Set PaymentSent::fee_paid_msat in abandoned case

If an outbound payment was abandoned with htlcs in-flight and later claimed, we
would previously have the PaymentSent::fee_paid_msat be set to None. This
contradicted some docs on the event that stated the field would always be Some
after 0.0.103.

Backport of 3e9e6e9

Conflicts resolved in:
 * lightning/src/ln/functional_tests.rs
 * lightning/src/ln/outbound_payment.rs
 * lightning/src/ln/payment_tests.rs

Author: valentinewallace

lightning/src/events/mod.rs

@@ -930,7 +930,8 @@ pub enum Event {
 		/// If the recipient or an intermediate node misbehaves and gives us free money, this may
 		/// overstate the amount paid, though this is unlikely.
 		///
-		/// This is only `None` for payments initiated on LDK versions prior to 0.0.103.
+		/// This is only `None` for payments abandoned but ultimately claimed when using LDK versions
+		/// prior to 0.3, 0.2.3, or 0.1.10.
 		///
 		/// [`Route::get_total_fees`]: crate::routing::router::Route::get_total_fees
 		fee_paid_msat: Option<u64>,

lightning/src/ln/functional_tests.rs

@@ -10281,7 +10281,7 @@ fn test_inconsistent_mpp_params() {
 	do_claim_payment_along_route(
 		ClaimAlongRouteArgs::new(&nodes[0], &[&[&nodes[1], &nodes[3]], &[&nodes[2], &nodes[3]]], our_payment_preimage)
 	);
-	expect_payment_sent(&nodes[0], our_payment_preimage, Some(None), true, true);
+	expect_payment_sent(&nodes[0], our_payment_preimage, Some(Some(2000)), true, true);
 }
 
 #[test]

lightning/src/ln/outbound_payment.rs

@@ -133,6 +133,9 @@ pub(crate) enum PendingOutboundPayment {
 		/// Will be `None` if the payment was serialized before 0.0.115 or if downgrading to 0.0.124
 		/// or later with a reason that was added after.
 		reason: Option<PaymentFailureReason>,
+		/// Preserved from `Retryable` so we can still report `fee_paid_msat` if an HTLC succeeds after
+		/// the payment was abandoned. Added in 0.3/0.1.10.
+		pending_fee_msat: Option<u64>,
 	},
 }
 
@@ -209,6 +212,7 @@ impl PendingOutboundPayment {
 	fn get_pending_fee_msat(&self) -> Option<u64> {
 		match self {
 			PendingOutboundPayment::Retryable { pending_fee_msat, .. } => pending_fee_msat.clone(),
+			PendingOutboundPayment::Abandoned { pending_fee_msat, .. } => pending_fee_msat.clone(),
 			_ => None,
 		}
 	}
@@ -251,6 +255,7 @@ impl PendingOutboundPayment {
 			},
 			_ => new_hash_set(),
 		};
+		let pending_fee_msat = self.get_pending_fee_msat();
 		match self {
 			Self::Retryable { payment_hash, .. } |
 				Self::InvoiceReceived { payment_hash, .. } |
@@ -260,6 +265,7 @@ impl PendingOutboundPayment {
 					session_privs,
 					payment_hash: *payment_hash,
 					reason: Some(reason),
+					pending_fee_msat,
 				};
 			},
 			_ => {}
@@ -2409,6 +2415,7 @@ impl_writeable_tlv_based_enum_upgradable!(PendingOutboundPayment,
 		(0, session_privs, required),
 		(1, reason, upgradable_option),
 		(2, payment_hash, required),
+		(5, pending_fee_msat, option),
 	},
 	(5, AwaitingInvoice) => {
 		(0, expiration, required),

lightning/src/ln/payment_tests.rs

@@ -1751,6 +1751,36 @@ fn abandoned_send_payment_idempotent() {
 	claim_payment(&nodes[0], &[&nodes[1]], second_payment_preimage);
 }
 
+#[test]
+fn abandoned_payment_fulfilled_preserves_fee_paid_msat() {
+	// Previously, if we abandoned a payment with HTLCs in-flight and the payment eventually
+	// succeeded, we would set the `Event::PaymentSent::fee_paid_msat` to None, even though we had
+	// docs guaranteeing that it would always be Some after 0.0.103.
+	let chanmon_cfgs = create_chanmon_cfgs(3);
+	let node_cfgs = create_node_cfgs(3, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[None, None, None]);
+	let nodes = create_network(3, &node_cfgs, &node_chanmgrs);
+
+	create_announced_chan_between_nodes(&nodes, 0, 1);
+	create_announced_chan_between_nodes(&nodes, 1, 2);
+
+	let amt_msat = 5_000_000;
+	let (route, payment_hash, payment_preimage, payment_secret) =
+		get_route_and_payment_hash!(&nodes[0], nodes[2], amt_msat);
+	let payment_id = PaymentId(payment_hash.0);
+	let onion = RecipientOnionFields::secret_only(payment_secret);
+	nodes[0].node.send_payment_with_route(route, payment_hash, onion, payment_id).unwrap();
+	check_added_monitors(&nodes[0], 1);
+
+	let path: &[&Node] = &[&nodes[1], &nodes[2]];
+	pass_along_route(&nodes[0], &[path], amt_msat, payment_hash, payment_secret);
+
+	nodes[0].node.abandon_payment(payment_id);
+	assert!(nodes[0].node.get_and_clear_pending_events().is_empty());
+
+	claim_payment_along_route(ClaimAlongRouteArgs::new(&nodes[0], &[path], payment_preimage));
+}
+
 #[derive(PartialEq)]
 enum InterceptTest {
 	Forward,