Cancelling events: Allow to inform waiting list

src/pretix/control/forms/orders.py

@@ -552,6 +552,12 @@ class EventCancelForm(forms.Form):
     )
     send_subject = forms.CharField()
     send_message = forms.CharField()
+    send_waitinglist = forms.BooleanField(
+        label=_("Send information to waiting list"),
+        required=False
+    )
+    send_waitinglist_subject = forms.CharField()
+    send_waitinglist_message = forms.CharField()
 
     def _set_field_placeholders(self, fn, base_parameters):
         phs = [
@@ -596,6 +602,28 @@ class EventCancelForm(forms.Form):
                                                       'order', 'event'])
         self._set_field_placeholders('send_message', ['event_or_subevent', 'refund_amount', 'position_or_address',
                                                       'order', 'event'])
+        self.fields['send_waitinglist_subject'] = I18nFormField(
+            label=_("Subject"),
+            required=True,
+            initial=_('Canceled: {event}'),
+            widget=I18nTextInput,
+            locales=self.event.settings.get('locales'),
+        )
+        self.fields['send_waitinglist_message'] = I18nFormField(
+            label=_('Message'),
+            widget=I18nTextarea,
+            required=True,
+            locales=self.event.settings.get('locales'),
+            initial=LazyI18nString.from_gettext(gettext_noop(
+                'Hello,\n\n'
+                'with this email, we regret to inform you that {event} has been canceled.\n\n'
+                'You will therefore not receive a ticket from the waiting list.\n\n'
+                'Best regards,\n\n'
+                'Your {event} team'
+            ))
+        )
+        self._set_field_placeholders('send_waitinglist_subject', ['event_or_subevent', 'event'])
+        self._set_field_placeholders('send_waitinglist_message', ['event_or_subevent', 'event'])
 
         if self.event.has_subevents:
             self.fields['subevent'].queryset = self.event.subevents.all()

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

@@ -43,6 +43,26 @@
             {% bootstrap_field form.send_subject layout="horizontal" %}
             {% bootstrap_field form.send_message layout="horizontal" %}
         </fieldset>
+        <fieldset>
+            <legend>{% trans "Waiting list" %}</legend>
+            <p>
+                {% blocktrans trimmed %}
+                    Your waiting list will not be deleted automatically, but it will receive no new tickets due to the
+                    products being disabled. You can choose to inform people on the waiting list by using this option.
+                {% endblocktrans %}
+            </p>
+            <p>
+                <strong>
+                    {% blocktrans trimmed %}
+                        You should not execute this function multiple times for the same event, or everyone on the
+                        waiting list will get multiple emails.
+                    {% endblocktrans %}
+                </strong>
+            </p>
+            {% bootstrap_field form.send_waitinglist layout="control" %}
+            {% bootstrap_field form.send_waitinglist_subject layout="horizontal" %}
+            {% bootstrap_field form.send_waitinglist_message layout="horizontal" %}
+        </fieldset>
         <div class="form-group submit-group">
             <button type="submit" class="btn btn-danger btn-save">
                 {% trans "Cancel all orders" %}

src/pretix/control/views/orders.py

@@ -1915,6 +1915,9 @@ class EventCancel(EventPermissionRequiredMixin, AsyncAction, FormView):
             send=form.cleaned_data.get('send'),
             send_subject=form.cleaned_data.get('send_subject').data,
             send_message=form.cleaned_data.get('send_message').data,
+            send_waitinglist=form.cleaned_data.get('send'),
+            send_waitinglist_subject=form.cleaned_data.get('send_waitinglist_subject').data,
+            send_waitinglist_message=form.cleaned_data.get('send_waitinglist_message').data,
             user=self.request.user.pk,
         )