openzeppelin-contracts/contracts/token/ERC20/extensions/ERC20Votes.sol

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/extensions/ERC20Votes.sol)

pragma solidity ^0.8.0;

import "../ERC20.sol";
import "../../../governance/utils/Votes.sol";
import "../../../utils/math/SafeCast.sol";

/**
 * @dev Extension of ERC20 to support Compound-like voting and delegation. This version is more generic than Compound's,
 * and supports token supply up to 2^224^ - 1, while COMP is limited to 2^96^ - 1.
 *
 * NOTE: If exact COMP compatibility is required, use the {ERC20VotesComp} variant of this module.
 *
 * This extension 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 {getVotes} and {getPastVotes}.
 *
 * 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.
 *
 * _Available since v4.2._
 */
abstract contract ERC20Votes is ERC20, Votes {
    /**
     * @dev Maximum token supply. Defaults to `type(uint224).max` (2^224^ - 1).
     */
    function _maxSupply() internal view virtual returns (uint224) {
        return type(uint224).max;
    }

    /**
     * @dev Move voting power when tokens are transferred.
     *
     * Emits a {IVotes-DelegateVotesChanged} event.
     */
    function _afterTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual override {
        _transferVotingUnits(from, to, amount);
        super._afterTokenTransfer(from, to, amount);
    }

    /**
     * @dev Get number of checkpoints for `account`.
     */
    function numCheckpoints(address account) public view virtual returns (uint32) {
        return _numCheckpoints(account);
    }

    /**
     * @dev Get the `pos`-th checkpoint for `account`.
     */
    function checkpoints(address account, uint32 pos) public view virtual returns (Checkpoints.Checkpoint memory) {
        return _checkpoints(account, pos);
    }

    /**
     * @dev Returns the balance of `account`.
     */
    function _getVotingUnits(address account) internal view virtual override returns (uint256) {
        return balanceOf(account);
    }

    /**
     * @dev Snapshots the totalSupply after it has been increased.
     */
    function _mint(address account, uint256 amount) internal virtual override {
        super._mint(account, amount);
        require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
    }
}