Some nitpicks 🙈

frame/support/src/lib.rs

@@ -1101,8 +1101,8 @@ pub mod tests {
 				// Note this is the incorrect answer (for now), since we are using v2 of
 				// `clear_prefix`.
 				// When we switch to v3, then this will become:
-				//   sp_io::ClearPrefixResult::NoneLeft { db: 0, total: 2 },
-				sp_io::ClearPrefixResult { maybe_cursor: None, db: 0, total: 0, loops: 0 },
+				//   sp_io::MultiRemovalResults::NoneLeft { db: 0, total: 2 },
+				sp_io::MultiRemovalResults { maybe_cursor: None, backend: 0, unique: 0, loops: 0 },
 			));
 			assert_eq!(DoubleMap::get(&key1, &key2), 0u64);
 			assert_eq!(DoubleMap::get(&key1, &(key2 + 1)), 0u64);

frame/support/src/storage/child.rs

@@ -21,7 +21,7 @@
 // NOTE: could replace unhashed by having only one kind of storage (top trie being the child info
 // of null length parent storage key).
 
-pub use crate::sp_io::{ClearPrefixResult, KillStorageResult};
+pub use crate::sp_io::{KillStorageResult, MultiRemovalResults};
 use crate::sp_std::prelude::*;
 use codec::{Codec, Decode, Encode};
 pub use sp_core::storage::{ChildInfo, ChildType, StateVersion};
@@ -166,8 +166,8 @@ pub fn kill_storage(child_info: &ChildInfo, limit: Option<u32>) -> KillStorageRe
 /// cursor need not be passed in an a `None` may be passed instead. This exception may be useful
 /// then making this call solely from a block-hook such as `on_initialize`.
 ///
-/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-/// field is `None`, then no further items remain to be deleted.
+/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once the
+/// resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 ///
 /// NOTE: After the initial call for any given child storage, it is important that no keys further
 /// keys are inserted. If so, then they may or may not be deleted by subsequent calls.
@@ -180,7 +180,7 @@ pub fn clear_storage(
 	child_info: &ChildInfo,
 	maybe_limit: Option<u32>,
 	_maybe_cursor: Option<&[u8]>,
-) -> ClearPrefixResult {
+) -> MultiRemovalResults {
 	// TODO: Once the network has upgraded to include the new host functions, this code can be
 	// enabled.
 	// sp_io::default_child_storage::storage_kill(prefix, maybe_limit, maybe_cursor)
@@ -189,11 +189,11 @@ pub fn clear_storage(
 			sp_io::default_child_storage::storage_kill(child_info.storage_key(), maybe_limit),
 	};
 	use sp_io::KillStorageResult::*;
-	let (maybe_cursor, db) = match r {
+	let (maybe_cursor, backend) = match r {
 		AllRemoved(db) => (None, db),
 		SomeRemaining(db) => (Some(child_info.storage_key().to_vec()), db),
 	};
-	ClearPrefixResult { maybe_cursor, db, total: db, loops: db }
+	MultiRemovalResults { maybe_cursor, backend, unique: backend, loops: backend }
 }
 
 /// Ensure `key` has no explicit entry in storage.

frame/support/src/storage/generator/double_map.rs

@@ -214,7 +214,7 @@ where
 		k1: KArg1,
 		limit: u32,
 		maybe_cursor: Option<&[u8]>,
-	) -> sp_io::ClearPrefixResult
+	) -> sp_io::MultiRemovalResults
 	where
 		KArg1: EncodeLike<K1>,
 	{

frame/support/src/storage/generator/nmap.rs

@@ -190,7 +190,7 @@ where
 		partial_key: KP,
 		limit: u32,
 		maybe_cursor: Option<&[u8]>,
-	) -> sp_io::ClearPrefixResult
+	) -> sp_io::MultiRemovalResults
 	where
 		K: HasKeyPrefix<KP>,
 	{

frame/support/src/storage/migration.rs

@@ -287,7 +287,7 @@ pub fn clear_storage_prefix(
 	hash: &[u8],
 	maybe_limit: Option<u32>,
 	maybe_cursor: Option<&[u8]>,
-) -> sp_io::ClearPrefixResult {
+) -> sp_io::MultiRemovalResults {
 	let mut key = vec![0u8; 32 + hash.len()];
 	let storage_prefix = storage_prefix(module, item);
 	key[0..32].copy_from_slice(&storage_prefix);

frame/support/src/storage/mod.rs

@@ -538,7 +538,7 @@ pub trait StorageDoubleMap<K1: FullEncode, K2: FullEncode, V: FullCodec> {
 		k1: KArg1,
 		limit: u32,
 		maybe_cursor: Option<&[u8]>,
-	) -> sp_io::ClearPrefixResult
+	) -> sp_io::MultiRemovalResults
 	where
 		KArg1: ?Sized + EncodeLike<K1>;
 
