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ERC20 extension for governance tokens (vote delegation and snapshots) (…
…#2632) Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
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| // SPDX-License-Identifier: MIT | ||
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| pragma solidity ^0.8.0; | ||
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| import "../token/ERC20/extensions/draft-ERC20Votes.sol"; | ||
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| contract ERC20VotesMock is ERC20Votes { | ||
| constructor ( | ||
| string memory name, | ||
| string memory symbol, | ||
| address initialAccount, | ||
| uint256 initialBalance | ||
| ) payable ERC20(name, symbol) ERC20Permit(name) { | ||
| _mint(initialAccount, initialBalance); | ||
| } | ||
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| function getChainId() external view returns (uint256) { | ||
| return block.chainid; | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,172 @@ | ||
| // SPDX-License-Identifier: MIT | ||
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| pragma solidity ^0.8.0; | ||
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| import "./draft-ERC20Permit.sol"; | ||
| import "./draft-IERC20Votes.sol"; | ||
| import "../../../utils/math/Math.sol"; | ||
| import "../../../utils/math/SafeCast.sol"; | ||
| import "../../../utils/cryptography/ECDSA.sol"; | ||
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| /** | ||
| * @dev Extension of the ERC20 token contract to support Compound's voting and delegation. | ||
| * | ||
| * This extensions keeps a history (checkpoints) of each account's vote power. Vote power can be delegated either | ||
| * by calling the {delegate} function directly, or by providing a signature to be used with {delegateBySig}. Voting | ||
| * power can be queried through the public accessors {getCurrentVotes} and {getPriorVotes}. | ||
| * | ||
| * By default, token balance does not account for voting power. This makes transfers cheaper. The downside is that it | ||
| * requires users to delegate to themselves in order to activate checkpoints and have their voting power tracked. | ||
| * Enabling self-delegation can easily be done by overriding the {delegates} function. Keep in mind however that this | ||
| * will significantly increase the base gas cost of transfers. | ||
| * | ||
| * _Available since v4.2._ | ||
| */ | ||
| abstract contract ERC20Votes is IERC20Votes, ERC20Permit { | ||
| bytes32 private constant _DELEGATION_TYPEHASH = keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)"); | ||
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| mapping (address => address) private _delegates; | ||
| mapping (address => Checkpoint[]) private _checkpoints; | ||
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| /** | ||
| * @dev Get the `pos`-th checkpoint for `account`. | ||
| */ | ||
| function checkpoints(address account, uint32 pos) external view virtual override returns (Checkpoint memory) { | ||
| return _checkpoints[account][pos]; | ||
| } | ||
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| /** | ||
| * @dev Get number of checkpoints for `account`. | ||
| */ | ||
| function numCheckpoints(address account) external view virtual override returns (uint32) { | ||
| return SafeCast.toUint32(_checkpoints[account].length); | ||
| } | ||
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| /** | ||
| * @dev Get the address `account` is currently delegating to. | ||
| */ | ||
| function delegates(address account) public view virtual override returns (address) { | ||
| return _delegates[account]; | ||
| } | ||
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| /** | ||
| * @dev Gets the current votes balance for `account` | ||
| */ | ||
| function getCurrentVotes(address account) external view override returns (uint256) { | ||
| uint256 pos = _checkpoints[account].length; | ||
| return pos == 0 ? 0 : _checkpoints[account][pos - 1].votes; | ||
| } | ||
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| /** | ||
| * @dev Determine the number of votes for `account` at the begining of `blockNumber`. | ||
| */ | ||
| function getPriorVotes(address account, uint256 blockNumber) external view override returns (uint256) { | ||
| require(blockNumber < block.number, "ERC20Votes::getPriorVotes: not yet determined"); | ||
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| Checkpoint[] storage ckpts = _checkpoints[account]; | ||
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| // We run a binary search to look for the earliest checkpoint taken after `blockNumber`. | ||
| // | ||
| // During the loop, the index of the wanted checkpoint remains in the range [low, high). | ||
| // With each iteration, either `low` or `high` is moved towards the middle of the range to maintain the invariant. | ||
| // - If the middle checkpoint is after `blockNumber`, we look in [low, mid) | ||
| // - If the middle checkpoint is before `blockNumber`, we look in [mid+1, high) | ||
| // Once we reach a single value (when low == high), we've found the right checkpoint at the index high-1, if not | ||
| // out of bounds (in which case we're looking too far in the past and the result is 0). | ||
