pallet-staking: Reorg migration, pallet and pallet impls (#9410)

* Reorg migration and pallet and pallet impls

* Fix imports in untouched modules

* Add file headers

* Add header for migrations

* Improve comment

* Move OnOffenceHandler impl for Pallet to impl.rs

* fmt

substrate/frame/staking/src/migrations.rs

@@ -0,0 +1,86 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2020-2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+
+//! Storage migrations for the Staking pallet.
+
+use super::*;
+
+pub mod v7 {
+	use super::*;
+
+	pub fn pre_migrate<T: Config>() -> Result<(), &'static str> {
+		assert!(CounterForValidators::<T>::get().is_zero(), "CounterForValidators already set.");
+		assert!(CounterForNominators::<T>::get().is_zero(), "CounterForNominators already set.");
+		assert!(StorageVersion::<T>::get() == Releases::V6_0_0);
+		Ok(())
+	}
+
+	pub fn migrate<T: Config>() -> Weight {
+		log!(info, "Migrating staking to Releases::V7_0_0");
+		let validator_count = Validators::<T>::iter().count() as u32;
+		let nominator_count = Nominators::<T>::iter().count() as u32;
+
+		CounterForValidators::<T>::put(validator_count);
+		CounterForNominators::<T>::put(nominator_count);
+
+		StorageVersion::<T>::put(Releases::V7_0_0);
+		log!(info, "Completed staking migration to Releases::V7_0_0");
+
+		T::DbWeight::get().reads_writes(validator_count.saturating_add(nominator_count).into(), 2)
+	}
+}
+
+pub mod v6 {
+	use super::*;
+	use frame_support::{generate_storage_alias, traits::Get, weights::Weight};
+
+	// NOTE: value type doesn't matter, we just set it to () here.
+	generate_storage_alias!(Staking, SnapshotValidators => Value<()>);
+	generate_storage_alias!(Staking, SnapshotNominators => Value<()>);
+	generate_storage_alias!(Staking, QueuedElected => Value<()>);
+	generate_storage_alias!(Staking, QueuedScore => Value<()>);
+	generate_storage_alias!(Staking, EraElectionStatus => Value<()>);
+	generate_storage_alias!(Staking, IsCurrentSessionFinal => Value<()>);
+
+	/// check to execute prior to migration.
+	pub fn pre_migrate<T: Config>() -> Result<(), &'static str> {
+		// these may or may not exist.
+		log!(info, "SnapshotValidators.exits()? {:?}", SnapshotValidators::exists());
+		log!(info, "SnapshotNominators.exits()? {:?}", SnapshotNominators::exists());
+		log!(info, "QueuedElected.exits()? {:?}", QueuedElected::exists());
+		log!(info, "QueuedScore.exits()? {:?}", QueuedScore::exists());
+		// these must exist.
+		assert!(IsCurrentSessionFinal::exists(), "IsCurrentSessionFinal storage item not found!");
+		assert!(EraElectionStatus::exists(), "EraElectionStatus storage item not found!");
+		Ok(())
+	}
+
+	/// Migrate storage to v6.
+	pub fn migrate<T: Config>() -> Weight {
+		log!(info, "Migrating staking to Releases::V6_0_0");
+
+		SnapshotValidators::kill();
+		SnapshotNominators::kill();
+		QueuedElected::kill();
+		QueuedScore::kill();
+		EraElectionStatus::kill();
+		IsCurrentSessionFinal::kill();
+
+		StorageVersion::<T>::put(Releases::V6_0_0);
+		log!(info, "Done.");
+		T::DbWeight::get().writes(6 + 1)
+	}
+}