feat(contracts): allow for dynamic emptyBallotRoots (#1695)

Pass emptyBallotRoots as argument to the maci contract and then the specific ballot root to each
deployed poll based on the vote option tree depth. This simplifies the process and does not require
setting a .env variable before deploying contracts.

.github/workflows/e2e.yml

@@ -5,9 +5,6 @@ on:
     branches: [dev]
   pull_request:
 
-env:
-  STATE_TREE_DEPTH: ${{ vars.STATE_TREE_DEPTH }}
-
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true

.github/workflows/release.yml

@@ -4,9 +4,6 @@ on:
   push:
     tags: ["*"]
 
-env:
-  STATE_TREE_DEPTH: ${{ vars.STATE_TREE_DEPTH }}
-
 jobs:
   draft-release:
     runs-on: ubuntu-22.04

contracts/contracts/MACI.sol

@@ -33,6 +33,9 @@ contract MACI is IMACI, DomainObjs, Params, Utilities {
   uint256 internal constant BLANK_STATE_LEAF_HASH =
     uint256(6769006970205099520508948723718471724660867171122235270773600567925038008762);
 
+  /// @notice The roots of the empty ballot trees
+  uint256[5] public emptyBallotRoots;
+
   /// @notice Each poll has an incrementing ID
   uint256 public nextPollId;
 
@@ -96,13 +99,15 @@ contract MACI is IMACI, DomainObjs, Params, Utilities {
   /// @param _signUpGatekeeper The SignUpGatekeeper contract
   /// @param _initialVoiceCreditProxy The InitialVoiceCreditProxy contract
   /// @param _stateTreeDepth The depth of the state tree
+  /// @param _emptyBallotRoots The roots of the empty ballot trees
   constructor(
     IPollFactory _pollFactory,
     IMessageProcessorFactory _messageProcessorFactory,
     ITallyFactory _tallyFactory,
     SignUpGatekeeper _signUpGatekeeper,
     InitialVoiceCreditProxy _initialVoiceCreditProxy,
-    uint8 _stateTreeDepth
+    uint8 _stateTreeDepth,
+    uint256[5] memory _emptyBallotRoots
   ) payable {
     // initialize and insert the blank leaf
     InternalLazyIMT._init(lazyIMTData, _stateTreeDepth);
@@ -115,6 +120,7 @@ contract MACI is IMACI, DomainObjs, Params, Utilities {
     initialVoiceCreditProxy = _initialVoiceCreditProxy;
     stateTreeDepth = _stateTreeDepth;
     maxSignups = uint256(TREE_ARITY) ** uint256(_stateTreeDepth);
+    emptyBallotRoots = _emptyBallotRoots;
 
     // Verify linked poseidon libraries
     if (hash2([uint256(1), uint256(1)]) == 0) revert PoseidonHashLibrariesNotLinked();
@@ -191,18 +197,24 @@ contract MACI is IMACI, DomainObjs, Params, Utilities {
       revert InvalidPubKey();
     }
 
+    uint256 voteOptionTreeDepth = _treeDepths.voteOptionTreeDepth;
+
     MaxValues memory maxValues = MaxValues({
       maxMessages: uint256(MESSAGE_TREE_ARITY) ** _treeDepths.messageTreeDepth,
-      maxVoteOptions: uint256(MESSAGE_TREE_ARITY) ** _treeDepths.voteOptionTreeDepth
+      maxVoteOptions: uint256(MESSAGE_TREE_ARITY) ** voteOptionTreeDepth
     });
 
-    // the owner of the message processor and tally contract will be the msg.sender
-    address _msgSender = msg.sender;
-
-    address p = pollFactory.deploy(_duration, maxValues, _treeDepths, _coordinatorPubKey, address(this));
-
-    address mp = messageProcessorFactory.deploy(_verifier, _vkRegistry, p, _msgSender, _mode);
-    address tally = tallyFactory.deploy(_verifier, _vkRegistry, p, mp, _msgSender, _mode);
+    address p = pollFactory.deploy(
+      _duration,
+      maxValues,
+      _treeDepths,
+      _coordinatorPubKey,
+      address(this),
+      emptyBallotRoots[voteOptionTreeDepth - 1]
+    );
+
+    address mp = messageProcessorFactory.deploy(_verifier, _vkRegistry, p, msg.sender, _mode);
+    address tally = tallyFactory.deploy(_verifier, _vkRegistry, p, mp, msg.sender, _mode);
 
