feat: add FeeDistributorBALClaimer contract

pkg/liquidity-mining/contracts/fee-distribution/FeeDistributor.sol

@@ -208,7 +208,12 @@ contract FeeDistributor is IFeeDistributor, ReentrancyGuard {
      * @param tokens - An array of ERC20 token addresses to be claimed.
      * @return An array of the amounts of each token in `tokens` sent to `user` as a result of claiming.
      */
-    function claimTokens(address user, IERC20[] calldata tokens) external override nonReentrant returns (uint256[] memory) {
+    function claimTokens(address user, IERC20[] calldata tokens)
+        external
+        override
+        nonReentrant
+        returns (uint256[] memory)
+    {
         // Prevent someone from assigning tokens to an inaccessible week.
         require(block.timestamp > _startTime, "Fee distribution has not started yet");
         _checkpointTotalSupply();

pkg/liquidity-mining/contracts/fee-distribution/FeeDistributorBALClaimer.sol

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+pragma solidity ^0.7.0;
+pragma experimental ABIEncoderV2;
+
+import "@balancer-labs/v2-standalone-utils/contracts/interfaces/IBALTokenHolder.sol";
+
+import "../interfaces/IFeeDistributor.sol";
+import "../interfaces/ISingleRecipientLiquidityGauge.sol";
+
+/**
+ * @title FeeDistributorBALClaimer
+ * @notice Atomically mints any outstanding BAL from a SingleRecipientGauge and transfers it to the FeeDistributor
+ * in order for it to be distributed among veBAL holders.
+ */
+contract FeeDistributorBALClaimer {
+    IERC20 private immutable _balToken;
+    IFeeDistributor private immutable _feeDistributor;
+    ISingleRecipientLiquidityGauge private immutable _gauge;
+    IBALTokenHolder private immutable _balTokenHolder;
+
+    constructor(IFeeDistributor feeDistributor, ISingleRecipientLiquidityGauge gauge) {
+        IBALTokenHolder balTokenHolder = IBALTokenHolder(gauge.getRecipient());
+
+        _balToken = balTokenHolder.getBalancerToken();
+        _feeDistributor = feeDistributor;
+        _gauge = gauge;
+        _balTokenHolder = balTokenHolder;
+    }
+
+    /**
+     * @notice Mint any outstanding BAL emissions and send them to the FeeDistributor
+     */
+    function distributeBAL() external {
+        _gauge.checkpoint();
+        _balTokenHolder.withdrawFunds(address(_feeDistributor), _balToken.balanceOf(address(_balTokenHolder)));
+        _feeDistributor.checkpointToken(_balToken);
+    }
+}

pkg/liquidity-mining/contracts/gauges/StakelessGauge.sol

@@ -20,9 +20,9 @@ import "@balancer-labs/v2-solidity-utils/contracts/openzeppelin/ReentrancyGuard.
 import "../interfaces/IBalancerMinter.sol";
 import "../interfaces/IBalancerTokenAdmin.sol";
 import "../interfaces/IGaugeController.sol";
-import "../interfaces/ILiquidityGauge.sol";
+import "../interfaces/IStakelessGauge.sol";
 
-abstract contract StakelessGauge is ILiquidityGauge, ReentrancyGuard {
+abstract contract StakelessGauge is IStakelessGauge, ReentrancyGuard {
     IERC20 internal immutable _balToken;
     IBalancerTokenAdmin private immutable _tokenAdmin;
     IBalancerMinter private immutable _minter;
@@ -78,7 +78,7 @@ abstract contract StakelessGauge is ILiquidityGauge, ReentrancyGuard {
         _startEpochTime = _tokenAdmin.startEpochTimeWrite();
     }
 
