Use Votes for ERC20Votes

contracts/mocks/ERC721VotesMock.sol

@@ -15,7 +15,7 @@ contract ERC721VotesMock is ERC721Votes {
         _mint(account, tokenId);
     }
 
-    function burn(uint256 tokenId) public {
+    function burn(address, uint256 tokenId) public {
         _burn(tokenId);
     }
 

contracts/token/ERC20/extensions/ERC20Votes.sol

@@ -4,12 +4,8 @@
 pragma solidity ^0.8.0;
 
 import "../ERC20.sol";
-import "../../../utils/math/Math.sol";
-import "../../../utils/Nonces.sol";
-import "../../../governance/utils/IVotes.sol";
+import "../../../governance/utils/Votes.sol";
 import "../../../utils/math/SafeCast.sol";
-import "../../../utils/cryptography/EIP712.sol";
-import "../../../utils/cryptography/ECDSA.sol";
 
 /**
  * @dev Extension of ERC20 to support Compound-like voting and delegation. This version is more generic than Compound's,
@@ -26,148 +22,7 @@ import "../../../utils/cryptography/ECDSA.sol";
  *
  * _Available since v4.2._
  */
-abstract contract ERC20Votes is ERC20, IVotes, Nonces, EIP712 {
-    struct Checkpoint {
-        uint32 fromBlock;
-        uint224 votes;
-    }
-
-    bytes32 private constant _DELEGATION_TYPEHASH =
-        keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");
-
-    mapping(address => address) private _delegates;
-    mapping(address => Checkpoint[]) private _checkpoints;
-    Checkpoint[] private _totalSupplyCheckpoints;
-
-    /**
-     * @dev Get the `pos`-th checkpoint for `account`.
-     */
-    function checkpoints(address account, uint32 pos) public view virtual returns (Checkpoint memory) {
-        return _checkpoints[account][pos];
-    }
-
-    /**
-     * @dev Get number of checkpoints for `account`.
-     */
-    function numCheckpoints(address account) public view virtual returns (uint32) {
-        return SafeCast.toUint32(_checkpoints[account].length);
-    }
-
-    /**
-     * @dev Get the address `account` is currently delegating to.
-     */
-    function delegates(address account) public view virtual override returns (address) {
-        return _delegates[account];
-    }
-
-    /**
-     * @dev Gets the current votes balance for `account`
-     */
-    function getVotes(address account) public view virtual override returns (uint256) {
-        uint256 pos = _checkpoints[account].length;
-        unchecked {
-            return pos == 0 ? 0 : _checkpoints[account][pos - 1].votes;
-        }
-    }
-
-    /**
-     * @dev Retrieve the number of votes for `account` at the end of `blockNumber`.
-     *
-     * Requirements:
-     *
-     * - `blockNumber` must have been already mined
-     */
-    function getPastVotes(address account, uint256 blockNumber) public view virtual override returns (uint256) {
-        require(blockNumber < block.number, "ERC20Votes: block not yet mined");
-        return _checkpointsLookup(_checkpoints[account], blockNumber);
-    }
-
-    /**
-     * @dev Retrieve the `totalSupply` at the end of `blockNumber`. Note, this value is the sum of all balances.
-     * It is NOT the sum of all the delegated votes!
-     *
-     * Requirements:
-     *
-     * - `blockNumber` must have been already mined
-     */
-    function getPastTotalSupply(uint256 blockNumber) public view virtual override returns (uint256) {
-        require(blockNumber < block.number, "ERC20Votes: block not yet mined");
-        return _checkpointsLookup(_totalSupplyCheckpoints, blockNumber);
-    }
-
-    /**
-     * @dev Lookup a value in a list of (sorted) checkpoints.
-     */
-    function _checkpointsLookup(Checkpoint[] storage ckpts, uint256 blockNumber) private view returns (uint256) {
-        // We run a binary search to look for the earliest checkpoint taken after `blockNumber`.
-        //
-        // Initially we check if the block is recent to narrow the search range.
-        // During the loop, the index of the wanted checkpoint remains in the range [low-1, 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 or equal to `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 length = ckpts.length;
-
-        uint256 low = 0;
-        uint256 high = length;
-
-        if (length > 5) {
-            uint256 mid = length - Math.sqrt(length);
-            if (_unsafeAccess(ckpts, mid).fromBlock > blockNumber) {
-                high = mid;
-            } else {
-                low = mid + 1;
-            }
-        }
-
-        while (low < high) {
-            uint256 mid = Math.average(low, high);
-            if (_unsafeAccess(ckpts, mid).fromBlock > blockNumber) {
-                high = mid;
-            } else {
-                low = mid + 1;
-            }
-        }
-
-        unchecked {
-            return high == 0 ? 0 : _unsafeAccess(ckpts, high - 1).votes;
-        }
-    }
-
-    /**
-     * @dev Delegate votes from the sender to `delegatee`.
-     */
-    function delegate(address delegatee) public virtual override {
-        _delegate(_msgSender(), 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, "ERC20Votes: signature expired");
-        address signer = ECDSA.recover(
-            _hashTypedDataV4(keccak256(abi.encode(_DELEGATION_TYPEHASH, delegatee, nonce, expiry))),
-            v,
-            r,
-            s
-        );
-        require(nonce == _useNonce(signer), "ERC20Votes: invalid nonce");
-        _delegate(signer, delegatee);
-    }
-
+abstract contract ERC20Votes is ERC20, Votes {
     /**
      * @dev Maximum token supply. Defaults to `type(uint224).max` (2^224^ - 1).
      */
@@ -181,17 +36,15 @@ abstract contract ERC20Votes is ERC20, IVotes, Nonces, EIP712 {
     function _mint(address account, uint256 amount) internal virtual override {
         super._mint(account, amount);
         require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
-
-        _writeCheckpoint(_totalSupplyCheckpoints, _add, amount);
+        _transferVotingUnits(address(0), account, amount);
     }
 
