Add an upgrade test of splicing after upgrading from 0.1

diff --git a/lightning-tests/Cargo.toml b/lightning-tests/Cargo.toml
index 23c81fa..36b03a2 100644
--- a/lightning-tests/Cargo.toml
+++ b/lightning-tests/Cargo.toml
@@ -14,7 +14,7 @@ lightning-types = { path = "../lightning-types", features = ["_test_utils"] }
 lightning-invoice = { path = "../lightning-invoice", default-features = false }
 lightning-macros = { path = "../lightning-macros" }
 lightning = { path = "../lightning", features = ["_test_utils"] }
-lightning_0_1 = { package = "lightning", version = "0.1.1", features = ["_test_utils"] }
+lightning_0_1 = { package = "lightning", version = "0.1.7", features = ["_test_utils"] }
 lightning_0_0_125 = { package = "lightning", version = "0.0.125", features = ["_test_utils"] }
 
 bitcoin = { version = "0.32.2", default-features = false }
diff --git a/lightning-tests/src/upgrade_downgrade_tests.rs b/lightning-tests/src/upgrade_downgrade_tests.rs
index 0b3f5df..d1153b7 100644
--- a/lightning-tests/src/upgrade_downgrade_tests.rs
+++ b/lightning-tests/src/upgrade_downgrade_tests.rs
@@ -10,9 +10,15 @@
 //! Tests which test upgrading from previous versions of LDK or downgrading to previous versions of
 //! LDK.
 
+use lightning_0_1::commitment_signed_dance as commitment_signed_dance_0_1;
 use lightning_0_1::events::ClosureReason as ClosureReason_0_1;
+use lightning_0_1::expect_pending_htlcs_forwardable_ignore as expect_pending_htlcs_forwardable_ignore_0_1;
 use lightning_0_1::get_monitor as get_monitor_0_1;
+use lightning_0_1::ln::channelmanager::PaymentId as PaymentId_0_1;
+use lightning_0_1::ln::channelmanager::RecipientOnionFields as RecipientOnionFields_0_1;
 use lightning_0_1::ln::functional_test_utils as lightning_0_1_utils;
+use lightning_0_1::ln::msgs::ChannelMessageHandler as _;
+use lightning_0_1::routing::router as router_0_1;
 use lightning_0_1::util::ser::Writeable as _;
 
 use lightning_0_0_125::chain::ChannelMonitorUpdateStatus as ChannelMonitorUpdateStatus_0_0_125;
@@ -29,16 +35,23 @@ use lightning_0_0_125::ln::msgs::ChannelMessageHandler as _;
 use lightning_0_0_125::routing::router as router_0_0_125;
 use lightning_0_0_125::util::ser::Writeable as _;
 
-use lightning::chain::channelmonitor::ANTI_REORG_DELAY;
-use lightning::events::{ClosureReason, Event};
+use lightning::chain::channelmonitor::{ANTI_REORG_DELAY, HTLC_FAIL_BACK_BUFFER};
+use lightning::events::bump_transaction::sync::WalletSourceSync;
+use lightning::events::{ClosureReason, Event, HTLCHandlingFailureType};
 use lightning::ln::functional_test_utils::*;
+use lightning::ln::funding::SpliceContribution;
+use lightning::ln::msgs::BaseMessageHandler as _;
+use lightning::ln::msgs::ChannelMessageHandler as _;
+use lightning::ln::msgs::MessageSendEvent;
+use lightning::ln::splicing_tests::*;
+use lightning::ln::types::ChannelId;
 use lightning::sign::OutputSpender;
 
-use lightning_types::payment::PaymentPreimage;
+use lightning_types::payment::{PaymentHash, PaymentPreimage, PaymentSecret};
 
-use bitcoin::opcodes;
 use bitcoin::script::Builder;
 use bitcoin::secp256k1::Secp256k1;
+use bitcoin::{opcodes, Amount, TxOut};
 
 use std::sync::Arc;
 
