Added borrowETH to WETHGateway.

contracts/misc/WETHGateway.sol

@@ -96,6 +96,22 @@ contract WETHGateway is IWETHGateway, Ownable {
     if (msg.value > paybackAmount) _safeTransferETH(msg.sender, msg.value - paybackAmount);
   }
 
+  /**
+   * @dev borrow WETH, unwraps to ETH and send both the ETH and DebtTokens to msg.sender, via `approveDelegation` and onBehalf argument in `LendingPool.borrow`.
+   * @param amount the amount of ETH to borrow
+   * @param interesRateMode the interest rate mode
+   * @param referralCode integrators are assigned a referral code and can potentially receive rewards
+   */
+  function borrowETH(
+    uint256 amount,
+    uint256 interesRateMode,
+    uint16 referralCode
+  ) external override {
+    POOL.borrow(address(WETH), amount, interesRateMode, referralCode, msg.sender);
+    WETH.withdraw(amount);
+    _safeTransferETH(msg.sender, amount);
+  }
+
   /**
    * @dev transfer ETH to an address, revert if it fails.
    * @param to recipient of the transfer

contracts/misc/interfaces/IWETHGateway.sol

@@ -11,4 +11,10 @@ interface IWETHGateway {
     uint256 rateMode,
     address onBehalfOf
   ) external payable;
+
+  function borrowETH(
+    uint256 amount,
+    uint256 interesRateMode,
+    uint16 referralCode
+  ) external;
 }

test/weth-gateway.spec.ts

@@ -8,6 +8,8 @@ import {getStableDebtToken, getVariableDebtToken} from '../helpers/contracts-get
 import {WethGateway} from '../types/WethGateway';
 import {use} from 'chai';
 import {deploySelfdestructTransferMock} from '../helpers/contracts-deployments';
+import {boolean} from '@nomiclabs/buidler/internal/core/params/argumentTypes';
+import {borrow} from './helpers/actions';
 
 const {expect} = require('chai');
 
@@ -185,6 +187,48 @@ makeSuite('Use native ETH at LendingPool via WETHGateway', (testEnv: TestEnv) =>
     expect(debtBalanceAfterFullRepay).to.be.eq(zero);
   });
 
+  it('Borrow ETH via delegateApprove ETH and repays back', async () => {
+    const {users, wethGateway, aWETH, weth, helpersContract} = testEnv;
+    const borrowSize = parseEther('1');
+    const user = users[2];
+    const {variableDebtTokenAddress} = await helpersContract.getReserveTokensAddresses(
+      weth.address
+    );
+    const varDebtToken = await getVariableDebtToken(variableDebtTokenAddress);
+
+    const priorDebtBalance = await varDebtToken.balanceOf(user.address);
+    expect(priorDebtBalance).to.be.eq(zero);
+
+    // Deposit WETH with native ETH
+    await wethGateway.connect(user.signer).depositETH(user.address, '0', {value: depositSize});
+
+    const aTokensBalance = await aWETH.balanceOf(user.address);
+
+    expect(aTokensBalance).to.be.gt(zero);
+    expect(aTokensBalance).to.be.gte(depositSize);
+
+    // Delegates borrowing power of WETH to WETHGateway
+    await waitForTx(
+      await varDebtToken.connect(user.signer).approveDelegation(wethGateway.address, borrowSize)
+    );
+
+    // Borrows ETH with WETH as collateral
+    await waitForTx(await wethGateway.connect(user.signer).borrowETH(borrowSize, '2', '0'));
+
+    const debtBalance = await varDebtToken.balanceOf(user.address);
+
+    expect(debtBalance).to.be.gt(zero);
+
+    // Full Repay WETH loan with native ETH
+    await waitForTx(
+      await wethGateway
+        .connect(user.signer)
+        .repayETH(MAX_UINT_AMOUNT, '2', user.address, {value: borrowSize.mul(2)})
+    );
+    const debtBalanceAfterFullRepay = await varDebtToken.balanceOf(user.address);
+    expect(debtBalanceAfterFullRepay).to.be.eq(zero);
+  });
+
   it('Should revert if receiver function receives Ether if not WETH', async () => {
     const {users, wethGateway} = testEnv;
     const user = users[0];