     /**
      * @dev Snapshots the totalSupply after it has been decreased.
      */
     function _burn(address account, uint256 amount) internal virtual override {
         super._burn(account, amount);
-
-        _writeCheckpoint(_totalSupplyCheckpoints, _subtract, amount);
+        _transferVotingUnits(account, address(0), amount);
     }
 
     /**
@@ -204,79 +57,14 @@ abstract contract ERC20Votes is ERC20, IVotes, Nonces, EIP712 {
         address to,
         uint256 amount
     ) internal virtual override {
+        _transferVotingUnits(from, to, amount);
         super._afterTokenTransfer(from, to, amount);
-
-        _moveVotingPower(delegates(from), delegates(to), amount);
     }
 
     /**
-     * @dev Change delegation for `delegator` to `delegatee`.
-     *
-     * Emits events {IVotes-DelegateChanged} and {IVotes-DelegateVotesChanged}.
+     * @dev Returns the balance of `account`.
      */
-    function _delegate(address delegator, address delegatee) internal virtual {
-        address currentDelegate = delegates(delegator);
-        uint256 delegatorBalance = balanceOf(delegator);
-        _delegates[delegator] = delegatee;
-
-        emit DelegateChanged(delegator, currentDelegate, delegatee);
-
-        _moveVotingPower(currentDelegate, delegatee, delegatorBalance);
-    }
-
-    function _moveVotingPower(
-        address src,
-        address dst,
-        uint256 amount
-    ) private {
-        if (src != dst && amount > 0) {
-            if (src != address(0)) {
-                (uint256 oldWeight, uint256 newWeight) = _writeCheckpoint(_checkpoints[src], _subtract, amount);
-                emit DelegateVotesChanged(src, oldWeight, newWeight);
-            }
-
-            if (dst != address(0)) {
-                (uint256 oldWeight, uint256 newWeight) = _writeCheckpoint(_checkpoints[dst], _add, amount);
-                emit DelegateVotesChanged(dst, oldWeight, newWeight);
-            }
-        }
-    }
-
-    function _writeCheckpoint(
-        Checkpoint[] storage ckpts,
-        function(uint256, uint256) view returns (uint256) op,
-        uint256 delta
-    ) private returns (uint256 oldWeight, uint256 newWeight) {
-        uint256 pos = ckpts.length;
-
-        unchecked {
-            Checkpoint memory oldCkpt = pos == 0 ? Checkpoint(0, 0) : _unsafeAccess(ckpts, pos - 1);
-
-            oldWeight = oldCkpt.votes;
-            newWeight = op(oldWeight, delta);
-
-            if (pos > 0 && oldCkpt.fromBlock == block.number) {
-                _unsafeAccess(ckpts, pos - 1).votes = SafeCast.toUint224(newWeight);
-            } else {
-                ckpts.push(
-                    Checkpoint({fromBlock: SafeCast.toUint32(block.number), votes: SafeCast.toUint224(newWeight)})
-                );
-            }
-        }
-    }
-
-    function _add(uint256 a, uint256 b) private pure returns (uint256) {
-        return a + b;
-    }
-
-    function _subtract(uint256 a, uint256 b) private pure returns (uint256) {
-        return a - b;
-    }
-
-    function _unsafeAccess(Checkpoint[] storage ckpts, uint256 pos) private pure returns (Checkpoint storage result) {
-        assembly {
-            mstore(0, ckpts.slot)
-            result.slot := add(keccak256(0, 0x20), pos)
-        }
+    function _getVotingUnits(address account) internal view virtual override returns (uint256) {
+        return balanceOf(account);
     }
 }