refactor: generate witness as public field

src/Orders.sol

@@ -50,7 +50,9 @@ abstract contract OrderDestination is IOrders, OrdersPermit2 {
     /// @custom:emits Filled
     function fillPermit2(Output[] memory outputs, OrdersPermit2.Permit2Batch calldata permit2) external {
         // transfer all tokens to the Output recipients via permit2 (includes check on nonce & deadline)
-        _permitWitnessTransferFrom(outputs, _fillTransferDetails(outputs, permit2.permit.permitted), permit2);
+        _permitWitnessTransferFrom(
+            outputsWitness(outputs), _fillTransferDetails(outputs, permit2.permit.permitted), permit2
+        );
 
         // emit
         emit Filled(outputs);
@@ -123,7 +125,9 @@ abstract contract OrderOrigin is IOrders, OrdersPermit2 {
         OrdersPermit2.Permit2Batch calldata permit2
     ) external {
         // transfer all tokens to the tokenRecipient via permit2 (includes check on nonce & deadline)
-        _permitWitnessTransferFrom(outputs, _initiateTransferDetails(tokenRecipient, permit2.permit.permitted), permit2);
+        _permitWitnessTransferFrom(
+            outputsWitness(outputs), _initiateTransferDetails(tokenRecipient, permit2.permit.permitted), permit2
+        );
 
         // emit
         emit Order(permit2.permit.deadline, _inputs(permit2.permit.permitted), outputs);

src/Passage.sol

@@ -109,7 +109,7 @@ contract Passage is PassagePermit2 {
         public
     {
         // transfer tokens to this contract via permit2
-        _permitWitnessTransferFrom(_enterWitness(rollupChainId, rollupRecipient), true, permit2);
+        _permitWitnessTransferFrom(enterWitness(rollupChainId, rollupRecipient), permit2);
         // check and emit
         _enterToken(rollupChainId, rollupRecipient, permit2.permit.permitted.token, permit2.permit.permitted.amount);
     }
@@ -197,7 +197,7 @@ contract RollupPassage is PassagePermit2 {
     /// @custom:emits ExitToken
     function exitTokenPermit2(address hostRecipient, PassagePermit2.Permit2 calldata permit2) public {
         // transfer tokens to this contract
-        _permitWitnessTransferFrom(_exitWitness(hostRecipient), false, permit2);
+        _permitWitnessTransferFrom(exitWitness(hostRecipient), permit2);
         // burn and emit
         _exitToken(hostRecipient, permit2.permit.permitted.token, permit2.permit.permitted.amount);
     }

src/permit2/UsesPermit2.sol

@@ -5,6 +5,12 @@ import {ISignatureTransfer} from "permit2/src/interfaces/ISignatureTransfer.sol"
 import {IOrders} from "../interfaces/IOrders.sol";
 
 abstract contract UsesPermit2 {
+    /// @notice Struct to hold the pre-hashed witness field and the witness type string.
+    struct Witness {
+        bytes32 witnessHash;
+        string witnessTypeString;
+    }
+
     /// @notice The Permit2 contract address.
     address immutable permit2Contract;
 
@@ -33,34 +39,35 @@ abstract contract OrdersPermit2 is UsesPermit2 {
     error OutputMismatch();
 
     /// @notice Transfer a batch of tokens using permit2.
-    /// @param outputs - the Outputs for the witness field.
+    /// @param _witness - the hashed witness and its typestring.
     /// @param transferDetails - the TokenPermissions for the transfer, generated based on the use-case (see `_initiateTransferDetails` and `_fillTransferDetails`).
     /// @param permit2 - the Permit2Batch information.
     function _permitWitnessTransferFrom(
-        IOrders.Output[] memory outputs,
+        Witness memory _witness,
         ISignatureTransfer.SignatureTransferDetails[] memory transferDetails,
         Permit2Batch calldata permit2
     ) internal {
         ISignatureTransfer(permit2Contract).permitWitnessTransferFrom(
             permit2.permit,
             transferDetails,
             permit2.owner,
-            _witness(outputs),
-            _OUTPUT_WITNESS_TYPESTRING,
+            _witness.witnessHash,
+            _witness.witnessTypeString,
             permit2.signature
         );
     }
 