@@ -299,3 +312,188 @@ fn test_0_1_legacy_remote_key_derivation() {
 		panic!("Wrong event");
 	}
 }
+
+fn do_test_0_1_htlc_forward_after_splice(fail_htlc: bool) {
+	// Test what happens if an HTLC set to be forwarded in 0.1 is forwarded after the inbound
+	// channel is spliced. In the initial splice code, this could have led to a dangling HTLC if
+	// the HTLC is failed as the backwards-failure would use the channel's original SCID which is
+	// no longer valid.
+	// In some later splice code, this also failed because the `KeysManager` would have tried to
+	// rotate the `to_remote` key, which we aren't able to do in the splicing protocol.
+	let (node_a_ser, node_b_ser, node_c_ser, mon_a_1_ser, mon_b_1_ser, mon_b_2_ser, mon_c_1_ser);
+	let (node_a_id, node_b_id, node_c_id);
+	let (chan_id_bytes_a, chan_id_bytes_b);
+	let (payment_secret_bytes, payment_hash_bytes, payment_preimage_bytes);
+	let (node_a_blocks, node_b_blocks, node_c_blocks);
+
+	const EXTRA_BLOCKS_BEFORE_FAIL: u32 = 145;
+
+	{
+		let chanmon_cfgs = lightning_0_1_utils::create_chanmon_cfgs(3);
+		let node_cfgs = lightning_0_1_utils::create_node_cfgs(3, &chanmon_cfgs);
+		let node_chanmgrs =
+			lightning_0_1_utils::create_node_chanmgrs(3, &node_cfgs, &[None, None, None]);
+		let nodes = lightning_0_1_utils::create_network(3, &node_cfgs, &node_chanmgrs);
+
+		node_a_id = nodes[0].node.get_our_node_id();
+		node_b_id = nodes[1].node.get_our_node_id();
+		node_c_id = nodes[2].node.get_our_node_id();
+		let chan_id_a = lightning_0_1_utils::create_announced_chan_between_nodes_with_value(
+			&nodes, 0, 1, 10_000_000, 0,
+		)
+		.2;
+		chan_id_bytes_a = chan_id_a.0;
+
+		let chan_id_b = lightning_0_1_utils::create_announced_chan_between_nodes_with_value(
+			&nodes, 1, 2, 50_000, 0,
+		)
+		.2;
+		chan_id_bytes_b = chan_id_b.0;
+
+		// Ensure all nodes are at the same initial height.
+		let node_max_height = nodes.iter().map(|node| node.best_block_info().1).max().unwrap();
+		for node in &nodes {
+			let blocks_to_mine = node_max_height - node.best_block_info().1;
+			if blocks_to_mine > 0 {
+				lightning_0_1_utils::connect_blocks(node, blocks_to_mine);
+			}
+		}
+
+		let (preimage, hash, secret) =
+			lightning_0_1_utils::get_payment_preimage_hash(&nodes[2], Some(1_000_000), None);
+		payment_preimage_bytes = preimage.0;
+		payment_hash_bytes = hash.0;
+		payment_secret_bytes = secret.0;
+
+		let pay_params = router_0_1::PaymentParameters::from_node_id(
+			node_c_id,
+			lightning_0_1_utils::TEST_FINAL_CLTV,
+		)
+		.with_bolt11_features(nodes[2].node.bolt11_invoice_features())
+		.unwrap();
+
+		let route_params =
+			router_0_1::RouteParameters::from_payment_params_and_value(pay_params, 1_000_000);
+		let mut route = lightning_0_1_utils::get_route(&nodes[0], &route_params).unwrap();
+		route.paths[0].hops[1].cltv_expiry_delta =
+			EXTRA_BLOCKS_BEFORE_FAIL + HTLC_FAIL_BACK_BUFFER + 1;
+		if fail_htlc {
+			// Pay more than the channel's value (and probably not enough fee)
+			route.paths[0].hops[1].fee_msat = 50_000_000;
+		}
+
+		let onion = RecipientOnionFields_0_1::secret_only(secret);
+		let id = PaymentId_0_1(hash.0);
+		nodes[0].node.send_payment_with_route(route, hash, onion, id).unwrap();
+
+		lightning_0_1_utils::check_added_monitors(&nodes[0], 1);
+		let send_event = lightning_0_1_utils::SendEvent::from_node(&nodes[0]);
+
+		nodes[1].node.handle_update_add_htlc(node_a_id, &send_event.msgs[0]);
+		commitment_signed_dance_0_1!(nodes[1], nodes[0], send_event.commitment_msg, false);
+		expect_pending_htlcs_forwardable_ignore_0_1!(nodes[1]);
+
+		// We now have an HTLC pending in node B's forwarding queue with the original channel's
+		// SCID as the source.
+		// We now upgrade to 0.2 and splice before forwarding that HTLC...
+		node_a_ser = nodes[0].node.encode();
+		node_b_ser = nodes[1].node.encode();
+		node_c_ser = nodes[2].node.encode();
+		mon_a_1_ser = get_monitor_0_1!(nodes[0], chan_id_a).encode();
+		mon_b_1_ser = get_monitor_0_1!(nodes[1], chan_id_a).encode();
+		mon_b_2_ser = get_monitor_0_1!(nodes[1], chan_id_b).encode();
+		mon_c_1_ser = get_monitor_0_1!(nodes[2], chan_id_b).encode();
+
+		node_a_blocks = Arc::clone(&nodes[0].blocks);
+		node_b_blocks = Arc::clone(&nodes[1].blocks);
+		node_c_blocks = Arc::clone(&nodes[2].blocks);
+	}
+
+	// Create a dummy node to reload over with the 0.1 state
+	let mut chanmon_cfgs = create_chanmon_cfgs(3);
+
