feat: Add DirectBurn function on RemotePool (#21)

* feat: withdraw liquidity on burnMint

* test: more verbose

* doc: expand and fix typo

* chore: mv withdrawLiquidity burnLiquidity

* chore: mv burnLiquidity directBurn

* doc: upd for `directBurn`

* Update contracts/src/v0.8/ccip/pools/GHO/UpgradeableBurnMintTokenPool.sol

Co-authored-by: miguelmtz <[email protected]>

* Update contracts/src/v0.8/ccip/pools/GHO/UpgradeableBurnMintTokenPool.sol

Co-authored-by: miguelmtz <[email protected]>

* chore: doc on burnMint

* doc: update `directBurn` doc

---------

Co-authored-by: miguelmtz <[email protected]>

Author: DhairyaSethi

contracts/src/v0.8/ccip/pools/GHO/UpgradeableBurnMintTokenPool.sol

@@ -17,6 +17,7 @@ import {IRouter} from "../../interfaces/IRouter.sol";
 /// - Implementation of Initializable to allow upgrades
 /// - Move of allowlist and router definition to initialization stage
 /// - Inclusion of rate limit admin who may configure rate limits in addition to owner
+/// - Addition of authorized function to to directly burn liquidity, thereby reducing the facilitator's bucket level.
 /// - Modifications from inherited contract (see contract for more details):
 ///   - UpgradeableTokenPool: Modify `onlyOnRamp` & `onlyOffRamp` modifier to accept transactions from ProxyPool
 contract UpgradeableBurnMintTokenPool is Initializable, UpgradeableBurnMintTokenPoolAbstract, ITypeAndVersion {
@@ -84,6 +85,16 @@ contract UpgradeableBurnMintTokenPool is Initializable, UpgradeableBurnMintToken
     _setRateLimitConfig(remoteChainSelector, outboundConfig, inboundConfig);
   }
 
+  /// @notice Burn an amount of tokens with no additional logic.
+  /// @dev This GHO-specific functionality is designed for migrating bucket levels between
+  /// facilitators. The new pool is expected to mint amount of tokens, while the old pool
+  /// burns an equivalent amount. This ensures the facilitator can be offboarded, as all
+  /// liquidity minted by it must be fully burned
+  /// @param amount The amount of tokens to burn.
+  function directBurn(uint256 amount) external onlyOwner {
+    _burn(amount);
+  }
+
   /// @inheritdoc UpgradeableBurnMintTokenPoolAbstract
   function _burn(uint256 amount) internal virtual override {
     IBurnMintERC20(address(i_token)).burn(amount);

contracts/src/v0.8/ccip/pools/GHO/diffs/UpgradeableBurnMintTokenPool_diff.md

@@ -1,9 +1,9 @@
 ```diff
 diff --git a/src/v0.8/ccip/pools/BurnMintTokenPool.sol b/src/v0.8/ccip/pools/GHO/UpgradeableBurnMintTokenPool.sol
-index 9af0f22f4c..a5cecc0430 100644
+index 9af0f22f4c..f19106fd4d 100644
 --- a/src/v0.8/ccip/pools/BurnMintTokenPool.sol
 +++ b/src/v0.8/ccip/pools/GHO/UpgradeableBurnMintTokenPool.sol
-@@ -1,28 +1,90 @@
+@@ -1,28 +1,101 @@
  // SPDX-License-Identifier: BUSL-1.1
 -pragma solidity 0.8.19;
 +pragma solidity ^0.8.0;
@@ -28,6 +28,7 @@ index 9af0f22f4c..a5cecc0430 100644
 +/// - Implementation of Initializable to allow upgrades
 +/// - Move of allowlist and router definition to initialization stage
 +/// - Inclusion of rate limit admin who may configure rate limits in addition to owner
++/// - Addition of authorized function to to directly burn liquidity, thereby reducing the facilitator's bucket level.
 +/// - Modifications from inherited contract (see contract for more details):
 +///   - UpgradeableTokenPool: Modify `onlyOnRamp` & `onlyOffRamp` modifier to accept transactions from ProxyPool
 +contract UpgradeableBurnMintTokenPool is Initializable, UpgradeableBurnMintTokenPoolAbstract, ITypeAndVersion {
@@ -106,6 +107,16 @@ index 9af0f22f4c..a5cecc0430 100644
 +    _setRateLimitConfig(remoteChainSelector, outboundConfig, inboundConfig);
 +  }
 +
++  /// @notice Burn an amount of tokens with no additional logic.
++  /// @dev This GHO-specific functionality is designed for migrating bucket levels between
++  /// facilitators. The new pool is expected to mint amount of tokens, while the old pool
++  /// burns an equivalent amount. This ensures the facilitator can be offboarded, as all
++  /// liquidity minted by it must be fully burned
++  /// @param amount The amount of tokens to burn.
++  function directBurn(uint256 amount) external onlyOwner {
++    _burn(amount);
++  }
++
 +  /// @inheritdoc UpgradeableBurnMintTokenPoolAbstract
    function _burn(uint256 amount) internal virtual override {
      IBurnMintERC20(address(i_token)).burn(amount);

contracts/src/v0.8/ccip/test/pools/GHO/GhoTokenPoolRemote.t.sol

@@ -398,3 +398,24 @@ contract GhoTokenPoolRemote_proxyPool is GhoTokenPoolRemoteSetup {
     assertEq(s_pool.getProxyPool(), proxyPool);
   }
 }
+
+contract GhoTokenPoolRemote_directBurn is GhoTokenPoolRemoteSetup {
+  function testDirectBurnOnlyOwner() public {
+    vm.startPrank(STRANGER);
+    vm.expectRevert("Only callable by owner");
+    s_pool.directBurn(13e7);
+  }
+
+  function testFuzzDirectBurnSuccess(uint256 amount) public {
+    amount = bound(amount, 1, type(uint128).max); // bound to bucket capacity
+    // prank previously bridged supply
+    vm.startPrank(address(s_pool));
+    s_burnMintERC677.mint(address(s_pool), amount);
+
+    vm.startPrank(AAVE_DAO);
+    s_pool.directBurn(amount);
+
+    assertEq(s_burnMintERC677.balanceOf(address(s_pool)), 0);
+    assertEq(GhoToken(address(s_burnMintERC677)).getFacilitator(address(s_pool)).bucketLevel, 0);
+  }
+}