@@ -686,8 +686,8 @@ pub trait StorageNMap<K: KeyGenerator, V: FullCodec> {
 
 	/// Attempt to remove items from the map matching a `partial_key` prefix.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map which match the `partial key`. If so, then the map may not be
@@ -711,7 +711,7 @@ pub trait StorageNMap<K: KeyGenerator, V: FullCodec> {
 		partial_key: KP,
 		limit: u32,
 		maybe_cursor: Option<&[u8]>,
-	) -> sp_io::ClearPrefixResult
+	) -> sp_io::MultiRemovalResults
 	where
 		K: HasKeyPrefix<KP>;
 
@@ -1172,8 +1172,8 @@ pub trait StoragePrefixedMap<Value: FullCodec> {
 
 	/// Attempt to remove all items from the map.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map. If so, then the map may not be empty when the resultant
@@ -1193,7 +1193,7 @@ pub trait StoragePrefixedMap<Value: FullCodec> {
 	/// passed once (in the initial call) for any given storage map. Subsequent calls
 	/// operating on the same map should always pass `Some`, and this should be equal to the
 	/// previous call result's `maybe_cursor` field.
-	fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::ClearPrefixResult {
+	fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::MultiRemovalResults {
 		unhashed::clear_prefix(&Self::final_prefix(), Some(limit), maybe_cursor)
 	}
 

frame/support/src/storage/types/counted_map.rs

@@ -31,7 +31,7 @@ use crate::{
 	Never,
 };
 use codec::{Decode, Encode, EncodeLike, FullCodec, MaxEncodedLen, Ref};
-use sp_io::ClearPrefixResult;
+use sp_io::MultiRemovalResults;
 use sp_runtime::traits::Saturating;
 use sp_std::prelude::*;
 
@@ -284,8 +284,8 @@ where
 
 	/// Attempt to remove all items from the map.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map. If so, then the map may not be empty when the resultant
@@ -305,11 +305,11 @@ where
 	/// passed once (in the initial call) for any given storage map. Subsequent calls
 	/// operating on the same map should always pass `Some`, and this should be equal to the
 	/// previous call result's `maybe_cursor` field.
-	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> ClearPrefixResult {
+	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> MultiRemovalResults {
 		let result = <Self as MapWrapper>::Map::clear(limit, maybe_cursor);
 		match result.maybe_cursor {
 			None => CounterFor::<Prefix>::kill(),
-			Some(_) => CounterFor::<Prefix>::mutate(|x| x.saturating_reduce(result.total)),
+			Some(_) => CounterFor::<Prefix>::mutate(|x| x.saturating_reduce(result.unique)),
 		}
 		result
 	}

frame/support/src/storage/types/double_map.rs

@@ -240,8 +240,8 @@ where
 
 	/// Attempt to remove items from the map matching a `first_key` prefix.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map which match the `first_key`. If so, then the map may not be
@@ -265,7 +265,7 @@ where
 		first_key: KArg1,
 		limit: u32,
 		maybe_cursor: Option<&[u8]>,
-	) -> sp_io::ClearPrefixResult
+	) -> sp_io::MultiRemovalResults
 	where
 		KArg1: ?Sized + EncodeLike<Key1>,
 	{
@@ -407,8 +407,8 @@ where
 
