[FIX] sale_loyalty: prevent tax splitting on discount line

[fw-bot]

Steps to produce:

• Install website_sale, l10n_ca & accountant modules with demo data.
• Switch to a Canadian (CA) company.
• Go to Settings and enable Discounts, Loyalty & Gift Cards.
• Go to Website > eCommerce > Loyalty > Discount & Loyalty.
• Create a new program > Set Program Type to Discount Code > Under Conditional Rules, set Minimum Purchase to 0 > Under Rewards, choose Discount on Order.
• Go to website > configuration > websites > Create a new website for the CA company > Set it as default (first in sequence).
• Create new product > Set Sales Taxes to 14.975% GST + QST > Publish the product.
• Open the website in an incognito window > Add the product to the cart > Apply the discount code.
• In the main tab > Go to Website > eCommerce > Orders > Open the corresponding order > In the Other Info tab, change the fiscal position to Quebec (QC) > Click to update taxes.

Issue:

• The tax on the discount line is split into: 14.975% GST + QST & 9.975% QST.

Root cause:

• When a discount is applied in the cart, the discount line initially carries split taxes: 5% GST and 9.975% QST.
• After changing the fiscal position to Quebec (QC), the system replaces 5% GST with 14.975% GST + QST because 5% GST is present in replace of 14.975% GST. so at [1] it replaces 5% GST with 14.975% GST and do nothing for 9.975% QST.
• In 17.0, the discount line directly uses 14.975% GST + QST (no tax splitting), so this issue does not occur.
• In 18.0, at [2], taxes are explicitly split and added to the base line, and the same split taxes are reused during grouping. This leads to multiple taxes being displayed on the sale order line.

Fix:

• Avoid splitting taxes on the discount line in the sale order.
• Keep the original tax structure intact to prevent duplication after fiscal position changes.

[1]

odoo/addons/account/models/partner.py

Lines 151 to 156 in c6d9fa5

	def map_tax(self, taxes):
	return self.env['account.tax'].browse(unique(
	tax_id
	for tax in taxes
	for tax_id in (self.tax_map or {}).get(tax.id, [tax.id])
	))

[2]

odoo/addons/sale_loyalty/models/sale_order.py

Line 296 in c6d9fa5

taxes = base_line['tax_ids'].flatten_taxes_hierarchy()

opw-6145674

I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

Forward-Port-Of: #265233
Forward-Port-Of: #262147

[robodoo]

[fw-bot]

This PR targets saas-18.3 and is part of the forward-port chain. Further PRs will be created up to master.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[fw-bot]

@krip-odoo ci/runbot failed on this forward-port PR