Rename ClosingMonitorUpdate MonitorUpdateRegeneratedOnStartup

This makes much clearer at sites generating such events that they
will be lost on restart, to reduce risk of bugs creeping in due to
lost monitor updates.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -501,9 +501,11 @@ struct ClaimablePayments {
 /// for some reason. They are handled in timer_tick_occurred, so may be processed with
 /// quite some time lag.
 enum BackgroundEvent {
-	/// Handle a ChannelMonitorUpdate that closes a channel, broadcasting its current latest holder
-	/// commitment transaction.
-	ClosingMonitorUpdate((OutPoint, ChannelMonitorUpdate)),
+	/// Handle a ChannelMonitorUpdate
+	///
+	/// Note that any such events are lost on shutdown, so in general they must be updates which
+	/// are regenerated on startup.
+	MonitorUpdateRegeneratedOnStartup((OutPoint, ChannelMonitorUpdate)),
 }
 
 #[derive(Debug)]
@@ -3774,7 +3776,7 @@ where
 
 		for event in background_events.drain(..) {
 			match event {
-				BackgroundEvent::ClosingMonitorUpdate((funding_txo, update)) => {
+				BackgroundEvent::MonitorUpdateRegeneratedOnStartup((funding_txo, update)) => {
 					// The channel has already been closed, so no use bothering to care about the
 					// monitor updating completing.
 					let _ = self.chain_monitor.update_channel(funding_txo, &update);
@@ -5694,7 +5696,7 @@ where
 				if let ChannelMonitorUpdateStep::ChannelForceClosed { should_broadcast } = update.updates[0] {
 					assert!(should_broadcast);
 				} else { unreachable!(); }
-				self.pending_background_events.lock().unwrap().push(BackgroundEvent::ClosingMonitorUpdate((funding_txo, update)));
+				self.pending_background_events.lock().unwrap().push(BackgroundEvent::MonitorUpdateRegeneratedOnStartup((funding_txo, update)));
 			}
 			self.finish_force_close_channel(failure);
 		}
@@ -7449,10 +7451,10 @@ where
 		}
 
 		// LDK versions prior to 0.0.116 wrote the `pending_background_events`
-		// `ClosingMonitorUpdate`s here, however there was never a reason to do so - the closing
-		// monitor updates were always effectively replayed on startup (either directly by calling
-		// `broadcast_latest_holder_commitment_txn` on a `ChannelMonitor` during deserialization
-		// or, in 0.0.115, by regenerating the monitor update itself).
+		// `MonitorUpdateRegeneratedOnStartup`s here, however there was never a reason to do so -
+		// the closing monitor updates were always effectively replayed on startup (either directly
+		// by calling `broadcast_latest_holder_commitment_txn` on a `ChannelMonitor` during
+		// deserialization or, in 0.0.115, by regenerating the monitor update itself).
 		0u64.write(writer)?;
 
 		// Prior to 0.0.111 we tracked node_announcement serials here, however that now happens in
@@ -7768,7 +7770,7 @@ where
 						log_bytes!(channel.channel_id()), monitor.get_latest_update_id(), channel.get_latest_monitor_update_id());
 					let (monitor_update, mut new_failed_htlcs) = channel.force_shutdown(true);
 					if let Some(monitor_update) = monitor_update {
-						pending_background_events.push(BackgroundEvent::ClosingMonitorUpdate(monitor_update));
+						pending_background_events.push(BackgroundEvent::MonitorUpdateRegeneratedOnStartup(monitor_update));
 					}
 					failed_htlcs.append(&mut new_failed_htlcs);
 					channel_closures.push_back((events::Event::ChannelClosed {
@@ -7843,7 +7845,7 @@ where
 					update_id: CLOSED_CHANNEL_UPDATE_ID,
 					updates: vec![ChannelMonitorUpdateStep::ChannelForceClosed { should_broadcast: true }],
 				};
-				pending_background_events.push(BackgroundEvent::ClosingMonitorUpdate((*funding_txo, monitor_update)));
+				pending_background_events.push(BackgroundEvent::MonitorUpdateRegeneratedOnStartup((*funding_txo, monitor_update)));
 			}
 		}
 
@@ -7900,7 +7902,7 @@ where
 		for _ in 0..background_event_count {
 			match <u8 as Readable>::read(reader)? {
 				0 => {
-					// LDK versions prior to 0.0.116 wrote pending `ClosingMonitorUpdate`s here,
+					// LDK versions prior to 0.0.116 wrote pending `MonitorUpdateRegeneratedOnStartup`s here,
 					// however we really don't (and never did) need them - we regenerate all
 					// on-startup monitor updates.
 					let _: OutPoint = Readable::read(reader)?;