     /// @notice Encode the Output array according to EIP-712 for use as a permit2 witness.
     /// @param outputs - the Outputs to encode.
-    /// @return witness - the encoded witness field.
-    function _witness(IOrders.Output[] memory outputs) internal pure returns (bytes32 witness) {
+    /// @return _witness - the encoded witness field.
+    function outputsWitness(IOrders.Output[] memory outputs) public pure returns (Witness memory _witness) {
         uint256 num = outputs.length;
         bytes32[] memory hashes = new bytes32[](num);
         for (uint256 i = 0; i < num; ++i) {
             hashes[i] = keccak256(abi.encode(_OUTPUT_TYPEHASH, outputs[i]));
         }
-        witness = keccak256(abi.encodePacked(hashes));
+        _witness.witnessHash = keccak256(abi.encodePacked(hashes));
+        _witness.witnessTypeString = _OUTPUT_WITNESS_TYPESTRING;
     }
 
     /// @notice transform Output and TokenPermissions structs to TransferDetails structs, for passing to permit2.
@@ -145,29 +152,36 @@ abstract contract PassagePermit2 is UsesPermit2 {
     }
 
     /// @notice Transfer tokens using permit2.
-    /// @param witness - the pre-hashed witness field.
+    /// @param _witness - the hashed witness and its typestring.
     /// @param permit2 - the Permit2 information.
-    function _permitWitnessTransferFrom(bytes32 witness, bool isEnter, Permit2 calldata permit2) internal {
+    function _permitWitnessTransferFrom(Witness memory _witness, Permit2 calldata permit2) internal {
         ISignatureTransfer(permit2Contract).permitWitnessTransferFrom(
             permit2.permit,
             _passageTransferDetails(permit2.permit.permitted),
             permit2.owner,
-            witness,
-            isEnter ? _ENTER_WITNESS_TYPESTRING : _EXIT_WITNESS_TYPESTRING,
+            _witness.witnessHash,
+            _witness.witnessTypeString,
             permit2.signature
         );
     }
 
     /// @notice Encode & hash the rollupChainId and rollupRecipient for use as a permit2 witness.
-    /// @return witness - the encoded witness field.
-    function _enterWitness(uint256 rollupChainId, address rollupRecipient) internal pure returns (bytes32 witness) {
-        witness = keccak256(abi.encode(_ENTER_WITNESS_TYPEHASH, EnterWitness(rollupChainId, rollupRecipient)));
+    /// @return _witness - the hashed witness and its typestring.
+    function enterWitness(uint256 rollupChainId, address rollupRecipient)
+        public
+        pure
+        returns (Witness memory _witness)
+    {
+        _witness.witnessHash =
+            keccak256(abi.encode(_ENTER_WITNESS_TYPEHASH, EnterWitness(rollupChainId, rollupRecipient)));
+        _witness.witnessTypeString = _ENTER_WITNESS_TYPESTRING;
     }
 
     /// @notice Hash the hostRecipient for use as a permit2 witness.
-    /// @return witness - the encoded witness field.
-    function _exitWitness(address hostRecipient) internal pure returns (bytes32 witness) {
-        witness = keccak256(abi.encode(_EXIT_WITNESS_TYPEHASH, ExitWitness(hostRecipient)));
+    /// @return _witness - the hashed witness and its typestring.
+    function exitWitness(address hostRecipient) public pure returns (Witness memory _witness) {
+        _witness.witnessHash = keccak256(abi.encode(_EXIT_WITNESS_TYPEHASH, ExitWitness(hostRecipient)));
+        _witness.witnessTypeString = _EXIT_WITNESS_TYPESTRING;
     }
 
     /// @notice transform TokenPermissions to TransferDetails, for passing to permit2.

test/Passage.t.sol

@@ -21,8 +21,6 @@ contract PassageTest is Test {
     uint256 gas = 10_000_000;
     uint256 maxFeePerGas = 50;
 
-    uint256 tokenAdminKey = 123;
-
     event Enter(uint256 indexed rollupChainId, address indexed rollupRecipient, uint256 amount);
 
     event EnterToken(