lib.rs

// Copyright 2017-2020 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate 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.

// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! # Balances Module
//!
//! The Balances module provides functionality for handling accounts and balances.
//!
//! - [`balances::Trait`](./trait.Trait.html)
//! - [`Call`](./enum.Call.html)
//! - [`Module`](./struct.Module.html)
//!
//! ## Overview
//!
//! The Balances module provides functions for:
//!
//! - Getting and setting free balances.
//! - Retrieving total, reserved and unreserved balances.
//! - Repatriating a reserved balance to a beneficiary account that exists.
//! - Transferring a balance between accounts (when not reserved).
//! - Slashing an account balance.
//! - Account creation and removal.
//! - Managing total issuance.
//! - Setting and managing locks.
//!
//! ### Terminology
//!
//! - **Existential Deposit:** The minimum balance required to create or keep an account open. This prevents
//! "dust accounts" from filling storage. When the free plus the reserved balance (i.e. the total balance)
//!   fall below this, then the account is said to be dead; and it loses its functionality as well as any
//!   prior history and all information on it is removed from the chain's state.
//!   No account should ever have a total balance that is strictly between 0 and the existential
//!   deposit (exclusive). If this ever happens, it indicates either a bug in this module or an
//!   erroneous raw mutation of storage.
//!
//! - **Total Issuance:** The total number of units in existence in a system.
//!
//! - **Reaping an account:** The act of removing an account by resetting its nonce. Happens after its
//! total balance has become zero (or, strictly speaking, less than the Existential Deposit).
//!
//! - **Free Balance:** The portion of a balance that is not reserved. The free balance is the only
//!   balance that matters for most operations.
//!
//! - **Reserved Balance:** Reserved balance still belongs to the account holder, but is suspended.
//!   Reserved balance can still be slashed, but only after all the free balance has been slashed.
//!
//! - **Imbalance:** A condition when some funds were credited or debited without equal and opposite accounting
//! (i.e. a difference between total issuance and account balances). Functions that result in an imbalance will
//! return an object of the `Imbalance` trait that can be managed within your runtime logic. (If an imbalance is
//! simply dropped, it should automatically maintain any book-keeping such as total issuance.)
//!
//! - **Lock:** A freeze on a specified amount of an account's free balance until a specified block number. Multiple
//! locks always operate over the same funds, so they "overlay" rather than "stack".
//!
//! ### Implementations
//!
//! The Balances module provides implementations for the following traits. If these traits provide the functionality
//! that you need, then you can avoid coupling with the Balances module.
//!
//! - [`Currency`](../frame_support/traits/trait.Currency.html): Functions for dealing with a
//! fungible assets system.
//! - [`ReservableCurrency`](../frame_support/traits/trait.ReservableCurrency.html):
//! Functions for dealing with assets that can be reserved from an account.
//! - [`LockableCurrency`](../frame_support/traits/trait.LockableCurrency.html): Functions for
//! dealing with accounts that allow liquidity restrictions.
//! - [`Imbalance`](../frame_support/traits/trait.Imbalance.html): Functions for handling
//! imbalances between total issuance in the system and account balances. Must be used when a function
//! creates new funds (e.g. a reward) or destroys some funds (e.g. a system fee).
//! - [`IsDeadAccount`](../frame_system/trait.IsDeadAccount.html): Determiner to say whether a
//! given account is unused.
//!
//! ## Interface
//!
//! ### Dispatchable Functions
//!
//! - `transfer` - Transfer some liquid free balance to another account.
//! - `set_balance` - Set the balances of a given account. The origin of this call must be root.
//!
//! ## Usage
//!
//! The following examples show how to use the Balances module in your custom module.
//!
//! ### Examples from the SRML
//!
//! The Contract module uses the `Currency` trait to handle gas payment, and its types inherit from `Currency`:
//!
//! ```
//! use frame_support::traits::Currency;
//! # pub trait Trait: frame_system::Trait {
//! # 	type Currency: Currency<Self::AccountId>;
//! # }
//!
//! pub type BalanceOf<T> = <<T as Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::Balance;
//! pub type NegativeImbalanceOf<T> = <<T as Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::NegativeImbalance;
//!
//! # fn main() {}
//! ```
//!
//! The Staking module uses the `LockableCurrency` trait to lock a stash account's funds:
//!
//! ```
//! use frame_support::traits::{WithdrawReasons, LockableCurrency};
//! use sp_runtime::traits::Bounded;
//! pub trait Trait: frame_system::Trait {
//! 	type Currency: LockableCurrency<Self::AccountId, Moment=Self::BlockNumber>;
//! }
//! # struct StakingLedger<T: Trait> {
//! # 	stash: <T as frame_system::Trait>::AccountId,
//! # 	total: <<T as Trait>::Currency as frame_support::traits::Currency<<T as frame_system::Trait>::AccountId>>::Balance,
//! # 	phantom: std::marker::PhantomData<T>,
//! # }
//! # const STAKING_ID: [u8; 8] = *b"staking ";
//!
//! fn update_ledger<T: Trait>(
//! 	controller: &T::AccountId,
//! 	ledger: &StakingLedger<T>
//! ) {
//! 	T::Currency::set_lock(
//! 		STAKING_ID,
//! 		&ledger.stash,
//! 		ledger.total,
//! 		WithdrawReasons::all()
//! 	);
//! 	// <Ledger<T>>::insert(controller, ledger); // Commented out as we don't have access to Staking's storage here.
//! }
//! # fn main() {}
//! ```
//!
//! ## Genesis config
//!
//! The Balances module depends on the [`GenesisConfig`](./struct.GenesisConfig.html).
//!
//! ## Assumptions
//!
//! * Total issued balanced of all accounts should be less than `Trait::Balance::max_value()`.

