emit Transfer event on flow create/delete and units changing from/to 0

Author: d10r

packages/ethereum-contracts/contracts/agreements/ConstantFlowAgreementV1.sol

@@ -453,6 +453,13 @@ contract ConstantFlowAgreementV1 is
                 ctx, currentContext);
         }
 
+        if (
+            oldFlowData.flowRate == 0 && flowParams.flowRate != 0 ||
+            oldFlowData.flowRate != 0 && flowParams.flowRate == 0
+        ) {
+            flowVars.token.emitZeroTransfer(flowVars.sender, flowVars.receiver);
+        }
+
         _requireAvailableBalance(flowVars.token, flowVars.sender, currentContext);
     }
 

packages/ethereum-contracts/contracts/agreements/gdav1/GeneralDistributionAgreementV1.sol

@@ -801,6 +801,14 @@ contract GeneralDistributionAgreementV1 is AgreementBase, TokenMonad, IGeneralDi
         return true;
     }
 
+    function tokenEmitZeroTransfer(ISuperfluidToken superToken, address from, address to) external {
+        if (superToken.isPool(this, msg.sender) == false) {
+            revert GDA_ONLY_SUPER_TOKEN_POOL();
+        }
+
+        superToken.emitZeroTransfer(from, to);
+    }
+
     //////////////////////////////////////////////////////////////////////////////////////////////////////
     // TokenMonad interface
     //////////////////////////////////////////////////////////////////////////////////////////////////////

packages/ethereum-contracts/contracts/agreements/gdav1/SuperfluidPool.sol

@@ -453,6 +453,11 @@ contract SuperfluidPool is ISuperfluidPool, BeaconProxiable {
             _membersData[memberAddr] = _pdPoolMemberToMemberData(pdPoolMember, claimedValue);
             assert(GDA.appendIndexUpdateByPool(superToken, p, t));
         }
+
+        if (oldUnits == 0 && newUnits != 0 || oldUnits != 0 && newUnits == 0) {
+            GDA.tokenEmitZeroTransfer(superToken, memberAddr, address(0));
+        }
+
         emit MemberUnitsUpdated(superToken, memberAddr, oldUnits, newUnits);
     }
 

packages/ethereum-contracts/contracts/interfaces/superfluid/ISuperfluidToken.sol

@@ -431,4 +431,11 @@ interface ISuperfluidToken {
         uint256 rewardAmount,
         uint256 bailoutAmount
     );
+
+    /**
+     * @dev Emit an ERC20.Transfer event with zero amount, helps indexers track token holders.
+     * @param from The address from which the transfer is happening
+     * @param to The address to which the transfer is happening
+     */
+    function emitZeroTransfer(address from, address to) external;
 }

packages/ethereum-contracts/contracts/superfluid/SuperfluidToken.sol

@@ -376,6 +376,10 @@ abstract contract SuperfluidToken is ISuperfluidToken
         );
     }
 
+    function emitZeroTransfer(address from, address to) external onlyAgreement {
+        emit IERC20.Transfer(from, to, 0);
+    }
+
     /**************************************************************************
     * Modifiers
     *************************************************************************/