Emit DiscardFunding event when no splice transaction confirms

When adding support for emitting these events in the channel monitor, we
only covered the case where one of the splice transaction candidates
confirmed. We also need to emit an event when none of them can confirm
due to a commitment transaction confirming (and no longer under reorg
risk) for the pre-splice funding.

Author: wpaulino

lightning/src/chain/channelmonitor.rs

@@ -5571,6 +5571,17 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 				OnchainEvent::FundingSpendConfirmation { commitment_tx_to_counterparty_output, .. } => {
 					self.funding_spend_confirmed = Some(entry.txid);
 					self.confirmed_commitment_tx_counterparty_output = commitment_tx_to_counterparty_output;
+					if self.alternative_funding_confirmed.is_none() {
+						for funding in self.pending_funding.drain(..) {
+							self.outputs_to_watch.remove(&funding.funding_txid());
+							self.pending_events.push(Event::DiscardFunding {
+								channel_id: self.channel_id,
+								funding_info: crate::events::FundingInfo::OutPoint {
+									outpoint: funding.funding_outpoint(),
+								},
+							});
+						}
+					}
 				},
 				OnchainEvent::AlternativeFundingConfirmation {} => {
 					// An alternative funding transaction has irrevocably confirmed and we're no

lightning/src/ln/splicing_tests.rs

@@ -9,9 +9,11 @@
 
 use crate::chain::chaininterface::FEERATE_FLOOR_SATS_PER_KW;
 use crate::chain::channelmonitor::{ANTI_REORG_DELAY, LATENCY_GRACE_PERIOD_BLOCKS};
+use crate::chain::transaction::OutPoint;
 use crate::events::bump_transaction::sync::WalletSourceSync;
-use crate::events::{ClosureReason, Event, HTLCHandlingFailureType};
+use crate::events::{ClosureReason, Event, FundingInfo, HTLCHandlingFailureType};
 use crate::ln::chan_utils;
+use crate::ln::channelmanager::BREAKDOWN_TIMEOUT;
 use crate::ln::functional_test_utils::*;
 use crate::ln::funding::{FundingTxInput, SpliceContribution};
 use crate::ln::msgs::{self, BaseMessageHandler, ChannelMessageHandler, MessageSendEvent};
@@ -305,7 +307,8 @@ fn lock_splice_after_blocks<'a, 'b, 'c, 'd>(
 		panic!();
 	}
 
-	// Remove the corresponding outputs and transactions the chain source is watching.
+	// Remove the corresponding outputs and transactions the chain source is watching for the
+	// old funding as it is no longer being tracked.
 	node_a
 		.chain_source
 		.remove_watched_txn_and_outputs(prev_funding_outpoint, prev_funding_script.clone());
@@ -560,4 +563,42 @@ fn do_test_splice_commitment_broadcast(splice_status: SpliceStatus, claim_htlcs:
 		);
 	}
 	check_added_monitors(&nodes[0], 2); // Two `ReleasePaymentComplete` monitor updates
+
+	// When the splice never confirms and we see a commitment transaction broadcast and confirm for
+	// the current funding instead, we should expect to see an `Event::DiscardFunding` for the
+	// splice transaction.
+	if splice_status == SpliceStatus::Unconfirmed {
+		// Remove the corresponding outputs and transactions the chain source is watching for the
+		// splice as it is no longer being tracked.
+		connect_blocks(&nodes[0], BREAKDOWN_TIMEOUT as u32);
+		let (vout, txout) = splice_tx
+			.output
+			.iter()
+			.enumerate()
+			.find(|(_, output)| output.script_pubkey.is_p2wsh())
+			.unwrap();
+		let funding_outpoint = OutPoint { txid: splice_tx.compute_txid(), index: vout as u16 };
+		nodes[0]
+			.chain_source
+			.remove_watched_txn_and_outputs(funding_outpoint, txout.script_pubkey.clone());
+		nodes[1]
+			.chain_source
+			.remove_watched_txn_and_outputs(funding_outpoint, txout.script_pubkey.clone());
+
+		// `SpendableOutputs` events are also included here, but we don't care for them.
+		let events = nodes[0].chain_monitor.chain_monitor.get_and_clear_pending_events();
+		assert_eq!(events.len(), if claim_htlcs { 2 } else { 4 }, "{events:?}");
+		if let Event::DiscardFunding { funding_info, .. } = &events[0] {
+			assert_eq!(*funding_info, FundingInfo::OutPoint { outpoint: funding_outpoint });
+		} else {
+			panic!();
+		}
+		let events = nodes[1].chain_monitor.chain_monitor.get_and_clear_pending_events();
+		assert_eq!(events.len(), if claim_htlcs { 2 } else { 1 }, "{events:?}");
+		if let Event::DiscardFunding { funding_info, .. } = &events[0] {
+			assert_eq!(*funding_info, FundingInfo::OutPoint { outpoint: funding_outpoint });
+		} else {
+			panic!();
+		}
+	}
 }