DAO accounting for the nouns fungible token

packages/nouns-contracts/contracts/governance/NounsDAOAdmin.sol

@@ -461,6 +461,15 @@ library NounsDAOAdmin {
      */
     function _setErc20TokensToIncludeInFork(address[] calldata erc20tokens) public onlyAdmin {
         checkForDuplicates(erc20tokens);
+        address fungibleToken = ds().nounsFungibleToken;
+        if (fungibleToken != address(0)) {
+            for (uint256 i = 0; i < erc20tokens.length; i++) {
+                require(
+                    erc20tokens[i] != fungibleToken,
+                    'NounsDAO::_setErc20TokensToIncludeInFork: cannot include fungible token'
+                );
+            }
+        }
 
         emit ERC20TokensToIncludeInForkSet(ds().erc20TokensToIncludeInFork, erc20tokens);
 
@@ -537,12 +546,10 @@ library NounsDAOAdmin {
     }
 
     /**
-     * @notice Admin function for zeroing out the state variable `voteSnapshotBlockSwitchProposalId`
-     * @dev We want to zero-out this state slot so we can remove this temporary variable from contract code and 
-     * be ready to reuse this slot.
+     * @notice Admin function for setting the canonical Nouns Fungible Token address
      */
-    function _zeroOutVoteSnapshotBlockSwitchProposalId() external onlyAdmin {
-        ds().voteSnapshotBlockSwitchProposalId = 0;
+    function _setNounsFungibleToken(address newNounsFungibleToken) public onlyAdmin {
+        ds().nounsFungibleToken = newNounsFungibleToken;
     }
 
     function _writeQuorumParamsCheckpoint(NounsDAOTypes.DynamicQuorumParams memory params) internal {

packages/nouns-contracts/contracts/governance/NounsDAOInterfaces.sol

@@ -404,9 +404,8 @@ interface NounsDAOTypes {
         uint256 forkThresholdBPS;
         /// @notice Address of the original timelock
         INounsDAOExecutor timelockV1;
-        /// @dev Make sure this stays the last variable in this struct, so we can delete it in the next version
-        /// @dev To be zeroed-out in the upcoming DAO upgrade.
-        uint256 voteSnapshotBlockSwitchProposalId;
+        /// @notice The address of the Nouns-backed ERC20 token
+        address nounsFungibleToken;
     }
 
     struct Proposal {

packages/nouns-contracts/contracts/governance/NounsDAOLogicV4.sol

@@ -925,9 +925,5 @@ contract NounsDAOLogicV4 is NounsDAOStorage, NounsDAOEventsV3 {
         return address(ds.timelockV1);
     }
 
-    function voteSnapshotBlockSwitchProposalId() public view returns (uint256) {
-        return ds.voteSnapshotBlockSwitchProposalId;
-    }
-
     receive() external payable {}
 }

packages/nouns-contracts/contracts/governance/fork/NounsDAOFork.sol

@@ -21,6 +21,10 @@ import { NounsDAOTypes, INounsDAOForkEscrow, INounsDAOExecutorV2 } from '../Noun
 import { IERC20 } from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
 import { NounsTokenFork } from './newdao/token/NounsTokenFork.sol';
 
+interface NounsFungibleToken {
+    function balanceToBackingNFTCount(address account) external view returns (uint256);
+}
+
 library NounsDAOFork {
     error ForkThresholdNotMet();
     error ForkPeriodNotActive();
@@ -220,7 +224,16 @@ library NounsDAOFork {
      * This is used when calculating proposal threshold, quorum, fork threshold & treasury split.
      */
     function adjustedTotalSupply(NounsDAOTypes.Storage storage ds) internal view returns (uint256) {
-        return ds.nouns.totalSupply() - ds.nouns.balanceOf(address(ds.timelock)) - ds.forkEscrow.numTokensOwnedByDAO();
+        uint256 nounsHeldViaFungibleToken = 0;
+        address tokenAddress = ds.nounsFungibleToken;
+        if (tokenAddress != address(0)) {
+            nounsHeldViaFungibleToken = NounsFungibleToken(tokenAddress).balanceToBackingNFTCount(address(ds.timelock));
+        }
+        return
+            ds.nouns.totalSupply() -
+            ds.nouns.balanceOf(address(ds.timelock)) -
+            ds.forkEscrow.numTokensOwnedByDAO() -
+            nounsHeldViaFungibleToken;
     }
 
     /**

packages/nouns-contracts/test/foundry/NounsDAOLogic/NounsDAOAdmin.t.sol

@@ -349,18 +349,6 @@ contract NounsDAOLogicAdminTest is NounsDAOLogicBaseTest {
         assertEq(dao.forkThresholdBPS(), 42);
     }
 
-    function test__zeroOutVoteSnapshotBlockSwitchProposalId_onlyAdmin() public {
-        vm.expectRevert(NounsDAOAdmin.AdminOnly.selector);
-        dao._zeroOutVoteSnapshotBlockSwitchProposalId();
-    }
-
-    function test__zeroOutVoteSnapshotBlockSwitchProposalId_works() public {
-        vm.prank(address(dao.timelock()));
-        dao._zeroOutVoteSnapshotBlockSwitchProposalId();
-
-        assertEq(dao.voteSnapshotBlockSwitchProposalId(), 0);
-    }
-
     function test_setErc20TokensToIncludeInFork_onlyAdmin() public {
         tokens = [address(1), address(2)];
 

packages/nouns-contracts/test/foundry/Upgrade/UpgradeMainnetFork.t.sol

@@ -44,6 +44,11 @@ abstract contract UpgradeMainnetForkBaseTest is Test {
         vm.deal(address(NOUNS_DAO_PROXY_MAINNET), 100 ether);
         vm.fee(50 gwei);
         vm.txGasPrice(50 gwei);
+
+        // zero-out the slot where `voteSnapshotBlockSwitchProposalId` was
+        // as will happen in the upcoming upgrade
+        // so that `nounsFungibleToken` will be address(0) by default
+        vm.store(address(NOUNS_DAO_PROXY_MAINNET), bytes32(uint256(0x19)), bytes32(uint256(0)));
     }
 
     function propose(
@@ -177,20 +182,6 @@ contract DAOUpgradeMainnetForkTest is UpgradeMainnetForkBaseTest {
         assertEq(expectedVotingDelay, NOUNS_DAO_PROXY_MAINNET.votingDelay());
     }
 
-    function test_voteSnapshotBlockSwitchProposalId_zeroOutWorks() public {
-        assertNotEq(NOUNS_DAO_PROXY_MAINNET.voteSnapshotBlockSwitchProposalId(), 0);
-
-        uint256 proposalId = propose(
-            address(NOUNS_DAO_PROXY_MAINNET),
-            0,
-            '_zeroOutVoteSnapshotBlockSwitchProposalId()',
-            ''
-        );
-        voteAndExecuteProposal(proposalId);
-
-        assertEq(NOUNS_DAO_PROXY_MAINNET.voteSnapshotBlockSwitchProposalId(), 0);
-    }
-
     function test_clientId_savedOnProposals() public {
         uint32 expectedClientId = 42;
         uint256 proposalId = propose(address(NOUNS_DAO_PROXY_MAINNET), 0, '', '', expectedClientId);