Automatically re-render PDF for files lost due to bug

src/pretix/presale/views/order.py

@@ -20,7 +20,8 @@ from pretix.base.models.orders import (
 )
 from pretix.base.payment import PaymentException
 from pretix.base.services.invoices import (
-    generate_cancellation, generate_invoice, invoice_pdf, invoice_qualified,
+    generate_cancellation, generate_invoice, invoice_pdf, invoice_pdf_task,
+    invoice_qualified,
 )
 from pretix.base.services.orders import cancel_order
 from pretix.base.services.tickets import (
@@ -673,6 +674,10 @@ class InvoiceDownload(EventViewMixin, OrderDetailMixin, View):
                                         'now. Please try again in a few seconds.'))
             return redirect(self.get_order_url())
 
-        resp = FileResponse(invoice.file.file, content_type='application/pdf')
+        try:
+            resp = FileResponse(invoice.file.file, content_type='application/pdf')
+        except FileNotFoundError:
+            invoice_pdf_task.apply(args=(invoice.pk,))
+            return self.get(request, *args, **kwargs)
         resp['Content-Disposition'] = 'attachment; filename="{}.pdf"'.format(invoice.number)
         return resp