+	// Our TestChannelSigner will fail as we're jumping ahead, so disable its state-based checks
+	chanmon_cfgs[0].keys_manager.disable_all_state_policy_checks = true;
+	chanmon_cfgs[1].keys_manager.disable_all_state_policy_checks = true;
+	chanmon_cfgs[2].keys_manager.disable_all_state_policy_checks = true;
+
+	chanmon_cfgs[0].tx_broadcaster.blocks = node_a_blocks;
+	chanmon_cfgs[1].tx_broadcaster.blocks = node_b_blocks;
+	chanmon_cfgs[2].tx_broadcaster.blocks = node_c_blocks;
+
+	let node_cfgs = create_node_cfgs(3, &chanmon_cfgs);
+	let (persister_a, persister_b, persister_c, chain_mon_a, chain_mon_b, chain_mon_c);
+	let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[None, None, None]);
+	let (node_a, node_b, node_c);
+	let mut nodes = create_network(3, &node_cfgs, &node_chanmgrs);
+
+	let config = test_default_channel_config();
+	let a_mons = &[&mon_a_1_ser[..]];
+	reload_node!(nodes[0], config.clone(), &node_a_ser, a_mons, persister_a, chain_mon_a, node_a);
+	let b_mons = &[&mon_b_1_ser[..], &mon_b_2_ser[..]];
+	reload_node!(nodes[1], config.clone(), &node_b_ser, b_mons, persister_b, chain_mon_b, node_b);
+	let c_mons = &[&mon_c_1_ser[..]];
+	reload_node!(nodes[2], config, &node_c_ser, c_mons, persister_c, chain_mon_c, node_c);
+
+	reconnect_nodes(ReconnectArgs::new(&nodes[0], &nodes[1]));
+	let mut reconnect_b_c_args = ReconnectArgs::new(&nodes[1], &nodes[2]);
+	reconnect_b_c_args.send_channel_ready = (true, true);
+	reconnect_b_c_args.send_announcement_sigs = (true, true);
+	reconnect_nodes(reconnect_b_c_args);
+
+	let contribution = SpliceContribution::SpliceOut {
+		outputs: vec![TxOut {
+			value: Amount::from_sat(1_000),
+			script_pubkey: nodes[0].wallet_source.get_change_script().unwrap(),
+		}],
+	};
+	let splice_tx = splice_channel(&nodes[0], &nodes[1], ChannelId(chan_id_bytes_a), contribution);
+	for node in nodes.iter() {
+		mine_transaction(node, &splice_tx);
+		connect_blocks(node, ANTI_REORG_DELAY - 1);
+	}
+
+	let splice_locked = get_event_msg!(nodes[0], MessageSendEvent::SendSpliceLocked, node_b_id);
+	lock_splice(&nodes[0], &nodes[1], &splice_locked, false);
+
+	for node in nodes.iter() {
+		connect_blocks(node, EXTRA_BLOCKS_BEFORE_FAIL - ANTI_REORG_DELAY);
+	}
+
+	// Now release the HTLC to be failed back to node A
+	nodes[1].node.process_pending_htlc_forwards();
+
+	let pay_secret = PaymentSecret(payment_secret_bytes);
+	let pay_hash = PaymentHash(payment_hash_bytes);
+	let pay_preimage = PaymentPreimage(payment_preimage_bytes);
+
+	if fail_htlc {
+		let failure = HTLCHandlingFailureType::Forward {
+			node_id: Some(node_c_id),
+			channel_id: ChannelId(chan_id_bytes_b),
+		};
+		expect_and_process_pending_htlcs_and_htlc_handling_failed(&nodes[1], &[failure]);
+		check_added_monitors(&nodes[1], 1);
+
+		let updates = get_htlc_update_msgs(&nodes[1], &node_a_id);
+		nodes[0].node.handle_update_fail_htlc(node_b_id, &updates.update_fail_htlcs[0]);
+		commitment_signed_dance!(nodes[0], nodes[1], updates.commitment_signed, false);
+		let conditions = PaymentFailedConditions::new();
+		expect_payment_failed_conditions(&nodes[0], pay_hash, false, conditions);
+	} else {
+		check_added_monitors(&nodes[1], 1);
+		let forward_event = SendEvent::from_node(&nodes[1]);
+		nodes[2].node.handle_update_add_htlc(node_b_id, &forward_event.msgs[0]);
+		commitment_signed_dance!(nodes[2], nodes[1], forward_event.commitment_msg, false);
+
+		expect_and_process_pending_htlcs(&nodes[2], false);
+		expect_payment_claimable!(nodes[2], pay_hash, pay_secret, 1_000_000);
+		claim_payment(&nodes[0], &[&nodes[1], &nodes[2]], pay_preimage);
+	}
+}
+
+#[test]
+fn test_0_1_htlc_forward_after_splice() {
+	do_test_0_1_htlc_forward_after_splice(true);
+	do_test_0_1_htlc_forward_after_splice(false);
+}
diff --git a/lightning/src/chain/channelmonitor.rs b/lightning/src/chain/channelmonitor.rs
index e2f0eff..4acba6f 100644
--- a/lightning/src/chain/channelmonitor.rs
+++ b/lightning/src/chain/channelmonitor.rs
@@ -327,7 +327,7 @@ pub const ARCHIVAL_DELAY_BLOCKS: u32 = 4032;
 /// (2) is the same, but with an additional buffer to avoid accepting an HTLC which is immediately
 /// in a race condition between the user connecting a block (which would fail it) and the user
 /// providing us the preimage (which would claim it).
-pub(crate) const HTLC_FAIL_BACK_BUFFER: u32 = CLTV_CLAIM_BUFFER + LATENCY_GRACE_PERIOD_BLOCKS;
+pub const HTLC_FAIL_BACK_BUFFER: u32 = CLTV_CLAIM_BUFFER + LATENCY_GRACE_PERIOD_BLOCKS;
 
