API: Allow to answer file upload questions during ticket redemption

src/pretix/base/models/items.py

@@ -1026,7 +1026,7 @@ class Question(LoggedModel):
         (TYPE_PHONENUMBER, _("Phone number")),
     )
     UNLOCALIZED_TYPES = [TYPE_DATE, TYPE_TIME, TYPE_DATETIME]
-    ASK_DURING_CHECKIN_UNSUPPORTED = [TYPE_FILE, TYPE_PHONENUMBER]
+    ASK_DURING_CHECKIN_UNSUPPORTED = [TYPE_PHONENUMBER]
 
     event = models.ForeignKey(
         Event,
@@ -1069,6 +1069,7 @@ class Question(LoggedModel):
     )
     ask_during_checkin = models.BooleanField(
         verbose_name=_('Ask during check-in instead of in the ticket buying process'),
+        help_text=_('Not supported by all check-in apps for all question types.'),
         default=False
     )
     hidden = models.BooleanField(

src/pretix/base/services/checkin.py

@@ -1,6 +1,7 @@
 from datetime import timedelta
 
 import dateutil
+from django.core.files import File
 from django.db import transaction
 from django.db.models.functions import TruncDate
 from django.dispatch import receiver
@@ -125,6 +126,14 @@ def _save_answers(op, answers, given_answers):
             else:
                 qa = op.answers.create(question=q, answer=", ".join([str(o) for o in a]))
             qa.options.add(*a)
+        elif isinstance(a, File):
+            if q in answers:
+                qa = answers[q]
+            else:
+                qa = op.answers.create(question=q, answer=str(a))
+            qa.file.save(a.name, a, save=False)
+            qa.answer = 'file://' + qa.file.name
+            qa.save()
         else:
             if q in answers:
                 qa = answers[q]