Merge pull request #419 from plone/icalendar-6-pytz

Support icalendar 6 by forcing it to use pytz

news/6.bugfix

@@ -0,0 +1,5 @@
+Support ``icalendar`` 6 by forcing it to use its ``pytz`` timezone implementation.
+The new ``zoneinfo`` support in ``icalendar`` 6 does not work for us yet, giving indexing problems.
+So we call ``icalendar.use_pytz`` at startup.
+If this fails, we must be using an older version where ``pytz`` is the only option anyway, so we ignore this.
+[maurits]

plone/app/event/__init__.py

@@ -1,10 +1,27 @@
 from AccessControl.Permission import addPermission
 from zope.i18nmessageid import MessageFactory
 
+import icalendar
+import logging
 
+
+logger = logging.getLogger(__name__)
 packageName = __name__
 _ = MessageFactory("plone")
 
+# We are not yet ready to use the standard zoneinfo implementation
+# introduced in icalendar 6.  For starters, the tests fail when
+# Products.DateRecurringIndex.index.index_object is called:
+# SystemError: <class 'BTrees.IIBTree.IISet'> returned a result with an exception set
+try:
+    icalendar.use_pytz()
+    logger.info("icalendar has been set up to use pytz instead of zoneinfo.")
+except AttributeError:
+    # If use_pytz does not exist, we either have an older icalender version
+    # that only supports pytz anyway, or we have a newer version that no
+    # longer supports it at all.
+    pass
+
 # BBB Permissions
 PORTAL_ADD_PERMISSION = "Add portal events"  # CMFCalendar/ATCT permissions