 	/// Attempt to remove all items from the map.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map. If so, then the map may not be empty when the resultant
@@ -428,7 +428,7 @@ where
 	/// passed once (in the initial call) for any given storage map. Subsequent calls
 	/// operating on the same map should always pass `Some`, and this should be equal to the
 	/// previous call result's `maybe_cursor` field.
-	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::ClearPrefixResult {
+	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::MultiRemovalResults {
 		<Self as crate::storage::StoragePrefixedMap<Value>>::clear(limit, maybe_cursor)
 	}
 

frame/support/src/storage/types/map.rs

@@ -255,8 +255,8 @@ where
 
 	/// Attempt to remove all items from the map.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map. If so, then the map may not be empty when the resultant
@@ -276,7 +276,7 @@ where
 	/// passed once (in the initial call) for any given storage map. Subsequent calls
 	/// operating on the same map should always pass `Some`, and this should be equal to the
 	/// previous call result's `maybe_cursor` field.
-	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::ClearPrefixResult {
+	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::MultiRemovalResults {
 		<Self as crate::storage::StoragePrefixedMap<Value>>::clear(limit, maybe_cursor)
 	}
 

frame/support/src/storage/types/nmap.rs

@@ -196,8 +196,8 @@ where
 
 	/// Attempt to remove items from the map matching a `partial_key` prefix.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map which match the `partial key`. If so, then the map may not be
@@ -221,7 +221,7 @@ where
 		partial_key: KP,
 		limit: u32,
 		maybe_cursor: Option<&[u8]>,
-	) -> sp_io::ClearPrefixResult
+	) -> sp_io::MultiRemovalResults
 	where
 		Key: HasKeyPrefix<KP>,
 	{
@@ -347,8 +347,8 @@ where
 
 	/// Attempt to remove all items from the map.
 	///
-	/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-	/// field is `None`, then no further items remain to be deleted.
+	/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once
+	/// the resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 	///
 	/// NOTE: After the initial call for any given map, it is important that no further items
 	/// are inserted into the map. If so, then the map may not be empty when the resultant
@@ -368,7 +368,7 @@ where
 	/// passed once (in the initial call) for any given storage map. Subsequent calls
 	/// operating on the same map should always pass `Some`, and this should be equal to the
 	/// previous call result's `maybe_cursor` field.
-	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::ClearPrefixResult {
+	pub fn clear(limit: u32, maybe_cursor: Option<&[u8]>) -> sp_io::MultiRemovalResults {
 		<Self as crate::storage::StoragePrefixedMap<Value>>::clear(limit, maybe_cursor)
 	}
 

frame/support/src/storage/unhashed.rs

@@ -126,8 +126,8 @@ pub fn kill_prefix(prefix: &[u8], limit: Option<u32>) -> sp_io::KillStorageResul
 /// cursor need not be passed in an a `None` may be passed instead. This exception may be useful
 /// then making this call solely from a block-hook such as `on_initialize`.
 ///
-/// Returns [`ClearPrefixResult`] to inform about the result. Once the resultant `maybe_cursor`
-/// field is `None`, then no further items remain to be deleted.
+/// Returns [`MultiRemovalResults`](sp_io::MultiRemovalResults) to inform about the result. Once the
+/// resultant `maybe_cursor` field is `None`, then no further items remain to be deleted.
 ///
 /// NOTE: After the initial call for any given child storage, it is important that no keys further
 /// keys are inserted. If so, then they may or may not be deleted by subsequent calls.
@@ -140,17 +140,17 @@ pub fn clear_prefix(
 	prefix: &[u8],
 	maybe_limit: Option<u32>,
 	_maybe_cursor: Option<&[u8]>,
-) -> sp_io::ClearPrefixResult {
+) -> sp_io::MultiRemovalResults {
 	// TODO: Once the network has upgraded to include the new host functions, this code can be
 	// enabled.
 	// sp_io::storage::clear_prefix(prefix, maybe_limit, maybe_cursor)
-	use sp_io::{ClearPrefixResult, KillStorageResult::*};
+	use sp_io::{KillStorageResult::*, MultiRemovalResults};
 	#[allow(deprecated)]
 	let (maybe_cursor, i) = match kill_prefix(prefix, maybe_limit) {
 		AllRemoved(i) => (None, i),
 		SomeRemaining(i) => (Some(prefix.to_vec()), i),
 	};
-	ClearPrefixResult { maybe_cursor, db: i, total: i, loops: i }
+	MultiRemovalResults { maybe_cursor, backend: i, unique: i, loops: i }
 }
 
 /// Get a Vec of bytes from storage.

primitives/externalities/src/lib.rs

@@ -53,6 +53,8 @@ pub enum Error {
 }
 
 /// Results concerning an operation to remove many keys.
+#[derive(codec::Encode, codec::Decode)]
+#[must_use]
 pub struct MultiRemovalResults {
 	/// A continuation cursor which, if `Some` must be provided to the subsequent removal call.
 	/// If `None` then all removals are complete and no further calls are needed.