Add a governor module to protect against late quorum (#2973)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Changelog
 
+## Unreleased
+ * `GovernorExtendedVoting`: add new module to ensure a minimum voting duration is available after the quorum is reached. ([#2973](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2973))
+
 ## Unreleased
 
 * `GovernorTimelockControl`: improve the `state()` function to have it reflect cases where a proposal has been canceled directly on the timelock. ([#2977](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2977))

contracts/governance/Governor.sol

@@ -110,24 +110,37 @@ abstract contract Governor is Context, ERC165, EIP712, IGovernor {
      * @dev See {IGovernor-state}.
      */
     function state(uint256 proposalId) public view virtual override returns (ProposalState) {
-        ProposalCore memory proposal = _proposals[proposalId];
+        ProposalCore storage proposal = _proposals[proposalId];
 
         if (proposal.executed) {
             return ProposalState.Executed;
-        } else if (proposal.canceled) {
+        }
+
+        if (proposal.canceled) {
             return ProposalState.Canceled;
-        } else if (proposal.voteStart.getDeadline() >= block.number) {
+        }
-            return ProposalState.Pending;
+
-        } else if (proposal.voteEnd.getDeadline() >= block.number) {
+        uint256 snapshot = proposalSnapshot(proposalId);
-            return ProposalState.Active;
+
-        } else if (proposal.voteEnd.isExpired()) {
+        if (snapshot == 0) {
-            return
-                _quorumReached(proposalId) && _voteSucceeded(proposalId)
-                    ? ProposalState.Succeeded
-                    : ProposalState.Defeated;
-        } else {
             revert("Governor: unknown proposal id");
         }
+
+        if (snapshot >= block.number) {
+            return ProposalState.Pending;
+        }
+
+        uint256 deadline = proposalDeadline(proposalId);
+
+        if (deadline >= block.number) {
+            return ProposalState.Active;
+        }
+
+        if (_quorumReached(proposalId) && _voteSucceeded(proposalId)) {
+            return ProposalState.Succeeded;
+        } else {
+            return ProposalState.Defeated;
+        }
     }
 
     /**

contracts/governance/README.adoc

@@ -42,6 +42,8 @@ Other extensions can customize the behavior or interface in multiple ways.
 
 * {GovernorSettings}: Manages some of the settings (voting delay, voting period duration, and proposal threshold) in a way that can be updated through a governance proposal, without requiering an upgrade.
 
+* {GovernorPreventLateQuorum}: Ensures there is a minimum voting period after quorum is reached as a security protection against large voters.
+
 In addition to modules and extensions, the core contract requires a few virtual functions to be implemented to your particular specifications:
 
 * <<Governor-votingDelay-,`votingDelay()`>>: Delay (in number of blocks) since the proposal is submitted until voting power is fixed and voting starts. This can be used to enforce a delay after a proposal is published for users to buy tokens, or delegate their votes.
@@ -74,6 +76,8 @@ NOTE: Functions of the `Governor` contract do not include access control. If you
 
 {{GovernorSettings}}
 
+{{GovernorPreventLateQuorum}}
+
 {{GovernorCompatibilityBravo}}
 
 === Deprecated

contracts/governance/extensions/GovernorPreventLateQuorum.sol

@@ -0,0 +1,106 @@
+// 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;
+    }
+}