 // Deprecated, use [`HolderCommitment`] or [`HolderCommitmentTransaction`].
 #[derive(Clone, PartialEq, Eq)]
diff --git a/lightning/src/ln/mod.rs b/lightning/src/ln/mod.rs
index bae5558..9473142 100644
--- a/lightning/src/ln/mod.rs
+++ b/lightning/src/ln/mod.rs
@@ -120,8 +120,8 @@ mod reorg_tests;
 #[cfg(test)]
 #[allow(unused_mut)]
 mod shutdown_tests;
-#[cfg(test)]
-mod splicing_tests;
+#[cfg(any(feature = "_test_utils", test))]
+pub mod splicing_tests;
 #[cfg(any(test, feature = "_externalize_tests"))]
 #[allow(unused_mut)]
 pub mod update_fee_tests;
diff --git a/lightning/src/ln/splicing_tests.rs b/lightning/src/ln/splicing_tests.rs
index 2b415a1..f95883e 100644
--- a/lightning/src/ln/splicing_tests.rs
+++ b/lightning/src/ln/splicing_tests.rs
@@ -7,6 +7,8 @@
 // You may not use this file except in accordance with one or both of these
 // licenses.
 
+#![cfg_attr(not(test), allow(unused_imports))]
+
 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;
@@ -68,7 +70,7 @@ fn test_v1_splice_in_negative_insufficient_inputs() {
 	}
 }
 
