[FIX] sale_loyalty: prevent coupon removal on double apply

Addresses the issue where reapplying an already applied coupon
in the website shop led to the disappearance of the discount.
With this fix, the discount remains applied, and the system
continues to inform the user that the coupon has already been
used, preventing confusion and maintaining consistency in the
discount application process.

task-3621246

closes odoo/odoo#153485

Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

addons/sale_loyalty/models/sale_order.py

@@ -992,7 +992,7 @@ class SaleOrder(models.Model):
         if not program.filtered_domain(self._get_program_domain()):
             return {'error': _('The program is not available for this order.')}
         elif program in self._get_applied_programs():
-            return {'error': _('This program is already applied to this order.')}
+            return {'error': _('This program is already applied to this order.'), 'already_applied': True}
         # Check for applicability from the program's triggers/rules.
         # This step should also compute the amount of points to give for that program on that order.
         status = self._program_check_compute_points(program)[program]
@@ -1058,7 +1058,7 @@ class SaleOrder(models.Model):
             if 'error' in apply_result and (not program.is_nominative or (program.is_nominative and not coupon)):
                 if rule:
                     self.code_enabled_rule_ids -= rule
-                if coupon:
+                if coupon and not apply_result.get('already_applied', False):
                     self.applied_coupon_ids -= coupon
                 return apply_result
             coupon = apply_result.get('coupon', self.env['loyalty.card'])

addons/website_sale_loyalty/tests/test_shop_sale_coupon.py

@@ -1,10 +1,14 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 from datetime import timedelta
 
-from odoo import fields
+from odoo import fields, http
 from odoo.exceptions import ValidationError
-from odoo.tests import HttpCase, tagged, TransactionCase
+from odoo.fields import Command
+from odoo.tests import HttpCase, tagged
+
 from odoo.addons.sale.tests.test_sale_product_attribute_value_config import TestSaleProductAttributeValueCommon
+from odoo.addons.website.tools import MockRequest
+from odoo.addons.website_sale_loyalty.controllers.main import WebsiteSale
 
 
 @tagged('post_install', '-at_install')
@@ -366,3 +370,55 @@ class TestWebsiteSaleCoupon(HttpCase):
 
         msg = "The coupon should've been removed from the order"
         self.assertEqual(len(order.applied_coupon_ids), 0, msg=msg)
+
+    def test_04_apply_coupon_code_twice(self):
+        """This test ensures that applying a coupon with code twice will:
+            1. Raise an error
+            2. Not delete the coupon
+        """
+        website = self.env['website'].browse(1)
+
+        # Create product
+        product = self.env['product.product'].create({
+            'name': 'Product',
+            'list_price': 100,
+            'sale_ok': True,
+            'taxes_id': [],
+        })
+
+        order = self.empty_order
+        order.write({
+            'website_id': website.id,
+            'order_line': [
+                Command.create({
+                    'product_id': product.id,
+                }),
+            ]
+        })
+
+        WebsiteSaleController = WebsiteSale()
+
+        installed_modules = set(self.env['ir.module.module'].search([
+            ('state', '=', 'installed'),
+        ]).mapped('name'))
+        for _ in http._generate_routing_rules(installed_modules, nodb_only=False):
+            pass
+
+        with MockRequest(self.env, website=website, sale_order_id=order.id) as request:
+            # Check the base cart value
+            self.assertEqual(order.amount_total, 100.0, "The base cart value is incorrect.")
+
+            # Apply coupon for the first time
+            WebsiteSaleController.pricelist(promo=self.coupon.code)
+
+            # Check that the coupon has been applied
+            self.assertEqual(order.amount_total, 90.0, "The coupon is not applied.")
+
+            # Apply the coupon again
+            WebsiteSaleController.pricelist(promo=self.coupon.code)
+            WebsiteSaleController.cart()
+            error_msg = request.session.get('error_promo_code')
+
+            # Check that the coupon stay applied
+            self.assertEqual(bool(error_msg), True, "Apply a coupon twice should display an error message")
+            self.assertEqual(order.amount_total, 90.0, "Apply a coupon twice shouldn't delete it")