| // Note that if the latest checkpoint available is exactly for `blockNumber`, we end up with an index that is | ||
| // past the end of the array, so we technically don't find a checkpoint after `blockNumber`, but it works out | ||
| // the same. | ||
| uint256 high = ckpts.length; | ||
| uint256 low = 0; | ||
| while (low < high) { | ||
| uint256 mid = Math.average(low, high); | ||
| if (ckpts[mid].fromBlock > blockNumber) { | ||
| high = mid; | ||
| } else { | ||
| low = mid + 1; | ||
| } | ||
| } | ||
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| return high == 0 ? 0 : ckpts[high - 1].votes; | ||
| } | ||
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| /** | ||
| * @dev Delegate votes from the sender to `delegatee`. | ||
| */ | ||
| function delegate(address delegatee) public virtual override { | ||
| return _delegate(_msgSender(), delegatee); | ||
| } | ||
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| /** | ||
| * @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, "ERC20Votes::delegateBySig: signature expired"); | ||
| address signer = ECDSA.recover( | ||
| _hashTypedDataV4(keccak256(abi.encode( | ||
| _DELEGATION_TYPEHASH, | ||
| delegatee, | ||
| nonce, | ||
| expiry | ||
| ))), | ||
| v, r, s | ||
| ); | ||
| require(nonce == _useNonce(signer), "ERC20Votes::delegateBySig: invalid nonce"); | ||
| return _delegate(signer, delegatee); | ||
| } | ||
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| /** | ||
| * @dev Change delegation for `delegator` to `delegatee`. | ||
| */ | ||
| function _delegate(address delegator, address delegatee) internal virtual { | ||
| address currentDelegate = delegates(delegator); | ||
| uint256 delegatorBalance = balanceOf(delegator); | ||
| _delegates[delegator] = delegatee; | ||
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| emit DelegateChanged(delegator, currentDelegate, delegatee); | ||
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| _moveVotingPower(currentDelegate, delegatee, delegatorBalance); | ||
| } | ||
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| function _moveVotingPower(address src, address dst, uint256 amount) private { | ||
| if (src != dst && amount > 0) { | ||
| if (src != address(0)) { | ||
| uint256 srcCkptLen = _checkpoints[src].length; | ||
| uint256 srcCkptOld = srcCkptLen == 0 ? 0 : _checkpoints[src][srcCkptLen - 1].votes; | ||
| uint256 srcCkptNew = srcCkptOld - amount; | ||
| _writeCheckpoint(src, srcCkptLen, srcCkptOld, srcCkptNew); | ||
| } | ||
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| if (dst != address(0)) { | ||
| uint256 dstCkptLen = _checkpoints[dst].length; | ||
| uint256 dstCkptOld = dstCkptLen == 0 ? 0 : _checkpoints[dst][dstCkptLen - 1].votes; | ||
| uint256 dstCkptNew = dstCkptOld + amount; | ||
| _writeCheckpoint(dst, dstCkptLen, dstCkptOld, dstCkptNew); | ||
| } | ||
| } | ||
| } | ||
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| function _writeCheckpoint(address delegatee, uint256 pos, uint256 oldWeight, uint256 newWeight) private { | ||
| if (pos > 0 && _checkpoints[delegatee][pos - 1].fromBlock == block.number) { | ||
| _checkpoints[delegatee][pos - 1].votes = SafeCast.toUint224(newWeight); | ||
| } else { | ||
| _checkpoints[delegatee].push(Checkpoint({ | ||
| fromBlock: SafeCast.toUint32(block.number), | ||
| votes: SafeCast.toUint224(newWeight) | ||
| })); | ||
| } | ||
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| emit DelegateVotesChanged(delegatee, oldWeight, newWeight); | ||
| } | ||
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| function _mint(address account, uint256 amount) internal virtual override { | ||
| super._mint(account, amount); | ||
| require(totalSupply() <= type(uint224).max, "ERC20Votes: total supply exceeds 2**224"); | ||
| } | ||
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| function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override { | ||
| _moveVotingPower(delegates(from), delegates(to), amount); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,23 @@ | ||
| // SPDX-License-Identifier: MIT | ||
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| pragma solidity ^0.8.0; | ||
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| import "../IERC20.sol"; | ||
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| interface IERC20Votes is IERC20 { | ||
| struct Checkpoint { | ||
| uint32 fromBlock; | ||
| uint224 votes; | ||
| } | ||
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| event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate); | ||
| event DelegateVotesChanged(address indexed delegate, uint256 previousBalance, uint256 newBalance); | ||
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| function delegates(address owner) external view returns (address); | ||
| function checkpoints(address account, uint32 pos) external view returns (Checkpoint memory); | ||
| function numCheckpoints(address account) external view returns (uint32); | ||
| function getCurrentVotes(address account) external view returns (uint256); | ||
| function getPriorVotes(address account, uint256 blockNumber) external view returns (uint256); | ||
| function delegate(address delegatee) external; | ||
| function delegateBySig(address delegatee, uint nonce, uint expiry, uint8 v, bytes32 r, bytes32 s) external; | ||
| } |
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