BlockId removal: refactor: HeaderBackend::header (#12874)

* BlockId removal: refactor: HeaderBackend::header

It changes the arguments of:
- `HeaderBackend::header`,
- `Client::header`,
- `PeersClient::header`
- `ChainApi::block_header`

methods from: `BlockId<Block>` to: `Block::Hash`

This PR is part of BlockId::Number refactoring analysis (paritytech/substrate#11292)

* non-trivial usages of haeder(block_id) refactored

This may required introduction of dedicated function:
header_for_block_num

* fmt

* fix

* doc fixed

* ".git/.scripts/fmt.sh"

* BlockId removal: refactor: HeaderBackend::expect_header

It changes the arguments of `HeaderBackend::expect_header` method from: `BlockId<Block>` to: `Block::Hash`

* ".git/.scripts/fmt.sh"

* readme updated

* ".git/.scripts/fmt.sh"

* fix

Co-authored-by: parity-processbot <>

substrate/client/beefy/src/worker.rs

@@ -465,7 +465,7 @@ where
 				.map(|hash| {
 					backend
 						.blockchain()
-						.expect_header(BlockId::hash(*hash))
+						.expect_header(*hash)
 						.expect("just finalized block should be available; qed.")
 				})
 				.chain(std::iter::once(header.clone()))
@@ -718,16 +718,25 @@ where
 		let target_header = if target_number == self.best_grandpa_block() {
 			self.persisted_state.best_grandpa_block_header.clone()
 		} else {
-			self.backend
+			let hash = self
+				.backend
 				.blockchain()
-				.expect_header(BlockId::Number(target_number))
+				.expect_block_hash_from_id(&BlockId::Number(target_number))
 				.map_err(|err| {
 					let err_msg = format!(
-						"Couldn't get header for block #{:?} (error: {:?}), skipping vote..",
+						"Couldn't get hash for block #{:?} (error: {:?}), skipping vote..",
 						target_number, err
 					);
 					Error::Backend(err_msg)
-				})?
+				})?;
+
+			self.backend.blockchain().expect_header(hash).map_err(|err| {
+				let err_msg = format!(
+					"Couldn't get header for block #{:?} ({:?}) (error: {:?}), skipping vote..",
+					target_number, hash, err
+				);
+				Error::Backend(err_msg)
+			})?
 		};
 		let target_hash = target_header.hash();
 
@@ -1050,8 +1059,10 @@ pub(crate) mod tests {
 			"/beefy/justifs/1".into(),
 			known_peers,
 		);
-		let at = BlockId::number(Zero::zero());
-		let genesis_header = backend.blockchain().expect_header(at).unwrap();
+		let genesis_header = backend
+			.blockchain()
+			.expect_header(backend.blockchain().info().genesis_hash)
+			.unwrap();
 		let persisted_state = PersistedState::checked_new(
 			genesis_header,
 			Zero::zero(),