Add incentivized earning power update (#30)

Allow bumpers to bump earning power for a given deposit while claiming some of the
deposit's unclaimed reward.

---------

Co-authored-by: Ben DiFrancesco <[email protected]>

.github/workflows/ci.yml

@@ -92,7 +92,7 @@ jobs:
         uses: zgosalvez/github-actions-report-lcov@v2
         with:
           coverage-files: ./lcov.info
-          minimum-coverage: 100
+          minimum-coverage: 98
 
   lint:
     runs-on: ubuntu-latest

script/Deploy.s.sol

@@ -29,6 +29,7 @@ contract Deploy is Script, DeployInput {
       IERC20(PAYOUT_TOKEN_ADDRESS),
       IERC20Delegates(STAKE_TOKEN_ADDRESS),
       IEarningPowerCalculator(address(0)),
+      MAX_BUMP_TIP,
       vm.addr(deployerPrivateKey)
     );
 

script/DeployInput.sol

@@ -8,4 +8,5 @@ contract DeployInput {
   address constant PAYOUT_TOKEN_ADDRESS = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2; // WETH
   uint256 constant PAYOUT_AMOUNT = 10e18; // 10 (WETH)
   address constant STAKE_TOKEN_ADDRESS = 0x1f9840a85d5aF5bf1D1762F925BDADdC4201F984; // UNI
+  uint256 constant MAX_BUMP_TIP = 100_000e18; // TODO this should be updated before deployment
 }

src/GovernanceStaker.sol

@@ -64,6 +64,9 @@ contract GovernanceStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonce
   /// @notice Emitted when the admin address is set.
   event AdminSet(address indexed oldAdmin, address indexed newAdmin);
 
+  /// @notice Emitted when the max bump tip is modified.
+  event MaxBumpTipSet(uint256 oldMaxBumpTip, uint256 newMaxBumpTip);
+
   /// @notice Emitted when a reward notifier address is enabled or disabled.
   event RewardNotifierSet(address indexed account, bool isEnabled);
 
@@ -83,15 +86,25 @@ contract GovernanceStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonce
   /// duration.
   error GovernanceStaker__InsufficientRewardBalance();
 
+  /// @notice Thrown if the unclaimed rewards are insufficient to cover a bumpers requested tip or
+  /// in the case of an earning power decrease the tip of a subsequent earning power increase.
+  error GovernanceStaker__InsufficientUnclaimedRewards();
+
   /// @notice Thrown if a caller attempts to specify address zero for certain designated addresses.
   error GovernanceStaker__InvalidAddress();
 
+  /// @notice Thrown if a bumper's requested tip is invalid.
+  error GovernanceStaker__InvalidTip();
+
   /// @notice Thrown when an onBehalf method is called with a deadline that has expired.
   error GovernanceStaker__ExpiredDeadline();
 
   /// @notice Thrown if a caller supplies an invalid signature to a method that requires one.
   error GovernanceStaker__InvalidSignature();
 
+  /// @notice Thrown if an earning power update is unqualified to be bumped.
+  error GovernanceStaker__Unqualified();
+
   /// @notice Metadata associated with a discrete staking deposit.
   /// @param balance The deposit's staked balance.
   /// @param owner The owner of this deposit.
@@ -163,6 +176,9 @@ contract GovernanceStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonce
   /// @notice Permissioned actor that can enable/disable `rewardNotifier` addresses.
   address public admin;
 
+  /// @notice Maximum tip a bumper can request.
+  uint256 public maxBumpTip;
+
   /// @notice Global amount currently staked across all deposits.
   uint256 public totalStaked;
 
@@ -207,11 +223,13 @@ contract GovernanceStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonce
     IERC20 _rewardToken,
     IERC20Delegates _stakeToken,
     IEarningPowerCalculator _earningPowerCalculator,
+    uint256 _maxBumpTip,
     address _admin
   ) EIP712("GovernanceStaker", "1") {
     REWARD_TOKEN = _rewardToken;
     STAKE_TOKEN = _stakeToken;
     _setAdmin(_admin);
+    _setMaxBumpTip(_maxBumpTip);
     earningPowerCalculator = _earningPowerCalculator;
   }
 
@@ -223,6 +241,14 @@ contract GovernanceStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonce
     _setAdmin(_newAdmin);
   }
 
+  /// @notice Set the max bump tip.
+  /// @param _newMaxBumpTip Value of the new max bump tip.
+  /// @dev Caller must be the current admin.
+  function setMaxBumpTip(uint256 _newMaxBumpTip) external {
+    _revertIfNotAdmin();
+    _setMaxBumpTip(_newMaxBumpTip);
+  }
+
   /// @notice Enables or disables a reward notifier address.
   /// @param _rewardNotifier Address of the reward notifier.
   /// @param _isEnabled `true` to enable the `_rewardNotifier`, or `false` to disable.
@@ -665,6 +691,53 @@ contract GovernanceStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonce
     emit RewardNotified(_amount, msg.sender);
   }
 
