f: remove i64 casts in channel build_commitment_transaction

Author: tankyleo

lightning/src/ln/channel.rs

@@ -4567,7 +4567,8 @@ where
 
 		let num_htlcs = self.pending_inbound_htlcs.len() + self.pending_outbound_htlcs.len();
 		let mut htlcs_included: Vec<(HTLCOutputInCommitment, Option<&HTLCSource>)> = Vec::with_capacity(num_htlcs);
-		let mut value_to_self_msat_offset = 0;
+		let mut value_to_self_claimed_msat = 0;
+		let mut value_to_remote_claimed_msat = 0;
 
 		log_trace!(logger, "Building commitment transaction number {} (really {} xor {}) for channel {} for {}, generated by {} with fee {}...",
 			commitment_number, (INITIAL_COMMITMENT_NUMBER - commitment_number),
@@ -4605,7 +4606,7 @@ where
 				log_trace!(logger, "   ...not including inbound HTLC {} (hash {}) with value {} due to state ({})", htlc.htlc_id, htlc.payment_hash, htlc.amount_msat, htlc.state);
 				if let Some(preimage) = htlc.state.preimage() {
 					inbound_htlc_preimages.push(preimage);
-					value_to_self_msat_offset += htlc.amount_msat as i64;
+					value_to_self_claimed_msat += htlc.amount_msat;
 				}
 			}
 		};
@@ -4620,26 +4621,24 @@ where
 			} else {
 				log_trace!(logger, "   ...not including outbound HTLC {} (hash {}) with value {} due to state ({})", htlc.htlc_id, htlc.payment_hash, htlc.amount_msat, htlc.state);
 				if htlc.state.preimage().is_some() {
-					value_to_self_msat_offset -= htlc.amount_msat as i64;
+					value_to_remote_claimed_msat += htlc.amount_msat;
 				}
 			}
 		};
 
 		// # Panics
 		//
-		// While we expect `value_to_self_msat_offset` to be negative in some cases, the local
-		// balance MUST remain greater than or equal to 0.
+		// After all HTLC claims have been accounted for, the local balance MUST remain greater than or equal to 0.
 
-		// TODO: When MSRV >= 1.66.0, use u64::checked_add_signed
-		let value_to_self_with_offset_msat = (funding.value_to_self_msat as i64 + value_to_self_msat_offset).try_into().unwrap();
+		let value_to_self_msat = (funding.value_to_self_msat + value_to_self_claimed_msat).checked_sub(value_to_remote_claimed_msat).unwrap();
 
 		let (tx, stats) = SpecTxBuilder {}.build_commitment_transaction(
 			local,
 			commitment_number,
 			per_commitment_point,
 			&funding.channel_transaction_parameters,
 			&self.secp_ctx,
-			value_to_self_with_offset_msat,
+			value_to_self_msat,
 			htlcs_included.iter().map(|(htlc, _source)| htlc).cloned().collect(),
 			feerate_per_kw,
 			broadcaster_dust_limit_sat,