-fn negotiate_splice_tx<'a, 'b, 'c, 'd>(
+pub fn negotiate_splice_tx<'a, 'b, 'c, 'd>(
 	initiator: &'a Node<'b, 'c, 'd>, acceptor: &'a Node<'b, 'c, 'd>, channel_id: ChannelId,
 	initiator_contribution: SpliceContribution,
 ) -> msgs::CommitmentSigned {
@@ -83,7 +85,7 @@ fn negotiate_splice_tx<'a, 'b, 'c, 'd>(
 	)
 }
 
-fn complete_splice_handshake<'a, 'b, 'c, 'd>(
+pub fn complete_splice_handshake<'a, 'b, 'c, 'd>(
 	initiator: &'a Node<'b, 'c, 'd>, acceptor: &'a Node<'b, 'c, 'd>, channel_id: ChannelId,
 	initiator_contribution: SpliceContribution,
 ) -> ScriptBuf {
@@ -120,7 +122,7 @@ fn complete_splice_handshake<'a, 'b, 'c, 'd>(
 	new_funding_script
 }
 
-fn complete_interactive_funding_negotiation<'a, 'b, 'c, 'd>(
+pub fn complete_interactive_funding_negotiation<'a, 'b, 'c, 'd>(
 	initiator: &'a Node<'b, 'c, 'd>, acceptor: &'a Node<'b, 'c, 'd>, channel_id: ChannelId,
 	initiator_contribution: SpliceContribution, new_funding_script: ScriptBuf,
 ) -> msgs::CommitmentSigned {
@@ -209,7 +211,7 @@ fn complete_interactive_funding_negotiation<'a, 'b, 'c, 'd>(
 	}
 }
 
-fn sign_interactive_funding_tx<'a, 'b, 'c, 'd>(
+pub fn sign_interactive_funding_tx<'a, 'b, 'c, 'd>(
 	initiator: &'a Node<'b, 'c, 'd>, acceptor: &'a Node<'b, 'c, 'd>,
 	initial_commit_sig_for_acceptor: msgs::CommitmentSigned, is_0conf: bool,
 ) -> (Transaction, Option<(msgs::SpliceLocked, PublicKey)>) {
@@ -277,7 +279,7 @@ fn sign_interactive_funding_tx<'a, 'b, 'c, 'd>(
 	(tx, splice_locked)
 }
 