     polls[pollId] = p;
 

contracts/contracts/Poll.sol

@@ -3,7 +3,6 @@ pragma solidity ^0.8.20;
 
 import { Params } from "./utilities/Params.sol";
 import { SnarkCommon } from "./crypto/SnarkCommon.sol";
-import { EmptyBallotRoots } from "./trees/EmptyBallotRoots.sol";
 import { IPoll } from "./interfaces/IPoll.sol";
 import { Utilities } from "./utilities/Utilities.sol";
 import { CurveBabyJubJub } from "./crypto/BabyJubJub.sol";
@@ -13,7 +12,7 @@ import { CurveBabyJubJub } from "./crypto/BabyJubJub.sol";
 /// which can be either votes or key change messages.
 /// @dev Do not deploy this directly. Use PollFactory.deploy() which performs some
 /// checks on the Poll constructor arguments.
-contract Poll is Params, Utilities, SnarkCommon, EmptyBallotRoots, IPoll {
+contract Poll is Params, Utilities, SnarkCommon, IPoll {
   /// @notice Whether the Poll has been initialized
   bool internal isInit;
 
@@ -32,6 +31,9 @@ contract Poll is Params, Utilities, SnarkCommon, EmptyBallotRoots, IPoll {
   // The duration of the polling period, in seconds
   uint256 internal immutable duration;
 
+  /// @notice The root of the empty ballot tree at a given voteOptionTree depth
+  uint256 public immutable emptyBallotRoot;
+
   /// @notice Whether the MACI contract's stateAq has been merged by this contract
   bool public stateMerged;
 
@@ -89,7 +91,8 @@ contract Poll is Params, Utilities, SnarkCommon, EmptyBallotRoots, IPoll {
     MaxValues memory _maxValues,
     TreeDepths memory _treeDepths,
     PubKey memory _coordinatorPubKey,
-    ExtContracts memory _extContracts
+    ExtContracts memory _extContracts,
+    uint256 _emptyBallotRoot
   ) payable {
     // check that the coordinator public key is valid
     if (!CurveBabyJubJub.isOnCurve(_coordinatorPubKey.x, _coordinatorPubKey.y)) {
@@ -110,6 +113,8 @@ contract Poll is Params, Utilities, SnarkCommon, EmptyBallotRoots, IPoll {
     treeDepths = _treeDepths;
     // Record the current timestamp
     deployTime = block.timestamp;
+    // store the empty ballot root
+    emptyBallotRoot = _emptyBallotRoot;
   }
 
   /// @notice A modifier that causes the function to revert if the voting period is
@@ -207,7 +212,7 @@ contract Poll is Params, Utilities, SnarkCommon, EmptyBallotRoots, IPoll {
     // Set currentSbCommitment
     uint256[3] memory sb;
     sb[0] = _mergedStateRoot;
-    sb[1] = emptyBallotRoots[treeDepths.voteOptionTreeDepth - 1];
+    sb[1] = emptyBallotRoot;
     sb[2] = uint256(0);
 
     currentSbCommitment = hash3(sb);

contracts/contracts/PollFactory.sol

@@ -26,7 +26,8 @@ contract PollFactory is Params, DomainObjs, IPollFactory {
     MaxValues calldata _maxValues,
     TreeDepths calldata _treeDepths,
     PubKey calldata _coordinatorPubKey,
-    address _maci
+    address _maci,
+    uint256 _emptyBallotRoot
   ) public virtual returns (address pollAddr) {
     /// @notice Validate _maxValues
     /// maxVoteOptions must be less than 2 ** 50 due to circuit limitations;
@@ -43,7 +44,7 @@ contract PollFactory is Params, DomainObjs, IPollFactory {
     ExtContracts memory extContracts = ExtContracts({ maci: IMACI(_maci), messageAq: messageAq });
 
