refactor(contracts): revisit functions visibility and inheritance

Ensure contracts integrating MACI can override certain functions, as well as use public for
functions which are likely to be called from within an inheriting contract. Also remove private for
constants in favour of internal.

contracts/contracts/MACI.sol

@@ -221,7 +221,15 @@ contract MACI is IMACI, Params, Utilities, Ownable {
 
     address _owner = owner();
 
-    address p = pollFactory.deploy(_duration, maxValues, _treeDepths, _coordinatorPubKey, this, topupCredit, _owner);
+    address p = pollFactory.deploy(
+      _duration,
+      maxValues,
+      _treeDepths,
+      _coordinatorPubKey,
+      address(this),
+      topupCredit,
+      _owner
+    );
 
     address mp = messageProcessorFactory.deploy(_verifier, _vkRegistry, p, _owner);
     address tally = tallyFactory.deploy(_verifier, _vkRegistry, p, mp, _owner);

contracts/contracts/MessageProcessor.sol

@@ -29,7 +29,7 @@ contract MessageProcessor is Ownable, SnarkCommon, Hasher, CommonUtilities, IMes
   error BatchEndIndexTooLarge();
 
   // the number of children per node in the merkle trees
-  uint256 private constant TREE_ARITY = 5;
+  uint256 internal constant TREE_ARITY = 5;
 
   /// @inheritdoc IMessageProcessor
   bool public processingComplete;

contracts/contracts/PollFactory.sol

@@ -30,10 +30,10 @@ contract PollFactory is Params, DomainObjs, IPollFactory {
     MaxValues calldata _maxValues,
     TreeDepths calldata _treeDepths,
     PubKey calldata _coordinatorPubKey,
-    IMACI _maci,
+    address _maci,
     TopupCredit _topupCredit,
     address _pollOwner
-  ) public returns (address pollAddr) {
+  ) public virtual returns (address pollAddr) {
     /// @notice Validate _maxValues
     /// maxVoteOptions must be less than 2 ** 50 due to circuit limitations;
     /// it will be packed as a 50-bit value along with other values as one
@@ -46,7 +46,11 @@ contract PollFactory is Params, DomainObjs, IPollFactory {
     AccQueue messageAq = new AccQueueQuinaryMaci(_treeDepths.messageTreeSubDepth);
 
     /// @notice the smart contracts that a Poll would interact with
-    ExtContracts memory extContracts = ExtContracts({ maci: _maci, messageAq: messageAq, topupCredit: _topupCredit });
+    ExtContracts memory extContracts = ExtContracts({
+      maci: IMACI(_maci),
+      messageAq: messageAq,
+      topupCredit: _topupCredit
+    });
 
     // deploy the poll
     Poll poll = new Poll(_duration, _maxValues, _treeDepths, _coordinatorPubKey, extContracts);

contracts/contracts/Tally.sol

@@ -15,7 +15,7 @@ import { CommonUtilities } from "./utilities/CommonUtilities.sol";
 /// @notice The Tally contract is used during votes tallying
 /// and by users to verify the tally results.
 contract Tally is Ownable, SnarkCommon, CommonUtilities, Hasher {
-  uint256 private constant TREE_ARITY = 5;
+  uint256 internal constant TREE_ARITY = 5;
 
   /// @notice The commitment to the tally results. Its initial value is 0, but after
   /// the tally of each batch is proven on-chain via a zk-SNARK, it should be

contracts/contracts/TallyFactory.sol

@@ -14,7 +14,7 @@ contract TallyFactory is ITallySubsidyFactory {
     address _poll,
     address _messageProcessor,
     address _owner
-  ) public returns (address tallyAddr) {
+  ) public virtual returns (address tallyAddr) {
     // deploy Tally for this Poll
     Tally tally = new Tally(_verifier, _vkRegistry, _poll, _messageProcessor);
     tally.transferOwnership(_owner);

contracts/contracts/TallyNonQv.sol

@@ -15,7 +15,7 @@ import { CommonUtilities } from "./utilities/CommonUtilities.sol";
 /// @notice The TallyNonQv contract is used during votes tallying
 /// and by users to verify the tally results.
 contract TallyNonQv is Ownable, SnarkCommon, CommonUtilities, Hasher {
-  uint256 private constant TREE_ARITY = 5;
+  uint256 internal constant TREE_ARITY = 5;
 
   /// @notice The commitment to the tally results. Its initial value is 0, but after
   /// the tally of each batch is proven on-chain via a zk-SNARK, it should be
@@ -79,7 +79,7 @@ contract TallyNonQv is Ownable, SnarkCommon, CommonUtilities, Hasher {
 
   /// @notice Check if all ballots are tallied
   /// @return tallied whether all ballots are tallied
-  function isTallied() external view returns (bool tallied) {
+  function isTallied() public view returns (bool tallied) {
     (uint8 intStateTreeDepth, , , ) = poll.treeDepths();
     (uint256 numSignUps, ) = poll.numSignUpsAndMessages();
 

contracts/contracts/TallyNonQvFactory.sol

@@ -14,7 +14,7 @@ contract TallyNonQvFactory is ITallySubsidyFactory {
     address _poll,
     address _messageProcessor,
     address _owner
-  ) public returns (address tallyAddr) {
+  ) public virtual returns (address tallyAddr) {
     // deploy Tally for this Poll
     TallyNonQv tally = new TallyNonQv(_verifier, _vkRegistry, _poll, _messageProcessor);
     tally.transferOwnership(_owner);

contracts/contracts/interfaces/IPollFactory.sol

@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.10;
 
-import { IMACI } from "./IMACI.sol";
 import { TopupCredit } from "../TopupCredit.sol";
 import { Params } from "../utilities/Params.sol";
 import { DomainObjs } from "../utilities/DomainObjs.sol";
@@ -23,7 +22,7 @@ interface IPollFactory {
     Params.MaxValues memory _maxValues,
     Params.TreeDepths memory _treeDepths,
     DomainObjs.PubKey memory _coordinatorPubKey,
-    IMACI _maci,
+    address _maci,
     TopupCredit _topupCredit,
     address _pollOwner
   ) external returns (address);