Fix infinite price adjustment loop when combining free prices, country-dependent tax rates, and vouchers

src/pretix/base/models/tax.py

@@ -174,7 +174,7 @@ class TaxRule(LoggedModel):
         return Decimal(self.rate)
 
     def tax(self, base_price, base_price_is='auto', currency=None, override_tax_rate=None, invoice_address=None,
-            subtract_from_gross=Decimal('0.00')):
+            subtract_from_gross=Decimal('0.00'), gross_price_is_tax_rate: Decimal = None):
         from .event import Event
         try:
             currency = currency or self.event.currency
@@ -186,7 +186,9 @@ class TaxRule(LoggedModel):
             rate = override_tax_rate
         elif invoice_address:
             adjust_rate = self.tax_rate_for(invoice_address)
-            if adjust_rate != rate:
+            if adjust_rate == gross_price_is_tax_rate and base_price_is == 'gross':
+                rate = adjust_rate
+            elif adjust_rate != rate:
                 normal_price = self.tax(base_price, base_price_is, currency, subtract_from_gross=subtract_from_gross)
                 base_price = normal_price.net
                 base_price_is = 'net'

src/pretix/base/services/orders.py

@@ -618,8 +618,10 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
             except ItemBundle.MultipleObjectsReturned:
                 raise OrderError("Invalid product configuration (duplicate bundle)")
             price = get_price(cp.item, cp.variation, cp.voucher, bprice, cp.subevent, custom_price_is_net=False,
+                              custom_price_is_tax_rate=cp.override_tax_rate,
                               invoice_address=address, force_custom_price=True, max_discount=max_discount)
             pbv = get_price(cp.item, cp.variation, None, bprice, cp.subevent, custom_price_is_net=False,
+                            custom_price_is_tax_rate=cp.override_tax_rate,
                             invoice_address=address, force_custom_price=True, max_discount=max_discount)
             changed_prices[cp.pk] = bprice
         else:
@@ -631,10 +633,10 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
 
             price = get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent, custom_price_is_net=False,
                               addon_to=cp.addon_to, invoice_address=address, bundled_sum=bundled_sum,
-                              max_discount=max_discount)
+                              max_discount=max_discount, custom_price_is_tax_rate=cp.override_tax_rate)
             pbv = get_price(cp.item, cp.variation, None, cp.price, cp.subevent, custom_price_is_net=False,
                             addon_to=cp.addon_to, invoice_address=address, bundled_sum=bundled_sum,
-                            max_discount=max_discount)
+                            max_discount=max_discount, custom_price_is_tax_rate=cp.override_tax_rate)
 
         if max_discount is not None:
             v_budget[cp.voucher] = v_budget[cp.voucher] + current_discount - (pbv.gross - price.gross)

src/pretix/base/services/pricing.py

@@ -11,6 +11,7 @@ from pretix.base.models.tax import TAXED_ZERO, TaxedPrice, TaxRule
 def get_price(item: Item, variation: ItemVariation = None,
               voucher: Voucher = None, custom_price: Decimal = None,
               subevent: SubEvent = None, custom_price_is_net: bool = False,
+              custom_price_is_tax_rate: Decimal=None,
               addon_to: AbstractPosition = None, invoice_address: InvoiceAddress = None,
               force_custom_price: bool = False, bundled_sum: Decimal = Decimal('0.00'),
               max_discount: Decimal = None, tax_rule=None) -> TaxedPrice:
@@ -66,7 +67,7 @@ def get_price(item: Item, variation: ItemVariation = None,
             price = tax_rule.tax(max(custom_price, price.net), base_price_is='net',
                                  invoice_address=invoice_address, subtract_from_gross=bundled_sum)
         else:
-            price = tax_rule.tax(max(custom_price, price.gross), base_price_is='gross',
+            price = tax_rule.tax(max(custom_price, price.gross), base_price_is='gross', gross_price_is_tax_rate=custom_price_is_tax_rate,
                                  invoice_address=invoice_address, subtract_from_gross=bundled_sum)
     else:
         price = tax_rule.tax(price, invoice_address=invoice_address, subtract_from_gross=bundled_sum)

src/tests/presale/test_checkout.py

@@ -402,6 +402,44 @@ class CheckoutTestCase(BaseCheckoutTestCase, TestCase):
         cr1.refresh_from_db()
         assert cr1.price == Decimal('23.20')
 
+    def test_country_taxing_free_price_and_voucher(self):
+        self._enable_country_specific_taxing()
+
+        self.ticket.free_price = True
+        self.ticket.save()
+
+        with scopes_disabled():
+            cr1 = CartPosition.objects.create(
+                event=self.event, cart_id=self.session_key, item=self.ticket,
+                price=23, expires=now() + timedelta(minutes=10),
+                voucher=self.event.vouchers.create()
+            )
+
+        with mock.patch('vat_moss.id.validate') as mock_validate:
+            mock_validate.return_value = ('AT', 'AT123456', 'Foo')
+            self.client.post('/%s/%s/checkout/questions/' % (self.orga.slug, self.event.slug), {
+                'is_business': 'individual',
+                'name': 'Bar',
+                'street': 'Baz',
+                'zipcode': '12345',
+                'city': 'Here',
+                'country': 'AT',
+                'email': 'admin@localhost'
+            }, follow=True)
+
+        cr1.refresh_from_db()
+        assert cr1.price == Decimal('23.20')
+
+        self.client.post('/%s/%s/checkout/payment/' % (self.orga.slug, self.event.slug), {
+            'payment': 'banktransfer'
+        }, follow=True)
+
+        self.client.post('/%s/%s/checkout/confirm/' % (self.orga.slug, self.event.slug), follow=True)
+        with scopes_disabled():
+            assert not CartPosition.objects.filter(pk=cr1.pk).exists()
+            o = Order.objects.last()
+            assert o.positions.get().price == Decimal('23.20')
+
     def test_country_taxing_switch(self):
         self.test_country_taxing()