AddToCartForm should support multiple instances

Does this have to do with the static counter added in #2827721: AddToCartForm should support all purchasable entities instead of when it was based on the product ID? Not quite sure, but would be worth checking out.

@steveoliver
Try applying #575 and see if that will work for you.

drugan the issue is the form ID. Using a static counter was not working because it didn't increment properly.

This ensures a unique add to cart form ID.

-    $form_id .= '_' . self::$formInstanceId;
 +    $form_id .= '_' . $this->entity->getPurchasedEntity()->id();

@mglaman

It didn't increment properly because it should be changed like this:

    if ($this->operation != 'default') {
      $form_id = $form_id . '_' . $this->operation;
    }
-    $form_id .= '_' . self::$formInstanceId;
+    $form_id .= '_' . static::$formInstanceId;

But anyway, if we'll get right incrementing the bug indicating by steveoliver #4 is still there. As I think the issue not only on the add to cart form ID, but also with not properly detected $selected_variation.

See ProductVariationAttributesWidget.php

    if (!empty($user_input)) {
      $selected_variation = $this->selectVariationFromUserInput($variations, $user_input);
    }

For me #575 has resolved the steveoliver's issue. Still the ajax wrapper is not working properly because when you choose an attribute option, let's say on the seventh add to cart form in the view then you thrown up to the first add to cart form in the view instead of staying at the seventh form.

Let's go back to #2827721: AddToCartForm should support all purchasable entities since that's where the regression originated.