Fix Stalwart test failures: add compatibility hints and guards

Three tests for TestForServerStalwart were failing:
- testTodoDatesearch (assert 3==5, then DTSTART expansion check)
- testRecurringDateSearch (assert 0==1)
- testRecurringDateWithExceptionSearch (assert 3==2)

Compatibility hints added for Stalwart:
- search.recurrences.includes-implicit.event: fragile (works for
  datetime events but not for all-day/VALUE=DATE events)
- search.recurrences.includes-implicit.todo: fragile (server returns
  recurring todos but expansion doesn't work reliably)
- search.recurrences.expanded.exception: unsupported (server-side
  expansion is wrong for events with exceptions)
- save-load.event.recurrences.exception: unsupported (Stalwart stores
  master+exception VEVENTs as separate calendar objects)
- vtodo_datesearch_nodtstart_task_is_skipped old_flag (already existed
  in prior commits but consolidated here)
- no_search_openended old_flag (open-ended VTODO date searches fail)

Library behavior change (search.py): when expand=True is requested and
the server splits exception VEVENTs into separate objects (unsupported
save-load.event.recurrences.exception), automatically fall back to
server-side CALDAV:expand when the server supports it correctly.

Test changes:
- testRecurringDateWithExceptionSearch: guard "assert len(r)==2" and
  "assert len(rs)==2" for servers that can't handle exceptions; the rs
  assertion now also requires expanded.exception support
- testTodoDatesearch: guard isinstance(todos[0]) assertions with
  no_search_openended flag (consolidating todos1/todos2/todos3 under
  one condition)

New FEATURES entry: save-load.event.recurrences.exception

Co-Authored-By: Claude <noreply@anthropic.com>

Author: tobixen

CHANGELOG.md

@@ -27,9 +27,15 @@ This project should adhere to [Semantic Versioning](https://semver.org/spec/v2.0
 * Fixed inconsistent URL quoting for calendar object UIDs containing slashes -- both `_generate_url()` and `_find_id_and_path()` in `calendarobject_ops.py` now share a single `_quote_uid()` helper (related to https://github.com/python-caldav/caldav/issues/143).
 * Fixed `expand_simple_props()` return value handling.
 
+### Added (compatibility)
+
+* New feature flag `save-load.event.recurrences.exception` to express whether the server stores master+exception VEVENTs as a single calendar object (per RFC) or splits them into separate objects. When a server stores them separately, `expand=True` searches now automatically fall back to server-side `CALDAV:expand` (when supported), since client-side expansion of the master alone would otherwise yield duplicate occurrences.
+* Added Stalwart compatibility hints: `search.recurrences.includes-implicit.event` (fragile — broken for all-day/VALUE=DATE events), `search.recurrences.includes-implicit.todo` (fragile), `search.recurrences.expanded.exception` (unsupported), `save-load.event.recurrences.exception` (unsupported — exceptions stored as separate objects), `vtodo_datesearch_nodtstart_task_is_skipped` and `no_search_openended` old-flags.
+
 ### Test Framework
 
 * Added async rate-limit unit tests matching the sync test suite.
+* caldav-server-tester: `CheckRecurrenceSearch` now also verifies implicit recurrence support for all-day (VALUE=DATE) recurring events, marking the feature as `fragile` (with behaviour description) when only datetime recurring events work.
 
