refactor: add global feature.Gates variable (#1167)

**What problem does this PR solve?**:
Refactoring the feature gate code to make it easier to use.
Added a new `feature.Gate` readonly variable that can be used anywhere
in the codebase to determine if a specific feature gate was set.

This is based on CAPI's implementation
https://github.com/kubernetes-sigs/cluster-api/tree/main/feature

**Which issue(s) this PR fixes**:
Fixes #

**How Has This Been Tested?**:
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Author: dkoshkin

cmd/main.go

@@ -13,7 +13,6 @@ import (
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	clientgoscheme "k8s.io/client-go/kubernetes/scheme"
 	cliflag "k8s.io/component-base/cli/flag"
-	"k8s.io/component-base/featuregate"
 	"k8s.io/component-base/logs"
 	logsv1 "k8s.io/component-base/logs/api/v1"
 	"k8s.io/component-base/version/verflag"
@@ -33,7 +32,7 @@ import (
 	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/common/pkg/capi/clustertopology/handlers"
 	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/common/pkg/server"
 	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/pkg/controllers/namespacesync"
-	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/pkg/features"
+	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/pkg/feature"
 	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/pkg/handlers/aws"
 	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/pkg/handlers/docker"
 	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/pkg/handlers/generic"
@@ -132,10 +131,8 @@ func main() {
 	pflag.CommandLine.SetNormalizeFunc(cliflag.WordSepNormalizeFunc)
 	pflag.CommandLine.AddGoFlagSet(flag.CommandLine)
 
-	// Add feature gate flags.
-	featureGate := featuregate.NewFeatureGate()
-	utilruntime.Must(featureGate.Add(features.DefaultFeatureGates()))
-	featureGate.AddFlag(pflag.CommandLine)
+	// Add feature gate flag.
+	feature.MutableGates.AddFlag(pflag.CommandLine)
 
 	pflag.Parse()
 

pkg/features/feature_gates.go renamed to pkg/feature/feature.go

@@ -1,13 +1,15 @@
 // Copyright 2024 Nutanix. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-package features
+package feature
 
-import "k8s.io/component-base/featuregate"
+import (
+	"k8s.io/component-base/featuregate"
+)
 
-// DefaultFeatureGates returns all known feature gates.
+// defaultFeatureGates returns all known feature gates.
 // To add a new feature, define a key for it above and add it here. The features will be
 // available throughout the codebase.
-func DefaultFeatureGates() map[featuregate.Feature]featuregate.FeatureSpec {
+func defaultFeatureGates() map[featuregate.Feature]featuregate.FeatureSpec {
 	return map[featuregate.Feature]featuregate.FeatureSpec{}
 }

pkg/feature/gates.go

@@ -0,0 +1,31 @@
+// Copyright 2025 Nutanix. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package feature
+
+import (
+	"k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/component-base/featuregate"
+)
+
+//nolint:gochecknoinits // Code is copied from upstream.
+func init() {
+	runtime.Must(MutableGates.Add(defaultFeatureGates()))
+}
+
+var (
+	// MutableGates is a mutable version of DefaultFeatureGate.
+	// Only top-level commands/options setup should make use of this.
+	// Tests that need to modify feature gates for the duration of their test should use:
+	//   featuregatetesting "k8s.io/component-base/featuregate/testing"
+	//   featuregatetesting.SetFeatureGateDuringTest(
+	//     t,
+	//     features.Gates,
+	//     features.<FeatureName>,
+	//     <value>,
+	//   )()
+	MutableGates featuregate.MutableFeatureGate = featuregate.NewFeatureGate()
+
+	// Gates is a shared global FeatureGate.
+	Gates featuregate.FeatureGate = MutableGates
+)