Test we consider route hints if we are the src of the first hop

Previously, we would only consider route hints if the entry point was
in our first hops or in the network graph. We fixed this by also
considering hints if our own node ID was the first src.

Here, we add test coverage for this behavior.

Author: tnull

lightning/src/routing/router.rs

@@ -7841,6 +7841,57 @@ mod tests {
 		assert_eq!(route.paths[0].hops[1].short_channel_id, 45);
 		assert_eq!(route.get_total_fees(), 123);
 	}
+
+	#[test]
+	fn allow_us_being_first_hint() {
+		// Check that we consider a route hint even if we are the src of the first hop.
+		let secp_ctx = Secp256k1::new();
+		let logger = Arc::new(ln_test_utils::TestLogger::new());
+		let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+		let scorer = ln_test_utils::TestScorer::new();
+		let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+		let random_seed_bytes = keys_manager.get_secure_random_bytes();
+		let config = UserConfig::default();
+
+		let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
+
+		let amt_msat = 1_000_000;
+		let dest_node_id = nodes[1];
+
+		let first_hop = get_channel_details(Some(1), nodes[0], channelmanager::provided_init_features(&config), 10_000_000);
+		let first_hops = vec![first_hop];
+
+		let route_hint = RouteHint(vec![RouteHintHop {
+			src_node_id: our_node_id,
+			short_channel_id: 44,
+			fees: RoutingFees {
+				base_msat: 123,
+				proportional_millionths: 0,
+			},
+			cltv_expiry_delta: 10,
+			htlc_minimum_msat: None,
+			htlc_maximum_msat: None,
+		}]);
+
+		let payment_params = PaymentParameters::from_node_id(dest_node_id, 42)
+			.with_route_hints(vec![route_hint]).unwrap()
+			.with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap();
+
+		let route_params = RouteParameters::from_payment_params_and_value(
+			payment_params, amt_msat);
+
+
+		let route = get_route(&our_node_id, &route_params, &network_graph.read_only(),
+			Some(&first_hops.iter().collect::<Vec<_>>()), Arc::clone(&logger), &scorer,
+			&Default::default(), &random_seed_bytes).unwrap();
+
+		assert_eq!(route.paths.len(), 1);
+		assert_eq!(route.get_total_amount(), amt_msat);
+		assert_eq!(route.get_total_fees(), 0);
+		assert_eq!(route.paths[0].hops.len(), 1);
+
+		assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
+	}
 }
 
 #[cfg(all(any(test, ldk_bench), not(feature = "no-std")))]