feat[contracts]: Have Messenger contracts emit an event on failed relay (#596)

* feat[contracts]: Have messengers emit events on failed relay

* chore[contracts]: Add changeset

.changeset/violet-falcons-hunt.md

+---
+"@eth-optimism/contracts": patch
+---
+
+Add an extra event to messenger contracts to emit when a message is unsuccessfully relayed

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/messaging/OVM_L1CrossDomainMessenger.sol

@@ -128,6 +128,8 @@ contract OVM_L1CrossDomainMessenger is iOVM_L1CrossDomainMessenger, Abs_BaseCros
         if (success == true) {
             successfulMessages[xDomainCalldataHash] = true;
             emit RelayedMessage(xDomainCalldataHash);
+        } else {
+            emit FailedRelayedMessage(xDomainCalldataHash);
         }
 
         // Store an identifier that can be used to prove that the given message was relayed by some

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/messaging/OVM_L2CrossDomainMessenger.sol

@@ -93,6 +93,8 @@ contract OVM_L2CrossDomainMessenger is iOVM_L2CrossDomainMessenger, Abs_BaseCros
         if (success == true) {
             successfulMessages[xDomainCalldataHash] = true;
             emit RelayedMessage(xDomainCalldataHash);
+        } else {
+            emit FailedRelayedMessage(xDomainCalldataHash);
         }
 
         // Store an identifier that can be used to prove that the given message was relayed by some

packages/contracts/contracts/optimistic-ethereum/iOVM/bridge/messaging/iAbs_BaseCrossDomainMessenger.sol

@@ -10,14 +10,19 @@ interface iAbs_BaseCrossDomainMessenger {
     /**********
      * Events *
      **********/
+
     event SentMessage(bytes message);
     event RelayedMessage(bytes32 msgHash);
+    event FailedRelayedMessage(bytes32 msgHash);
+
+
+    /*************
+     * Variables *
+     *************/
 
-    /**********************
-     * Contract Variables *
-     **********************/
     function xDomainMessageSender() external view returns (address);
 
+
     /********************
      * Public Functions *
      ********************/