#![cfg_attr(not(feature = "std"), no_std)]

#[cfg(test)]
mod mock;
#[cfg(test)]
mod tests;
mod migration;
mod benchmarking;

use sp_std::prelude::*;
use sp_std::{cmp, result, mem, fmt::Debug, ops::BitOr};
use codec::{Codec, Encode, Decode};
use frame_support::{
	StorageValue, Parameter, decl_event, decl_storage, decl_module, decl_error, ensure,
		weights::SimpleDispatchInfo, traits::{
		UpdateBalanceOutcome, Currency, OnReapAccount, OnUnbalanced, TryDrop,
		WithdrawReason, WithdrawReasons, LockIdentifier, LockableCurrency, ExistenceRequirement,
		Imbalance, SignedImbalance, ReservableCurrency, Get, ExistenceRequirement::KeepAlive
	}
};
use sp_runtime::{
	RuntimeDebug, DispatchResult, DispatchError,
	traits::{
		Zero, AtLeast32Bit, StaticLookup, Member, CheckedAdd, CheckedSub,
		MaybeSerializeDeserialize, Saturating, Bounded,
	},
};
use frame_system::{self as system, IsDeadAccount, OnNewAccount, ensure_signed, ensure_root};
use migration::{get_storage_value, put_storage_value, StorageIterator};

pub use self::imbalances::{PositiveImbalance, NegativeImbalance};

pub trait Subtrait<I: Instance = DefaultInstance>: frame_system::Trait {
	/// The balance of an account.
	type Balance: Parameter + Member + AtLeast32Bit + Codec + Default + Copy +
		MaybeSerializeDeserialize + Debug;

	/// A function that is invoked when the free-balance and the reserved-balance has fallen below
	/// the existential deposit and both have been reduced to zero.
	///
	/// All resources should be cleaned up all resources associated with the given account.
	type OnReapAccount: OnReapAccount<Self::AccountId>;

	/// Handler for when a new account is created.
	type OnNewAccount: OnNewAccount<Self::AccountId>;

	/// The minimum amount required to keep an account open.
	type ExistentialDeposit: Get<Self::Balance>;

	/// The fee required to create an account. If you're doing significant stuff with `OnNewAccount`
	/// then you'll probably want to make this non-zero.
	type CreationFee: Get<Self::Balance>;