Allow not to ask for invoice addresses on free orders

src/pretix/presale/views/__init__.py

@@ -205,6 +205,34 @@ def get_cart_total(request):
     return request._cart_total_cache
 
 
+def get_cart_invoice_address(request):
+    from pretix.presale.views.cart import cart_session
+
+    if not hasattr(request, '_checkout_flow_invoice_address'):
+        cs = cart_session(request)
+        iapk = cs.get('invoice_address')
+        if not iapk:
+            request._checkout_flow_invoice_address = InvoiceAddress()
+        else:
+            try:
+                request._checkout_flow_invoice_address = InvoiceAddress.objects.get(pk=iapk, order__isnull=True)
+            except InvoiceAddress.DoesNotExist:
+                request._checkout_flow_invoice_address = InvoiceAddress()
+    return request._checkout_flow_invoice_address
+
+
+def get_cart_is_free(request):
+    from pretix.presale.views.cart import cart_session
+
+    if not hasattr(request, '_cart_free_cache'):
+        cs = cart_session(request)
+        ia = get_cart_invoice_address(request)
+        total = get_cart_total(request)
+        fees = get_fees(request.event, request, total, ia, cs.get('payment'))
+        request._cart_free_cache = total + sum(f.value for f in fees) == Decimal('0.00')
+    return request._cart_free_cache
+
+
 class EventViewMixin:
     def get_context_data(self, **kwargs):
         context = super().get_context_data(**kwargs)

src/pretix/presale/views/order.py

@@ -122,6 +122,9 @@ class OrderDetails(EventViewMixin, OrderDetailMixin, CartMixin, TemplateView):
                 'secret': self.order.secret
             }
         )
+        ctx['invoice_address_asked'] = self.request.event.settings.invoice_address_asked and (
+            self.order.total != Decimal('0.00') or not self.request.event.settings.invoice_address_not_asked_free
+        )
 
         if self.order.status == Order.STATUS_PENDING:
             ctx['pending_sum'] = self.order.pending_sum
@@ -526,7 +529,8 @@ class OrderModify(EventViewMixin, OrderDetailMixin, OrderQuestionsViewMixin, Tem
             messages.error(self.request,
                            _("We had difficulties processing your input. Please review the errors below."))
             return self.get(request, *args, **kwargs)
-        self.invoice_form.save()
+        if hasattr(self.invoice_form, 'save'):
+            self.invoice_form.save()
         self.order.log_action('pretix.event.order.modified', {
             'invoice_data': self.invoice_form.cleaned_data,
             'data': [{