Allow to mark add-ons as "included" in price

src/pretix/base/services/cart.py

@@ -340,6 +340,7 @@ class CartManager:
         quota_diff = Counter()  # Quota -> Number of usages
         operations = []
         available_categories = defaultdict(set)  # CartPos -> Category IDs to choose from
+        price_included = defaultdict(dict)  # CartPos -> CategoryID -> bool(price is included)
         toplevel_cp = self.positions.filter(
             addon_to__isnull=True
         ).prefetch_related(
@@ -349,6 +350,7 @@ class CartManager:
         # Prefill some of the cache containers
         for cp in toplevel_cp:
             available_categories[cp.pk] = {iao.addon_category_id for iao in cp.item.addons.all()}
+            price_included[cp.pk] = {iao.addon_category_id: iao.price_included for iao in cp.item.addons.all()}
             cpcache[cp.pk] = cp
             current_addons[cp] = {
                 (a.item_id, a.variation_id): a
@@ -392,7 +394,10 @@ class CartManager:
                 for quota in quotas:
                     quota_diff[quota] += 1
 
-                price = self._get_price(item, variation, None, None, cp.subevent)
+                if price_included[cp.pk].get(item.category_id):
+                    price = Decimal('0.00')
+                else:
+                    price = self._get_price(item, variation, None, None, cp.subevent)
 
                 op = self.AddOperation(
                     count=1, item=item, variation=variation, price=price, voucher=None, quotas=quotas,

src/pretix/base/services/orders.py

@@ -282,7 +282,8 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
             # Other checks are not necessary
             continue
 
-        price = get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent, custom_price_is_net=False)
+        price = get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent, custom_price_is_net=False,
+                          addon_to=cp.addon_to)
 
         if price is False or len(quotas) == 0:
             err = err or error_messages['unavailable']

src/pretix/base/services/pricing.py

@@ -1,13 +1,24 @@
 from decimal import Decimal
 
 from pretix.base.decimal import round_decimal
-from pretix.base.models import Item, ItemVariation, Voucher
+from pretix.base.models import (
+    AbstractPosition, Item, ItemAddOn, ItemVariation, Voucher,
+)
 from pretix.base.models.event import SubEvent
 
 
 def get_price(item: Item, variation: ItemVariation = None,
               voucher: Voucher = None, custom_price: Decimal = None,
-              subevent: SubEvent = None, custom_price_is_net: bool = False):
+              subevent: SubEvent = None, custom_price_is_net: bool = False,
+              addon_to: AbstractPosition = None):
+    if addon_to:
+        try:
+            iao = addon_to.item.addons.get(addon_category_id=item.category_id)
+            if iao.price_included:
+                return Decimal('0.00')
+        except ItemAddOn.DoesNotExist:
+            pass
+
     price = item.default_price
     if subevent and item.pk in subevent.item_price_overrides:
         price = subevent.item_price_overrides[item.pk]