Order changes: Correctly respect tax rules when adding or changing items (Z#23190086)

src/pretix/base/models/items.py

@@ -821,7 +821,8 @@ class Item(LoggedModel):
     def ask_attendee_data(self):
         return self.admission and self.personalized
 
-    def tax(self, price=None, base_price_is='auto', currency=None, invoice_address=None, override_tax_rate=None, include_bundled=False):
+    def tax(self, price=None, base_price_is='auto', currency=None, invoice_address=None, override_tax_rate=None,
+            include_bundled=False, force_fixed_gross_price=False):
         price = price if price is not None else self.default_price
 
         bundled_sum = Decimal('0.00')
@@ -850,7 +851,7 @@ class Item(LoggedModel):
         else:
             t = self.tax_rule.tax(price, base_price_is=base_price_is, invoice_address=invoice_address,
                                   override_tax_rate=override_tax_rate, currency=currency or self.event.currency,
-                                  subtract_from_gross=bundled_sum)
+                                  subtract_from_gross=bundled_sum, force_fixed_gross_price=force_fixed_gross_price)
 
         if bundled_sum:
             t.name = "MIXED!"

src/pretix/base/services/orders.py

@@ -1689,7 +1689,8 @@ class OrderChangeManager:
 
     def change_price(self, position: OrderPosition, price: Decimal):
         tax_rule = self._current_tax_rules().get(position.pk, position.tax_rule) or TaxRule.zero()
-        price = tax_rule.tax(price, base_price_is='gross')
+        price = tax_rule.tax(price, base_price_is='gross', invoice_address=self._invoice_address,
+                             force_fixed_gross_price=True)
 
         if position.issued_gift_cards.exists():
             raise OrderError(self.error_messages['gift_card_change'])
@@ -1754,7 +1755,8 @@ class OrderChangeManager:
         self._operations.append(self.AddFeeOperation(fee, fee.value))
 
     def change_fee(self, fee: OrderFee, value: Decimal):
-        value = (fee.tax_rule or TaxRule.zero()).tax(value, base_price_is='gross')
+        value = (fee.tax_rule or TaxRule.zero()).tax(value, base_price_is='gross', invoice_address=self._invoice_address,
+                                                     force_fixed_gross_price=True)
         self._totaldiff += value.gross - fee.value
         self._invoice_dirty = True
         self._operations.append(self.FeeValueOperation(fee, value, value.gross - fee.value))
@@ -1789,7 +1791,8 @@ class OrderChangeManager:
             if price is None:
                 price = get_price(item, variation, subevent=subevent, invoice_address=self._invoice_address)
             elif not isinstance(price, TaxedPrice):
-                price = item.tax(price, base_price_is='gross', invoice_address=self._invoice_address)
+                price = item.tax(price, base_price_is='gross', invoice_address=self._invoice_address,
+                                 force_fixed_gross_price=True)
         except TaxRule.SaleNotAllowed:
             raise OrderError(self.error_messages['tax_rule_country_blocked'])
 

src/tests/base/test_orders.py

@@ -1581,6 +1581,27 @@ class OrderChangeManagerTests(TestCase):
         assert round_decimal(self.op1.price * (1 - 100 / (100 + self.op1.tax_rate))) == self.op1.tax_value
         assert self.order.total == self.op1.price + self.op2.price
 
+    @classscope(attr='o')
+    def test_change_price_reverse_charge_success(self):
+        self._enable_reverse_charge()
+        self.op1.tax_rate = Decimal("0.00")
+        self.op1.tax_value = Decimal("0.00")
+        self.op1.tax_code = "AE"
+        self.op1.save()
+        self.op2.tax_rate = Decimal("0.00")
+        self.op2.tax_value = Decimal("0.00")
+        self.op2.tax_code = "AE"
+        self.op2.save()
+        self.ocm.change_price(self.op1, Decimal('1000.00'))
+        self.ocm.commit()
+        self.op1.refresh_from_db()
+        self.order.refresh_from_db()
+        assert self.op1.item == self.ticket
+        assert self.op1.price == Decimal('1000.00')
+        assert self.op1.tax_value == Decimal('0.00')
+        assert self.op1.tax_rate == Decimal('0.00')
+        assert self.order.total == self.op1.price + self.op2.price
+
     @classscope(attr='o')
     def test_cancel_success(self):
         s = self.op1.secret
@@ -1994,6 +2015,22 @@ class OrderChangeManagerTests(TestCase):
         assert nop.positionid == 3
         assert self.order.transactions.filter(item=self.shirt).last().tax_code == "AE"
 
+    @classscope(attr='o')
+    def test_add_item_with_price_reverse_charge(self):
+        self._enable_reverse_charge()
+        self.ocm.add_position(self.shirt, None, Decimal("1.00"), None)
+        self.ocm.commit()
+        self.order.refresh_from_db()
+        assert self.order.positions.count() == 3
+        nop = self.order.positions.last()
+        assert nop.item == self.shirt
+        assert nop.price == Decimal('1.00')
+        assert nop.tax_rate == Decimal('0.00')
+        assert nop.tax_value == Decimal('0.00')
+        assert self.order.total == self.op1.price + self.op2.price + nop.price
+        assert nop.positionid == 3
+        assert self.order.transactions.filter(item=self.shirt).last().tax_code == "AE"
+
     @classscope(attr='o')
     def test_add_item_custom_price(self):
         self.ocm.add_position(self.shirt, None, Decimal('13.00'), None)