Simplify some Option / Result / ? operator patterns (#8653)

* Simplify some Option / Result / ? operator patterns

When those match a combinator exactly.

Tool-aided by [comby-rust](https://github.com/huitseeker/comby-rust).

* adjust after review

* adjust post-review

substrate/client/consensus/aura/src/import_queue.rs

@@ -72,10 +72,7 @@ fn check_header<C, B: BlockT, P: Pair>(
 	C: sc_client_api::backend::AuxStore,
 	P::Public: Encode + Decode + PartialEq + Clone,
 {
-	let seal = match header.digest_mut().pop() {
-		Some(x) => x,
-		None => return Err(Error::HeaderUnsealed(hash)),
-	};
+	let seal = header.digest_mut().pop().ok_or_else(|| Error::HeaderUnsealed(hash))?;
 
 	let sig = seal.as_aura_seal().ok_or_else(|| {
 		aura_err(Error::HeaderBadSeal(hash))
@@ -89,10 +86,8 @@ fn check_header<C, B: BlockT, P: Pair>(
 	} else {
 		// check the signature is valid under the expected authority and
 		// chain state.
-		let expected_author = match slot_author::<P>(slot, &authorities) {
-			None => return Err(Error::SlotAuthorNotFound),
-			Some(author) => author,
-		};
+		let expected_author = slot_author::<P>(slot, &authorities)
+			.ok_or_else(|| Error::SlotAuthorNotFound)?;
 
 		let pre_hash = header.hash();
 

substrate/client/consensus/babe/src/verification.rs

@@ -71,10 +71,8 @@ pub(super) fn check_header<B: BlockT + Sized>(
 	let pre_digest = pre_digest.map(Ok).unwrap_or_else(|| find_pre_digest::<B>(&header))?;
 
 	trace!(target: "babe", "Checking header");
-	let seal = match header.digest_mut().pop() {
-		Some(x) => x,
-		None => return Err(babe_err(Error::HeaderUnsealed(header.hash()))),
-	};
+	let seal = header.digest_mut().pop()
+		.ok_or_else(|| babe_err(Error::HeaderUnsealed(header.hash())))?;
 
 	let sig = seal.as_babe_seal().ok_or_else(|| {
 		babe_err(Error::HeaderBadSeal(header.hash()))

substrate/client/consensus/manual-seal/src/seal_block.rs

@@ -104,10 +104,7 @@ pub async fn seal_block<B, BI, SC, C, E, P>(
 		// or fetch the best_block.
 		let parent = match parent_hash {
 			Some(hash) => {
-				match client.header(BlockId::Hash(hash))? {
-					Some(header) => header,
-					None => return Err(Error::BlockNotFound(format!("{}", hash))),
-				}
+				client.header(BlockId::Hash(hash))?.ok_or_else(|| Error::BlockNotFound(format!("{}", hash)))?
 			}
 			None => select_chain.best_chain()?
 		};

substrate/client/consensus/slots/src/lib.rs

@@ -256,10 +256,7 @@ pub trait SimpleSlotWorker<B: BlockT> {
 			return None;
 		}
 
-		let claim = match self.claim_slot(&chain_head, slot, &epoch_data) {
-			None => return None,
-			Some(claim) => claim,
-		};
+		let claim = self.claim_slot(&chain_head, slot, &epoch_data)?;
 
 		if self.should_backoff(slot, &chain_head) {
 			return None;

substrate/client/consensus/slots/src/slots.rs

@@ -135,10 +135,7 @@ impl<SC: SlotCompatible> Slots<SC> {
 				Err(err) => return Err(sp_consensus::Error::InherentData(err)),
 			};
 			let result = self.timestamp_extractor.extract_timestamp_and_slot(&inherent_data);
-			let (timestamp, slot, offset) = match result {
-				Ok(v) => v,
-				Err(err) => return Err(err),
-			};
+			let (timestamp, slot, offset) = result?;
 			// reschedule delay for next slot.
 			let ends_in = offset +
 				time_until_next(timestamp.as_duration(), self.slot_duration);