Fixed a bug where update cart could return unnecessary validation errors

Author: nfourtythree

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release Notes for Craft Commerce
 
+## Unreleased
+
+- Fixed a bug where the `commerce/cart/update-cart` action could return unnecessary validation errors. ([3873](https://github.com/craftcms/commerce/issues/3873))
+
 ## 4.9.2 - 2025-08-20
 
 - Fixed a PHP error that could occur when saving an order from an `EVENT_ORDER_STATUS_CHANGE` event handler. ([#4101](https://github.com/craftcms/commerce/issues/4101))

src/elements/Variant.php

@@ -882,7 +882,7 @@ public function populateLineItem(LineItem $lineItem): void
         // Since we do not have a proper stock reservation system, we need deduct stock if they have more in the cart than is available, and to do this quietly.
         // If this occurs in the payment request, the user will be notified the order has changed.
         if (($order = $lineItem->getOrder()) && !$order->isCompleted) {
-            if (($lineItem->qty > $this->stock) && !$this->hasUnlimitedStock) {
+            if (($lineItem->qty > $this->stock) && !$this->hasUnlimitedStock && $this->stock > 0) {
                 /** @var Order $order */
                 $message = Craft::t('commerce', '{description} only has {stock} in stock.', ['description' => $lineItem->getDescription(), 'stock' => $this->stock]);
                 /** @var OrderNotice $notice */

src/elements/traits/OrderValidatorsTrait.php

@@ -111,6 +111,7 @@ public function validateAddressReuse(string $attribute): void
      */
     public function validateLineItems(): void
     {
+        OrderHelper::normalizeLineItemPurchasableAvailability($this);
         OrderHelper::mergeDuplicateLineItems($this);
 
         foreach ($this->getLineItems() as $key => $lineItem) {

src/helpers/Order.php

@@ -7,7 +7,13 @@
 
 namespace craft\commerce\helpers;
 
+use Craft;
+use craft\commerce\base\Purchasable;
 use craft\commerce\elements\Order as OrderElement;
+use craft\commerce\elements\Variant;
+use craft\commerce\models\OrderNotice;
+use craft\commerce\Plugin;
+use yii\base\InvalidConfigException;
 
 /**
  * Order helper
@@ -44,4 +50,54 @@ public static function mergeDuplicateLineItems(OrderElement $order): bool
 
         return $lineItems > $lineItemsByKey;
     }
+
+    /**
+     * Removes any line items from the cart that are no longer available.
+     * If a line item is available but the quantity is more than the available stock,
+     * the quantity will be reduced to the available stock.
+     * A notice will be added to the cart for each change.
+     *
+     * @param OrderElement $order
+     * @return void
+     * @throws InvalidConfigException
+     * @since 4.9.3
+     */
+    public static function normalizeLineItemPurchasableAvailability(OrderElement $order): void
+    {
+        if ($order->isCompleted) {
+            return;
+        }
+
+        foreach ($order->getLineItems() as $lineItem) {
+            /* @var $purchasable Purchasable */
+            $purchasable = $lineItem->getPurchasable();
+            if (!$purchasable || !Plugin::getInstance()->getPurchasables()->isPurchasableAvailable($purchasable, $order)) {
+                $message = Craft::t('commerce', '{description} is no longer available.', ['description' => $lineItem->getDescription()]);
+                /** @var OrderNotice $notice */
+                $notice = Craft::createObject([
+                    'class' => OrderNotice::class,
+                    'attributes' => [
+                        'message' => $message,
+                        'type' => 'lineItemRemoved',
+                        'attribute' => 'lineItems',
+                    ],
+                ]);
+                $order->addNotice($notice);
+                $order->removeLineItem($lineItem);
+            } elseif ($purchasable instanceof Variant && ($lineItem->qty > $purchasable->stock) && !$purchasable->hasUnlimitedStock && $purchasable->stock > 0) {
+                $message = Craft::t('commerce', '{description} only has {stock} in stock.', ['description' => $lineItem->getDescription(), 'stock' => $purchasable->stock]);
+                /** @var OrderNotice $notice */
+                $notice = Craft::createObject([
+                    'class' => OrderNotice::class,
+                    'attributes' => [
+                        'type' => 'lineItemSalePriceChanged',
+                        'attribute' => "lineItems.$lineItem->id.qty",
+                        'message' => $message,
+                    ],
+                ]);
+                $order->addNotice($notice);
+                $lineItem->qty = $purchasable->stock;
+            }
+        }
+    }
 }