Simplify some Option / Result / ? operator patterns (#2920)

* Simplify some Option / Result / ? operator patterns

When they identically match a combinator on those types.

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

* adjust review comments

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

polkadot/bridges/modules/ethereum/src/validators.rs

@@ -188,10 +188,7 @@ impl<'a> Validators<'a> {
 		finalized_blocks: &[(HeaderId, Option<S::Submitter>)],
 	) -> Option<ChangeToEnact> {
 		// if we haven't finalized any blocks, no changes may be finalized
-		let newest_finalized_id = match finalized_blocks.last().map(|(id, _)| id) {
+		let newest_finalized_id = finalized_blocks.last().map(|(id, _)| id)?;
-			Some(last_finalized_id) => last_finalized_id,
-			None => return None,
-		};
 		let oldest_finalized_id = finalized_blocks
 			.first()
 			.map(|(id, _)| id)

polkadot/node/core/approval-voting/src/approval_checking.rs

@@ -317,10 +317,7 @@ pub fn tranches_to_approve(
 	tranches_with_gaps_filled
 		.scan(Some(initial_state), |state, (tranche, assignments)| {
 			// The `Option` here is used for early exit.
-			let s = match state.take() {
+			let s = state.take()?;
-				None => return None,
-				Some(s) => s,
-			};
 
 			let clock_drift = s.clock_drift(no_show_duration);
 			let drifted_tick_now = tick_now.saturating_sub(clock_drift);

polkadot/node/network/approval-distribution/src/lib.rs

@@ -463,8 +463,7 @@ impl State {
 		if !range.is_empty() && !blocks.is_empty() {
 			self.blocks_by_number
 			.range(range)
-			.map(|(_number, hashes)| hashes)
+			.flat_map(|(_number, hashes)| hashes)
-			.flatten()
 			.for_each(|hash| {
 				if let Some(entry) = blocks.get_mut(hash) {
 					entry.known_by.remove(&peer_id);

polkadot/node/network/availability-distribution/src/tests/mod.rs

@@ -101,8 +101,7 @@ fn check_fetch_retry() {
 	let valid_candidate_hashes: HashSet<_> = state.cores
 		.get(&state.relay_chain[1])
 		.iter()
-		.map(|v| v.iter())
+		.flat_map(|v| v.iter())
-		.flatten()
 		.filter_map(|c| {
 			match c {
 				CoreState::Occupied(core) => Some(core.candidate_hash),

polkadot/node/network/availability-recovery/src/lib.rs

@@ -142,10 +142,7 @@ impl RequestFromBackersPhase {
 		);
 		loop {
 			// Pop the next backer, and proceed to next phase if we're out.
-			let validator_index = match self.shuffled_backers.pop() {
+			let validator_index = self.shuffled_backers.pop().ok_or_else(|| RecoveryError::Unavailable)?;
-				None => return Err(RecoveryError::Unavailable),
-				Some(i) => i,
-			};
 
 			// Request data.
 			let (req, res) = OutgoingRequest::new(

polkadot/node/network/statement-distribution/src/lib.rs

@@ -1308,12 +1308,7 @@ async fn handle_incoming_message<'a>(
 		ctx,
 		req_sender,
 		metrics,
-	).await;
+	).await?;
-
-	let statement = match statement {
-		None => return None,
-		Some(statement) => statement,
-	};
 
 	match active_head.check_useful_or_unknown(statement.clone()) {
 		Ok(()) => {},