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/rpc/src/chain/mod.rs

@@ -31,8 +31,8 @@ use jsonrpsee::{core::RpcResult, types::SubscriptionResult, SubscriptionSink};
 use sc_client_api::BlockchainEvents;
 use sp_rpc::{list::ListOrValue, number::NumberOrHex};
 use sp_runtime::{
-	generic::{BlockId, SignedBlock},
-	traits::{Block as BlockT, Header, NumberFor},
+	generic::SignedBlock,
+	traits::{Block as BlockT, NumberFor},
 };
 
 use self::error::Error;
@@ -80,11 +80,7 @@ where
 					))
 				})?;
 				let block_num = <NumberFor<Block>>::from(block_num);
-				Ok(self
-					.client()
-					.header(BlockId::number(block_num))
-					.map_err(client_err)?
-					.map(|h| h.hash()))
+				self.client().hash(block_num).map_err(client_err)
 			},
 		}
 	}