Use old validator set nonce instead of latest nonce. (#121)

* Use old validator set nonce instead of latest nonce.

* Update go wrapper.

src/QuantumGravityBridge.sol

@@ -243,12 +243,15 @@ contract QuantumGravityBridge is IDAOracle {
     ///
     /// The validator set hash that is signed over is domain separated as per
     /// `domainSeparateValidatorSetHash`.
-    /// @param _newValidatorSetHash The hash of the new validator set.
     /// @param _newNonce The new event nonce.
+    /// @param _oldNonce The nonce of the latest update to the validator set.
+    /// @param _newPowerThreshold At least this much power must have signed.
+    /// @param _newValidatorSetHash The hash of the new validator set.
     /// @param _currentValidatorSet The current validator set.
     /// @param _sigs Signatures.
     function updateValidatorSet(
         uint256 _newNonce,
+        uint256 _oldNonce,
         uint256 _newPowerThreshold,
         bytes32 _newValidatorSetHash,
         Validator[] calldata _currentValidatorSet,
@@ -272,7 +275,7 @@ contract QuantumGravityBridge is IDAOracle {
         // Check that the supplied current validator set matches the saved checkpoint.
         bytes32 currentValidatorSetHash = computeValidatorSetHash(_currentValidatorSet);
         if (
-            domainSeparateValidatorSetHash(BRIDGE_ID, currentNonce, currentPowerThreshold, currentValidatorSetHash) !=
+            domainSeparateValidatorSetHash(BRIDGE_ID, _oldNonce, currentPowerThreshold, currentValidatorSetHash) !=
             state_lastValidatorSetCheckpoint
         ) {
             revert SuppliedValidatorSetInvalid();

src/test/QuantumGravityBridge.t.sol

@@ -47,6 +47,8 @@ contract RelayerTest is DSTest {
     }
 
     function testUpdateValidatorSet() public {
+        uint256 initialVelsetNonce = 0;
+
         // Save the old test validator set before we add to it.
         Validator[] memory oldVS = new Validator[](1);
         oldVS[0] = Validator(cheats.addr(testPriv1), votingPower);
@@ -64,7 +66,7 @@ contract RelayerTest is DSTest {
         (uint8 v, bytes32 r, bytes32 s) = cheats.sign(testPriv1, digest_eip191);
         sigs[0] = Signature(v, r, s);
 
-        bridge.updateValidatorSet(newNonce, newPowerThreshold, newVSHash, oldVS, sigs);
+        bridge.updateValidatorSet(newNonce, initialVelsetNonce, newPowerThreshold, newVSHash, oldVS, sigs);
 
         assertEq(bridge.state_eventNonce(), newNonce);
         assertEq(bridge.state_powerThreshold(), newPowerThreshold);