v4 patch

contracts/v4-patch/GovernancePatchUpgrade.sol

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.6.0;
+pragma experimental ABIEncoderV2;
+
+import "../v1/Governance.sol";
+import "../v3-relayer-registry/GovernanceStakingUpgrade.sol";
+
+contract GovernancePatchProposal is GovernanceStakingUpgrade {
+  mapping(uint256 => bytes32) public _proposalCodeHashes;
+
+  event CodeHashDifferent(address target, bytes32 oldHash, bytes32 newHash);
+
+  function execute(uint256 proposalId) external payable virtual override(Governance) {
+    Proposal storage proposal = proposals[proposalId];
+
+    if (proposal.target.codehash == _proposalCodeHashes[proposalId]) {
+      super.execute(proposalId);
+    } else {
+      proposal.executed = true;
+      emit CodeHashDifferent(proposal.target, _proposalCodeHashes[proposalId], proposal.target.codehash);
+    }
+  }
+
+  function _propose(
+    address proposer,
+    address target,
+    string memory description
+  ) internal virtual override(Governance) {
+    uint256 proposalId = super._propose(proposer, target, description);
+    _proposalCodeHashes[proposalId] = target.codeHash;
+  }
+}