-    function checkpoint() external payable nonReentrant returns (bool) {
+    function checkpoint() external payable override nonReentrant returns (bool) {
         require(msg.sender == address(_authorizerAdaptor), "SENDER_NOT_ALLOWED");
         uint256 lastPeriod = _period;
         uint256 currentPeriod = _currentPeriod();

pkg/liquidity-mining/contracts/interfaces/IFeeDistributor.sol

@@ -25,7 +25,6 @@ import "./IVotingEscrow.sol";
  * holders simply transfer the tokens to the `FeeDistributor` contract and then call `checkpointToken`.
  */
 interface IFeeDistributor {
-
     event TokenCheckpointed(IERC20 token, uint256 amount, uint256 lastCheckpointTimestamp);
     event TokensClaimed(address user, IERC20 token, uint256 amount, uint256 userTokenTimeCursor);
 
@@ -38,11 +37,13 @@ interface IFeeDistributor {
      * @notice Returns the global time cursor representing the most earliest uncheckpointed week.
      */
     function getTimeCursor() external view returns (uint256);
+
     /**
      * @notice Returns the user-level time cursor representing the most earliest uncheckpointed week.
      * @param user - The address of the user to query.
      */
     function getUserTimeCursor(address user) external view returns (uint256);
+
     /**
      * @notice Returns the token-level time cursor storing the timestamp at up to which tokens have been distributed.
      * @param token - The ERC20 token address to query.
@@ -77,6 +78,7 @@ interface IFeeDistributor {
      * @notice Returns the FeeDistributor's cached balance of `token`.
      */
     function getTokenLastBalance(IERC20 token) external view returns (uint256);
+
     // Checkpointing
 
     /**

pkg/liquidity-mining/contracts/interfaces/ISingleRecipientLiquidityGauge.sol

@@ -14,9 +14,9 @@
 
 pragma solidity ^0.7.0;
 
-import "./ILiquidityGauge.sol";
+import "./IStakelessGauge.sol";
 
-interface ISingleRecipientLiquidityGauge is ILiquidityGauge {
+interface ISingleRecipientLiquidityGauge is IStakelessGauge {
     function initialize(address recipient) external;
 
     function getRecipient() external view returns (address);

pkg/liquidity-mining/contracts/interfaces/IStakelessGauge.sol

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+pragma solidity ^0.7.0;
+
+import "./ILiquidityGauge.sol";
+
+interface IStakelessGauge is ILiquidityGauge {
+    function checkpoint() external payable returns (bool);
+}

pkg/standalone-utils/contracts/BALTokenHolder.sol

@@ -18,7 +18,6 @@ import "@balancer-labs/v2-solidity-utils/contracts/helpers/Authentication.sol";
 import "@balancer-labs/v2-solidity-utils/contracts/openzeppelin/SafeERC20.sol";
 
 import "@balancer-labs/v2-vault/contracts/interfaces/IVault.sol";
-import "@balancer-labs/v2-liquidity-mining/contracts/interfaces/IBalancerToken.sol";
 
 import "./interfaces/IBALTokenHolder.sol";
 
@@ -51,7 +50,7 @@ contract BALTokenHolder is IBALTokenHolder, Authentication {
         _name = name;
     }
 
-    function getBalancerToken() external view returns (IBalancerToken) {
+    function getBalancerToken() external view override returns (IBalancerToken) {
         return _balancerToken;
     }
 

pkg/standalone-utils/contracts/interfaces/IBALTokenHolder.sol

@@ -16,8 +16,12 @@ pragma solidity ^0.7.0;
 
 import "@balancer-labs/v2-solidity-utils/contracts/helpers/IAuthentication.sol";
 import "@balancer-labs/v2-solidity-utils/contracts/openzeppelin/IERC20.sol";
+import "@balancer-labs/v2-liquidity-mining/contracts/interfaces/IBalancerToken.sol";
+
 
 interface IBALTokenHolder is IAuthentication {
+    function getBalancerToken() external view returns (IBalancerToken);
+
     function withdrawFunds(address recipient, uint256 amount) external;
 
     function sweepTokens(