Clarify ChannelManager docs somewhat around full blocks

As suggested by Val.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -4007,8 +4007,9 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> Writeable f
 ///    ChannelManager)>::read(reader, args).
 ///    This may result in closing some Channels if the ChannelMonitor is newer than the stored
 ///    ChannelManager state to ensure no loss of funds. Thus, transactions may be broadcasted.
-/// 3) Register all relevant ChannelMonitor outpoints with your chain watch mechanism using
-///    ChannelMonitor::get_outputs_to_watch() and ChannelMonitor::get_funding_txo().
+/// 3) If you are not fetching full blocks, register all relevant ChannelMonitor outpoints the same
+///    way you would handle a `chain::Filter` call using ChannelMonitor::get_outputs_to_watch() and
+///    ChannelMonitor::get_funding_txo().
 /// 4) Reconnect blocks on your ChannelMonitors.
 /// 5) Disconnect/connect blocks on the ChannelManager.
 /// 6) Move the ChannelMonitors into your local chain::Watch.

lightning/src/ln/reorg_tests.rs

@@ -278,6 +278,8 @@ fn do_test_unconf_chan(reload_node: bool, reorg_after_reload: bool) {
 		}
 	}
 
+	// With expect_channel_force_closed set the TestChainMonitor will enforce that the next update
+	// is a ChannelForcClosed on the right channel with should_broadcast set.
 	*nodes[0].chain_monitor.expect_channel_force_closed.lock().unwrap() = Some((chan_id, true));
 	nodes[0].node.test_process_background_events(); // Required to free the pending background monitor update
 	check_added_monitors!(nodes[0], 1);

lightning/src/util/test_utils.rs

@@ -82,9 +82,12 @@ pub struct TestChainMonitor<'a> {
 	pub chain_monitor: chainmonitor::ChainMonitor<EnforcingSigner, &'a TestChainSource, &'a chaininterface::BroadcasterInterface, &'a TestFeeEstimator, &'a TestLogger, &'a channelmonitor::Persist<EnforcingSigner>>,
 	pub keys_manager: &'a TestKeysInterface,
 	pub update_ret: Mutex<Option<Result<(), channelmonitor::ChannelMonitorUpdateErr>>>,
-	// If this is set to Some(), after the next return, we'll always return this until update_ret
-	// is changed:
+	/// If this is set to Some(), after the next return, we'll always return this until update_ret
+	/// is changed:
 	pub next_update_ret: Mutex<Option<Result<(), channelmonitor::ChannelMonitorUpdateErr>>>,
+	/// If this is set to Some(), the next update_channel call (not watch_channel) must be a
+	/// ChannelForceClosed event for the given channel_id with should_broadcast set to the given
+	/// boolean.
 	pub expect_channel_force_closed: Mutex<Option<([u8; 32], bool)>>,
 }
 impl<'a> TestChainMonitor<'a> {