Remove unnecessary cancelled attribute

packages/contracts/evm-contracts/contracts/orderbook/IOrderbookDex.sol

@@ -11,7 +11,6 @@ interface IOrderbookDex is IERC1155Receiver {
         uint256 assetId;
         uint256 assetAmount;
         uint256 pricePerAsset;
-        bool cancelled;
     }
 
     event OrderCreated(
@@ -48,7 +47,6 @@ interface IOrderbookDex is IERC1155Receiver {
     /// @dev Transfers portions of msg.value to the orders' sellers according to the price.
     /// The sum of asset amounts of filled orders MUST be at least `minimumAsset`.
     /// If msg.value is more than the sum of orders' prices, it MUST refund the excess back to msg.sender.
-    /// An order whose `cancelled` parameter has value `true` MUST NOT be filled.
     /// MUST change the `assetAmount` parameter for the specified order according to how much of it was filled.
     /// MUST emit `OrderFilled` event for each order accordingly.
     function fillOrdersExactEth(
@@ -61,7 +59,6 @@ interface IOrderbookDex is IERC1155Receiver {
     /// by providing a possibly surplus amount of ETH and requesting an exact amount of asset to receive.
     /// @dev Transfers portions of msg.value to the orders' sellers according to the price.
     /// The sum of asset amounts of filled orders MUST be exactly `assetAmount`. Excess ETH MUST be returned back to `msg.sender`.
-    /// An order whose `cancelled` parameter has value `true` MUST NOT be filled.
     /// MUST change the `assetAmount` parameter for the specified order according to how much of it was filled.
     /// MUST emit `OrderFilled` event for each order accordingly.
     /// If msg.value is more than the sum of orders' prices, it MUST refund the difference back to msg.sender.
@@ -72,7 +69,7 @@ interface IOrderbookDex is IERC1155Receiver {
     ) external payable;
 
     /// @notice Cancels the sell order identified by combination `<msg.sender, orderId>`, making it unfillable.
-    /// @dev MUST change the `cancelled` parameter for the specified order to `true`.
+    /// @dev MUST change the `assetAmount` parameter for the specified order to `0`.
     /// MUST emit `OrderCancelled` event.
     function cancelSellOrder(uint256 orderId) external;
 }

packages/contracts/evm-contracts/contracts/orderbook/OrderbookDex.sol

@@ -57,8 +57,7 @@ contract OrderbookDex is IOrderbookDex, ERC1155Holder, ReentrancyGuard {
         Order memory newOrder = Order({
             assetId: assetId,
             assetAmount: assetAmount,
-            pricePerAsset: pricePerAsset,
-            cancelled: false
+            pricePerAsset: pricePerAsset
         });
         uint256 orderId = sellersOrderId[msg.sender];
         orders[msg.sender][orderId] = newOrder;
@@ -71,7 +70,6 @@ contract OrderbookDex is IOrderbookDex, ERC1155Holder, ReentrancyGuard {
     /// @dev Transfers portions of msg.value to the orders' sellers according to the price.
     /// The sum of asset amounts of filled orders MUST be at least `minimumAsset`.
     /// If msg.value is more than the sum of orders' prices, it MUST refund the excess back to msg.sender.
-    /// An order whose `cancelled` parameter has value `true` MUST NOT be filled.
     /// MUST change the `assetAmount` parameter for the specified order according to how much of it was filled.
     /// MUST emit `OrderFilled` event for each order accordingly.
     function fillOrdersExactEth(
@@ -89,7 +87,7 @@ contract OrderbookDex is IOrderbookDex, ERC1155Holder, ReentrancyGuard {
             address payable seller = sellers[i];
             uint256 orderId = orderIds[i];
             Order storage order = orders[seller][orderId];
-            if (order.cancelled || order.assetAmount == 0 || order.pricePerAsset == 0) {
+            if (order.assetAmount == 0) {
                 continue;
             }
             uint256 assetsToBuy = remainingEth / order.pricePerAsset;
@@ -127,7 +125,6 @@ contract OrderbookDex is IOrderbookDex, ERC1155Holder, ReentrancyGuard {
     /// by providing a possibly surplus amount of ETH and requesting an exact amount of asset to receive.
     /// @dev Transfers portions of msg.value to the orders' sellers according to the price.
     /// The sum of asset amounts of filled orders MUST be exactly `assetAmount`. Excess ETH MUST be returned back to `msg.sender`.
-    /// An order whose `cancelled` parameter has value `true` MUST NOT be filled.
     /// MUST change the `assetAmount` parameter for the specified order according to how much of it was filled.
     /// MUST emit `OrderFilled` event for each order accordingly.
     /// If msg.value is more than the sum of orders' prices, it MUST refund the difference back to msg.sender.
@@ -146,7 +143,7 @@ contract OrderbookDex is IOrderbookDex, ERC1155Holder, ReentrancyGuard {
             address payable seller = sellers[i];
             uint256 orderId = orderIds[i];
             Order storage order = orders[seller][orderId];
-            if (order.cancelled || order.assetAmount == 0 || order.pricePerAsset == 0) {
+            if (order.assetAmount == 0) {
                 continue;
             }
             uint256 assetsToBuy = order.assetAmount;
@@ -181,14 +178,14 @@ contract OrderbookDex is IOrderbookDex, ERC1155Holder, ReentrancyGuard {
     }
 
     /// @notice Cancels the sell order identified by combination `<msg.sender, orderId>`, making it unfillable.
-    /// @dev MUST change the `cancelled` parameter for the specified order to `true`.
+    /// @dev MUST change the `assetAmount` parameter for the specified order to `0`.
     /// MUST emit `OrderCancelled` event.
     function cancelSellOrder(uint256 orderId) public virtual {
         Order memory order = orders[msg.sender][orderId];
         if (order.assetAmount == 0) {
             revert OrderDoesNotExist(orderId);
         }
-        orders[msg.sender][orderId].cancelled = true;
+        orders[msg.sender][orderId].assetAmount = 0;
         asset.safeTransferFrom(
             address(this),
             msg.sender,

packages/contracts/evm-contracts/test/OrderbookDex.t.sol

@@ -52,7 +52,6 @@ contract OrderbookDexTest is CTest, ERC1155Holder {
         assertEq(order.assetId, assetId);
         assertEq(order.assetAmount, assetAmount);
         assertEq(order.pricePerAsset, pricePerAsset);
-        assertTrue(!order.cancelled);
         assertEq(asset.balanceOf(address(dex), assetId), assetAmount);
     }
 
@@ -66,7 +65,7 @@ contract OrderbookDexTest is CTest, ERC1155Holder {
         emit IOrderbookDex.OrderCancelled(address(this), orderId);
         dex.cancelSellOrder(orderId);
         IOrderbookDex.Order memory order = dex.getOrder(address(this), orderId);
-        assertTrue(order.cancelled);
+        assertEq(order.assetAmount, 0);
         assertEq(asset.balanceOf(address(dex), assetId), 0);
         assertEq(asset.balanceOf(address(this), assetId), assetAmount);
     }