feat: single tx block root rollup (#11096)

- Remove `PrivateKernelEmpty` and `EmptyNested`.
- Introduce a new `SingleTxBlockRootRollup` circuit.
- Allow submitting a block without txs using `EmptyBlockRootRollup`.
  - Which allows updating the `l1_to_l2_message_tree`.

l1-contracts/foundry.toml

@@ -16,6 +16,8 @@ remappings = [
 fs_permissions = [
   {access = "read", path = "./test/fixtures/mixed_block_1.json"},
   {access = "read", path = "./test/fixtures/mixed_block_2.json"},
+  {access = "read", path = "./test/fixtures/single_tx_block_1.json"},
+  {access = "read", path = "./test/fixtures/single_tx_block_2.json"},
   {access = "read", path = "./test/fixtures/empty_block_1.json"},
   {access = "read", path = "./test/fixtures/empty_block_2.json"},
   {access = "read", path = "./test/fixtures/fee_data_points.json"},

l1-contracts/src/core/libraries/ConstantsGen.sol

@@ -70,22 +70,21 @@ library Constants {
   uint256 internal constant MAX_UNENCRYPTED_LOGS_PER_TX = 8;
   uint256 internal constant MAX_CONTRACT_CLASS_LOGS_PER_TX = 1;
   uint256 internal constant NUMBER_OF_L1_L2_MESSAGES_PER_ROLLUP = 16;
-  uint256 internal constant EMPTY_NESTED_INDEX = 0;
-  uint256 internal constant PRIVATE_KERNEL_EMPTY_INDEX = 1;
-  uint256 internal constant PRIVATE_KERNEL_INIT_INDEX = 2;
-  uint256 internal constant PRIVATE_KERNEL_INNER_INDEX = 3;
-  uint256 internal constant PRIVATE_KERNEL_TAIL_INDEX = 4;
-  uint256 internal constant PRIVATE_KERNEL_TAIL_TO_PUBLIC_INDEX = 5;
-  uint256 internal constant TUBE_VK_INDEX = 6;
-  uint256 internal constant PRIVATE_BASE_ROLLUP_VK_INDEX = 8;
-  uint256 internal constant PUBLIC_BASE_ROLLUP_VK_INDEX = 9;
-  uint256 internal constant BASE_PARITY_INDEX = 10;
-  uint256 internal constant ROOT_PARITY_INDEX = 11;
-  uint256 internal constant MERGE_ROLLUP_INDEX = 12;
-  uint256 internal constant BLOCK_ROOT_ROLLUP_INDEX = 13;
-  uint256 internal constant BLOCK_MERGE_ROLLUP_INDEX = 14;
-  uint256 internal constant ROOT_ROLLUP_INDEX = 15;
-  uint256 internal constant BLOCK_ROOT_ROLLUP_EMPTY_INDEX = 16;
+  uint256 internal constant PRIVATE_KERNEL_INIT_INDEX = 0;
+  uint256 internal constant PRIVATE_KERNEL_INNER_INDEX = 1;
+  uint256 internal constant PRIVATE_KERNEL_TAIL_INDEX = 2;
+  uint256 internal constant PRIVATE_KERNEL_TAIL_TO_PUBLIC_INDEX = 3;
+  uint256 internal constant TUBE_VK_INDEX = 4;
+  uint256 internal constant PRIVATE_BASE_ROLLUP_VK_INDEX = 6;
+  uint256 internal constant PUBLIC_BASE_ROLLUP_VK_INDEX = 7;
+  uint256 internal constant MERGE_ROLLUP_INDEX = 8;
+  uint256 internal constant BLOCK_ROOT_ROLLUP_INDEX = 9;
+  uint256 internal constant BLOCK_ROOT_ROLLUP_SINGLE_TX_INDEX = 10;
+  uint256 internal constant BLOCK_ROOT_ROLLUP_EMPTY_INDEX = 11;
+  uint256 internal constant BLOCK_MERGE_ROLLUP_INDEX = 12;
+  uint256 internal constant ROOT_ROLLUP_INDEX = 13;
+  uint256 internal constant BASE_PARITY_INDEX = 14;
+  uint256 internal constant ROOT_PARITY_INDEX = 15;
   uint256 internal constant PRIVATE_KERNEL_RESET_INDEX = 20;
   uint256 internal constant FUNCTION_SELECTOR_NUM_BYTES = 4;
   uint256 internal constant INITIALIZATION_SLOT_SEPARATOR = 1000000000;

