Do not call longest chain by default (#6704)

* Do not call longest chain by default

We always called longest chain by default just for some potential
logging. This was probably some oversight for when this select chain
implementation was introduced.

* Fix tests

polkadot/node/service/src/relay_chain_selection.rs

@@ -203,19 +203,12 @@ where
 		target_hash: Hash,
 		maybe_max_number: Option<BlockNumber>,
 	) -> Result<Hash, ConsensusError> {
-		let longest_chain_best =
-			self.longest_chain.finality_target(target_hash, maybe_max_number).await?;
-
 		if let IsDisputesAwareWithOverseer::Yes(ref selection) = self.selection {
 			selection
-				.finality_target_with_longest_chain(
-					target_hash,
-					longest_chain_best,
-					maybe_max_number,
-				)
+				.finality_target_with_longest_chain(target_hash, maybe_max_number)
 				.await
 		} else {
-			Ok(longest_chain_best)
+			self.longest_chain.finality_target(target_hash, maybe_max_number).await
 		}
 	}
 }
@@ -364,11 +357,9 @@ where
 	pub(crate) async fn finality_target_with_longest_chain(
 		&self,
 		target_hash: Hash,
-		best_leaf: Hash,
 		maybe_max_number: Option<BlockNumber>,
 	) -> Result<Hash, ConsensusError> {
 		let mut overseer = self.overseer.clone();
-		gum::trace!(target: LOG_TARGET, ?best_leaf, "Longest chain");
 
 		let subchain_head = {
 			let (tx, rx) = oneshot::channel();
@@ -414,7 +405,7 @@ where
 				let subchain_header = self.block_header(subchain_head)?;
 
 				if subchain_header.number <= max {
-					gum::trace!(target: LOG_TARGET, ?best_leaf, "Constrained sub-chain head",);
+					gum::trace!(target: LOG_TARGET, ?subchain_head, "Constrained sub-chain head",);
 					subchain_head
 				} else {
 					let (ancestor_hash, _) =

polkadot/node/service/src/tests.rs

@@ -88,7 +88,7 @@ fn test_harness<T: Future<Output = VirtualOverseer>>(
 	let target_hash = case_vars.target_block.clone();
 	let selection_process = async move {
 		let best = select_relay_chain
-			.finality_target_with_longest_chain(target_hash, target_hash, None)
+			.finality_target_with_longest_chain(target_hash, None)
 			.await
 			.unwrap();
 		finality_target_tx.send(Some(best)).unwrap();