Added signals that allow to modify the voucher form

src/pretix/control/signals.py

@@ -73,3 +73,24 @@ should return a list of dictionaries, where each dictionary can have the keys:
 
 This is a regular django signal (no pretix event signal).
 """
+
+voucher_form_html = EventPluginSignal(
+    providing_args=['form']
+)
+"""
+This signal allows you to add additional HTML to the form that is used for modifying vouchers.
+You receive the form object in the ``form`` keyword argument.
+
+As with all plugin signals, the ``sender`` keyword argument will contain the event.
+"""
+
+voucher_form_class = EventPluginSignal(
+    providing_args=['cls']
+)
+"""
+This signal allows you to replace the form class that is used for modifying vouchers.
+You will receive the default form class (or the class set by a previous plugin) in the
+``cls`` argument such that you can inherit from it.
+
+As with all plugin signals, the ``sender`` keyword argument will contain the event.
+"""

src/pretix/control/templates/pretixcontrol/vouchers/detail.html

@@ -1,6 +1,7 @@
 {% extends "pretixcontrol/items/base.html" %}
 {% load i18n %}
 {% load bootstrap3 %}
+{% load eventsignal %}
 {% block title %}{% trans "Voucher" %}{% endblock %}
 {% block inside %}
     <h1>{% trans "Voucher" %}</h1>
@@ -36,6 +37,7 @@
             {% bootstrap_field form.tag layout="horizontal" %}
             {% bootstrap_field form.comment layout="horizontal" %}
         </fieldset>
+        {% eventsignal request.event "pretix.control.signals.voucher_form_html" form=form %}
         <div class="form-group submit-group">
             <button type="submit" class="btn btn-primary btn-save">
                 {% trans "Save" %}

src/pretix/control/views/vouchers.py

@@ -11,6 +11,7 @@ from django.views.generic import CreateView, DeleteView, ListView, UpdateView
 from pretix.base.models import Voucher
 from pretix.control.forms.vouchers import VoucherBulkForm, VoucherForm
 from pretix.control.permissions import EventPermissionRequiredMixin
+from pretix.control.signals import voucher_form_class
 
 
 class VoucherList(EventPermissionRequiredMixin, ListView):
@@ -70,11 +71,17 @@ class VoucherDelete(EventPermissionRequiredMixin, DeleteView):
 
 class VoucherUpdate(EventPermissionRequiredMixin, UpdateView):
     model = Voucher
-    form_class = VoucherForm
     template_name = 'pretixcontrol/vouchers/detail.html'
     permission = 'can_change_vouchers'
     context_object_name = 'voucher'
 
+    def get_form_class(self):
+        form_class = VoucherForm
+        for receiver, response in voucher_form_class.send(self.request.event, cls=form_class):
+            if response:
+                form_class = response
+        return form_class
+
     def get_object(self, queryset=None) -> VoucherForm:
         url = resolve(self.request.path_info)
         try:
@@ -104,11 +111,17 @@ class VoucherUpdate(EventPermissionRequiredMixin, UpdateView):
 
 class VoucherCreate(EventPermissionRequiredMixin, CreateView):
     model = Voucher
-    form_class = VoucherForm
     template_name = 'pretixcontrol/vouchers/detail.html'
     permission = 'can_change_vouchers'
     context_object_name = 'voucher'
 
+    def get_form_class(self):
+        form_class = VoucherForm
+        for receiver, response in voucher_form_class.send(self.request.event, cls=form_class):
+            if response:
+                form_class = response
+        return form_class
+
     def get_success_url(self) -> str:
         return reverse('control:event.vouchers', kwargs={
             'organizer': self.request.event.organizer.slug,