Magento2: Apply coupon code to regular price not to special price

Question

When applying a coupon, it gives a discount to final price (special price if set). How to make modification that discount would apply only to regular prices (before the previous discount).

Note: I don't want to exclude discounted items from the cart.

For instance, I have a discounted product which regular price is 30€ (special price 25€). I apply a coupon which gives a fixed 10€ discount. Final price becomes 15€. It should become 20€.

I've tried not to use special prices on products and set discounts in Catalog Price Rule. Then set Discard subsequent rules on the coupon to Yes expecting that Cart Price Rule would ignore Catalog Price Rule. But it doesn't.

The solution could be to make a module for a custom discount like https://webkul.com/blog/set-custom-discount-fee-cart-magento-2/ described. But how to get the regular price? and applied coupon name is needed to know, too.

Answer 1

I attempted to get around this by enabling special price attribute to be included in promo rules, but was unsuccessful in ignoring special price to apply discount to original price. This should be an option for cart price rules. I'd love to know if there is a better way than to just ignore items in cart with special price thereby allowing special price to be the discount going forward when using that discount shopping cart price rule.