Cannot Place Order with Configurable Product on Custom Stock.

[nmalevanec]

Preconditions

1. Magento with enabled MSI
2. branch MSI-992

Steps to reproduce

1. Login to admin area.
2. Navigate to Store > Manage Sources.
3. Add new source "Test Source"(code: "test_source").
4. Navigate to Store > Manage Stocks.
5. Add new stock "Test Stock". Assign it to current(default) website.
6. Assign "Test Source" to "Test Stock".
7. Perform reindex and flush cache.
8. Navigate to Catalog > Products.
9. Start creating configurable product.
10. Fill necessary data:
    Product Name: "configurable product"
    SKU: configurable product
    Price: 3
11. Start creating configurations.
12. At "Select Attributes" step select color attribute.
13. At "Attribute Value" step create two options: "blue" and "red".
14. At "Bulk Images & Price" step check "Apply single quantity to each SKUs" and assign "test_source" with qty = 100 (NOTE: do not make assign options to Default Source).
15. Generate products.
16. Set some weight for generated products.
17. Save configurable.
18. Navigate to storefront, configurable product view page
19. Add some configurable product option to cart.
20. Proceed to checkout.
21. Try to place order

Expected result

1. Order placed successfully.

Actual result

1. "Product type is not supported on Default Stock." error message appears.

Looks like we have to rework validation in:
https://github.com/magento-engcom/msi/blob/3321569a87e81abaca18819eafe3d58f0a73f401/app/code/Magento/InventorySales/Model/CheckItemsQuantity.php#L72

[naydav]

#1204

[naydav]

#1205