feat(pihole)!: deprecate v5 API support

provider/pihole/pihole.go

@@ -22,6 +22,7 @@ import (
 	"slices"
 
 	"github.com/google/go-cmp/cmp"
+	log "github.com/sirupsen/logrus"
 
 	"sigs.k8s.io/external-dns/endpoint"
 	"sigs.k8s.io/external-dns/plan"
@@ -32,6 +33,10 @@ import (
 // in the environment.
 var ErrNoPiholeServer = errors.New("no pihole server found in the environment or flags")
 
+const (
+	warningMsg = "Pi-hole v5 API support is deprecated. Set --pihole-api-version=\"6\" to use the Pi-hole v6 API. The v5 API will be removed in a future release."
+)
+
 // PiholeProvider is an implementation of Provider for Pi-hole Local DNS.
 type PiholeProvider struct {
 	provider.BaseProvider
@@ -69,6 +74,7 @@ func NewPiholeProvider(cfg PiholeConfig) (*PiholeProvider, error) {
 	case "6":
 		api, err = newPiholeClientV6(cfg)
 	default:
+		log.Warn(warningMsg)
 		api, err = newPiholeClient(cfg)
 	}
 	if err != nil {

provider/pihole/pihole_test.go

@@ -21,7 +21,10 @@ import (
 	"reflect"
 	"testing"
 
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/require"
 	"sigs.k8s.io/external-dns/endpoint"
+	"sigs.k8s.io/external-dns/internal/testutils"
 	"sigs.k8s.io/external-dns/plan"
 )
 
@@ -81,6 +84,42 @@ func TestNewPiholeProvider(t *testing.T) {
 	}
 }
 
+func TestNewPiholeProvider_APIVersions(t *testing.T) {
+	tests := []struct {
+		name    string
+		config  PiholeConfig
+		wantMsg bool
+	}{
+		{
+			name: "API version 5 with server",
+			config: PiholeConfig{
+				APIVersion: "5",
+				Server:     "test.example.com",
+			},
+			wantMsg: true,
+		},
+		{
+			name: "API version 6 with server",
+			config: PiholeConfig{
+				APIVersion: "6",
+				Server:     "test.example.com",
+			},
+			wantMsg: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			hook := testutils.LogsUnderTestWithLogLevel(log.DebugLevel, t)
+			_, err := NewPiholeProvider(tt.config)
+			require.NoError(t, err)
+			if tt.wantMsg {
+				testutils.TestHelperLogContains(warningMsg, hook, t)
+			}
+		})
+	}
+}
+
 func TestProvider_InitialState(t *testing.T) {
 	requests := requestTracker{}
 	p := &PiholeProvider{