Fix #372 -- Plugin hook for "Copy from event"

doc/development/api/general.rst

@@ -11,7 +11,7 @@ Core
 ----
 
 .. automodule:: pretix.base.signals
-   :members: periodic_task, event_live_issues
+   :members: periodic_task, event_live_issues, event_copy_data
 
 Order events
 """"""""""""

src/pretix/base/models/event.py

@@ -226,6 +226,8 @@ class Event(LoggedModel):
 
     def copy_data_from(self, other):
         from . import ItemAddOn, ItemCategory, Item, Question, Quota
+        from ..signals import event_copy_data
+
         self.plugins = other.plugins
         self.save()
 
@@ -297,6 +299,8 @@ class Event(LoggedModel):
                 s.value = 'file://' + newname
             s.save()
 
+        event_copy_data.send(sender=self, other=other)
+
 
 def generate_invite_token():
     return get_random_string(length=32, allowed_chars=string.ascii_lowercase + string.digits)

src/pretix/base/signals.py

@@ -153,6 +153,21 @@ to the user. The receivers are expected to return HTML code.
 As with all event-plugin signals, the ``sender`` keyword argument will contain the event.
 """
 
+event_copy_data = EventPluginSignal(
+    providing_args=["other"]
+)
+"""
+This signal is sent out when a new event is created as a clone of an existing event, i.e.
+the settings from the older event are copied to the newer one. You can listen to this
+signal to copy data or configuration stored within your plugin's models as well.
+
+You don't need to copy data inside the general settings storage which is cloned automatically,
+but you might need to modify that data.
+
+The ``sender`` keyword argument will contain the event of the **new** event. The ``other``
+keyword argument will contain the event to **copy from**.
+"""
+
 periodic_task = django.dispatch.Signal()
 """
 This is a regular django signal (no pretix event signal) that we send out every