openzeppelin-contracts/contracts/governance/extensions/GovernorPreventLateQuorum.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../Governor.sol";
import "../../utils/math/Math.sol";

/**
 * @dev A module that ensures there is a minimum voting period after quorum is reached. This prevents a large voter from
 * swaying a vote and triggering quorum at the last minute, by ensuring there is always time for other voters to react
 * and try to oppose the decision.
 *
 * If a vote causes quorum to be reached, the proposal's voting period may be extended so that it does not end before at
 * least a given number of blocks have passed (the "vote extension" parameter). This parameter can be set by the
 * governance executor (e.g. through a governance proposal).
 *
 * _Available since v4.5._
 */
abstract contract GovernorPreventLateQuorum is Governor {
    using SafeCast for uint256;
    using Timers for Timers.BlockNumber;

    uint64 private _voteExtension;
    mapping(uint256 => Timers.BlockNumber) private _extendedDeadlines;

    /// @dev Emitted when a proposal deadline is pushed back due to reaching quorum late in its voting period.
    event ProposalExtended(uint256 indexed proposalId, uint64 extendedDeadline);

    /// @dev Emitted when the {lateQuorumVoteExtension} parameter is changed.
    event LateQuorumVoteExtensionSet(uint64 oldVoteExtension, uint64 newVoteExtension);

    /**
     * @dev Initializes the vote extension parameter: the number of blocks that are required to pass since a proposal
     * reaches quorum until its voting period ends. If necessary the voting period will be extended beyond the one set
     * at proposal creation.
     */
    constructor(uint64 initialVoteExtension) {
        _setLateQuorumVoteExtension(initialVoteExtension);
    }

    /**
     * @dev Returns the proposal deadline, which may have been extended beyond that set at proposal creation, if the
     * proposal reached quorum late in the voting period. See {Governor-proposalDeadline}.
     */
    function proposalDeadline(uint256 proposalId) public view virtual override returns (uint256) {
        return Math.max(super.proposalDeadline(proposalId), _extendedDeadlines[proposalId].getDeadline());
    }

    /**
     * @dev Casts a vote and detects if it caused quorum to be reached, potentially extending the voting period. See
     * {Governor-_castVote}.
     *
     * May emit a {ProposalExtended} event.
     */
    function _castVote(
        uint256 proposalId,
        address account,
        uint8 support,
        string memory reason
    ) internal virtual override returns (uint256) {
        uint256 result = super._castVote(proposalId, account, support, reason);

        Timers.BlockNumber storage extendedDeadline = _extendedDeadlines[proposalId];

        if (extendedDeadline.isUnset() && _quorumReached(proposalId)) {
            uint64 extendedDeadlineValue = block.number.toUint64() + lateQuorumVoteExtension();

            if (extendedDeadlineValue > proposalDeadline(proposalId)) {
                emit ProposalExtended(proposalId, extendedDeadlineValue);
            }

            extendedDeadline.setDeadline(extendedDeadlineValue);
        }

        return result;
    }

    /**
     * @dev Returns the current value of the vote extension parameter: the number of blocks that are required to pass
     * from the time a proposal reaches quorum until its voting period ends.
     */
    function lateQuorumVoteExtension() public view virtual returns (uint64) {
        return _voteExtension;
    }

    /**
     * @dev Changes the {lateQuorumVoteExtension}. This operation can only be performed by the governance executor,
     * generally through a governance proposal.
     *
     * Emits a {LateQuorumVoteExtensionSet} event.
     */
    function setLateQuorumVoteExtension(uint64 newVoteExtension) public virtual onlyGovernance {
        _setLateQuorumVoteExtension(newVoteExtension);
    }

    /**
     * @dev Changes the {lateQuorumVoteExtension}. This is an internal function that can be exposed in a public function
     * like {setLateQuorumVoteExtension} if another access control mechanism is needed.
     *
     * Emits a {LateQuorumVoteExtensionSet} event.
     */
    function _setLateQuorumVoteExtension(uint64 newVoteExtension) internal virtual {
        emit LateQuorumVoteExtensionSet(_voteExtension, newVoteExtension);
        _voteExtension = newVoteExtension;
    }
}