feat: add test for the return data

packages/contracts-bedrock/interfaces/L2/IL2ToL2CrossDomainMessenger.sol

@@ -104,7 +104,14 @@ interface IL2ToL2CrossDomainMessenger {
     ///         already received once and is currently being replayed.
     /// @param _id          Identifier of the SentMessage event to be relayed
     /// @param _sentMessage Message payload of the `SentMessage` event
-    function relayMessage(Identifier calldata _id, bytes calldata _sentMessage) external payable;
+    /// @return returnData_ Return data from the target contract call.
+    function relayMessage(
+        Identifier calldata _id,
+        bytes calldata _sentMessage
+    )
+        external
+        payable
+        returns (bytes memory returnData_);
 
     function messageVersion() external view returns (uint16);
 

packages/contracts-bedrock/snapshots/abi/L2ToL2CrossDomainMessenger.json

@@ -110,7 +110,13 @@
       }
     ],
     "name": "relayMessage",
-    "outputs": [],
+    "outputs": [
+      {
+        "internalType": "bytes",
+        "name": "returnData_",
+        "type": "bytes"
+      }
+    ],
     "stateMutability": "payable",
     "type": "function"
   },

packages/contracts-bedrock/snapshots/semver-lock.json

@@ -100,8 +100,8 @@
     "sourceCodeHash": "0xaef8ea36c5b78cd12e0e62811d51db627ccf0dfd2cc5479fb707a10ef0d42048"
   },
   "src/L2/L2ToL2CrossDomainMessenger.sol": {
-    "initCodeHash": "0x45564b97c63419cc12eadc60425c6d001857a3eea688ecaf1439ae7ede6aa9aa",
-    "sourceCodeHash": "0xed64736338b43a42f6bc6a88cca734403e1bb9ceafa55e4738605dfdedd1a99f"
+    "initCodeHash": "0xc56db8cb569efa0467fd53ab3fa218af3051e54f5517d7fafb7b5831b4350618",
+    "sourceCodeHash": "0x72062343a044e9c56f4143dcfc71706286eb205902006c2afcf6a4cd90c3e9f8"
   },
   "src/L2/OptimismSuperchainERC20.sol": {
     "initCodeHash": "0xdac32a1057a6bc8a8d2ffdce1db8f34950cd0ffd1454d2133865736d21869192",

packages/contracts-bedrock/src/L2/L2ToL2CrossDomainMessenger.sol

@@ -5,7 +5,6 @@ pragma solidity 0.8.25;
 import { Encoding } from "src/libraries/Encoding.sol";
 import { Hashing } from "src/libraries/Hashing.sol";
 import { Predeploys } from "src/libraries/Predeploys.sol";
-import { SafeCall } from "src/libraries/SafeCall.sol";
 import { TransientReentrancyAware } from "src/libraries/TransientContext.sol";
 
 // Interfaces
@@ -72,8 +71,8 @@ contract L2ToL2CrossDomainMessenger is ISemver, TransientReentrancyAware {
     uint16 public constant messageVersion = uint16(0);
 
     /// @notice Semantic version.
-    /// @custom:semver 1.0.0-beta.13
-    string public constant version = "1.0.0-beta.13";
+    /// @custom:semver 1.0.0-beta.14
+    string public constant version = "1.0.0-beta.14";
 
     /// @notice Mapping of message hashes to boolean receipt values. Note that a message will only be present in this
     ///         mapping if it has successfully been relayed on this chain, and can therefore not be relayed again.
@@ -160,7 +159,15 @@ contract L2ToL2CrossDomainMessenger is ISemver, TransientReentrancyAware {
     /// @param _id          Identifier of the SentMessage event to be relayed
     /// @param _sentMessage Message payload of the `SentMessage` event
     /// @return returnData_ Return data from the target contract call.
-    function relayMessage(Identifier calldata _id, bytes calldata _sentMessage) external payable nonReentrant returns (bytes memory returnData_) {
+    function relayMessage(
+        Identifier calldata _id,
+        bytes calldata _sentMessage
+    )
+        external
+        payable
+        nonReentrant
+        returns (bytes memory returnData_)
+    {
         // Ensure the log came from the messenger. Since the log origin is the CDM, there isn't a scenario where
         // this can be invoked from the CrossL2Inbox as the SentMessage log is not calldata for this function
         if (_id.origin != Predeploys.L2_TO_L2_CROSS_DOMAIN_MESSENGER) {
@@ -196,7 +203,7 @@ contract L2ToL2CrossDomainMessenger is ISemver, TransientReentrancyAware {
         _storeMessageMetadata(source, sender);
 
         bool success;
-        (success, returnData_) = target.call{value: msg.value}(message);
+        (success, returnData_) = target.call{ value: msg.value }(message);
 
         if (!success) {
             revert TargetCallFailed();

packages/contracts-bedrock/test/L2/L2ToL2CrossDomainMessenger.t.sol

@@ -393,6 +393,48 @@ contract L2ToL2CrossDomainMessengerTest is Test {
         assertEq(l2ToL2CrossDomainMessenger.crossDomainMessageSender(), address(0));
     }
 
+    /// @dev Tests the `relayMessage` function returns the expected return data of the call to the target contract.
+    function testFuzz_relayMessage_returnData_succeeds(
+        uint256 _source,
+        uint256 _nonce,
+        address _sender,
+        uint256 _value,
+        uint256 _blockNum,
+        uint256 _logIndex,
+        uint256 _time,
+        address _target,
+        bytes memory _mockedReturnData
+    )
+        public
+    {
+        // Declare a random call to be made over the target
+        bytes memory message = abi.encodeWithSignature("randomCall()");
+
+        // Construct the message
+        Identifier memory id =
+            Identifier(Predeploys.L2_TO_L2_CROSS_DOMAIN_MESSENGER, _blockNum, _logIndex, _time, _source);
+        bytes memory sentMessage = abi.encodePacked(
+            abi.encode(L2ToL2CrossDomainMessenger.SentMessage.selector, block.chainid, _target, _nonce), // topics
+            abi.encode(_sender, message) // data
+        );
+
+        // Ensure the CrossL2Inbox validates this message
+        vm.mockCall({
+            callee: Predeploys.CROSS_L2_INBOX,
+            data: abi.encodeCall(ICrossL2Inbox.validateMessage, (id, keccak256(message))),
+            returnData: ""
+        });
+
+        // Mock the random call over the target with the expected return data
+        vm.mockCall({ callee: _target, data: message, returnData: _mockedReturnData });
+
+        hoax(Predeploys.L2_TO_L2_CROSS_DOMAIN_MESSENGER, _value);
+        bytes memory returnData = l2ToL2CrossDomainMessenger.relayMessage{ value: _value }(id, sentMessage);
+
+        // Check that the return data is the mocked one
+        assertEq(returnData, _mockedReturnData);
+    }
+
     /// @dev Mock reentrant function that calls the `relayMessage` function.
     /// @param _source Source chain ID of the message.
     /// @param _nonce Nonce of the message.