l1-contracts/src/core/libraries/Errors.sol

@@ -38,7 +38,6 @@ library Errors {
     uint32 deadlinePassed
   ); // 0x5e789f34
   error Outbox__InvalidPathLength(uint256 expected, uint256 actual); // 0x481bcd9c
-  error Outbox__InsertingInvalidRoot(); // 0x73c2daca
   error Outbox__RootAlreadySetAtBlock(uint256 l2BlockNumber); // 0x3eccfd3e
   error Outbox__InvalidRecipient(address expected, address actual); // 0x57aad581
   error Outbox__AlreadyNullified(uint256 l2BlockNumber, uint256 leafIndex); // 0xfd71c2d4

l1-contracts/src/core/libraries/crypto/MerkleLib.sol

@@ -60,24 +60,27 @@ library MerkleLib {
    * @return (min, max) - The min and max path sizes.
    */
   function computeMinMaxPathLength(uint256 _numTxs) internal pure returns (uint256, uint256) {
-    uint256 numTxs = _numTxs < 2 ? 2 : _numTxs;
+    if (_numTxs < 2) {
+      return (0, 0);
+    }
+
     uint256 numSubtrees = 0;
     uint256 currentSubtreeSize = 1;
     uint256 currentSubtreeHeight = 0;
     uint256 firstSubtreeHeight;
     uint256 finalSubtreeHeight;
-    while (numTxs != 0) {
+    while (_numTxs != 0) {
       // If size & txs == 0, the subtree doesn't exist for this number of txs
-      if (currentSubtreeSize & numTxs == 0) {
+      if (currentSubtreeSize & _numTxs == 0) {
         currentSubtreeSize <<= 1;
         currentSubtreeHeight++;
         continue;
       }
       // Assign the smallest rightmost subtree height
       if (numSubtrees == 0) finalSubtreeHeight = currentSubtreeHeight;
       // Assign the largest leftmost subtree height
-      if (numTxs - currentSubtreeSize == 0) firstSubtreeHeight = currentSubtreeHeight;
-      numTxs -= currentSubtreeSize;
+      if (_numTxs - currentSubtreeSize == 0) firstSubtreeHeight = currentSubtreeHeight;
+      _numTxs -= currentSubtreeSize;
       currentSubtreeSize <<= 1;
       currentSubtreeHeight++;
       numSubtrees++;

l1-contracts/src/core/messagebridge/Outbox.sol

@@ -47,7 +47,6 @@ contract Outbox is IOutbox {
     override(IOutbox)
   {
     require(msg.sender == address(ROLLUP), Errors.Outbox__Unauthorized());
-    require(_root != bytes32(0), Errors.Outbox__InsertingInvalidRoot());
 
     roots[_l2BlockNumber].root = _root;
     roots[_l2BlockNumber].minHeight = _minHeight;

l1-contracts/test/Outbox.t.sol

@@ -67,14 +67,6 @@ contract OutboxTest is Test {
     outbox.insert(1, root, DEFAULT_TREE_HEIGHT);
   }
 
-  function testRevertIfInsertingEmptyRoot() public {
-    bytes32 root = bytes32(0);
-
-    vm.prank(ROLLUP_CONTRACT);
-    vm.expectRevert(abi.encodeWithSelector(Errors.Outbox__InsertingInvalidRoot.selector));
-    outbox.insert(1, root, DEFAULT_TREE_HEIGHT);
-  }
-
   // This function tests the insertion of random arrays of L2 to L1 messages
   // We make a naive tree with a computed height, insert the leafs into it, and compute a root. We then add the root as the root of the
   // L2 to L1 message tree, expect for the correct event to be emitted, and then query for the root in the contract—making sure the roots, as well as the

l1-contracts/test/Rollup.t.sol

@@ -626,10 +626,8 @@ contract RollupTest is DecoderBase, TimeFns {
     uint256 minHeightEmpty =
       uint256(vm.load(address(outbox), bytes32(uint256(keccak256(abi.encode(1, 0))) + 1)));
 
