Graphql - Merge cart not working correctly when Backorder is enabled

[tushardatar7]

Preconditions and environment

• Magento: 2.4.7-p5
  -PHP 8.3
• Backorder configuration enabled (Allow Qty Below 0)
• Simple / virtual product with 0 qty and Backorder flag set as (Use config settings)

Steps to reproduce

Admin -

1. Enable Backorders (Allow Qty Below 0)
2. Set Qty for product as 0

Frontend / Graphql-

1. Login as customer (mutation generateCustomerToken)
2. Create / Get Customer cart (customerCart query)
3. Add product with 2 qty
4. logout
5. Create empty guest cart (mutation createEmptyCart)
6. Add same product with 3 qty in guest cart.
7. Merge Guest cart to customer cart (mutation MergeCarts)
8. Fetch cart details (cart query)

Expected result

Customer Cart should have product with 5 qty.

Actual result

Customer cart have product with only 2 qty (guest qty is not merged)

Additional information

1. Merge Cart mutation calls Magento\QuoteGraphQl\Model\Cart\MergeCarts\CartQuantityValidatorInterface::validateFinalCartQuantities
2. In this, products current stock validates with customer cart qty + guest cart qty.
3. it deletes product from guest cart if product stock condition is not satisfied

if ($stockCurrentQty < $guestCartItem->getQty() + $customerCartItem->getQty()) {
$this->cartItemRepository->deleteById($guestCart->getId(), $guestCartItem->getItemId());
$modified = true;
}

Release note

No response

Triage and priority

• Severity: S0 - Affects critical data or functionality and leaves users without workaround.
• Severity: S1 - Affects critical data or functionality and forces users to employ a workaround.
• Severity: S2 - Affects non-critical data or functionality and forces users to employ a workaround.
• Severity: S3 - Affects non-critical data or functionality and does not force users to employ a workaround.
• Severity: S4 - Affects aesthetics, professional look and feel, “quality” or “usability”.

[m2-assistant]

Hi @tushardatar7. Thank you for your report.
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[tushardatar7]

@magento I am working on this

[m2-assistant]

Hi @engcom-November. Thank you for working on this issue.
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[tushardatar7]

@magento give me 2.4-develop instance

[tushardatar7]

@magento give me 2.4-develop instance