     // deploy the poll
-    Poll poll = new Poll(_duration, _maxValues, _treeDepths, _coordinatorPubKey, extContracts);
+    Poll poll = new Poll(_duration, _maxValues, _treeDepths, _coordinatorPubKey, extContracts, _emptyBallotRoot);
 
     // Make the Poll contract own the messageAq contract, so only it can
     // run enqueue/merge

contracts/contracts/interfaces/IPollFactory.sol

@@ -13,12 +13,14 @@ interface IPollFactory {
   /// @param _treeDepths The depths of the merkle trees
   /// @param _coordinatorPubKey The coordinator's public key
   /// @param _maci The MACI contract interface reference
+  /// @param _emptyBallotRoot The root of the empty ballot tree
   /// @return The deployed Poll contract
   function deploy(
     uint256 _duration,
     Params.MaxValues memory _maxValues,
     Params.TreeDepths memory _treeDepths,
     DomainObjs.PubKey memory _coordinatorPubKey,
-    address _maci
+    address _maci,
+    uint256 _emptyBallotRoot
   ) external returns (address);
 }

contracts/package.json

@@ -101,7 +101,6 @@
     "@nomicfoundation/hardhat-ethers": "^3.0.6",
     "@nomicfoundation/hardhat-toolbox": "^5.0.0",
     "@openzeppelin/contracts": "^5.0.2",
-    "@zk-kit/imt.sol": "2.0.0-beta.12",
     "circomlibjs": "^0.1.7",
     "ethers": "^6.13.1",
     "hardhat": "^2.22.6",

contracts/scripts/compileSol.ts

@@ -4,7 +4,6 @@ import fs from "fs";
 import path from "path";
 
 import { buildPoseidonT3, buildPoseidonT4, buildPoseidonT5, buildPoseidonT6 } from "../ts/buildPoseidon";
-import { genEmptyBallotRootsContract } from "../ts/genEmptyBallotRootsContract";
 import { genZerosContract } from "../ts/genZerosContract";
 
 const PATHS = [
@@ -75,10 +74,6 @@ async function main(): Promise<void> {
     ),
   );
 
-  await genEmptyBallotRootsContract().then((text) =>
-    fs.promises.writeFile(path.resolve(__dirname, "..", "contracts/trees/EmptyBallotRoots.sol"), `${text}\n`),
-  );
-
   await hre.run("compile");
 
   await Promise.all([buildPoseidonT3(), buildPoseidonT4(), buildPoseidonT5(), buildPoseidonT6()]);

contracts/tasks/deploy/maci/08-maci.ts

@@ -6,6 +6,7 @@ import type {
   SemaphoreGatekeeper,
 } from "../../../typechain-types";
 
+import { genEmptyBallotRoots } from "../../../ts/genEmptyBallotRoots";
 import { ContractStorage } from "../../helpers/ContractStorage";
 import { Deployment } from "../../helpers/Deployment";
 import { EContracts, IDeployParams } from "../../helpers/types";
@@ -62,6 +63,8 @@ deployment.deployTask("full:deploy-maci", "Deploy MACI contract").then((task) =>
     const stateTreeDepth =
       deployment.getDeployConfigField<number | null>(EContracts.MACI, "stateTreeDepth") ?? DEFAULT_STATE_TREE_DEPTH;
 
+    const emptyBallotRoots = genEmptyBallotRoots(stateTreeDepth);
+
     const maciContract = await deployment.deployContractWithLinkedLibraries<MACI>(
       { contractFactory: maciContractFactory },
       pollFactoryContractAddress,
@@ -70,6 +73,7 @@ deployment.deployTask("full:deploy-maci", "Deploy MACI contract").then((task) =>
       gatekeeperContractAddress,
       constantInitialVoiceCreditProxyContractAddress,
       stateTreeDepth,
+      emptyBallotRoots,
     );
 
     if (gatekeeper === EContracts.EASGatekeeper) {
@@ -115,6 +119,7 @@ deployment.deployTask("full:deploy-maci", "Deploy MACI contract").then((task) =>
         gatekeeperContractAddress,
         constantInitialVoiceCreditProxyContractAddress,
         stateTreeDepth,
+        emptyBallotRoots,
       ],
       network: hre.network.name,
     });

contracts/tests/PollFactory.test.ts

@@ -2,17 +2,20 @@ import { expect } from "chai";
 import { BaseContract, Signer, ZeroAddress } from "ethers";
 import { Keypair } from "maci-domainobjs";
 
