[16] product_margin_classification changes template list_price instead of variant_extra_price

[FreezeS]

Hi guys,

In the current implementation, product_margin_classification is completely unusable for products with variants that have different costs.
Changing the sale price of a variant will change the sale price of all the other variants.

How to reproduce in runboat:

• create a new attribute "Pins", radio, dynamically. Add 3 values: 5,10,15

• create a new product "Test1", at Attributes and Variants select Pins, add all 3 values

• make a new sales order, select product Test1, when popup appears, select Pins - 5. Repeat to create all 3 variants.

• go to the Test1 template, set list_price 50$.

• click on 3 Variants, edit each and set cost the same as pins value. After it should look like this:
  

• go to margin classifications, create a 33% margin like this:

• go to Inventory - Products - Product variants, select Test1 with Pins: 5 and set the margin classification

• click on Decrease price

What I expected to happen:

• variant_extra_price to be set at -42.5 resulting in a sales price of 7.5 for the variant and the sale price of the other variants to remain unchanged

What happens:

• list_price of the template Test1 is set to 7.5 affecting the sales price of all the other variants

• now if I go to another variant, select the same classification and set the price:

This changed the price for the 5 pin version as well:

Proposed fix

def use_theoretical_price(self):
        for product in self:
            product.lst_price = product.theoretical_price

should be

def use_theoretical_price(self):
        for product in self:
            product.variant_extra_price = product.theoretical_price - product.list_price

From my very limited experience, lst_price should not be edited directly as it affects the template list_price. Every modification of a variant's price should be via variant_extra_price.
Can anyone with more experience chime in?