Description (*)

Use the item_id as id on the request object to make reset_count work in: \Magento\Quote\Model\Quote\Item\Processor::prepare

Fixed Issues (if relevant)

1. Fixes Rest cart item update throws The requested qty is not available if quantity in cart and quantity to update to exceeds stock #38949

Manual testing scenarios (*)

1. Create guest cart with rest api:
   Post to https://11bfd466f8c258a1113feb50fd641584.instances-prod.magento-community.engineering/rest/V1/guest-carts/ and use that masked id.

2. Get the guest cart to determine quote id:
   Get to https://11bfd466f8c258a1113feb50fd641584.instances-prod.magento-community.engineering/rest/V1/guest-carts/{{masked_id}}

3. Add just 1 configurable to cart:
   Post to: https://11bfd466f8c258a1113feb50fd641584.instances-prod.magento-community.engineering/rest/V1/guest-carts/{{masked_id}}/items with body:

{
  "cartItem": {
    "sku": "MH02",
    "qty": 1,
    "quote_id": "{{quote_id}}",
    "product_option": {
      "extension_attributes": {
        "configurable_item_options": [
          {
            "option_id": "93",
            "option_value": 49
          },
          {
            "option_id": "142",
            "option_value": 166
          }
        ]
      }
    },
    "extension_attributes": {}
  }
}

4. Update the qty to 100 (default stock for a simple of a configurable product)
   

Note: Use the item_id of the configurable type (not the simple)

PUT to https://11bfd466f8c258a1113feb50fd641584.instances-prod.magento-community.engineering/rest/V1/guest-carts/{{masked_id}}/items/{{item_id}} with body:

{
  "cartItem": {
    "sku": "MH02",
    "qty": 100,
    "quote_id": "{{quote_id}}",
    "product_option": {
      "extension_attributes": {
        "configurable_item_options": [
          {
            "option_id": "93",
            "option_value": 49
          },
          {
            "option_id": "142",
            "option_value": 166
          }
        ]
      }
    },
    "extension_attributes": {}
  }
}

Now the response of the call is:

{
    "message": "The requested qty is not available"
}

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)