refactor(contracts): Only save transactionHash for queueElements

packages/contracts/contracts/L1/rollup/CanonicalTransactionChain.sol

@@ -53,7 +53,7 @@ contract CanonicalTransactionChain is ICanonicalTransactionChain, Lib_AddressRes
      ***************/
 
     uint40 private _nextQueueIndex; // index of the first queue element not yet included
-    Lib_OVMCodec.QueueElement[] queueElements;
+    bytes32[] queueElements;
 
 
     /***************
@@ -195,10 +195,15 @@ contract CanonicalTransactionChain is ICanonicalTransactionChain, Lib_AddressRes
         public
         view
         returns (
-            Lib_OVMCodec.QueueElement memory _element
+            Lib_OVMCodec.QueueElement memory
         )
     {
-        return queueElements[_index];
+        bytes32 transactionHash = queueElements[_index];
+        return Lib_OVMCodec.QueueElement({
+            transactionHash: transactionHash,
+            timestamp: 0,
+            blockNumber: 0
+        });
     }
 
     /**
@@ -303,14 +308,9 @@ contract CanonicalTransactionChain is ICanonicalTransactionChain, Lib_AddressRes
             )
         );
 
-        queueElements.push(
-            Lib_OVMCodec.QueueElement({
-                transactionHash: transactionHash,
-                timestamp: uint40(block.timestamp),
-                blockNumber: uint40(block.number)
-            })
-        );
+        queueElements.push(transactionHash);
         uint256 queueIndex = queueElements.length - 1;
+
         emit TransactionEnqueued(
             sender,
             _target,
@@ -389,24 +389,8 @@ contract CanonicalTransactionChain is ICanonicalTransactionChain, Lib_AddressRes
 
         // Generate the required metadata that we need to append this batch
         uint40 numQueuedTransactions = totalElementsToAppend - numSequencerTransactions;
-        uint40 blockTimestamp;
-        uint40 blockNumber;
-        if (curContext.numSubsequentQueueTransactions == 0) {
-            // The last element is a sequencer tx, therefore pull timestamp and block number from
-            // the last context.
-            blockTimestamp = uint40(curContext.timestamp);
-            blockNumber = uint40(curContext.blockNumber);
-        } else {
-            // The last element is a queue tx, therefore pull timestamp and block number from the
-            // queue element.
-            // curContext.numSubsequentQueueTransactions > 0 which means that we've processed at
-            // least one queue element. We increment nextQueueIndex after processing each queue
-            // element, so the index of the last element we processed is nextQueueIndex - 1.
-            Lib_OVMCodec.QueueElement memory lastElement = queueElements[nextQueueIndex - 1];
-
-            blockTimestamp = lastElement.timestamp;
-            blockNumber = lastElement.blockNumber;
-        }
+        uint40 blockTimestamp = uint40(curContext.timestamp);
+        uint40 blockNumber = uint40(curContext.blockNumber);
 
         // Cache the previous blockhash to ensure all transaction data can be retrieved efficiently.
         _appendBatch(

packages/contracts/test/contracts/L1/messaging/deposit.gas.spec.ts

@@ -146,7 +146,7 @@ describe('[GAS BENCHMARK] Depositing via the standard bridge', () => {
       const receipt = await res.wait()
       const gasUsed = receipt.gasUsed.toNumber()
       console.log('    - Gas used:', gasUsed)
-      expectApprox(gasUsed, 116_003, {
+      expectApprox(gasUsed, 95_017, {
         absoluteUpperDeviation: 500,
         // Assert a lower bound of 1% reduction on gas cost. If your tests are breaking because your
         // contracts are too efficient, consider updating the target value!
@@ -173,7 +173,7 @@ describe('[GAS BENCHMARK] Depositing via the standard bridge', () => {
       const receipt = await res.wait()
       const gasUsed = receipt.gasUsed.toNumber()
       console.log('    - Gas used:', gasUsed)
-      expectApprox(gasUsed, 163_844, {
+      expectApprox(gasUsed, 142_858, {
         absoluteUpperDeviation: 500,
         // Assert a lower bound of 1% reduction on gas cost. If your tests are breaking because your
         // contracts are too efficient, consider updating the target value!

packages/contracts/test/contracts/L1/rollup/CanonicalTransactionChain.gas.spec.ts

@@ -293,7 +293,7 @@ describe('[GAS BENCHMARK] CanonicalTransactionChain', () => {
 
       console.log('Benchmark complete.')
 
-      expectApprox(gasUsed, 187_081, {
+      expectApprox(gasUsed, 166_094, {
         absoluteUpperDeviation: 500,
         // Assert a lower bound of 1% reduction on gas cost. If your tests are breaking because your
         // contracts are too efficient, consider updating the target value!
@@ -314,7 +314,7 @@ describe('[GAS BENCHMARK] CanonicalTransactionChain', () => {
 
       console.log('Benchmark complete.')
 
-      expectApprox(gasUsed, 126_700, {
+      expectApprox(gasUsed, 105_713, {
         absoluteUpperDeviation: 500,
         // Assert a lower bound of 1% reduction on gas cost. If your tests are breaking because your
         // contracts are too efficient, consider updating the target value!

packages/contracts/test/contracts/L1/rollup/CanonicalTransactionChain.spec.ts

@@ -301,8 +301,8 @@ describe('CanonicalTransactionChain', () => {
               )
             ).to.deep.include({
               transactionHash,
-              timestamp,
-              blockNumber,
+              timestamp: 0,
+              blockNumber: 0,
             })
           })
         }
@@ -345,8 +345,8 @@ describe('CanonicalTransactionChain', () => {
               )
             ).to.deep.include({
               transactionHash,
-              timestamp,
-              blockNumber,
+              timestamp: 0,
+              blockNumber: 0,
             })
           })
         }
@@ -388,8 +388,8 @@ describe('CanonicalTransactionChain', () => {
               )
             ).to.deep.include({
               transactionHash,
-              timestamp,
-              blockNumber,
+              timestamp: 0,
+              blockNumber: 0,
             })
           })
         }