Hide ChannelPhase::Funded behind as_funded method

Exposing ChannelPhase in ChannelManager has led to verbose match
statements, which need to be modified each time a ChannelPhase is added.
Making ChannelPhase an implementation detail of Channel would help avoid
this.

As a step in this direction, introduce ChannelPhase::as_funded and
ChannelPhase::as_funded_mut for use in ChannelManager when a Channel (to
be later renamed FundedChannel) is needed.

Author: jkczyz

lightning/src/ln/chanmon_update_fail_tests.rs

@@ -20,7 +20,7 @@ use crate::chain::transaction::OutPoint;
 use crate::chain::{ChannelMonitorUpdateStatus, Listen, Watch};
 use crate::events::{Event, MessageSendEvent, MessageSendEventsProvider, PaymentPurpose, ClosureReason, HTLCDestination};
 use crate::ln::channelmanager::{RAACommitmentOrder, PaymentSendFailure, PaymentId, RecipientOnionFields};
-use crate::ln::channel::{AnnouncementSigsState, ChannelPhase};
+use crate::ln::channel::AnnouncementSigsState;
 use crate::ln::msgs;
 use crate::ln::types::ChannelId;
 use crate::ln::msgs::{ChannelMessageHandler, RoutingMessageHandler};
@@ -98,7 +98,7 @@ fn test_monitor_and_persister_update_fail() {
 	{
 		let mut node_0_per_peer_lock;
 		let mut node_0_peer_state_lock;
-		if let ChannelPhase::Funded(ref mut channel) = get_channel_ref!(nodes[0], nodes[1], node_0_per_peer_lock, node_0_peer_state_lock, chan.2) {
+		if let Some(channel) = get_channel_ref!(nodes[0], nodes[1], node_0_per_peer_lock, node_0_peer_state_lock, chan.2).as_funded_mut() {
 			if let Ok(Some(update)) = channel.commitment_signed(&updates.commitment_signed, &node_cfgs[0].logger) {
 				// Check that the persister returns InProgress (and will never actually complete)
 				// as the monitor update errors.

lightning/src/ln/channel.rs

@@ -1152,6 +1152,22 @@ impl<'a, SP: Deref> ChannelPhase<SP> where
 			ChannelPhase::UnfundedV2(ref mut chan) => &mut chan.context,
 		}
 	}
+
+	pub fn as_funded(&self) -> Option<&Channel<SP>> {
+		if let ChannelPhase::Funded(channel) = self {
+			Some(channel)
+		} else {
+			None
+		}
+	}
+
+	pub fn as_funded_mut(&mut self) -> Option<&mut Channel<SP>> {
+		if let ChannelPhase::Funded(channel) = self {
+			Some(channel)
+		} else {
+			None
+		}
+	}
 }
 
 /// Contains all state common to unfunded inbound/outbound channels.