contracts/mocks/GovernorPreventLateQuorumMock.sol

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../governance/extensions/GovernorPreventLateQuorum.sol";
+import "../governance/extensions/GovernorSettings.sol";
+import "../governance/extensions/GovernorCountingSimple.sol";
+import "../governance/extensions/GovernorVotes.sol";
+
+contract GovernorPreventLateQuorumMock is
+    GovernorSettings,
+    GovernorVotes,
+    GovernorCountingSimple,
+    GovernorPreventLateQuorum
+{
+    uint256 private _quorum;
+
+    constructor(
+        string memory name_,
+        ERC20Votes token_,
+        uint256 votingDelay_,
+        uint256 votingPeriod_,
+        uint256 quorum_,
+        uint64 voteExtension_
+    )
+        Governor(name_)
+        GovernorSettings(votingDelay_, votingPeriod_, 0)
+        GovernorVotes(token_)
+        GovernorPreventLateQuorum(voteExtension_)
+    {
+        _quorum = quorum_;
+    }
+
+    function quorum(uint256) public view virtual override returns (uint256) {
+        return _quorum;
+    }
+
+    function proposalDeadline(uint256 proposalId)
+        public
+        view
+        virtual
+        override(Governor, GovernorPreventLateQuorum)
+        returns (uint256)
+    {
+        return super.proposalDeadline(proposalId);
+    }
+
+    function proposalThreshold() public view virtual override(Governor, GovernorSettings) returns (uint256) {
+        return super.proposalThreshold();
+    }
+
+    function _castVote(
+        uint256 proposalId,
+        address account,
+        uint8 support,
+        string memory reason
+    ) internal virtual override(Governor, GovernorPreventLateQuorum) returns (uint256) {
+        return super._castVote(proposalId, account, support, reason);
+    }
+}

test/governance/GovernorWorkflow.behavior.js

@@ -65,7 +65,7 @@ function runGovernorWorkflow () {
     // vote
     if (tryGet(this.settings, 'voters')) {
       this.receipts.castVote = [];
-      for (const voter of this.settings.voters) {
+      for (const voter of this.settings.voters.filter(({ support }) => !!support)) {
         if (!voter.signature) {
           this.receipts.castVote.push(
             await getReceiptOrRevert(

