Invoice generation: Add way for renderers to signal they are not ready

src/pretix/base/invoicing/pdf.py

@@ -148,6 +148,10 @@ class NumberedCanvas(Canvas):
         self.restoreState()
 
 
+class InvoiceNotReadyException(Exception):
+    pass
+
+
 class BaseInvoiceRenderer:
     """
     This is the base class for all invoice renderers.

src/pretix/base/services/invoices.py

@@ -51,6 +51,7 @@ from django_scopes import scope, scopes_disabled
 from i18nfield.strings import LazyI18nString
 
 from pretix.base.i18n import language
+from pretix.base.invoicing.pdf import InvoiceNotReadyException
 from pretix.base.invoicing.transmission import (
     get_transmission_types, transmission_providers,
 )
@@ -504,7 +505,7 @@ def generate_invoice(order: Order, trigger_pdf=True):
     return invoice
 
 
-@app.task(base=TransactionAwareTask)
+@app.task(base=TransactionAwareTask, throws=(InvoiceNotReadyException,))
 def invoice_pdf_task(invoice: int):
     with scopes_disabled():
         i = Invoice.objects.get(pk=invoice)

src/pretix/base/templates/404.html

@@ -8,6 +8,9 @@
         <h1>{% trans "Not found" %}</h1>
         <p>{% trans "I'm afraid we could not find the the resource you requested." %}</p>
         <p>{{ exception }}</p>
+        <p class="links">
+            <a id='goback' href='#'>{% trans "Take a step back" %}</a>
+        </p>
         {% if request.user.is_staff and not staff_session %}
             <form action="{% url 'control:user.sudo' %}?next={{ request.path|add:"?"|add:request.GET.urlencode|urlencode }}" method="post">
                 <p>