feature: allow custom feature bits already set by default

docs/release-notes/release-notes-0.22.0.md

@@ -34,6 +34,12 @@
   the close transaction is actually broadcast, and
   `WaitingCloseChannel.ClosingTx` is never empty.
 
+* [Fixed a bug](https://github.com/lightningnetwork/lnd/pull/10888) where
+  configuring a `protocol.custom-init` or `protocol.custom-nodeann` feature bit
+  that lnd already advertises by default caused startup to fail with a
+  `feature bit: X already set` error. Such a duplicate now yields an identical
+  feature vector and is treated as a no-op.
+
 # New Features
 
 ## Functional Enhancements
@@ -89,3 +95,4 @@
 
 * Boris Nagaev
 * Erick Cestari
+* Lrifton92

feature/manager.go

@@ -239,9 +239,15 @@ func newManager(cfg Config, desc setDesc) (*Manager, error) {
 					set, set.Maximum())
 			}
 
+			// If the feature bit is already advertised in lnd's
+			// default feature vector, configuring it as a custom
+			// feature produces an identical vector. Treat this as a
+			// no-op rather than failing startup (see #10883).
+			// Genuine conflicts between the optional and required
+			// variants of a feature are still caught by SafeSet
+			// below.
 			if raw.IsSet(custom) {
-				return nil, fmt.Errorf("feature bit: %v "+
-					"already set", custom)
+				continue
 			}
 
 			if err := raw.SafeSet(custom); err != nil {

feature/manager_internal_test.go

@@ -291,3 +291,33 @@ func TestUpdateFeatureSets(t *testing.T) {
 		})
 	}
 }
+
+// TestManagerCustomFeatureAlreadyDefault asserts that configuring a custom
+// feature bit which lnd already advertises by default does not prevent the
+// feature manager from initializing. The resulting feature vector is identical,
+// so the duplicate must be treated as a no-op rather than a fatal error.
+//
+// See: https://github.com/lightningnetwork/lnd/issues/10883
+func TestManagerCustomFeatureAlreadyDefault(t *testing.T) {
+	t.Parallel()
+
+	// TLVOnionPayloadRequired is advertised by default in the Init set per
+	// testSetDesc, so configuring it as a custom feature for the same set
+	// duplicates an already-set bit. This previously failed startup with a
+	// "feature bit: ... already set" error.
+	cfg := Config{
+		CustomFeatures: map[Set][]lnwire.FeatureBit{
+			SetInit: {lnwire.TLVOnionPayloadRequired},
+		},
+	}
+
+	m, err := newManager(cfg, testSetDesc)
+	require.NoError(t, err)
+
+	// The required bit must still be advertised, and the duplicate must not
+	// have introduced its optional variant (which would form an invalid
+	// pairing). Check the exact bits via the raw vector.
+	rawInit := m.GetRaw(SetInit)
+	require.True(t, rawInit.IsSet(lnwire.TLVOnionPayloadRequired))
+	require.False(t, rawInit.IsSet(lnwire.TLVOnionPayloadOptional))
+}