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Votes.sol
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Votes.sol
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// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (governance/utils/Votes.sol)
pragma solidity ^0.8.0;
import "../../interfaces/IERC5805.sol";
import "../../utils/Context.sol";
import "../../utils/Counters.sol";
import "../../utils/Checkpoints.sol";
import "../../utils/cryptography/EIP712.sol";
/**
* @dev This is a base abstract contract that tracks voting units, which are a measure of voting power that can be
* transferred, and provides a system of vote delegation, where an account can delegate its voting units to a sort of
* "representative" that will pool delegated voting units from different accounts and can then use it to vote in
* decisions. In fact, voting units _must_ be delegated in order to count as actual votes, and an account has to
* delegate those votes to itself if it wishes to participate in decisions and does not have a trusted representative.
*
* This contract is often combined with a token contract such that voting units correspond to token units. For an
* example, see {ERC721Votes}.
*
* The full history of delegate votes is tracked on-chain so that governance protocols can consider votes as distributed
* at a particular block number to protect against flash loans and double voting. The opt-in delegate system makes the
* cost of this history tracking optional.
*
* When using this module the derived contract must implement {_getVotingUnits} (for example, make it return
* {ERC721-balanceOf}), and can use {_transferVotingUnits} to track a change in the distribution of those units (in the
* previous example, it would be included in {ERC721-_beforeTokenTransfer}).
*
* _Available since v4.5._
*/
abstract contract Votes is Context, EIP712, IERC5805 {
using Checkpoints for Checkpoints.Trace224;
using Counters for Counters.Counter;
bytes32 private constant _DELEGATION_TYPEHASH =
keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");
mapping(address => address) private _delegation;
/// @custom:oz-retyped-from mapping(address => Checkpoints.History)
mapping(address => Checkpoints.Trace224) private _delegateCheckpoints;
/// @custom:oz-retyped-from Checkpoints.History
Checkpoints.Trace224 private _totalCheckpoints;
mapping(address => Counters.Counter) private _nonces;
/**
* @dev Clock used for flagging checkpoints. Can be overridden to implement timestamp based
* checkpoints (and voting), in which case {CLOCK_MODE} should be overridden as well to match.
*/
function clock() public view virtual override returns (uint48) {
return SafeCast.toUint48(block.number);
}
/**
* @dev Machine-readable description of the clock as specified in EIP-6372.
*/
// solhint-disable-next-line func-name-mixedcase
function CLOCK_MODE() public view virtual override returns (string memory) {
// Check that the clock was not modified
require(clock() == block.number, "Votes: broken clock mode");
return "mode=blocknumber&from=default";
}
/**
* @dev Returns the current amount of votes that `account` has.
*/
function getVotes(address account) public view virtual override returns (uint256) {
return _delegateCheckpoints[account].latest();
}
/**
* @dev Returns the amount of votes that `account` had at a specific moment in the past. If the `clock()` is
* configured to use block numbers, this will return the value at the end of the corresponding block.
*
* Requirements:
*
* - `timepoint` must be in the past. If operating using block numbers, the block must be already mined.
*/
function getPastVotes(address account, uint256 timepoint) public view virtual override returns (uint256) {
require(timepoint < clock(), "Votes: future lookup");
return _delegateCheckpoints[account].upperLookupRecent(SafeCast.toUint32(timepoint));
}
/**
* @dev Returns the total supply of votes available at a specific moment in the past. If the `clock()` is
* configured to use block numbers, this will return the value at the end of the corresponding block.
*
* NOTE: This value is the sum of all available votes, which is not necessarily the sum of all delegated votes.
* Votes that have not been delegated are still part of total supply, even though they would not participate in a
* vote.
*
* Requirements:
*
* - `timepoint` must be in the past. If operating using block numbers, the block must be already mined.
*/
function getPastTotalSupply(uint256 timepoint) public view virtual override returns (uint256) {
require(timepoint < clock(), "Votes: future lookup");
return _totalCheckpoints.upperLookupRecent(SafeCast.toUint32(timepoint));
}
/**
* @dev Returns the current total supply of votes.
