Add back Address.functionDelegateCall

contracts/mocks/AddressImpl.sol

@@ -32,6 +32,11 @@ contract AddressImpl {
         emit CallReturnValue(abi.decode(returnData, (string)));
     }
 
+    function functionDelegateCall(address target, bytes calldata data) external {
+        bytes memory returnData = Address.functionDelegateCall(target, data);
+        emit CallReturnValue(abi.decode(returnData, (string)));
+    }
+
     // sendValue's tests require the contract to hold Ether
     receive () external payable { }
 }

contracts/utils/Address.sol

@@ -144,6 +144,30 @@ library Address {
         return _verifyCallResult(success, returndata, errorMessage);
     }
 
+    /**
+     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
+     * but performing a delegate call.
+     *
+     * _Available since v3.3._
+     */
+    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
+        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
+    }
+
+    /**
+     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
+     * but performing a delegate call.
+     *
+     * _Available since v3.3._
+     */
+    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
+        require(isContract(target), "Address: delegate call to non-contract");
+
+        // solhint-disable-next-line avoid-low-level-calls
+        (bool success, bytes memory returndata) = target.delegatecall(data);
+        return _verifyCallResult(success, returndata, errorMessage);
+    }
+
     function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
         if (success) {
             return returndata;