.io/utils/feature"
+)
+
+var (
+	libGates = &feature.GateSet{}
+
+	// Every feature gate should add method here following this template:
+	//
+	// // owner: @username
+	// // alpha: v1.4
+	// MyFeature featuregate.Feature = "MyFeature"
+	//
+	// Feature gates should be listed in alphabetical, case-sensitive
+	// (upper before any lower case character) order. This reduces the risk
+	// of code conflicts because changes are more likely to be scattered
+	// across the file.
+)
+
+// FeatureGates returns the set of feature gates exposed by this library.
+func FeatureGates() *feature.GateSet {
+	return libGates
+}