Provide a utility to log the ProbabilisticScorer's contents

I wrote this when debugging a user's scorer and figured it may be
useful upstream.

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -623,6 +623,40 @@ impl<G: Deref<Target = NetworkGraph>, L: Deref, T: Time> ProbabilisticScorerUsin
 		assert!(self.channel_liquidities.insert(short_channel_id, liquidity).is_none());
 		self
 	}
+
+	/// Dump the contents of this scorer into the configured logger.
+	///
+	/// Note that this writes roughly one line per channel for which we have a liquidity estimate,
+	/// which may be a substantial amount of log output.
+	fn debug_log_liquidity_stats(&self) {
+		let graph = self.network_graph.read_only();
+		for (scid, liq) in self.channel_liquidities.iter() {
+			if let Some(chan_debug) = graph.channels().get(scid) {
+				if let Some(dir_debug) = &chan_debug.one_to_two {
+					let amount = chan_debug.capacity_sats.map(|v| v*1000).or(dir_debug.htlc_maximum_msat);
+					if let Some(amt) = amount {
+						let dir_liq = liq.as_directed(&chan_debug.node_one, &chan_debug.node_two, amt, self.liquidity_offset_half_life);
+						log_debug!(self.logger, "Liquidity from {:?} to {:?} via {} is in the range ({}, {})",
+							chan_debug.node_one, chan_debug.node_two, scid, dir_liq.min_liquidity_msat(), dir_liq.max_liquidity_msat());
+					} else {
+						log_debug!(self.logger, "No amount known for SCID {} from {:?} to {:?}", scid, chan_debug.node_one, chan_debug.node_two);
+					}
+				}
+				if let Some(dir_debug) = &chan_debug.two_to_one {
+					let amount = chan_debug.capacity_sats.map(|v| v*1000).or(dir_debug.htlc_maximum_msat);
+					if let Some(amt) = amount {
+						let dir_liq = liq.as_directed(&chan_debug.node_two, &chan_debug.node_one, amt, self.liquidity_offset_half_life);
+						log_debug!(self.logger, "Liquidity from {:?} to {:?} via {} is in the range ({}, {})",
+							chan_debug.node_two, chan_debug.node_one, scid, dir_liq.min_liquidity_msat(), dir_liq.max_liquidity_msat());
+					} else {
+						log_debug!(self.logger, "No amount known for SCID {} from {:?} to {:?}", scid, chan_debug.node_two, chan_debug.node_one);
+					}
+				}
+			} else {
+				log_debug!(self.logger, "No network graph entry for SCID {}", scid);
+			}
+		}
+	}
 }
 
 impl ProbabilisticScoringParameters {