Add new signal validate_order

src/pretix/base/services/orders.py

@@ -46,7 +46,7 @@ from pretix.base.services.tasks import ProfiledTask
 from pretix.base.signals import (
     allow_ticket_download, order_approved, order_canceled, order_changed,
     order_denied, order_expired, order_fee_calculation, order_placed,
-    periodic_task,
+    periodic_task, validate_order,
 )
 from pretix.celery_app import app
 from pretix.helpers.models import modelcopy
@@ -670,6 +670,9 @@ def _perform_order(event: str, payment_provider: str, position_ids: List[str],
 
     positions = CartPosition.objects.filter(id__in=position_ids, event=event)
 
+    validate_order.send(event, payment_provider=pprov, email=email, positions=positions,
+                        locale=locale, invoice_address=addr, meta_info=meta_info)
+
     lockfn = NoLockManager
     locked = False
     if positions.filter(Q(voucher__isnull=False) | Q(expires__lt=now() + timedelta(minutes=2))).exists():

src/pretix/base/signals.py

@@ -240,6 +240,19 @@ subclass of pretix.base.exporter.BaseExporter
 As with all event-plugin signals, the ``sender`` keyword argument will contain the event.
 """
 
+validate_order = EventPluginSignal(
+    providing_args=["payment_provider", "positions", "email", "locale", "invoice_address",
+                    "meta_info"]
+)
+"""
+This signal is sent out when the user tries to confirm the order, before we actually create
+the order. It allows you to inspect the cart positions. Your return value will be ignored,
+but you can raise an OrderError with an appropriate exception message if you like to block
+the order. We strongly discourage making changes to the order here.
+
+As with all event-plugin signals, the ``sender`` keyword argument will contain the event.
+"""
+
 validate_cart = EventPluginSignal(
     providing_args=["positions"]
 )