Respond to comments.

Author: arik-so

lightning/src/chain/package.rs

@@ -203,10 +203,7 @@ impl CounterpartyOfferedHTLCOutput {
 
 impl Writeable for CounterpartyOfferedHTLCOutput {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-		let mut channel_type_features = Some(self.channel_type_features.clone());
-		if !self.channel_type_features.supports_anchors() {
-			channel_type_features = None;
-		}
+		let channel_type_features = self.channel_type_features.serializable_option();
 		write_tlv_fields!(writer, {
 			(0, self.per_commitment_point, required),
 			(2, self.counterparty_delayed_payment_base_key, required),
@@ -275,10 +272,7 @@ impl CounterpartyReceivedHTLCOutput {
 
 impl Writeable for CounterpartyReceivedHTLCOutput {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-		let mut channel_type_features = Some(self.channel_type_features.clone());
-		if !self.channel_type_features.supports_anchors() {
-			channel_type_features = None;
-		}
+		let channel_type_features = self.channel_type_features.serializable_option();
 		write_tlv_fields!(writer, {
 			(0, self.per_commitment_point, required),
 			(2, self.counterparty_delayed_payment_base_key, required),
@@ -351,10 +345,7 @@ impl HolderHTLCOutput {
 
 impl Writeable for HolderHTLCOutput {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-		let mut channel_type_features = Some(self.channel_type_features.clone());
-		if !self.channel_type_features.supports_anchors() {
-			channel_type_features = None;
-		}
+		let channel_type_features = self.channel_type_features.serializable_option();
 		write_tlv_fields!(writer, {
 			(0, self.amount_msat, required),
 			(2, self.cltv_expiry, required),
@@ -411,10 +402,7 @@ impl HolderFundingOutput {
 
 impl Writeable for HolderFundingOutput {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-		let mut channel_type_features = Some(self.channel_type_features.clone());
-		if !self.channel_type_features.supports_anchors() {
-			channel_type_features = None;
-		}
+		let channel_type_features = self.channel_type_features.serializable_option();
 		write_tlv_fields!(writer, {
 			(0, self.funding_redeemscript, required),
 			(2, channel_type_features, option),

lightning/src/ln/chan_utils.rs

@@ -878,10 +878,7 @@ impl_writeable_tlv_based!(CounterpartyChannelTransactionParameters, {
 
 impl Writeable for ChannelTransactionParameters {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-		let mut channel_type_features = Some(self.channel_type_features.clone());
-		if !self.channel_type_features.supports_anchors() {
-			channel_type_features = None;
-		}
+		let channel_type_features = self.channel_type_features.serializable_option();
 		write_tlv_fields!(writer, {
 			(0, self.holder_pubkeys, required),
 			(2, self.holder_selected_contest_delay, required),
@@ -1295,10 +1292,7 @@ impl PartialEq for CommitmentTransaction {
 
 impl Writeable for CommitmentTransaction {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-		let mut channel_type_features = Some(self.channel_type_features.clone());
-		if !self.channel_type_features.supports_anchors() {
-			channel_type_features = None;
-		}
+		let channel_type_features = self.channel_type_features.serializable_option();
 		write_tlv_fields!(writer, {
 			(0, self.commitment_number, required),
 			(2, self.to_broadcaster_value_sat, required),

lightning/src/ln/features.rs

@@ -631,6 +631,16 @@ impl ChannelTypeFeatures {
 			Self::only_static_remote_key()
 		}
 	}
+
+	/// To actually serialize the features in a manner that won't break the structs read by
+	/// older versions of LDK, we should skip serialization entirely if anchors are not supported.
+	/// This is a helper method to do just that.
+	pub(crate) fn serializable_option(&self) -> Option<Self> {
+		if !self.supports_anchors() {
+			return None;
+		}
+		Some(self.clone())
+	}
 }
 
 impl ToBase32 for InvoiceFeatures {

lightning/src/sign/mod.rs

@@ -835,7 +835,8 @@ impl InMemorySigner {
 	pub fn get_channel_parameters(&self) -> &ChannelTransactionParameters {
 		self.channel_parameters.as_ref().unwrap()
 	}
-	/// Returns whether anchors should be used.
+	/// Returns the channel type features of the channel parameters. Should be helpful to for
+	/// determining a channel's category, i. e. legacy/anchors/taproot/etc.
 	///
 	/// Will panic if [`ChannelSigner::provide_channel_parameters`] has not been called before.
 	pub fn channel_type_features(&self) -> ChannelTypeFeatures {