Allow two Parachains to swap

runtime/common/src/crowdloan/migration.rs

@@ -0,0 +1,84 @@
+// Copyright 2017-2020 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+use super::*;
+use frame_support::generate_storage_alias;
+
+/// Migrations for using fund index to create fund accounts instead of para ID.
+pub mod crowdloan_index_migration {
+	// The old way we generated fund accounts.
+	fn old_fund_account_id<T: Config>(index: ParaId) -> T::AccountId {
+		T::PalletId::get().into_sub_account(index)
+	}
+
+	pub fn pre_migration<T: Config>() {
+		// `NextTrieIndex` should have a value.
+		generate_storage_alias!(Crowdloan, NextTrieIndex => Value<FundIndex>);
+		let next_index = NextTrieIndex::take().unwrap_or_default();
+		assert!(next_index > 0);
+
+		// Each fund should have some non-zero balance.
+		Funds::<T>::iter().for_each(|(para_id, fund)| {
+			let old_fund_account = old_fund_account_id::<T>(para_id);
+			let total_balance = T::Currency::total_balance(old_fund_account);
+
+			assert_eq!(total_balance, fund.raised);
+			assert!(total_balance > Zero::zero());
+		});
+	}
+
+	/// This migration converts crowdloans to use a crowdloan index rather than the parachain id as a
+	/// unique identifier. This makes it easier to swap two crowdloans between parachains.
+	pub fn migrate<T: Config>() {
+		// First migrate `NextTrieIndex` counter to `NextFundIndex`.
+		generate_storage_alias!(Crowdloan, NextTrieIndex => Value<FundIndex>);
+
+		let next_index = NextTrieIndex::take().unwrap_or_default();
+		NextFundIndex::<T>::set(next_index);
+
+		// Migrate all accounts from `old_fund_account` to `fund_account` using `fund_index`.
+		Funds::<T>::iter().for_each(|(para_id, fund)| {
+			let old_fund_account = old_fund_account_id::<T>(para_id);
+			let new_fund_account = Pallet::<T>::fund_account_id(fund.fund_index);
+
+			// Funds should only have a free balance and a reserve balance. Both of these are in the
+			// `Account` storage item, so we just swap them.
+			let account_info = frame_system::Account::<T>::take(old_fund_account);
+			frame_system::Account::<T>::insert(new_fund_account, account_info);
+		});
+	}
+
+	pub fn post_migrate<T: Config>() {
+		// `NextTrieIndex` should not have a value, and `NextFundIndex` should.
+		generate_storage_alias!(Crowdloan, NextTrieIndex => Value<FundIndex>);
+		assert!(NextTrieIndex::take().is_none());
+		assert!(NextFundIndex::get() > 0);
+
+		// Each fund should have balance migrated correctly.
+		Funds::<T>::iter().for_each(|(para_id, fund)| {
+			// Old fund account is deleted.
+			let old_fund_account = old_fund_account_id::<T>(para_id);
+			assert_eq!(frame_system::Account::<T>::get(old_fund_account_id), Default::default());
+
+			// New fund account has the correct balance.
+			let new_fund_account = Pallet::<T>::fund_account_id(fund.fund_index);
+			let total_balance = T::Currency::total_balance(new_fund_account);
+
+			assert_eq!(total_balance, fund.raised);
+			assert!(total_balance > Zero::zero());
+		});
+	}
+}