Improve logging of pathfinding behavior

lightning/src/routing/router.rs

@@ -1267,6 +1267,29 @@ where L::Target: Logger {
 					// around again with a higher amount.
 					if !contributes_sufficient_value || exceeds_max_path_length ||
 						exceeds_cltv_delta_limit || payment_failed_on_this_channel {
+						let empty_vec: Vec<&ChannelDetails> = Vec::new();
+						let target = match first_hop_targets.get(&NodeId::from_pubkey(&our_node_pubkey)) {
+					  		Some(value) => value,
+    							None => {
+        							&empty_vec
+    						 	}
+						};
+						for channel_details in target {
+							if let Some(short_channel_id_target) = channel_details.short_channel_id {
+								if short_channel_id == short_channel_id_target { // short_channel_id is hop id of candidate.
+									if !contributes_sufficient_value {
+        									log_trace!(logger, "First Hop {short_channel_id} is excluded due to insufficient balance");
+    									} else if exceeds_max_path_length {
+    										log_trace!(logger, "First Hop {short_channel_id} is excluded due to candidate hop excluded max path length");
+    									} else if exceeds_cltv_delta_limit {
+    										log_trace!(logger, "First Hop {short_channel_id} is excluded beacause it exceed the maximum total cltv expiry limit");
+    									} else if payment_failed_on_this_channel {
+    										log_trace!(logger, "First Hop {short_channel_id} is excluded beacause it was failed previously");
+    									}
+
+    								}
+							}
+						}
 						// Path isn't useful, ignore it and move on.
 					} else if may_overpay_to_meet_path_minimum_msat {
 						hit_minimum_limit = true;