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/frame/assets/src/functions.rs

@@ -163,10 +163,7 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		who: &T::AccountId,
 		keep_alive: bool,
 	) -> Result<T::Balance, Error<T, I>> {
-		let details = match Asset::<T, I>::get(id) {
-			Some(details) => details,
-			None => return Err(Error::<T, I>::Unknown),
-		};
+		let details = Asset::<T, I>::get(id).ok_or_else(|| Error::<T, I>::Unknown)?;
 		ensure!(!details.is_frozen, Error::<T, I>::Frozen);
 
 		let account = Account::<T, I>::get(id, who);

substrate/frame/authorship/src/lib.rs

@@ -490,10 +490,7 @@ mod tests {
 			let pre_runtime_digests = header.digest.logs.iter().filter_map(|d| d.as_pre_runtime());
 			let seals = header.digest.logs.iter().filter_map(|d| d.as_seal());
 
-			let author = match AuthorGiven::find_author(pre_runtime_digests) {
-				None => return Err("no author"),
-				Some(author) => author,
-			};
+			let author = AuthorGiven::find_author(pre_runtime_digests).ok_or_else(|| "no author")?;
 
 			for (id, seal) in seals {
 				if id == TEST_ID {

substrate/frame/contracts/src/gas.rs

@@ -127,10 +127,7 @@ where
 		}
 
 		let amount = token.calculate_amount(metadata);
-		let new_value = match self.gas_left.checked_sub(amount) {
-			None => None,
-			Some(val) => Some(val),
-		};
+		let new_value = self.gas_left.checked_sub(amount);
 
 		// We always consume the gas even if there is not enough gas.
 		self.gas_left = new_value.unwrap_or_else(Zero::zero);

substrate/frame/contracts/src/migration.rs

@@ -26,16 +26,12 @@ pub fn migrate<T: Config>() -> Weight {
 		Some(version) if version == PalletVersion::new(3, 0, 0) => {
 			weight = weight.saturating_add(T::DbWeight::get().reads_writes(1, 1));
 			let _ = <CurrentSchedule<T>>::translate::<u32, _>(|version| {
-				if let Some(version) = version {
-					Some(Schedule {
+				version.map(|version| Schedule {
 						version: version.saturating_add(1),
 						// Default limits were not decreased. Therefore it is OK to overwrite
 						// the schedule with the new defaults.
 						.. Default::default()
 					})
-				} else {
-					None
-				}
 			});
 		}
 		_ => (),

substrate/frame/contracts/src/rent.rs

@@ -407,10 +407,7 @@ where
 		);
 
 		// Check what happened after enaction of the verdict.
-		let alive_contract_info = match new_contract_info.map_err(|_| IsTombstone)? {
-			None => return Err(IsTombstone),
-			Some(contract) => contract,
-		};
+		let alive_contract_info = new_contract_info.map_err(|_| IsTombstone)?.ok_or_else(|| IsTombstone)?;
 
 		// Compute how much would the fee per block be with the *updated* balance.
 		let total_balance = T::Currency::total_balance(account);

substrate/frame/democracy/src/lib.rs

@@ -1653,10 +1653,7 @@ impl<T: Config> Module<T> {
 		// To decode the enum variant we only need the first byte.
 		let mut buf = [0u8; 1];
 		let key = <Preimages<T>>::hashed_key_for(proposal_hash);
-		let bytes = match sp_io::storage::read(&key, &mut buf, 0) {
-			Some(bytes) => bytes,
-			None => return Err(Error::<T>::NotImminent.into()),
-		};
+		let bytes = sp_io::storage::read(&key, &mut buf, 0).ok_or_else(|| Error::<T>::NotImminent)?;
 		// The value may be smaller that 1 byte.
 		let mut input = &buf[0..buf.len().min(bytes as usize)];
 
@@ -1684,10 +1681,7 @@ impl<T: Config> Module<T> {
 		// * at most 5 bytes to decode a `Compact<u32>`
 		let mut buf = [0u8; 6];
 		let key = <Preimages<T>>::hashed_key_for(proposal_hash);
-		let bytes = match sp_io::storage::read(&key, &mut buf, 0) {
-			Some(bytes) => bytes,
-			None => return Err(Error::<T>::PreimageMissing.into()),
-		};
+		let bytes = sp_io::storage::read(&key, &mut buf, 0).ok_or_else(|| Error::<T>::PreimageMissing)?;
 		// The value may be smaller that 6 bytes.
 		let mut input = &buf[0..buf.len().min(bytes as usize)];
 
@@ -1761,10 +1755,7 @@ impl<T: Config> Module<T> {
 fn decode_compact_u32_at(key: &[u8]) -> Option<u32> {
 	// `Compact<u32>` takes at most 5 bytes.
 	let mut buf = [0u8; 5];
-	let bytes = match sp_io::storage::read(&key, &mut buf, 0) {
-		Some(bytes) => bytes,
-		None => return None,
-	};
+	let bytes = sp_io::storage::read(&key, &mut buf, 0)?;
 	// The value may be smaller than 5 bytes.
 	let mut input = &buf[0..buf.len().min(bytes as usize)];
 	match codec::Compact::<u32>::decode(&mut input) {

substrate/frame/grandpa/src/lib.rs

@@ -518,21 +518,13 @@ impl<T: Config> Module<T> {
 			None
 		} else {
 			let session_index =
-				if let Some(session_id) = Self::session_for_set(set_id - 1) {
-					session_id
-				} else {
-					return Err(Error::<T>::InvalidEquivocationProof.into());
-				};
+				Self::session_for_set(set_id - 1).ok_or_else(|| Error::<T>::InvalidEquivocationProof)?;
 
 			Some(session_index)
 		};
 
 		let set_id_session_index =
-			if let Some(session_id) = Self::session_for_set(set_id) {
-				session_id
-			} else {
-				return Err(Error::<T>::InvalidEquivocationProof.into());
-			};
+			Self::session_for_set(set_id).ok_or_else(|| Error::<T>::InvalidEquivocationProof)?;
 
 		// check that the session id for the membership proof is within the
 		// bounds of the set id reported in the equivocation.

substrate/frame/staking/src/lib.rs

@@ -2736,11 +2736,8 @@ impl<T: Config> Convert<T::AccountId, Option<Exposure<T::AccountId, BalanceOf<T>
 	for ExposureOf<T>
 {
 	fn convert(validator: T::AccountId) -> Option<Exposure<T::AccountId, BalanceOf<T>>> {
-		if let Some(active_era) = <Module<T>>::active_era() {
-			Some(<Module<T>>::eras_stakers(active_era.index, &validator))
-		} else {
-			None
-		}
+		<Module<T>>::active_era()
+			.map(|active_era| <Module<T>>::eras_stakers(active_era.index, &validator))
 	}
 }
 

substrate/frame/support/src/storage/generator/value.rs

@@ -77,10 +77,8 @@ impl<T: FullCodec, G: StorageValue<T>> storage::StorageValue<T> for G {
 		let key = Self::storage_value_final_key();
 
 		// attempt to get the length directly.
-		let maybe_old = match unhashed::get_raw(&key) {
-			Some(old_data) => Some(O::decode(&mut &old_data[..]).map_err(|_| ())?),
-			None => None,
-		};
+		let maybe_old = unhashed::get_raw(&key)
+			.map(|old_data| O::decode(&mut &old_data[..]).map_err(|_| ())).transpose()?;
 		let maybe_new = f(maybe_old);
 		if let Some(new) = maybe_new.as_ref() {
 			new.using_encoded(|d| unhashed::put_raw(&key, d));