Support multicall for LockstakeEngine

src/LockstakeEngine.sol

@@ -17,6 +17,7 @@
 pragma solidity ^0.8.16;
 
 import { LockstakeUrn } from "src/LockstakeUrn.sol";
+import { Multicall } from "src/Multicall.sol";
 
 interface DelegateFactoryLike {
     function gov() external view returns (GemLike);
@@ -55,7 +56,7 @@ interface JugLike {
     function drip(bytes32) external returns (uint256);
 }
 
-contract LockstakeEngine {
+contract LockstakeEngine is Multicall {
     // --- storage variables ---
 
     mapping(address => uint256)                     public wards;        // usr => 1 == access
@@ -192,7 +193,6 @@ contract LockstakeEngine {
     function isUrnAuth(address urn, address usr) external view returns (bool ok) {
         ok = _urnAuth(urn, usr);
     }
-
     // --- urn/delegation functions ---
 
     function open() external returns (address urn) {

src/Multicall.sol

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+// Based on https://github.com/Uniswap/v3-periphery/blob/697c2474757ea89fec12a4e6db16a574fe259610/contracts/base/Multicall.sol
+
+pragma solidity ^0.8.16;
+
+// Enables calling multiple methods in a single call to the contract
+abstract contract Multicall  {
+    function multicall(bytes[] calldata data) public returns (bytes[] memory results) {
+        results = new bytes[](data.length);
+        for (uint256 i = 0; i < data.length; i++) {
+            (bool success, bytes memory result) = address(this).delegatecall(data[i]);
+
+            if (!success) {
+                // Next 5 lines from https://ethereum.stackexchange.com/a/83577
+                if (result.length < 68) revert();
+                assembly {
+                    result := add(result, 0x04)
+                }
+                revert(abi.decode(result, (string)));
+            }
+
+            results[i] = result;
+        }
+    }
+}

test/LockstakeEngine.t.sol

@@ -431,6 +431,20 @@ contract AllocatorVaultTest is DssTest {
         assertEq(farm.balanceOf(address(urn)), 45_000 * 10**18);
     }
 
+    function testOpenLockStakeMulticall() public {
+        vm.prank(pauseProxy); engine.addFarm(address(farm));
+        gov.approve(address(engine), 100_000 * 10**18);
+
+        address urn = engine.getUrn(address(this), 0);
+
+        bytes[] memory callsToExecute = new bytes[](4);
+        callsToExecute[0] = abi.encodeWithSignature("open()");
+        callsToExecute[1] = abi.encodeWithSignature("lock(address,uint256)", urn, 100_000 * 10**18);
+        callsToExecute[2] = abi.encodeWithSignature("selectFarm(address,address)", urn, address(farm));
+        callsToExecute[3] = abi.encodeWithSignature("stake(address,uint256,uint16)", urn, 100_000 * 10**18, 1);
+        engine.multicall(callsToExecute);
+    }
+
     function testGetReward() public {
         vm.prank(pauseProxy); engine.addFarm(address(farm));
         address urn = engine.open();