Make cancel notifications optional

src/pretix/base/services/orders.py

@@ -732,10 +732,10 @@ def perform_order(self, event: str, payment_provider: str, positions: List[str],
 
 
 @app.task(base=ProfiledTask, bind=True, max_retries=5, default_retry_delay=1, throws=(OrderError,))
-def cancel_order(self, order: int, user: int=None):
+def cancel_order(self, order: int, user: int=None, send_mail: bool=True):
     try:
         try:
-            return _cancel_order(order, user)
+            return _cancel_order(order, user, send_mail)
         except LockTimeoutException:
             self.retry(exc=OrderError(error_messages['busy']))
     except (MaxRetriesExceededError, LockTimeoutException):

src/pretix/control/templates/pretixcontrol/order/cancel.html

@@ -13,7 +13,13 @@
 
     <form method="post" href="">
         {% csrf_token %}
-        <input type="hidden" name="status" value="c" />
+        <input type="hidden" name="status" value="c"/>
+        <div class="checkbox">
+            <label>
+                <input type="checkbox" name="send_email" value="on" checked="checked">
+                {% trans "Notify user by e-mail" %}
+            </label>
+        </div>
         <div class="row checkout-button-row">
             <div class="col-md-4">
                 <a class="btn btn-block btn-default btn-lg"

src/pretix/control/views/orders.py

@@ -206,7 +206,7 @@ class OrderTransition(OrderView):
             else:
                 messages.success(self.request, _('The order has been marked as paid.'))
         elif self.order.status == Order.STATUS_PENDING and to == 'c':
-            cancel_order(self.order, user=self.request.user)
+            cancel_order(self.order, user=self.request.user, send_mail=self.request.POST.get("send_email") == "on")
             messages.success(self.request, _('The order has been canceled.'))
         elif self.order.status == Order.STATUS_PAID and to == 'n':
             self.order.status = Order.STATUS_PENDING