Merge pull request #888 from lidofinance/committee-replace-bitmap

fix: use array instead of bitmap

contracts/0.8.25/vaults/Delegation.sol

@@ -392,32 +392,67 @@ contract Delegation is Dashboard, IReportReceiver {
     }
 
     /**
-     * @dev Modifier that requires approval from all committee members within a voting period.
-     * Uses a bitmap to track new votes within the call instead of updating storage immediately.
-     * @param _committee Array of role identifiers that form the voting committee.
-     * @param _votingPeriod Time window in seconds during which votes remain valid.
+     * @dev Modifier that implements a mechanism for multi-role committee approval.
+     * Each unique function call (identified by msg.data: selector + arguments) requires
+     * approval from all committee role members within a specified time window.
+     *
+     * The voting process works as follows:
+     * 1. When a committee member calls the function:
+     *    - Their vote is counted immediately
+     *    - If not enough votes exist, their vote is recorded
+     *    - If they're not a committee member, the call reverts
+     *
+     * 2. Vote counting:
+     *    - Counts the current caller's votes if they're a committee member
+     *    - Counts existing votes that are within the voting period
+     *    - All votes must occur within the same voting period window
+     *
+     * 3. Execution:
+     *    - If all committee members have voted within the period, executes the function
+     *    - On successful execution, clears all voting state for this call
+     *    - If not enough votes, stores the current votes
+     *    - Thus, if the caller has all the roles, the function is executed immediately
+     *
+     * 4. Gas Optimization:
+     *    - Votes are stored in a deferred manner using a memory array
+     *    - Vote storage writes only occur if the function cannot be executed immediately
+     *    - This prevents unnecessary storage writes when all votes are present,
+     *      because the votes are cleared anyway after the function is executed,
+     *    - i.e. this optimization is beneficial for the deciding caller and
+     *      saves 1 storage write for each role the deciding caller has
+     *
+     * @param _committee Array of role identifiers that form the voting committee
+     * @param _votingPeriod Time window in seconds during which votes remain valid
+     *
+     * @notice Votes expire after the voting period and must be recast
+     * @notice All committee members must vote within the same voting period
+     * @notice Only committee members can initiate votes
+     *
+     * @custom:security-note Each unique function call (including parameters) requires its own set of votes
      */
     modifier onlyIfVotedBy(bytes32[] memory _committee, uint256 _votingPeriod) {
         bytes32 callId = keccak256(msg.data);
         uint256 committeeSize = _committee.length;
         uint256 votingStart = block.timestamp - _votingPeriod;
         uint256 voteTally = 0;
-        uint256 votesToUpdateBitmap = 0;
+        bool[] memory deferredVotes = new bool[](committeeSize);
+        bool isCommitteeMember = false;
 
         for (uint256 i = 0; i < committeeSize; ++i) {
             bytes32 role = _committee[i];
 
             if (super.hasRole(role, msg.sender)) {
+                isCommitteeMember = true;
                 voteTally++;
-                votesToUpdateBitmap |= (1 << i);
+                deferredVotes[i] = true;
 
                 emit RoleMemberVoted(msg.sender, role, block.timestamp, msg.data);
             } else if (votings[callId][role] >= votingStart) {
                 voteTally++;
             }
         }
 
-        if (votesToUpdateBitmap == 0) revert NotACommitteeMember();
+        if (!isCommitteeMember) revert NotACommitteeMember();
 
         if (voteTally == committeeSize) {
             for (uint256 i = 0; i < committeeSize; ++i) {
@@ -427,7 +462,7 @@ contract Delegation is Dashboard, IReportReceiver {
             _;
         } else {
             for (uint256 i = 0; i < committeeSize; ++i) {
-                if ((votesToUpdateBitmap & (1 << i)) != 0) {
+                if (deferredVotes[i]) {
                     bytes32 role = _committee[i];
                     votings[callId][role] = block.timestamp;
                 }