Improve enum and string list flag parse handling

cmd/gce-pd-csi-driver/main.go

@@ -28,6 +28,7 @@ import (
 	"time"
 
 	"k8s.io/klog/v2"
+	"k8s.io/utils/strings/slices"
 
 	"sigs.k8s.io/gcp-compute-persistent-disk-csi-driver/pkg/common"
 	"sigs.k8s.io/gcp-compute-persistent-disk-csi-driver/pkg/deviceutils"
@@ -98,7 +99,7 @@ func init() {
 	// Use V(4) for general debug information logging
 	// Use V(5) for GCE Cloud Provider Call informational logging
 	// Use V(6) for extra repeated/polling information
-	enumFlag(&computeEnvironment, "compute-environment", allowedComputeEnvironment, "Operating compute environment")
+	stringEnumFlag(&computeEnvironment, "compute-environment", allowedComputeEnvironment, "Operating compute environment")
 	urlFlag(&computeEndpoint, "compute-endpoint", "Compute endpoint")
 	klog.InitFlags(flag.CommandLine)
 	flag.Set("logtostderr", "true")
@@ -175,23 +176,23 @@ func handle() {
 	identityServer := driver.NewIdentityServer(gceDriver)
 
 	// Initialize requisite zones
-	fallbackRequisiteZones := strings.Split(*fallbackRequisiteZonesFlag, ",")
+	fallbackRequisiteZones := parseCSVFlag(*fallbackRequisiteZonesFlag)
 
 	// Initialize multi-zone disk types
-	multiZoneVolumeHandleDiskTypes := strings.Split(*multiZoneVolumeHandleDiskTypesFlag, ",")
+	multiZoneVolumeHandleDiskTypes := parseCSVFlag(*multiZoneVolumeHandleDiskTypesFlag)
 	multiZoneVolumeHandleConfig := driver.MultiZoneVolumeHandleConfig{
 		Enable:    *multiZoneVolumeHandleEnableFlag,
 		DiskTypes: multiZoneVolumeHandleDiskTypes,
 	}
 
 	// Initialize waitForAttach config
-	useInstanceAPIOnWaitForAttachDiskTypes := strings.Split(*useInstanceAPIOnWaitForAttachDiskTypesFlag, ",")
+	useInstanceAPIOnWaitForAttachDiskTypes := parseCSVFlag(*useInstanceAPIOnWaitForAttachDiskTypesFlag)
 	waitForAttachConfig := gce.WaitForAttachConfig{
 		UseInstancesAPIForDiskTypes: useInstanceAPIOnWaitForAttachDiskTypes,
 	}
 
 	// Initialize listVolumes config
-	instancesListFilters := strings.Split(*instancesListFiltersFlag, ",")
+	instancesListFilters := parseCSVFlag(*instancesListFiltersFlag)
 	listInstancesConfig := gce.ListInstancesConfig{
 		Filters: instancesListFilters,
 	}
@@ -252,18 +253,48 @@ func handle() {
 	gceDriver.Run(*endpoint, *grpcLogCharCap, *enableOtelTracing)
 }
 
-func enumFlag(target *gce.Environment, name string, allowedComputeEnvironment []gce.Environment, usage string) {
+func notEmpty(v string) bool {
+	return v != ""
+}
+
+func parseCSVFlag(list string) []string {
+	return slices.Filter(nil, strings.Split(list, ","), notEmpty)
+}
+
+type enumConverter[T any] interface {
+	convert(v string) (T, error)
+	eq(a, b T) bool
+}
+
+type stringConverter[T ~string] struct{}
+
+func (s stringConverter[T]) convert(v string) (T, error) {
+	return T(v), nil
+}
+
+func (s stringConverter[T]) eq(a, b T) bool {
+	return a == b
+}
+
+func stringEnumFlag[T ~string](target *T, name string, allowed []T, usage string) {
+	enumFlag(target, name, stringConverter[T]{}, allowed, usage)
+}
+
+func enumFlag[T any](target *T, name string, converter enumConverter[T], allowed []T, usage string) {
 	flag.Func(name, usage, func(flagValue string) error {
-		for _, allowedValue := range allowedComputeEnvironment {
-			if gce.Environment(flagValue) == allowedValue {
-				*target = gce.Environment(flagValue)
+		tValue, err := converter.convert(flagValue)
+		if err != nil {
+			return err
+		}
+		for _, allowedValue := range allowed {
+			if converter.eq(allowedValue, tValue) {
+				*target = tValue
 				return nil
 			}
 		}
 		errMsg := fmt.Sprintf(`must be one of %v`, allowedComputeEnvironment)
 		return errors.New(errMsg)
 	})
-
 }
 
 func urlFlag(target **url.URL, name string, usage string) {