-    assertNotEq(rootEmpty, bytes32(0), "Invalid root");
+    assertEq(rootEmpty, bytes32(0), "Invalid root");
     assertNotEq(minHeightEmpty, 0, "Invalid min height");
-    assertNotEq(rootEmpty, rootMixed, "Invalid root");
-    assertNotEq(minHeightEmpty, minHeightMixed, "Invalid min height");
   }
 
   function testShouldNotBeTooEagerToPrune() public setUpFor("mixed_block_1") {
@@ -841,6 +839,26 @@ contract RollupTest is DecoderBase, TimeFns {
     assertEq(rollup.getProvenBlockNumber(), 0 + toProve, "Invalid proven block number");
   }
 
+  function testSingleBlock(bool _toProve) public setUpFor("single_tx_block_1") {
+    _testBlock("single_tx_block_1", _toProve);
+
+    assertEq(rollup.getPendingBlockNumber(), 1, "Invalid pending block number");
+    assertEq(rollup.getProvenBlockNumber(), _toProve ? 1 : 0, "Invalid proven block number");
+  }
+
+  function testConsecutiveSingleTxBlocks(uint256 _blocksToProve)
+    public
+    setUpFor("single_tx_block_1")
+  {
+    uint256 toProve = bound(_blocksToProve, 0, 2);
+
+    _testBlock("single_tx_block_1", toProve > 0);
+    _testBlock("single_tx_block_2", toProve > 1);
+
+    assertEq(rollup.getPendingBlockNumber(), 2, "Invalid pending block number");
+    assertEq(rollup.getProvenBlockNumber(), 0 + toProve, "Invalid proven block number");
+  }
+
   function testRevertSubmittingProofForBlocksAcrossEpochs() public setUpFor("mixed_block_1") {
     _testBlock("mixed_block_1", false, 1);
     _testBlock("mixed_block_2", false, TestConstants.AZTEC_EPOCH_DURATION + 1);
@@ -1275,19 +1293,20 @@ contract RollupTest is DecoderBase, TimeFns {
     }
 
     bytes32 l2ToL1MessageTreeRoot;
-    {
+    uint32 numTxs = full.block.numTxs;
+    if (numTxs != 0) {
       // NB: The below works with full blocks because we require the largest possible subtrees
       // for L2 to L1 messages - usually we make variable height subtrees, the roots of which
       // form a balanced tree
 
       // The below is a little janky - we know that this test deals with full txs with equal numbers
       // of msgs or txs with no messages, so the division works
       // TODO edit full.messages to include information about msgs per tx?
-      uint32 numTxs = full.block.numTxs;
       uint256 subTreeHeight = full.messages.l2ToL1Messages.length == 0
         ? 0
         : merkleTestUtil.calculateTreeHeightFromSize(full.messages.l2ToL1Messages.length / numTxs);
-      uint256 outHashTreeHeight = merkleTestUtil.calculateTreeHeightFromSize(numTxs);
+      uint256 outHashTreeHeight =
+        numTxs == 1 ? 0 : merkleTestUtil.calculateTreeHeightFromSize(numTxs);
       uint256 numMessagesWithPadding = numTxs * Constants.MAX_L2_TO_L1_MSGS_PER_TX;
 
       uint256 treeHeight = subTreeHeight + outHashTreeHeight;

