Send peers error messages for failures due to invalid batch funding

If we fail to fund a batch open we'll force-close all channels in
the batch, however would previously fail to send error messages to
our peers for any channels we were due to test after the one that
failed.

This commit fixes that issue, sending the required error messages
to allow our peers to clean up their state.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -4726,11 +4726,20 @@ where
 				for (channel_id, counterparty_node_id) in channels_to_remove {
 					per_peer_state.get(&counterparty_node_id)
 						.map(|peer_state_mutex| peer_state_mutex.lock().unwrap())
-						.and_then(|mut peer_state| peer_state.channel_by_id.remove(&channel_id))
-						.map(|mut chan| {
+						.and_then(|mut peer_state| peer_state.channel_by_id.remove(&channel_id).map(|chan| (chan, peer_state)))
+						.map(|(mut chan, mut peer_state)| {
 							update_maps_on_chan_removal!(self, &chan.context());
 							let closure_reason = ClosureReason::ProcessingError { err: e.clone() };
 							shutdown_results.push(chan.context_mut().force_shutdown(false, closure_reason));
+							peer_state.pending_msg_events.push(events::MessageSendEvent::HandleError {
+								node_id: counterparty_node_id,
+								action: msgs::ErrorAction::SendErrorMessage {
+									msg: msgs::ErrorMessage {
+										channel_id,
+										data: "Failed to fund channel".to_owned(),
+									}
+								},
+							});
 						});
 				}
 			}

lightning/src/ln/functional_tests.rs

@@ -10110,14 +10110,9 @@ fn test_non_final_funding_tx() {
 		},
 		_ => panic!()
 	}
-	let events = nodes[0].node.get_and_clear_pending_events();
-	assert_eq!(events.len(), 1);
-	match events[0] {
-		Event::ChannelClosed { channel_id, .. } => {
-			assert_eq!(channel_id, temp_channel_id);
-		},
-		_ => panic!("Unexpected event"),
-	}
+	let err = "Error in transaction funding: Misuse error: Funding transaction absolute timelock is non-final".to_owned();
+	check_closed_events(&nodes[0], &[ExpectedCloseEvent::from_id_reason(temp_channel_id, false, ClosureReason::ProcessingError { err })]);
+	assert_eq!(get_err_msg(&nodes[0], &nodes[1].node.get_our_node_id()).data, "Failed to fund channel");
 }
 
 #[test]

lightning/src/ln/shutdown_tests.rs

@@ -1434,9 +1434,14 @@ fn batch_funding_failure() {
 	// We currently spuriously send `FundingCreated` for the first channel and then immediately
 	// fail both channels, which isn't ideal but should be fine.
 	assert!(matches!(msgs[0],
-		MessageSendEvent::SendFundingCreated { msg: msgs::FundingCreated { temporary_channel_id: temp_chan_id_a, .. }, .. }
+		MessageSendEvent::HandleError { action: msgs::ErrorAction::SendErrorMessage {
+			msg: msgs::ErrorMessage { channel_id: temp_chan_id_b, .. }, ..
+		}, .. }
 	));
 	assert!(matches!(msgs[1],
+		MessageSendEvent::SendFundingCreated { msg: msgs::FundingCreated { temporary_channel_id: temp_chan_id_a, .. }, .. }
+	));
+	assert!(matches!(msgs[2],
 		MessageSendEvent::HandleError { action: msgs::ErrorAction::SendErrorMessage {
 			msg: msgs::ErrorMessage { channel_id: post_funding_chan_id_a, .. }, ..
 		}, .. }