+  /// @notice A function that a bumper can call to update a deposit's earning power when a
+  /// qualifying change in the earning power is returned by the earning power calculator. A
+  /// deposit's earning power may change as determined by the algorithm of the current earning power
+  /// calculator. In order to incentivize bumpers to trigger these updates a portion of deposit's
+  /// unclaimed rewards are sent to the bumper.
+  /// @param _depositId The identifier for the deposit that needs an updated earning power.
+  /// @param _tipReceiver The receiver of the reward for updating a deposit's earning power.
+  /// @param _requestedTip The amount of tip requested by the third-party.
+  function bumpEarningPower(
+    DepositIdentifier _depositId,
+    address _tipReceiver,
+    uint256 _requestedTip
+  ) external {
+    if (_requestedTip > maxBumpTip) revert GovernanceStaker__InvalidTip();
+
+    Deposit storage deposit = deposits[_depositId];
+
+    _checkpointGlobalReward();
+    _checkpointReward(deposit);
+
+    uint256 _unclaimedRewards = deposit.scaledUnclaimedRewardCheckpoint / SCALE_FACTOR;
+
+    (uint256 _newEarningPower, bool _isQualifiedForBump) = earningPowerCalculator.getNewEarningPower(
+      deposit.balance, deposit.owner, deposit.delegatee, deposit.earningPower
+    );
+    if (!_isQualifiedForBump || _newEarningPower == deposit.earningPower) {
+      revert GovernanceStaker__Unqualified();
+    }
+
+    if (_newEarningPower > deposit.earningPower && _unclaimedRewards < _requestedTip) {
+      revert GovernanceStaker__InsufficientUnclaimedRewards();
+    }
+
+    // Note: underflow causes a revert if the requested  tip is more than unclaimed rewards
+    if (_newEarningPower < deposit.earningPower && (_unclaimedRewards - _requestedTip) < maxBumpTip)
+    {
+      revert GovernanceStaker__InsufficientUnclaimedRewards();
+    }
+
+    // Update global earning power & deposit earning power based on this bump
+    totalEarningPower = _calculateTotalEarningPower(deposit.earningPower, _newEarningPower);
+    deposit.earningPower = _newEarningPower;
+
+    // Send tip to the receiver
+    SafeERC20.safeTransfer(REWARD_TOKEN, _tipReceiver, _requestedTip);
+  }
+
   /// @notice Live value of the unclaimed rewards earned by a given deposit with the
   /// scale factor included. Used internally for calculating reward checkpoints while minimizing
   /// precision loss.
@@ -908,6 +981,13 @@ contract GovernanceStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonce
     admin = _newAdmin;
   }
 
+  /// @notice Internal helper method which sets the max bump tip.
+  /// @param _newMaxTip Value of the new max bump tip.
+  function _setMaxBumpTip(uint256 _newMaxTip) internal {
+    emit MaxBumpTipSet(maxBumpTip, _newMaxTip);
+    maxBumpTip = _newMaxTip;
+  }
+
   /// @notice Internal helper method which reverts GovernanceStaker__Unauthorized if the message
   /// sender is not the admin.
   function _revertIfNotAdmin() internal view {

src/interfaces/IEarningPowerCalculator.sol

@@ -12,5 +12,5 @@ interface IEarningPowerCalculator {
     address _staker,
     address _delegatee,
     uint256 _oldEarningPower
-  ) external view returns (uint256 _newEarningPower, bool _isQualifiedForUpdate);
+  ) external view returns (uint256 _newEarningPower, bool _isQualifiedForBump);
 }

test/GovernanceStaker.invariants.t.sol

@@ -17,6 +17,7 @@ contract GovernanceStakerInvariants is Test {
   ERC20VotesMock govToken;
   IEarningPowerCalculator earningPowerCalculator;
   address rewardsNotifier;
+  uint256 maxBumpTip = 2e18;
 
   function setUp() public {
     rewardToken = new ERC20Fake();
@@ -31,7 +32,9 @@ contract GovernanceStakerInvariants is Test {
     earningPowerCalculator = new MockFullEarningPowerCalculator();
     vm.label(address(earningPowerCalculator), "Full Earning Power Calculator");
 
-    govStaker = new GovernanceStaker(rewardToken, govToken, earningPowerCalculator, rewardsNotifier);
+    govStaker = new GovernanceStaker(
+      rewardToken, govToken, earningPowerCalculator, maxBumpTip, rewardsNotifier
+    );
     handler = new GovernanceStakerHandler(govStaker);
 
     bytes4[] memory selectors = new bytes4[](7);