payments/migration1: wire KV→SQL migration in the main pkg

Hook the payments KV→SQL migration into the SQL migration config.
The migration is still only available when building with the build tag
"test_native_sql".

Moreover a tombstone protection similar to the invoice migration is added
to prevent re-runningi with the KV backend  once migration completes.

payments/db/kv_tombstone.go

@@ -0,0 +1,71 @@
+package paymentsdb
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/kvdb"
+)
+
+var (
+	// paymentsBucketTombstone is the key used to mark the payments bucket
+	// as permanently closed after a successful migration.
+	paymentsBucketTombstone = []byte("payments-tombstone")
+)
+
+// SetPaymentsBucketTombstone sets the tombstone key in the payments bucket to
+// mark the bucket as permanently closed. This prevents it from being reopened
+// in the future.
+func SetPaymentsBucketTombstone(db kvdb.Backend) error {
+	return kvdb.Update(db, func(tx kvdb.RwTx) error {
+		// Access the top-level payments bucket.
+		payments := tx.ReadWriteBucket(paymentsRootBucket)
+
+		// In case the bucket doesn't exist, because we start
+		// immediately with the native SQL schema, we create it as well
+		// to make sure the user cannot switch back to the KV store.
+		if payments == nil {
+			var err error
+			payments, err = tx.CreateTopLevelBucket(
+				paymentsRootBucket,
+			)
+			if err != nil {
+				return fmt.Errorf("failed to create payments "+
+					"bucket: %w", err)
+			}
+		}
+
+		// Add the tombstone key to the payments bucket.
+		err := payments.Put(paymentsBucketTombstone, []byte("1"))
+		if err != nil {
+			return fmt.Errorf("failed to set tombstone: %w", err)
+		}
+
+		return nil
+	}, func() {})
+}
+
+// GetPaymentsBucketTombstone checks if the tombstone key exists in the payments
+// bucket. It returns true if the tombstone is present and false otherwise.
+func GetPaymentsBucketTombstone(db kvdb.Backend) (bool, error) {
+	var tombstoneExists bool
+
+	err := kvdb.View(db, func(tx kvdb.RTx) error {
+		// Access the top-level payments bucket.
+		payments := tx.ReadBucket(paymentsRootBucket)
+		if payments == nil {
+			tombstoneExists = false
+			return nil
+		}
+
+		// Check if the tombstone key exists.
+		tombstone := payments.Get(paymentsBucketTombstone)
+		tombstoneExists = tombstone != nil
+
+		return nil
+	}, func() {})
+	if err != nil {
+		return false, err
+	}
+
+	return tombstoneExists, nil
+}

payments/db/log.go

@@ -3,6 +3,7 @@ package paymentsdb
 import (
 	"github.com/btcsuite/btclog/v2"
 	"github.com/lightningnetwork/lnd/build"
+	paymentsmig1 "github.com/lightningnetwork/lnd/payments/db/migration1"
 )
 
 // log is a logger that is initialized with no output filters.  This
@@ -29,4 +30,5 @@ func DisableLog() {
 // using btclog.
 func UseLogger(logger btclog.Logger) {
 	log = logger
+	paymentsmig1.UseLogger(logger)
 }