test/governance/extensions/GovernorPreventLateQuorum.test.js

@@ -0,0 +1,247 @@
+const { BN, expectEvent, expectRevert, time } = require('@openzeppelin/test-helpers');
+const Enums = require('../../helpers/enums');
+
+const {
+  runGovernorWorkflow,
+} = require('../GovernorWorkflow.behavior');
+
+const Token = artifacts.require('ERC20VotesCompMock');
+const Governor = artifacts.require('GovernorPreventLateQuorumMock');
+const CallReceiver = artifacts.require('CallReceiverMock');
+
+contract('GovernorPreventLateQuorum', function (accounts) {
+  const [ owner, proposer, voter1, voter2, voter3, voter4 ] = accounts;
+
+  const name = 'OZ-Governor';
+  // const version = '1';
+  const tokenName = 'MockToken';
+  const tokenSymbol = 'MTKN';
+  const tokenSupply = web3.utils.toWei('100');
+  const votingDelay = new BN(4);
+  const votingPeriod = new BN(16);
+  const lateQuorumVoteExtension = new BN(8);
+  const quorum = web3.utils.toWei('1');
+
+  beforeEach(async function () {
+    this.owner = owner;
+    this.token = await Token.new(tokenName, tokenSymbol);
+    this.mock = await Governor.new(
+      name,
+      this.token.address,
+      votingDelay,
+      votingPeriod,
+      quorum,
+      lateQuorumVoteExtension,
+    );
+    this.receiver = await CallReceiver.new();
+    await this.token.mint(owner, tokenSupply);
+    await this.token.delegate(voter1, { from: voter1 });
+    await this.token.delegate(voter2, { from: voter2 });
+    await this.token.delegate(voter3, { from: voter3 });
+    await this.token.delegate(voter4, { from: voter4 });
+  });
+
+  it('deployment check', async function () {
+    expect(await this.mock.name()).to.be.equal(name);
+    expect(await this.mock.token()).to.be.equal(this.token.address);
+    expect(await this.mock.votingDelay()).to.be.bignumber.equal(votingDelay);
+    expect(await this.mock.votingPeriod()).to.be.bignumber.equal(votingPeriod);
+    expect(await this.mock.quorum(0)).to.be.bignumber.equal(quorum);
+    expect(await this.mock.lateQuorumVoteExtension()).to.be.bignumber.equal(lateQuorumVoteExtension);
+  });
+
+  describe('nominal is unaffected', function () {
+    beforeEach(async function () {
+      this.settings = {
+        proposal: [
+          [ this.receiver.address ],
+          [ 0 ],
+          [ this.receiver.contract.methods.mockFunction().encodeABI() ],
+          '<proposal description>',
+        ],
+        proposer,
+        tokenHolder: owner,
+        voters: [
+          { voter: voter1, weight: web3.utils.toWei('1'), support: Enums.VoteType.For, reason: 'This is nice' },
+          { voter: voter2, weight: web3.utils.toWei('7'), support: Enums.VoteType.For },
+          { voter: voter3, weight: web3.utils.toWei('5'), support: Enums.VoteType.Against },
+          { voter: voter4, weight: web3.utils.toWei('2'), support: Enums.VoteType.Abstain },
+        ],
+      };
+    });
+
+    afterEach(async function () {
+      expect(await this.mock.hasVoted(this.id, owner)).to.be.equal(false);
+      expect(await this.mock.hasVoted(this.id, voter1)).to.be.equal(true);
+      expect(await this.mock.hasVoted(this.id, voter2)).to.be.equal(true);
+
+      await this.mock.proposalVotes(this.id).then(result => {
+        for (const [key, value] of Object.entries(Enums.VoteType)) {
+          expect(result[`${key.toLowerCase()}Votes`]).to.be.bignumber.equal(
+            Object.values(this.settings.voters).filter(({ support }) => support === value).reduce(
+              (acc, { weight }) => acc.add(new BN(weight)),
+              new BN('0'),
+            ),
+          );
+        }
+      });
+
+      const startBlock = new BN(this.receipts.propose.blockNumber).add(votingDelay);
+      const endBlock = new BN(this.receipts.propose.blockNumber).add(votingDelay).add(votingPeriod);
+      expect(await this.mock.proposalSnapshot(this.id)).to.be.bignumber.equal(startBlock);
+      expect(await this.mock.proposalDeadline(this.id)).to.be.bignumber.equal(endBlock);
+
+      expectEvent(
+        this.receipts.propose,
+        'ProposalCreated',
+        {
+          proposalId: this.id,
+          proposer,
+          targets: this.settings.proposal[0],
+          // values: this.settings.proposal[1].map(value => new BN(value)),
+          signatures: this.settings.proposal[2].map(() => ''),
+          calldatas: this.settings.proposal[2],
+          startBlock,
+          endBlock,
+          description: this.settings.proposal[3],
+        },
+      );
+
+      this.receipts.castVote.filter(Boolean).forEach(vote => {
+        const { voter } = vote.logs.find(Boolean).args;
+        expectEvent(
+          vote,
+          'VoteCast',
+          this.settings.voters.find(({ address }) => address === voter),
