Prevent duplicate PaymentSent events

by removing all pending outbound payments associated with the same
MPP payment after the preimage is received

lightning/src/ln/channelmanager.rs

@@ -3137,6 +3137,9 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 					pending_events.push(events::Event::PaymentSent {
 						payment_preimage
 					});
+					self.pending_outbound_payments.lock().unwrap().retain(|p| {
+						mpp_id.is_none() || (mpp_id.is_some() && mpp_id != p.1)
+					});
 				} else {
 					log_trace!(self.logger, "Received duplicative fulfill for HTLC with payment_preimage {}", log_bytes!(payment_preimage.0));
 				}
@@ -5644,20 +5647,13 @@ mod tests {
 		nodes[0].node.handle_revoke_and_ack(&nodes[1].node.get_our_node_id(), &bs_third_raa);
 		check_added_monitors!(nodes[0], 1);
 
-		// There's an existing bug that generates a PaymentSent event for each MPP path, so handle that here.
 		let events = nodes[0].node.get_and_clear_pending_events();
 		match events[0] {
 			Event::PaymentSent { payment_preimage: ref preimage } => {
 				assert_eq!(payment_preimage, *preimage);
 			},
 			_ => panic!("Unexpected event"),
 		}
-		match events[1] {
-			Event::PaymentSent { payment_preimage: ref preimage } => {
-				assert_eq!(payment_preimage, *preimage);
-			},
-			_ => panic!("Unexpected event"),
-		}
 	}
 
 	#[test]

lightning/src/ln/functional_test_utils.rs

@@ -1237,9 +1237,11 @@ pub fn claim_payment_along_route<'a, 'b, 'c>(origin_node: &Node<'a, 'b, 'c>, exp
 
 		if !skip_last {
 			last_update_fulfill_dance!(origin_node, expected_route.first().unwrap());
-			expect_payment_sent!(origin_node, our_payment_preimage);
 		}
 	}
+	if !skip_last {
+		expect_payment_sent!(origin_node, our_payment_preimage);
+	}
 }
 
 pub fn claim_payment<'a, 'b, 'c>(origin_node: &Node<'a, 'b, 'c>, expected_route: &[&Node<'a, 'b, 'c>], our_payment_preimage: PaymentPreimage) {