Rename method, review

Author: optout21

lightning/src/ln/channel.rs

@@ -2100,8 +2100,8 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 				|err| APIError::APIMisuseError {
 					err: format!("Failed to get change script as new destination script, {:?}", err),
 				})?;
-			let _res = add_funding_change_output(
-				change_value, change_script, &mut funding_outputs, self.dual_funding_context.funding_feerate_sat_per_1000_weight);
+			add_funding_change_output(change_value, change_script,
+				&mut funding_outputs, self.dual_funding_context.funding_feerate_sat_per_1000_weight);
 		}
 
 		let constructor_args = InteractiveTxConstructorArgs {
@@ -4567,7 +4567,7 @@ fn get_v2_channel_reserve_satoshis(channel_value_satoshis: u64, dust_limit_satos
 fn add_funding_change_output(
 	change_value: u64, change_script: ScriptBuf,
 	funding_outputs: &mut Vec<OutputOwned>, funding_feerate_sat_per_1000_weight: u32,
-) -> TxOut {
+) {
 	let mut change_output = TxOut {
 		value: Amount::from_sat(change_value),
 		script_pubkey: change_script,
@@ -4576,7 +4576,6 @@ fn add_funding_change_output(
 	let change_output_fee = fee_for_weight(funding_feerate_sat_per_1000_weight, change_output_weight);
 	change_output.value = Amount::from_sat(change_value.saturating_sub(change_output_fee));
 	funding_outputs.push(OutputOwned::Single(change_output.clone()));
-	change_output
 }
 
 pub(super) fn calculate_our_funding_satoshis(

lightning/src/ln/interactivetxs.rs

@@ -2728,4 +2728,58 @@ mod tests {
 			assert_eq!(res.unwrap(), 154);
 		}
 	}
+
+	#[test]
+	fn test_calculate_change_output_value_splice() {
+		let input_prevouts_owned = vec![
+			TxOut { value: Amount::from_sat(70_000), script_pubkey: ScriptBuf::new() },
+			TxOut { value: Amount::from_sat(60_000), script_pubkey: ScriptBuf::new() },
+		];
+		let input_prevouts: Vec<&TxOut> = input_prevouts_owned.iter().collect();
+		let our_contributed = 110_000;
+		let txout = TxOut { value: Amount::from_sat(148_000), script_pubkey: ScriptBuf::new() };
+		let outputs = vec![OutputOwned::Shared(SharedOwnedOutput::new(txout, our_contributed))];
+		let funding_feerate_sat_per_1000_weight = 3000;
+
+		let total_inputs: u64 = input_prevouts.iter().map(|o| o.value.to_sat()).sum();
+		let gross_change = total_inputs - our_contributed;
+		let fees = 1746;
+		let common_fees = 126;
+		{
+			// There is leftover for change
+			let res = calculate_change_output_value(
+				true,
+				our_contributed,
+				&input_prevouts,
+				&outputs,
+				funding_feerate_sat_per_1000_weight,
+				300,
+			);
+			assert_eq!(res.unwrap(), gross_change - fees - common_fees);
+		}
+		{
+			// Very small leftover
+			let res = calculate_change_output_value(
+				false,
+				128_100,
+				&input_prevouts,
+				&outputs,
+				funding_feerate_sat_per_1000_weight,
+				300,
+			);
+			assert!(res.is_none());
+		}
+		{
+			// Small leftover, but not dust
+			let res = calculate_change_output_value(
+				false,
+				128_100,
+				&input_prevouts,
+				&outputs,
+				funding_feerate_sat_per_1000_weight,
+				100,
+			);
+			assert_eq!(res.unwrap(), 154);
+		}
+	}
 }