+        );
+        expectEvent.notEmitted(
+          vote,
+          'ProposalExtended',
+        );
+      });
+      expectEvent(
+        this.receipts.execute,
+        'ProposalExecuted',
+        { proposalId: this.id },
+      );
+      await expectEvent.inTransaction(
+        this.receipts.execute.transactionHash,
+        this.receiver,
+        'MockFunctionCalled',
+      );
+    });
+    runGovernorWorkflow();
+  });
+
+  describe('Delay is extended to prevent last minute take-over', function () {
+    beforeEach(async function () {
+      this.settings = {
+        proposal: [
+          [ this.receiver.address ],
+          [ 0 ],
+          [ this.receiver.contract.methods.mockFunction().encodeABI() ],
+          '<proposal description>',
+        ],
+        proposer,
+        tokenHolder: owner,
+        voters: [
+          { voter: voter1, weight: web3.utils.toWei('0.2'), support: Enums.VoteType.Against },
+          { voter: voter2, weight: web3.utils.toWei('1.0') }, // do not actually vote, only getting tokens
+          { voter: voter3, weight: web3.utils.toWei('0.9') }, // do not actually vote, only getting tokens
+        ],
+        steps: {
+          wait: { enable: false },
+          execute: { enable: false },
+        },
+      };
+    });
+
+    afterEach(async function () {
+      expect(await this.mock.state(this.id)).to.be.bignumber.equal(Enums.ProposalState.Active);
+
+      const startBlock = new BN(this.receipts.propose.blockNumber).add(votingDelay);
+      const endBlock = new BN(this.receipts.propose.blockNumber).add(votingDelay).add(votingPeriod);
+      expect(await this.mock.proposalSnapshot(this.id)).to.be.bignumber.equal(startBlock);
+      expect(await this.mock.proposalDeadline(this.id)).to.be.bignumber.equal(endBlock);
+
+      // wait until the vote is almost over
+      await time.advanceBlockTo(endBlock.subn(1));
+      expect(await this.mock.state(this.id)).to.be.bignumber.equal(Enums.ProposalState.Active);
+
+      // try to overtake the vote at the last minute
+      const tx = await this.mock.castVote(this.id, Enums.VoteType.For, { from: voter2 });
+
+      // vote duration is extended
+      const extendedBlock = new BN(tx.receipt.blockNumber).add(lateQuorumVoteExtension);
+      expect(await this.mock.proposalDeadline(this.id)).to.be.bignumber.equal(extendedBlock);
+
+      expectEvent(
+        tx,
+        'ProposalExtended',
+        { proposalId: this.id, extendedDeadline: extendedBlock },
+      );
+
+      // vote is still active after expected end
+      await time.advanceBlockTo(endBlock.addn(1));
+      expect(await this.mock.state(this.id)).to.be.bignumber.equal(Enums.ProposalState.Active);
+
+      // Still possible to vote
+      await this.mock.castVote(this.id, Enums.VoteType.Against, { from: voter3 });
+
+      // proposal fails
+      await time.advanceBlockTo(extendedBlock.addn(1));
+      expect(await this.mock.state(this.id)).to.be.bignumber.equal(Enums.ProposalState.Defeated);
+    });
+    runGovernorWorkflow();
+  });
+
+  describe('setLateQuorumVoteExtension', function () {
+    beforeEach(async function () {
+      this.newVoteExtension = new BN(0); // disable voting delay extension
+    });
+
+    it('protected', async function () {
+      await expectRevert(
+        this.mock.setLateQuorumVoteExtension(this.newVoteExtension),
+        'Governor: onlyGovernance',
+      );
+    });
+
+    describe('using workflow', function () {
+      beforeEach(async function () {
+        this.settings = {
+          proposal: [
+            [ this.mock.address ],
+            [ web3.utils.toWei('0') ],
+            [ this.mock.contract.methods.setLateQuorumVoteExtension(this.newVoteExtension).encodeABI() ],
+            '<proposal description>',
+          ],
+          proposer,
+          tokenHolder: owner,
+          voters: [
+            { voter: voter1, weight: web3.utils.toWei('1.0'), support: Enums.VoteType.For },
+          ],
+        };
+      });
+      afterEach(async function () {
+        expectEvent(
+          this.receipts.propose,
+          'ProposalCreated',
+          { proposalId: this.id },
+        );
+        expectEvent(
+          this.receipts.execute,
+          'ProposalExecuted',
+          { proposalId: this.id },
+        );
+        expectEvent(
+          this.receipts.execute,
+          'LateQuorumVoteExtensionSet',
+          { oldVoteExtension: lateQuorumVoteExtension, newVoteExtension: this.newVoteExtension },
+        );
+        expect(await this.mock.lateQuorumVoteExtension()).to.be.bignumber.equal(this.newVoteExtension);
+      });
+      runGovernorWorkflow();
+    });
+  });
+});