Add typeahead suggestions for voucher tag field (#6058)

Suggest existing tags as the user types in the voucher tag field.
Waiting list voucher tags are excluded from suggestions.

src/pretix/control/forms/vouchers.py

@@ -106,6 +106,11 @@ class VoucherForm(I18nModelForm):
                 pass
         super().__init__(*args, **kwargs)
 
+        self.fields['tag'].widget.attrs['data-typeahead-url'] = reverse('control:event.vouchers.tags.typeahead', kwargs={
+            'event': instance.event.slug,
+            'organizer': instance.event.organizer.slug,
+        })
+
         if instance.event.has_subevents:
             self.fields['subevent'].queryset = instance.event.subevents.all()
             self.fields['subevent'].widget = Select2(

src/pretix/control/urls.py

@@ -370,6 +370,7 @@ urlpatterns = [
         re_path(r'^discounts/add$', discounts.DiscountCreate.as_view(), name='event.items.discounts.add'),
         re_path(r'^vouchers/$', vouchers.VoucherList.as_view(), name='event.vouchers'),
         re_path(r'^vouchers/tags/$', vouchers.VoucherTags.as_view(), name='event.vouchers.tags'),
+        re_path(r'^vouchers/tags/typeahead$', typeahead.voucher_tag_typeahead, name='event.vouchers.tags.typeahead'),
         re_path(r'^vouchers/rng$', vouchers.VoucherRNG.as_view(), name='event.vouchers.rng'),
         re_path(r'^vouchers/item_select$', typeahead.itemvarquota_select2, name='event.vouchers.itemselect2'),
         re_path(r'^vouchers/(?P<voucher>\d+)/$', vouchers.VoucherUpdate.as_view(), name='event.voucher'),

src/pretix/control/views/typeahead.py

@@ -975,6 +975,21 @@ def subevent_meta_values(request, organizer, event):
     })
 
 
+@event_permission_required('event.vouchers:read')
+def voucher_tag_typeahead(request, **kwargs):
+    q = request.GET.get('q', '')
+    tags = request.event.vouchers.filter(
+        tag__isnull=False,
+        waitinglistentries__isnull=True,
+    ).filter(
+        tag__icontains=q,
+    ).values_list('tag', flat=True).distinct().order_by('tag')[:10]
+
+    return JsonResponse({
+        'results': [{'name': t} for t in tags]
+    })
+
+
 def item_meta_values(request, organizer, event):
     q = request.GET.get('q')
     propname = request.GET.get('property')