Add VotesPlugin as opposition to ERC20Votes

contracts/VotingPlugin.sol

@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import { SafeCast } from "@openzeppelin/contracts/utils/math/SafeCast.sol";
+import { Checkpoints } from "@openzeppelin/contracts/utils/Checkpoints.sol";
+import { IERC20Plugins, DelegationPlugin } from "./DelegationPlugin.sol";
+
+contract VotingPlugin is DelegationPlugin {
+    using Checkpoints for Checkpoints.Trace224;
+
+    error ERC5805FutureLookup(uint256 timepoint, uint48 clock);
+
+    Checkpoints.Trace224 private _totalCheckpoints;
+    mapping(address => Checkpoints.Trace224) private _delegateCheckpoints;
+
+    constructor(string memory name, string memory symbol, IERC20Plugins token)
+        DelegationPlugin(name, symbol, token)
+    {}  // solhint-disable-line no-empty-blocks
+
+    /**
+     * @dev Get number of checkpoints for `account`.
+     */
+    function numCheckpoints(address account) public view virtual returns (uint32) {
+        return SafeCast.toUint32(_delegateCheckpoints[account].length());
+    }
+
+    /**
+     * @dev Get the `pos`-th checkpoint for `account`.
+     */
+    function checkpoints(address account, uint32 pos) public view virtual returns (Checkpoints.Checkpoint224 memory) {
+        return _delegateCheckpoints[account]._checkpoints[pos];
+    }
+
+    /**
+     * @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 returns (uint48) {
+        return SafeCast.toUint48(block.number);
+    }
+
+    /**
+     * @dev Returns the current amount of votes that `account` has.
+     */
+    function getVotes(address account) public view virtual 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 returns (uint256) {
+        uint48 currentTimepoint = clock();
+        if (timepoint >= currentTimepoint) {
+            revert ERC5805FutureLookup(timepoint, currentTimepoint);
+        }
+        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 returns (uint256) {
+        uint48 currentTimepoint = clock();
+        if (timepoint >= currentTimepoint) {
+            revert ERC5805FutureLookup(timepoint, currentTimepoint);
+        }
+        return _totalCheckpoints.upperLookupRecent(SafeCast.toUint32(timepoint));
+    }
+
+    function _updateBalances(address from, address to, address fromDelegatee, address toDelegatee, uint256 amount) internal virtual override {
+        super._updateBalances(from, to, fromDelegatee, toDelegatee, amount);
+
+        if (fromDelegatee != toDelegatee && amount > 0) {
+            if (fromDelegatee == address(0)) {
+                _delegateCheckpoints[toDelegatee].push(SafeCast.toUint32(clock()), SafeCast.toUint224(balanceOf(toDelegatee)));
+                _totalCheckpoints.push(SafeCast.toUint32(clock()), SafeCast.toUint224(totalSupply()));
+            } else if (toDelegatee == address(0)) {
+                _delegateCheckpoints[fromDelegatee].push(SafeCast.toUint32(clock()), SafeCast.toUint224(balanceOf(fromDelegatee)));
+                _totalCheckpoints.push(SafeCast.toUint32(clock()), SafeCast.toUint224(totalSupply()));
+            } else {
+                _delegateCheckpoints[fromDelegatee].push(SafeCast.toUint32(clock()), SafeCast.toUint224(balanceOf(fromDelegatee)));
+                _delegateCheckpoints[toDelegatee].push(SafeCast.toUint32(clock()), SafeCast.toUint224(balanceOf(toDelegatee)));
+            }
+        }
+    }
+}