make SelectChain async (#9128)

* make SelectChain async

* make JustificationImport async

substrate/client/consensus/common/src/longest_chain.rs

@@ -46,15 +46,15 @@ impl<B, Block> Clone for LongestChain<B, Block> {
 }
 
 impl<B, Block> LongestChain<B, Block>
-	where
-		B: backend::Backend<Block>,
-		Block: BlockT,
+where
+	B: backend::Backend<Block>,
+	Block: BlockT,
 {
 	/// Instantiate a new LongestChain for Backend B
 	pub fn new(backend: Arc<B>) -> Self {
 		LongestChain {
 			backend,
-			_phantom: Default::default()
+			_phantom: Default::default(),
 		}
 	}
 
@@ -75,30 +75,30 @@ impl<B, Block> LongestChain<B, Block>
 	}
 }
 
+#[async_trait::async_trait]
 impl<B, Block> SelectChain<Block> for LongestChain<B, Block>
-	where
-		B: backend::Backend<Block>,
-		Block: BlockT,
+where
+	B: backend::Backend<Block>,
+	Block: BlockT,
 {
-
-	fn leaves(&self) -> Result<Vec<<Block as BlockT>::Hash>, ConsensusError> {
-		LongestChain::leaves(self)
-			.map_err(|e| ConsensusError::ChainLookup(e.to_string()).into())
+	async fn leaves(&self) -> Result<Vec<<Block as BlockT>::Hash>, ConsensusError> {
+		LongestChain::leaves(self).map_err(|e| ConsensusError::ChainLookup(e.to_string()).into())
 	}
 
-	fn best_chain(&self) -> Result<<Block as BlockT>::Header, ConsensusError>
-	{
+	async fn best_chain(&self) -> Result<<Block as BlockT>::Header, ConsensusError> {
 		LongestChain::best_block_header(&self)
 			.map_err(|e| ConsensusError::ChainLookup(e.to_string()).into())
 	}
 
-	fn finality_target(
+	async fn finality_target(
 		&self,
 		target_hash: Block::Hash,
-		maybe_max_number: Option<NumberFor<Block>>
+		maybe_max_number: Option<NumberFor<Block>>,
 	) -> Result<Option<Block::Hash>, ConsensusError> {
 		let import_lock = self.backend.get_import_lock();
-		self.backend.blockchain().best_containing(target_hash, maybe_max_number, import_lock)
+		self.backend
+			.blockchain()
+			.best_containing(target_hash, maybe_max_number, import_lock)
 			.map_err(|e| ConsensusError::ChainLookup(e.to_string()).into())
 	}
 }