fix duplicate custom resources

pkg/app/server.go

@@ -53,6 +53,7 @@ import (
 	"k8s.io/kube-state-metrics/v2/pkg/metricshandler"
 	"k8s.io/kube-state-metrics/v2/pkg/optin"
 	"k8s.io/kube-state-metrics/v2/pkg/options"
+	"k8s.io/kube-state-metrics/v2/pkg/util/collections"
 	"k8s.io/kube-state-metrics/v2/pkg/util/proc"
 )
 
@@ -173,25 +174,25 @@ func RunKubeStateMetrics(ctx context.Context, opts *options.Options) error {
 
 	}
 
-	resources := make([]string, len(factories))
+	resources := collections.NewSet[string]()
 
-	for i, factory := range factories {
-		resources[i] = factory.Name()
+	for _, factory := range factories {
+		resources.Add(factory.Name())
 	}
 
 	switch {
 	case len(opts.Resources) == 0 && !opts.CustomResourcesOnly:
-		resources = append(resources, options.DefaultResources.AsSlice()...)
+		resources.Add(options.DefaultResources.AsSlice()...)
 		klog.InfoS("Used default resources")
 	case opts.CustomResourcesOnly:
 		// enable custom resource only
-		klog.InfoS("Used CRD resources only", "resources", resources)
+		klog.InfoS("Used CRD resources only", "resources", resources.String())
 	default:
-		resources = append(resources, opts.Resources.AsSlice()...)
-		klog.InfoS("Used resources", "resources", resources)
+		resources.Add(opts.Resources.AsSlice()...)
+		klog.InfoS("Used resources", "resources", resources.String())
 	}
 
-	if err := storeBuilder.WithEnabledResources(resources); err != nil {
+	if err := storeBuilder.WithEnabledResources(resources.AsSlice()); err != nil {
 		return fmt.Errorf("failed to set up resources: %v", err)
 	}
 

pkg/util/collections/set.go

@@ -0,0 +1,37 @@
+package collections
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+type Set[T comparable] map[T]struct{}
+
+func NewSet[T comparable](values ...T) Set[T] {
+	s := make(Set[T], len(values))
+	return s
+}
+
+func (s Set[T]) Add(values ...T) {
+	for _, val := range values {
+		s[val] = struct{}{}
+	}
+}
+
+func (s Set[T]) AsSlice() []T {
+	slice := make([]T, 0, len(s))
+	for val := range s {
+		slice = append(slice, val)
+	}
+	return slice
+}
+
+func (s *Set[T]) String() string {
+	ss := make([]string, 0, len(*s))
+	for val := range *s {
+		ss = append(ss, fmt.Sprint(val))
+	}
+	sort.Strings(ss)
+	return strings.Join(ss, ",")
+}