chore: Adding Core unit tests

.forge-snapshots/settler_metaTxn_uniswapV3_USDT-WETH.snap

@@ -1 +1 @@
-160735
+160734

.forge-snapshots/zeroEx_uniswapV3VIP_multiplex1_USDC-WETH.snap

@@ -1 +1 @@
-138683
+138686

.forge-snapshots/zeroEx_uniswapV3VIP_multiplex2_USDC-WETH.snap

@@ -1 +1 @@
-181465
+181468

README.md

@@ -31,7 +31,7 @@ Note: The following is more akin to `gasLimit` than it is `gasUsed`, this is due
 | VIP                 | DEX        | Pair      | Gas    | %      |
 | ------------------- | ---------- | --------- | ------ | ------ |
 | 0x V4 VIP           | Uniswap V3 | USDC/WETH | 125117 | 0.00%  |
-| 0x V4 Multiplex     | Uniswap V3 | USDC/WETH | 138683 | 10.84% |
+| 0x V4 Multiplex     | Uniswap V3 | USDC/WETH | 138686 | 10.85% |
 | Settler VIP (warm)  | Uniswap V3 | USDC/WETH | 134857 | 7.78%  |
 | AllowanceHolder VIP | Uniswap V3 | USDC/WETH | 130694 | 4.46%  |
 | UniswapRouter V3    | Uniswap V3 | USDC/WETH | 121137 | -3.18% |
@@ -73,7 +73,7 @@ Note: The following is more akin to `gasLimit` than it is `gasUsed`, this is due
 | Settler          | Uniswap V3 | DAI/WETH  | 154057 | -36.05% |
 |                  |            |           |        |         |
 | 0x V4 Multiplex  | Uniswap V3 | USDT/WETH | 243700 | 0.00%   |
-| Settler          | Uniswap V3 | USDT/WETH | 160735 | -34.04% |
+| Settler          | Uniswap V3 | USDT/WETH | 160734 | -34.04% |
 |                  |            |           |        |         |
 
 | OTC     | DEX     | Pair      | Gas    | %      |

foundry.toml

@@ -8,7 +8,7 @@ no_match_path = "*/integration/*"
 fuzz_runs = 10000
 # needed for marktoda/forge-gas-snapshot
 ffi = true
-fs_permissions = [{ access = "read-write", path = ".forge-snapshots/"}]
+fs_permissions = [{ access = "read-write", path = ".forge-snapshots/"},{ access = "read", path = "out"}]
 evm_version = "shanghai"
 
 [profile.integration]

src/core/Basic.sol

@@ -26,12 +26,14 @@ abstract contract Basic is Permit2PaymentAbstract {
             revert ConfusedDeputy();
         }
 
+        bool success;
+        bytes memory returnData;
         uint256 value;
         if (sellToken == IERC20(ETH_ADDRESS)) {
             value = address(this).balance.mulDiv(bips, 10_000);
             if (data.length == 0) {
                 if (offset != 0) revert InvalidOffset();
-                (bool success, bytes memory returnData) = payable(pool).call{value: value}("");
+                (success, returnData) = payable(pool).call{value: value}("");
                 success.maybeRevert(returnData);
                 return;
             } else {
@@ -56,7 +58,7 @@ abstract contract Basic is Permit2PaymentAbstract {
                 sellToken.safeApproveIfBelow(pool, amount);
             }
         }
-        (bool success, bytes memory returnData) = payable(pool).call{value: value}(data);
+        (success, returnData) = payable(pool).call{value: value}(data);
         success.maybeRevert(returnData);
         // forbid sending data to EOAs
         if (returnData.length == 0 && pool.code.length == 0) revert InvalidTarget();

src/core/OtcOrderSettlement.sol

@@ -19,12 +19,12 @@ abstract contract OtcOrderSettlement is SettlerAbstract {
         bool partialFillAllowed;
     }
 
