Fixes/improvements for disputes (#3753)

* More debugging output.

* Fix chain selection in case of disputes.

* Fix flaky test.

polkadot/node/service/src/relay_chain_selection.rs

@@ -434,7 +434,7 @@ where
 			overseer
 				.send_msg(
 					DisputeCoordinatorMessage::DetermineUndisputedChain {
-						base_number: target_number,
+						base: (target_number, target_hash),
 						block_descriptions: subchain_block_descriptions,
 						tx,
 					},
@@ -444,8 +444,7 @@ where
 			let (subchain_number, subchain_head) = rx
 				.await
 				.map_err(Error::OverseerDisconnected)
-				.map_err(|e| ConsensusError::Other(Box::new(e)))?
-				.unwrap_or_else(|| (subchain_number, subchain_head));
+				.map_err(|e| ConsensusError::Other(Box::new(e)))?;
 
 			// The the total lag accounting for disputes.
 			let lag_disputes = initial_leaf_number.saturating_sub(subchain_number);

polkadot/node/service/src/tests.rs

@@ -383,18 +383,20 @@ async fn test_skeleton(
 	);
 
 	tracing::trace!("determine undisputed chain response: {:?}", undisputed_chain);
+
+	let target_block_number = chain.number(target_block_hash).unwrap().unwrap();
 	assert_matches!(
 		overseer_recv(
 			virtual_overseer
 		).await,
 		AllMessages::DisputeCoordinator(
 			DisputeCoordinatorMessage::DetermineUndisputedChain {
-				base_number: _,
+				base: _,
 				block_descriptions: _,
 				tx,
 			}
 		) => {
-			tx.send(undisputed_chain).unwrap();
+			tx.send(undisputed_chain.unwrap_or((target_block_number, target_block_hash))).unwrap();
 	});
 }