Adding "out of stock" product confgurations to cart - wrong notification

[jakobfdev]

Preconditions

1. Magento 2.1.2 from composer
2. PHP 5.6, MySQL 5.7

Steps to reproduce

1. Fresh magento install
2. Create configurable product with a single config attribute and several simple products
3. Set one simple products stock quantity to 0 and to "Out of stock"
4. In the frontend go to the configurable, choose the config value of the "Out of stock" simple product and add it to cart

Try not to set the first of the configurations out of stock, otherwise you run into
#6799

Expected result

1. There should be a message like "This product is out of stock."

Actual result

1. The message says "You need to choose options for your item." as no configuration was selected.

[quienti]

Duplicate: #7069