Sale Pricelist Display Surcharge

In standard Odoo, a discount is only displayed when it benefits the customer; a surcharge (a price increase) is normally hidden. This module adds a new checkbox "Show Surcharge" on each pricelist rule (the price list item form, in the rule limits group).

When that checkbox is enabled on the pricelist rule used by a sales order line, the module changes how the line price and discount are computed:

• The unit price shown on the line is based on the price before the discount/surcharge is applied, so the surcharge becomes visible.
• The discount field is automatically filled with the resulting percentage, which will be negative when it is a surcharge.
• The calculation only runs when the line has no discount yet, the order has a pricelist, and the matching pricelist rule has the option enabled. A division-by-zero guard avoids errors when the base price is zero.

It touches the sales order line (sale.order.line) and the pricelist item (product.pricelist.item) models, and adds a field to the pricelist item form view. No new menus or reports are added; the option appears directly inside the existing pricelist rule configuration screen.