 ## [3.0.0a2] - 2026-02-25 (Alpha Release)
 

caldav/compatibility_hints.py

@@ -130,6 +130,16 @@ class FeatureSet:
         "save-load.event": {"description": "it's possible to save and load events to the calendar"},
         "save-load.event.recurrences": {"description": "it's possible to save and load recurring events to the calendar - events with an RRULE property set, including recurrence sets"},
         "save-load.event.recurrences.count": {"description": "The server will receive and store a recurring event with a count set in the RRULE", "default": {"support": "full"}},
+        ## This was Claude's suggestion and it works as of today, the
+        ## "unsupported" description matches the behaviour of the Stalwart server.
+        ## Stalwart apparently (in a breach with the RFC) stores the exception
+        ## information as a separate CalendarObjectResource.
+        ## Currently the search logic will do server-side expansion
+        ## if this flag is set to "unsupported", which is the correct behaviour for Stalwart.
+        ## The problem is that logically, this feature would also be "unsupported" if the exception
+        ## information was simply discarded, and the current search behaviour would in
+        ## such a case be incorrect if the exception is simply discarded.
+        "save-load.event.recurrences.exception": {"description": "When a VCALENDAR containing a master VEVENT (with RRULE) and exception VEVENT(s) (with RECURRENCE-ID) is stored, the server keeps them together as a single calendar object resource. When unsupported, the server splits exception VEVENTs into separate calendar objects, making client-side expansion unreliable (the master expands without knowing about its exceptions)."},
         "save-load.todo": {"description": "it's possible to save and load tasks to the calendar"},
         "save-load.todo.recurrences": {"description": "it's possible to save and load recurring tasks to the calendar"},
         "save-load.todo.recurrences.count": {"description": "The server will receive and store a recurring task with a count set in the RRULE", "default": {"support": "full"}},
@@ -1365,8 +1375,27 @@ def dotted_feature_set_list(self, compact=False):
     },
     'create-calendar.auto': True,
     'principal-search': {'support': 'ungraceful'},
-    'search.recurrences.expanded.exception': False,
     'search.time-range.alarm': False,
+    ## Stalwart supports implicit recurrence for datetime events but not for
+    ## all-day (VALUE=DATE) recurring events in time-range searches.
+    'search.recurrences.includes-implicit.event': {'support': 'fragile', 'behaviour': 'broken for all-day (VALUE=DATE) events'},
+    ## Stalwart returns the recurring todo in search results but doesn't return the
+    ## RRULE intact, so client-side expansion can't expand it to specific occurrences.
+    'search.recurrences.includes-implicit.todo': {'support': 'fragile'},
+    ## Stalwart doesn't handle exceptions properly in server-side CALDAV:expand:
+    ## returns 3 items instead of 2 for a recurring event with one exception
+    ## (the exception is stored as a separate object and returned twice).
+    'search.recurrences.expanded.exception': False,
+    ## Stalwart doesn't store master+exception VEVENTs correctly as a single resource
+    ## (returns 3 VEVENTs instead of 2 when the master+exception event is expanded).
+    ## Since server-side expansion is also broken, both paths give wrong results.
+    'save-load.event.recurrences.exception': {'support': 'unsupported'},
+    'old_flags': [
+        ## Stalwart does not return VTODO items without DTSTART in date searches
+        'vtodo_datesearch_nodtstart_task_is_skipped',
+        ## Stalwart does not return results for open-ended date searches on VTODOs
+        'no_search_openended',
+    ],
 }
 
 ## Lots of transient problems with purelymail

caldav/search.py

@@ -273,6 +273,17 @@ def _search_impl(
         if not self.expand and not server_expand:
             split_expanded = False
 
+        ## If the server stores exception VEVENTs as separate calendar objects, client-side
+        ## expansion is unreliable (the master expands without knowing its exceptions, yielding
+        ## duplicate occurrences).  Fall back to server-side expansion when it handles exceptions.
+        if (
+            self.expand
+            and not server_expand
+            and not calendar.client.features.is_supported("save-load.event.recurrences.exception")
+            and calendar.client.features.is_supported("search.recurrences.expanded.exception")
+        ):
+            server_expand = True
+
         if self.expand or server_expand:
             if not self.start or not self.end:
                 raise error.ReportError("can't expand without a date range")

tests/test_caldav.py

@@ -2642,9 +2642,9 @@ def testTodoDatesearch(self):
         todos2 = c.search(start=datetime(2025, 4, 14), todo=True, include_completed=True)
         todos3 = c.search(start=datetime(2025, 4, 14), todo=True)
 
-        assert isinstance(todos1[0], Todo)
-        assert isinstance(todos2[0], Todo)
         if not self.check_compatibility_flag("no_search_openended"):
+            assert isinstance(todos1[0], Todo)
+            assert isinstance(todos2[0], Todo)
             assert isinstance(todos3[0], Todo)
 
         ## * t6 should be returned, as it's a yearly task spanning over 2025
@@ -3283,12 +3283,19 @@ def testRecurringDateWithExceptionSearch(self):
             server_expand=True,
         )
 
-        assert len(r) == 2
-        if self.is_supported("search.recurrences.expanded.event"):
-            assert len(rs) == 2
+        ## Only assert exact count and RRULE-free output when exception handling
+        ## is reliable (either client-side or server-side expansion works correctly).
+        if self.is_supported("save-load.event.recurrences.exception") or self.is_supported(
+            "search.recurrences.expanded.exception"
+        ):
+            assert len(r) == 2
+            assert "RRULE" not in r[0].data
+            assert "RRULE" not in r[1].data
 
-        assert "RRULE" not in r[0].data
-        assert "RRULE" not in r[1].data
+        if self.is_supported("search.recurrences.expanded.event") and self.is_supported(
+            "search.recurrences.expanded.exception"
+        ):
+            assert len(rs) == 2
 
         asserts_on_results = [r]
         if self.is_supported("search.recurrences.expanded.exception"):