feat: Lido StETH deposit integration [TKR-90] (#260)

* feat: initial stab at the LidoSampler and the MixinLido

* feat: full integration of lido sampler and mixin

* fix: return pooled Ether amount not shares & properly unwrap WETH

* refactor: clean up Lido sampler and data passing

* fix: lower gas schedule for WETH to stETH deposits

* refactor: remove MixinLido unused ETH code path

* chore: add changelog entries

* fix: lower Lido gas schedule slightly

* fix: revert MixinLido on unsupported token pair

* fix: address review comments, improve early exit if wrong tokens

* fix: add contract addresses to Lido FQT

contracts/zero-ex/contracts/src/transformers/bridges/BridgeAdapter.sol

@@ -33,6 +33,7 @@ import "./mixins/MixinDodo.sol";
 import "./mixins/MixinDodoV2.sol";
 import "./mixins/MixinKyber.sol";
 import "./mixins/MixinKyberDmm.sol";
+import "./mixins/MixinLido.sol";
 import "./mixins/MixinMakerPSM.sol";
 import "./mixins/MixinMooniswap.sol";
 import "./mixins/MixinMStable.sol";
@@ -57,6 +58,7 @@ contract BridgeAdapter is
     MixinDodoV2,
     MixinKyber,
     MixinKyberDmm,
+    MixinLido,
     MixinMakerPSM,
     MixinMooniswap,
     MixinMStable,
@@ -80,6 +82,7 @@ contract BridgeAdapter is
         MixinDodo()
         MixinDodoV2()
         MixinKyber(weth)
+        MixinLido(weth)
         MixinMakerPSM()
         MixinMooniswap(weth)
         MixinMStable()
@@ -235,6 +238,13 @@ contract BridgeAdapter is
                 sellAmount,
                 order.bridgeData
             );
+        } else if (protocolId == BridgeProtocols.LIDO) {
+            boughtAmount = _tradeLido(
+                sellToken,
+                buyToken,
+                sellAmount,
+                order.bridgeData
+            );
         } else {
             boughtAmount = _tradeZeroExBridge(
                 sellToken,

contracts/zero-ex/contracts/src/transformers/bridges/BridgeProtocols.sol

@@ -48,4 +48,5 @@ library BridgeProtocols {
     uint128 internal constant UNISWAPV3   = 18;
     uint128 internal constant KYBERDMM    = 19;
     uint128 internal constant CURVEV2     = 20;
+    uint128 internal constant LIDO        = 21;
 }

contracts/zero-ex/contracts/src/transformers/bridges/mixins/MixinLido.sol

@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: Apache-2.0
+/*
+
+  Copyright 2021 ZeroEx Intl.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+*/
+
+pragma solidity ^0.6.5;
+pragma experimental ABIEncoderV2;
+
+import "@0x/contracts-erc20/contracts/src/v06/LibERC20TokenV06.sol";
+import "@0x/contracts-erc20/contracts/src/v06/IERC20TokenV06.sol";
+import "@0x/contracts-erc20/contracts/src/v06/IEtherTokenV06.sol";
+
+
+/// @dev Minimal interface for minting StETH
+interface ILido {
+    /// @dev Adds eth to the pool
+    /// @param _referral optional address for referrals
+    /// @return StETH Amount of shares generated
+    function submit(address _referral) external payable returns (uint256 StETH);
+    /// @dev Retrieve the current pooled ETH representation of the shares amount
+    /// @param _sharesAmount amount of shares
+    /// @return amount of pooled ETH represented by the shares amount
+    function getPooledEthByShares(uint256 _sharesAmount) external view returns (uint256);
+}
+
+
+contract MixinLido {
+    using LibERC20TokenV06 for IERC20TokenV06;
+    using LibERC20TokenV06 for IEtherTokenV06;
+
+    IEtherTokenV06 private immutable WETH;
+
+    constructor(IEtherTokenV06 weth)
+        public
+    {
+        WETH = weth;
+    }
+
+    function _tradeLido(
+        IERC20TokenV06 sellToken,
+        IERC20TokenV06 buyToken,
+        uint256 sellAmount,
+        bytes memory bridgeData
+    )
+        internal
+        returns (uint256 boughtAmount)
+    {
+        (ILido lido) = abi.decode(bridgeData, (ILido));
+        if (address(sellToken) == address(WETH) && address(buyToken) == address(lido)) {
+            WETH.withdraw(sellAmount);
+            boughtAmount = lido.getPooledEthByShares(lido.submit{ value: sellAmount}(address(0)));
+        } else {
+            revert("MixinLido/UNSUPPORTED_TOKEN_PAIR");
+        }
+    }
+}