-    /// @dev Emitted whenever an OTC order is filled.
+    /// @dev Emitted whenever an Otc order is filled.
     /// @param orderHash The canonical hash of the order. Formed as an EIP712 struct hash. See below.
     /// @param maker The maker of the order.
     /// @param taker The taker of the order.
-    /// @param makerTokenFilledAmount How much maker token was filled.
-    /// @param takerTokenFilledAmount How much taker token was filled.
+    /// @param makerTokenFilledAmount Amount of maker token filled.
+    /// @param takerTokenFilledAmount Amount of taker token filled.
     event OtcOrderFilled(
         bytes32 indexed orderHash,
         address maker,
@@ -79,9 +79,8 @@ abstract contract OtcOrderSettlement is SettlerAbstract {
     }
 
     /// @dev Settle an OtcOrder between maker and taker transfering funds directly between
-    /// the counterparties. Two Permit2 signatures are consumed, with the maker Permit2 containing
-    /// a witness of the OtcOrder.
-    /// This variant also includes a fee where the taker or maker pays the fee recipient
+    /// the counterparties. Either two Permit2 signatures are consumed, with the maker Permit2 containing
+    /// a witness of the OtcOrder, or AllowanceHolder is supported for the taker payment.
     function fillOtcOrder(
         address recipient,
         ISignatureTransfer.PermitTransferFrom memory makerPermit,
@@ -101,12 +100,12 @@ abstract contract OtcOrderSettlement is SettlerAbstract {
         bytes32 witness = _hashConsideration(consideration);
         // There is no taker witness (see below)
 
-        // Maker pays recipient (optional fee)
+        // Maker pays recipient
         _transferFrom(makerPermit, makerTransferDetails, maker, witness, CONSIDERATION_WITNESS, makerSig, false);
-        // Taker pays Maker (optional fee)
+        // Taker pays Maker
         // We don't need to include a witness here. Taker is `_msgSender()`, so
         // `recipient` and the maker's details are already authenticated. We're just
-        // using PERMIT2 to move tokens, not to provide authentication.
+        // using Permit2 or AllowanceHolder to move tokens, not to provide authentication.
         _transferFrom(takerPermit, takerTransferDetails, _msgSender(), takerSig);
 
         emit OtcOrderFilled(
@@ -128,6 +127,7 @@ abstract contract OtcOrderSettlement is SettlerAbstract {
     /// @dev Settle an OtcOrder between maker and taker transfering funds directly between
     /// the counterparties. Both Maker and Taker have signed the same order, and submission
     /// is via a third party
+    /// @dev `takerWitness` is not calculated nor verified here as caller is trusted
     function fillOtcOrderMetaTxn(
         address recipient,
         ISignatureTransfer.PermitTransferFrom memory makerPermit,
@@ -151,6 +151,7 @@ abstract contract OtcOrderSettlement is SettlerAbstract {
         makerConsideration.counterparty = taker;
 
         bytes32 makerWitness = _hashConsideration(makerConsideration);
+        // Note: takerWitness is not calculated here, but in the caller code
 
         _transferFrom(makerPermit, makerTransferDetails, maker, makerWitness, CONSIDERATION_WITNESS, makerSig, false);
         _transferFrom(takerPermit, takerTransferDetails, taker, takerWitness, ACTIONS_AND_SLIPPAGE_WITNESS, takerSig);
@@ -169,7 +170,7 @@ abstract contract OtcOrderSettlement is SettlerAbstract {
     /// @dev Settle an OtcOrder between maker and Settler retaining funds in this contract.
     /// @dev pre-condition: msgSender has been authenticated against the requestor
     /// One Permit2 signature is consumed, with the maker Permit2 containing a witness of the OtcOrder.
-    // In this variant, Maker pays Settler and Settler pays Maker
+    // In this variant, Maker pays recipient and Settler pays Maker
     function fillOtcOrderSelfFunded(
         address recipient,
         ISignatureTransfer.PermitTransferFrom memory permit,