-fn splice_channel<'a, 'b, 'c, 'd>(
+pub fn splice_channel<'a, 'b, 'c, 'd>(
 	initiator: &'a Node<'b, 'c, 'd>, acceptor: &'a Node<'b, 'c, 'd>, channel_id: ChannelId,
 	initiator_contribution: SpliceContribution,
 ) -> Transaction {
@@ -304,7 +306,7 @@ fn splice_channel<'a, 'b, 'c, 'd>(
 	splice_tx
 }
 
-fn lock_splice_after_blocks<'a, 'b, 'c, 'd>(
+pub fn lock_splice_after_blocks<'a, 'b, 'c, 'd>(
 	node_a: &'a Node<'b, 'c, 'd>, node_b: &'a Node<'b, 'c, 'd>, num_blocks: u32,
 ) {
 	connect_blocks(node_a, num_blocks);
@@ -316,7 +318,7 @@ fn lock_splice_after_blocks<'a, 'b, 'c, 'd>(
 	lock_splice(node_a, node_b, &splice_locked_for_node_b, false);
 }
 
-fn lock_splice<'a, 'b, 'c, 'd>(
+pub fn lock_splice<'a, 'b, 'c, 'd>(
 	node_a: &'a Node<'b, 'c, 'd>, node_b: &'a Node<'b, 'c, 'd>,
 	splice_locked_for_node_b: &msgs::SpliceLocked, is_0conf: bool,
 ) {
@@ -387,6 +389,7 @@ fn test_splice_state_reset_on_disconnect() {
 	do_test_splice_state_reset_on_disconnect(true);
 }
 
+#[cfg(test)]
 fn do_test_splice_state_reset_on_disconnect(reload: bool) {
 	// Tests that we're able to forget our pending splice state after a disconnect such that we can
 	// retry later.
@@ -714,6 +717,7 @@ fn test_splice_out() {
 	let _ = send_payment(&nodes[0], &[&nodes[1]], htlc_limit_msat);
 }
 
+#[cfg(test)]
 #[derive(PartialEq)]
 enum SpliceStatus {
 	Unconfirmed,
@@ -731,6 +735,7 @@ fn test_splice_commitment_broadcast() {
 	do_test_splice_commitment_broadcast(SpliceStatus::Locked, true);
 }
 
+#[cfg(test)]
 fn do_test_splice_commitment_broadcast(splice_status: SpliceStatus, claim_htlcs: bool) {
 	// Tests that we're able to enforce HTLCs onchain during the different stages of a splice.
 	let chanmon_cfgs = create_chanmon_cfgs(2);
@@ -926,6 +931,7 @@ fn test_splice_reestablish() {
 	do_test_splice_reestablish(true, true);
 }
 
+#[cfg(test)]
 fn do_test_splice_reestablish(reload: bool, async_monitor_update: bool) {
 	// Test that we're able to reestablish the channel succesfully throughout the lifecycle of a splice.
 	let chanmon_cfgs = create_chanmon_cfgs(2);
@@ -1188,6 +1194,7 @@ fn test_propose_splice_while_disconnected() {
 	do_test_propose_splice_while_disconnected(true, true);
 }
 
+#[cfg(test)]
 fn do_test_propose_splice_while_disconnected(reload: bool, use_0conf: bool) {
 	// Test that both nodes are able to propose a splice while the counterparty is disconnected, and
 	// whoever doesn't go first due to the quiescence tie-breaker, will retry their splice after the
@@ -1804,6 +1811,7 @@ fn fail_quiescent_action_on_channel_close() {
 	check_added_monitors(&nodes[0], 1);
 }
 
+#[cfg(test)]
 fn do_test_splice_with_inflight_htlc_forward_and_resolution(expire_scid_pre_forward: bool) {
 	// Test that we are still able to forward and resolve HTLCs while the original SCIDs contained
 	// in the onion packets have now changed due channel splices becoming locked.