*/
function _getTotalSupply() internal view virtual returns (uint256) {
return _totalCheckpoints.latest();
}
/**
* @dev Returns the delegate that `account` has chosen.
*/
function delegates(address account) public view virtual override returns (address) {
return _delegation[account];
}
/**
* @dev Delegates votes from the sender to `delegatee`.
*/
function delegate(address delegatee) public virtual override {
address account = _msgSender();
_delegate(account, delegatee);
}
/**
* @dev Delegates votes from signer to `delegatee`.
*/
function delegateBySig(
address delegatee,
uint256 nonce,
uint256 expiry,
uint8 v,
bytes32 r,
bytes32 s
) public virtual override {
require(block.timestamp <= expiry, "Votes: signature expired");
address signer = ECDSA.recover(
_hashTypedDataV4(keccak256(abi.encode(_DELEGATION_TYPEHASH, delegatee, nonce, expiry))),
v,
r,
s
);
require(nonce == _useNonce(signer), "Votes: invalid nonce");
_delegate(signer, delegatee);
}
/**
* @dev Delegate all of `account`'s voting units to `delegatee`.
*
* Emits events {IVotes-DelegateChanged} and {IVotes-DelegateVotesChanged}.
*/
function _delegate(address account, address delegatee) internal virtual {
address oldDelegate = delegates(account);
_delegation[account] = delegatee;
emit DelegateChanged(account, oldDelegate, delegatee);
_moveDelegateVotes(oldDelegate, delegatee, _getVotingUnits(account));
}
/**
* @dev Transfers, mints, or burns voting units. To register a mint, `from` should be zero. To register a burn, `to`
* should be zero. Total supply of voting units will be adjusted with mints and burns.
*/
function _transferVotingUnits(address from, address to, uint256 amount) internal virtual {
if (from == address(0)) {
_push(_totalCheckpoints, _add, SafeCast.toUint224(amount));
}
if (to == address(0)) {
_push(_totalCheckpoints, _subtract, SafeCast.toUint224(amount));
}
_moveDelegateVotes(delegates(from), delegates(to), amount);
}
/**
* @dev Moves delegated votes from one delegate to another.
*/
function _moveDelegateVotes(address from, address to, uint256 amount) private {
if (from != to && amount > 0) {
if (from != address(0)) {
(uint256 oldValue, uint256 newValue) = _push(
_delegateCheckpoints[from],
_subtract,
SafeCast.toUint224(amount)
);
emit DelegateVotesChanged(from, oldValue, newValue);
}
if (to != address(0)) {
(uint256 oldValue, uint256 newValue) = _push(
_delegateCheckpoints[to],
_add,
SafeCast.toUint224(amount)
);
emit DelegateVotesChanged(to, oldValue, newValue);
}
}
}
function _push(
Checkpoints.Trace224 storage store,
function(uint224, uint224) view returns (uint224) op,
uint224 delta
) private returns (uint224, uint224) {
return store.push(SafeCast.toUint32(clock()), op(store.latest(), delta));
}
function _add(uint224 a, uint224 b) private pure returns (uint224) {
return a + b;
}
function _subtract(uint224 a, uint224 b) private pure returns (uint224) {
return a - b;
}
/**
* @dev Consumes a nonce.
*
* Returns the current value and increments nonce.
*/
function _useNonce(address owner) internal virtual returns (uint256 current) {
Counters.Counter storage nonce = _nonces[owner];
current = nonce.current();
nonce.increment();
}
/**
* @dev Returns an address nonce.
*/
function nonces(address owner) public view virtual returns (uint256) {
return _nonces[owner].current();
}
/**
* @dev Returns the contract's {EIP712} domain separator.
*/
// solhint-disable-next-line func-name-mixedcase
function DOMAIN_SEPARATOR() external view returns (bytes32) {
return _domainSeparatorV4();
}
/**
* @dev Must return the voting units held by an account.
*/
function _getVotingUnits(address) internal view virtual returns (uint256);
}