-import { deployPollFactory, getDefaultSigner } from "../ts";
+import { deployPollFactory, genEmptyBallotRoots, getDefaultSigner } from "../ts";
 import { PollFactory } from "../typechain-types";
 
-import { maxValues, treeDepths } from "./constants";
+import { maxValues, STATE_TREE_DEPTH, treeDepths } from "./constants";
 
 describe("pollFactory", () => {
   let pollFactory: PollFactory;
   let signer: Signer;
 
   const { pubKey: coordinatorPubKey } = new Keypair();
 
+  const emptyBallotRoots = genEmptyBallotRoots(STATE_TREE_DEPTH);
+  const emptyBallotRoot = emptyBallotRoots[treeDepths.voteOptionTreeDepth];
+
   before(async () => {
     signer = await getDefaultSigner();
     pollFactory = (await deployPollFactory(signer, true)) as BaseContract as PollFactory;
@@ -26,6 +29,7 @@ describe("pollFactory", () => {
         treeDepths,
         coordinatorPubKey.asContractParam(),
         ZeroAddress,
+        emptyBallotRoot,
       );
       const receipt = await tx.wait();
       expect(receipt?.status).to.eq(1);
@@ -42,6 +46,7 @@ describe("pollFactory", () => {
           treeDepths,
           coordinatorPubKey.asContractParam(),
           ZeroAddress,
+          emptyBallotRoot,
         ),
       ).to.be.revertedWithCustomError(pollFactory, "InvalidMaxValues");
     });

contracts/ts/deploy.ts

@@ -33,6 +33,7 @@ import {
   SemaphoreGatekeeper,
 } from "../typechain-types";
 
+import { genEmptyBallotRoots } from "./genEmptyBallotRoots";
 import { log } from "./utils";
 
 /**
@@ -271,6 +272,8 @@ export const deployMaci = async ({
   stateTreeDepth = 10,
   quiet = true,
 }: IDeployMaciArgs): Promise<IDeployedMaci> => {
+  const emptyBallotRoots = genEmptyBallotRoots(stateTreeDepth);
+
   const { PoseidonT3Contract, PoseidonT4Contract, PoseidonT5Contract, PoseidonT6Contract } =
     await deployPoseidonContracts(signer, poseidonAddresses, quiet);
 
@@ -328,6 +331,7 @@ export const deployMaci = async ({
     signUpTokenGatekeeperContractAddress,
     initialVoiceCreditBalanceAddress,
     stateTreeDepth,
+    emptyBallotRoots,
   );
 
   return {

contracts/ts/genEmptyBallotRoots.ts

@@ -0,0 +1,22 @@
+import { STATE_TREE_ARITY } from "maci-core";
+import { IncrementalQuinTree, hash2 } from "maci-crypto";
+import { Ballot } from "maci-domainobjs";
+
+/**
+ * Generate empty ballot roots for a given state tree depth
+ * @param stateTreeDepth The depth of the state tree
+ * @returns The empty ballot roots
+ */
+export const genEmptyBallotRoots = (stateTreeDepth: number): bigint[] => {
+  const roots: bigint[] = [];
+
+  for (let i = 0; i < 5; i += 1) {
+    const ballot = new Ballot(0, i + 1);
+    // The empty Ballot tree root
+    const ballotTree = new IncrementalQuinTree(stateTreeDepth, ballot.hash(), STATE_TREE_ARITY, hash2);
+
+    roots.push(ballotTree.root);
+  }
+
+  return roots;
+};

contracts/ts/index.ts

@@ -16,6 +16,7 @@ export {
   deployVerifier,
 } from "./deploy";
 export { genMaciStateFromContract } from "./genMaciState";
+export { genEmptyBallotRoots } from "./genEmptyBallotRoots";
 export { formatProofForVerifierContract, getDefaultSigner, getDefaultNetwork, getSigners } from "./utils";
 export { EMode } from "./constants";
 export { Deployment } from "../tasks/helpers/Deployment";