magento2: [GraphQl] Cart error messages are faulty

@Usik2203 I’d rather have something that has to be unique to identify the product, because the product name can be identical for products. Also your solution doesn’t solve the null object that suddenly got added to the items array.

Thanks, @Hexmage the provided code is helpful; one more note here is to add to di.xml

    <type name="Magento\QuoteGraphQl\Model\Resolver\CartItems">
        <plugin name="Magento_CartItems_Add_Source_Errors" type="PathTo\Your\Class\Resolver\CartItems" />
    </type>

They removed the module : https://github.com/magento/magento2-pwa/commit/96c5f5f2ed31865f0b87f096221ddb9245f194da

@marwan-corals The Plugin

/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
declare(strict_types=1);

namespace Experius\CartFix\Plugin\Magento\QuoteGraphQl\Model\Resolver;

use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\GraphQl\Config\Element\Field;
use Magento\Framework\GraphQl\Exception\GraphQlNoSuchEntityException;
use Magento\Framework\GraphQl\Query\Uid;
use Magento\Framework\GraphQl\Schema\Type\ResolveInfo;
use Magento\Quote\Model\Quote;
use Magento\Quote\Model\Quote\Item as QuoteItem;
use Magento\QuoteGraphQl\Model\Cart\GetCartProducts;

/**
 * @inheritdoc
 */
class CartItems
{
    /**
     * @var GetCartProducts
     */
    private $getCartProducts;

    /** @var Uid */
    private $uidEncoder;

    /**
     * @param GetCartProducts $getCartProducts
     * @param Uid $uidEncoder
     */
    public function __construct(
        GetCartProducts $getCartProducts,
        Uid $uidEncoder
    ) {
        $this->getCartProducts = $getCartProducts;
        $this->uidEncoder = $uidEncoder;
    }

    /**
     * @inheritdoc
     */
    public function afterResolve($subject, $result, Field $field, $context, ResolveInfo $info, array $value = null, array $args = null)
    {
        if (!isset($value['model'])) {
            throw new LocalizedException(__('"model" value should be specified'));
        }
        /** @var Quote $cart */
        $cart = $value['model'];

        $itemsData = [];
        $cartProductsData = $this->getCartProductsData($cart);
        $cartItems = $cart->getAllVisibleItems();
        /** @var QuoteItem $cartItem */
        foreach ($cartItems as $cartItem) {
            $productId = $cartItem->getProduct()->getId();
            if (!isset($cartProductsData[$productId])) {
                $itemsData[] = new GraphQlNoSuchEntityException(
                    __("The product that was requested doesn't exist. Verify the product and try again.")
                );
                continue;
            }
            $productData = $cartProductsData[$productId];
            $errorMessages = null;
            if ($cart->getData('has_error')) {
                foreach ($cartItem->getErrorInfos() as $error) {
                    $errorMessages[] = $error;
                }
            }

            $itemsData[] = [
                'id' => $cartItem->getItemId(),
                'uid' => $this->uidEncoder->encode((string) $cartItem->getItemId()),
                'quantity' => $cartItem->getQty(),
                'product' => $productData,
                'errors' =>  $errorMessages,
                'model' => $cartItem,
            ];
        }
        return $itemsData;
    }

    /**
     * Get product data for cart items
     *
     * @param Quote $cart
     * @return array
     */
    private function getCartProductsData(Quote $cart): array
    {
        $products = $this->getCartProducts->execute($cart);
        $productsData = [];
        foreach ($products as $product) {
            $productsData[$product->getId()] = $product->getData();
            $productsData[$product->getId()]['model'] = $product;
            $productsData[$product->getId()]['uid'] = $this->uidEncoder->encode((string) $product->getId());
        }

        return $productsData;
    }
}

The schema.graphqls additions

interface CartItemInterface {
    errors: [Error]
}

type Error {
    origin: String
    type: Int
    message: String
}

@engcom-Hotel I also consider the fact that a null object appears in the items node when an error occurs very crucial to resolve. As it currently breaks default Venia.