l1-contracts/test/fixtures/empty_block_1.json

@@ -1,34 +1,51 @@
 {
   "populate": {
-    "l1ToL2Content": [],
-    "recipient": "0x0000000000000000000000000000000000000000000000000000000000000000",
+    "l1ToL2Content": [
+      "0x0000000000000000000000000000000000000000000000000000000000000401",
+      "0x0000000000000000000000000000000000000000000000000000000000000402",
+      "0x0000000000000000000000000000000000000000000000000000000000000403",
+      "0x0000000000000000000000000000000000000000000000000000000000000404",
+      "0x0000000000000000000000000000000000000000000000000000000000000405",
+      "0x0000000000000000000000000000000000000000000000000000000000000406",
+      "0x0000000000000000000000000000000000000000000000000000000000000407",
+      "0x0000000000000000000000000000000000000000000000000000000000000408",
+      "0x0000000000000000000000000000000000000000000000000000000000000409",
+      "0x000000000000000000000000000000000000000000000000000000000000040a",
+      "0x000000000000000000000000000000000000000000000000000000000000040b",
+      "0x000000000000000000000000000000000000000000000000000000000000040c",
+      "0x000000000000000000000000000000000000000000000000000000000000040d",
+      "0x000000000000000000000000000000000000000000000000000000000000040e",
+      "0x000000000000000000000000000000000000000000000000000000000000040f",
+      "0x0000000000000000000000000000000000000000000000000000000000000410"
+    ],
+    "recipient": "0x1647b194c649f5dd01d7c832f89b0f496043c9150797923ea89e93d5ac619a93",
     "sender": "0x9965507D1a55bcC2695C58ba16FB37d819B0A4dc"
   },
   "messages": {
     "l2ToL1Messages": []
   },
   "block": {
-    "archive": "0x2e558c94bd1a3d8512eaf74c297f8a5b28ca14c79636a9f81e0538804b21ff6c",
-    "blockHash": "0x20e7264407d9dad46301cd1ac2720619fa899e0dc07e2aeaaf1f58a9fe0d9b42",
+    "archive": "0x19d282bf5387d54a21db424a09ee23196be74da0dfbb4ca28a4939020da2adc4",
+    "blockHash": "0x0d03dd1cec142b914011e7ebf5375295b8ae9cec88accfb41b6bcbc5cb2e74f1",
     "body": "0x00000000",
     "decodedHeader": {
       "contentCommitment": {
         "blobsHash": "0x001cedbd7ea5309ef9d1d159209835409bf41b6b1802597a52fa70cc82e934d9",
         "inHash": "0x00089a9d421a82c4a25f7acbebe69e638d5b064fa8a60e018793dcb0be53752c",
-        "outHash": "0x00f5a5fd42d16a20302798ef6ed309979b43003d2320d9f0e8ea9831a92759fb",
-        "numTxs": 2
+        "outHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
+        "numTxs": 0
       },
       "globalVariables": {
         "blockNumber": 1,
-        "slotNumber": "0x0000000000000000000000000000000000000000000000000000000000000012",
+        "slotNumber": "0x000000000000000000000000000000000000000000000000000000000000001b",
         "chainId": 31337,
-        "timestamp": 1732961424,
+        "timestamp": 1736363020,
         "version": 1,
-        "coinbase": "0x2cf4a1c62581a88edae4234f887da6b9551ab171",
-        "feeRecipient": "0x0339e43debc9c5093c6862f6dea7ff66fcd7f45c01f87dfa61f802d30530ea4e",
+        "coinbase": "0xb3402d01fb3d2005f49fa063cc2470cd3dcd8cee",
+        "feeRecipient": "0x1e5f75a4eff0236113040956df38e3ec6b175c9a46e289972a69ffb812506b21",
         "gasFees": {
           "feePerDaGas": 0,
-          "feePerL2Gas": 54153588500
+          "feePerL2Gas": 54153579570
         }
       },
       "totalFees": "0x0000000000000000000000000000000000000000000000000000000000000000",
@@ -44,11 +61,11 @@
         },
         "partialStateReference": {
           "noteHashTree": {
-            "nextAvailableLeafIndex": 128,
+            "nextAvailableLeafIndex": 0,
             "root": "0x1fd848aa69e1633722fe249a5b7f53b094f1c9cef9f5c694b073fd1cc5850dfb"
           },
           "nullifierTree": {
-            "nextAvailableLeafIndex": 256,
+            "nextAvailableLeafIndex": 128,
             "root": "0x0c499b373a1f0fe1b510a63563546d2d39e206895056a5af0143c5f30d639073"
           },
           "publicDataTree": {
@@ -58,8 +75,8 @@
         }
       }
     },
-    "header": "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",
-    "publicInputsHash": "0x005838c184fb9da5be8d12382acd314219bbf72275c7242738bcb5c334f509ef",
+    "header": "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",
+    "publicInputsHash": "0x00275dc890b7255d4fa73d97e7ee5711f4bca05e6b8f8240b4c44468ff32f23e",
     "blobInputs": "0x01010657f37554c781402a22917dee2f75def7ab966d7b770905398eba3c4440140ac4f3ee53aedc4865073ae7fb664e7401d10eadbe3bbcc266c35059f14826bb0000000000000000000000000000000000000000000000000000000000000000c00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000c00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
     "numTxs": 0
   }