When there are product discountable true and variant discountable false in cart in the same time, discount is calculated for variant which is incorrect. (#4102)

* fix use get_is_discountable instead is_discountable attribute from product

* add test case

* add check discount percentage in test

* Fix test case

* remove file setting

* basket add product in test

* Make the test pass

---------

Co-authored-by: Kaew <ajchariya.ung@gmail.com>

src/oscar/apps/catalogue/abstract_models.py

 from django.utils.translation import pgettext, pgettext_lazy
 from treebeard.mp_tree import MP_Node
 
+from oscar.core.decorators import deprecated
 from oscar.core.loading import get_class, get_classes, get_model
 from oscar.core.utils import slugify
 from oscar.core.validators import non_python_keyword
             return self.product_class
     get_product_class.short_description = _("Product class")
 
+    @deprecated
     def get_is_discountable(self):
         """
-        At the moment, :py:attr:`.is_discountable` can't be set individually for child
-        products; they inherit it from their parent.
+        It used to be that, :py:attr:`.is_discountable` couldn't be set individually for child
+        products; so they had to inherit it from their parent. This is nolonger the case because
+        ranges can include child products as well. That make this method useless.
         """
-        if self.is_child:
-            return self.parent.is_discountable
-        else:
-            return self.is_discountable
+        return self.is_discountable
 
     def get_categories(self):
         """

src/oscar/apps/offer/abstract_models.py

             return False
         product = line.product
         return (self.range.contains_product(product)
-                and product.get_is_discountable())
+                and product.is_discountable)
 
     def get_applicable_lines(self, offer, basket, most_expensive_first=True):
         """
 class AbstractRange(models.Model):
     """
     Represents a range of products that can be used within an offer.
-
-    Ranges only support adding parent or stand-alone products. Offers will
-    consider child products automatically.
     """
     name = models.CharField(_("Name"), max_length=128, unique=True)
     slug = fields.AutoSlugField(

tests/integration/catalogue/test_product.py

             is_discountable=True)
         self.assertEqual("Parent product", p.get_title())
         self.assertEqual("Clothing", p.get_product_class().name)
-        self.assertEqual(False, p.get_is_discountable())
 
     def test_child_products_are_not_part_of_browsable_set(self):
         Product.objects.create(

tests/integration/offer/test_absolute_benefit.py

         assert line.line_price_excl_tax_incl_discounts == D(0)
         assert line.line_price_incl_tax_incl_discounts == D(0)
         assert basket.total_incl_tax == 0
+
+    def test_is_discountable_works_on_child_level(self):
+        rng = factories.RangeFactory(includes_all_products=True, name="klaazien")
+        benefit = factories.BenefitFactory(
+            range=rng, type=models.Benefit.PERCENTAGE, value=5, max_affected_items=100
+        )
+        condition = models.ValueCondition.objects.create(
+            range=rng,
+            type=models.Condition.COUNT,
+            value=1
+        )
+
+        factories.ConditionalOfferFactory(
+            priority=99999,
+            exclusive=False,
+            condition=condition,
+            benefit=benefit
+        )
+
+        basket = factories.create_basket(empty=True)
+
+        prod1 = factories.create_product(title="Gert is friends with Berrie", is_discountable=True, price=100)
+
+        parent_discountable_product = factories.create_product(structure='parent', is_discountable=True)
+        child = factories.create_product(
+            title="Undiscountable variant",
+            structure='child',
+            parent=parent_discountable_product,
+            is_discountable=False,
+            price=100
+        )
+
+        parent_product = factories.create_product(structure='parent', is_discountable=False)
+        child_discountable = factories.create_product(
+            title="Discountable variant ", structure='child', parent=parent_product, is_discountable=True, price=200)
+
+        basket.add_product(prod1, quantity=1)
+        basket.add_product(child, quantity=2)
+        basket.add_product(child_discountable, quantity=3)
+
+        Applicator().apply(basket)
+        line = basket.all_lines()
+        product_actual = benefit.can_apply_benefit(line[0])
+        assert product_actual
+        assert prod1.is_discountable
+        assert line[0].has_discount
+        assert line[0].discount_value == D(5)
+
+        variant_actual = benefit.can_apply_benefit(line[1])
+        assert not variant_actual
+        assert parent_discountable_product.is_discountable
+        assert not child.is_discountable
+        assert line[1].discount_value == D(0)
+
+        variant_discountable_actual = benefit.can_apply_benefit(line[2])
+        assert variant_discountable_actual
+        assert not parent_product.is_discountable
+        assert child_discountable.is_discountable
+        assert line[2].has_discount
+        assert line[2].discount_value == D(30)