Zp/update mockrouter

contracts/gas-snapshots/ccip.gas-snapshot

@@ -481,9 +481,9 @@ MerkleMultiProofTest:test_MerkleRootSingleLeaf_Success() (gas: 3649)
 MerkleMultiProofTest:test_SpecSync_gas() (gas: 34123)
 MockRouterTest:test_ccipSendWithInsufficientNativeTokens_Revert() (gas: 34019)
 MockRouterTest:test_ccipSendWithInvalidMsgValue_Revert() (gas: 60812)
-MockRouterTest:test_ccipSendWithLinkFeeTokenAndValidMsgValue_Success() (gas: 126480)
+MockRouterTest:test_ccipSendWithLinkFeeTokenAndValidMsgValue_Success() (gas: 126540)
 MockRouterTest:test_ccipSendWithLinkFeeTokenbutInsufficientAllowance_Revert() (gas: 63419)
-MockRouterTest:test_ccipSendWithSufficientNativeFeeTokens_Success() (gas: 43952)
+MockRouterTest:test_ccipSendWithSufficientNativeFeeTokens_Success() (gas: 44012)
 MultiAggregateRateLimiter_applyRateLimiterConfigUpdates:test_MultipleConfigsBothLanes_Success() (gas: 132457)
 MultiAggregateRateLimiter_applyRateLimiterConfigUpdates:test_MultipleConfigs_Success() (gas: 313023)
 MultiAggregateRateLimiter_applyRateLimiterConfigUpdates:test_OnlyCallableByOwner_Revert() (gas: 17750)

contracts/src/v0.8/ccip/test/mocks/MockRouter.sol

@@ -45,8 +45,19 @@ contract MockCCIPRouter is IRouter, IRouterClient {
     uint256 gasLimit,
     address receiver
   ) internal returns (bool success, bytes memory retData, uint256 gasUsed) {
-    // Only send through the router if the receiver is a contract and implements the IAny2EVMMessageReceiver interface.
-    if (receiver.code.length == 0 || !receiver.supportsInterface(type(IAny2EVMMessageReceiver).interfaceId)) {
+    // There are three cases in which we skip calling the receiver:
+    // 1. If the message data is empty AND the gas limit is 0.
+    //          This indicates a message that only transfers tokens. It is valid to only send tokens to a contract
+    //          that supports the IAny2EVMMessageReceiver interface, but without this first check we would call the
+    //          receiver without any gas, which would revert the transaction.
+    // 2. If the receiver is not a contract.
+    // 3. If the receiver is a contract but it does not support the IAny2EVMMessageReceiver interface.
+    //
+    // The ordering of these checks is important, as the first check is the cheapest to execute.
+    if (
+      (message.data.length == 0 && gasLimit == 0) || receiver.code.length == 0
+        || !receiver.supportsInterface(type(IAny2EVMMessageReceiver).interfaceId)
+    ) {
       return (true, "", 0);
     }