feat: compatibility features replace the old flags

caldav/compatibility_hints.py

@@ -32,11 +32,6 @@
 ## caldav_server_checker, and things got messy from there.  We should
 ## double-check the values where there is any doubt, and clean up.
 
-## NEW STYLE
-## (we're gradually moving stuff from the good old
-## "incompatibility_description" below over to
-## "compatibility_features")
-
 class FeatureSet:
     """Work in progress ... TODO: write a better class description.
 
@@ -433,6 +428,7 @@ class FeatureSet:
         "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"}},
         "save-load.todo.recurrences.thisandfuture": {"description": "Completing a recurring task with rrule_mode='thisandfuture' works (modifies RRULE and saves back to server)", "default": {"support": "full"}},
         "save-load.todo.mixed-calendar": {"description": "The same calendar may contain both events and tasks (Zimbra only allows tasks to be placed on special task lists)", "default": {"support": "full"}},
+        "save-load.todo.uncomplete": {"description": "A completed task can be made pending again (Todo.uncomplete()): after saving it with STATUS:NEEDS-ACTION and without COMPLETED, it loads back that way.", "default": {"support": "full"}},
         "save-load.journal": {
             "description": "The server will even accept journals",
             "default": { "support": "full" }
@@ -546,7 +542,12 @@ class FeatureSet:
         },
         "search.time-range.todo": {"description": "basic time range searches for tasks works", "default": {"support": "full"}},
         "search.time-range.todo.no-dtstart": {
-            "description": "A VTODO without DTSTART (but with DUE) is returned by a date-range search.  RFC5545 and RFC4791 section 9.9 say such a task has a defined time span and should be found, so 'full' (the default) is the compliant behaviour; some servers (Davical, Stalwart, Synology) skip any task lacking DTSTART.  Probed with a closed window; servers that skip such tasks only in closed ranges (returning them in open-ended ones) are instead tracked by the 'vtodo_datesearch_nodtstart_task_is_skipped_in_closed_date_range' flag.",
+            "description": "A VTODO without DTSTART (but with DUE) is returned by a date-range search.  RFC5545 and RFC4791 section 9.9 say such a task has a defined time span and should be found, so 'full' (the default) is the compliant behaviour; some servers (Davical, Stalwart, Synology) skip any task lacking DTSTART.  Probed with a closed window.",
+            "default": {"support": "full"},
+            "links": ["https://datatracker.ietf.org/doc/html/rfc4791#section-9.9"],
+        },
+        "search.time-range.todo.no-dtstart.no-due": {
+            "description": "A VTODO with neither DTSTART nor DUE (nor COMPLETED or CREATED) is returned by a date-range search.  RFC4791 section 9.9 says such a task overlaps every time range.  Zimbra only finds tasks with DTSTART or DUE set.  Unless set, it follows search.time-range.todo.no-dtstart, as a server skipping tasks without DTSTART skips these too.  Probed with a closed window.",
             "default": {"support": "full"},
             "links": ["https://datatracker.ietf.org/doc/html/rfc4791#section-9.9"],
         },
@@ -850,16 +851,13 @@ def __init__(self, feature_set_dict=None):
         if isinstance(feature_set_dict, FeatureSet):
             self._server_features = copy.deepcopy(feature_set_dict._server_features)
             self.backward_compatibility_mode = feature_set_dict.backward_compatibility_mode
-            self._old_flags = copy.copy(feature_set_dict._old_flags) if hasattr(feature_set_dict, '_old_flags') else []
             return
 
         ## TODO: copy the FEATURES dict, or just the feature_set dict?
         ## (anyways, that is an internal design decision that may be
         ## changed ... but we need test code in place)
         self.backward_compatibility_mode = feature_set_dict is None
         self._server_features = {}
-        ## TODO: remove this when it can be removed
-        self._old_flags = []
         if feature_set_dict:
             self._copy_feature_set(feature_set_dict, collapse=False)
 
@@ -908,10 +906,6 @@ def copy_feature_set(self, feature_set, collapse=True):
     ## warning with stacklevel=3 points at the user's code
     def _copy_feature_set(self, feature_set, collapse=True):
         for feature in feature_set:
-            ## TODO: temp - should be removed
-            if feature == 'old_flags':
-                self._old_flags = feature_set[feature]
-                continue
             if feature == 'write-delay':
                 warnings.warn(
                     "The 'write-delay' feature is deprecated - use 'synchronous-write', "
@@ -1357,60 +1351,10 @@ def compare(self, observed):
                 )
         return mismatches
 
-#### OLD STYLE
-
-## THE LIST BELOW IS TO BE REMOVED COMPLETELY.  DO NOT USE IT.
-
-## It's not considered to be part of the public API (though, it should
-## have been prefixed with _ to make it clear).  The list is being
-## removed little-by-little, without regards of SemVer.
-
-## The lists below are specifying what tests should be skipped or
-## modified to accept non-conforming resultsets from the different
-## calendar servers.  In addition there are some hacks in the library
-## code itself to work around some known compatibility issues, like
-## the caldav.lib.vcal.fix function.
-## Here is a list of all observed (in)compatibility issues the test framework needs to know about
-## TODO:
-## * references to the relevant parts of the RFC would be nice.
-## * Research should be done to triple-check that the issue is on the server side, and not on the client side
-## * Some of the things below should be possible to probe the server for.
-## * Perhaps some more readable format should be considered (yaml?).
-## * Consider how to get this into the documentation
-incompatibility_description = {
-    'event_by_url_is_broken':
-        """A GET towards a valid calendar object resource URL will yield 404 (wtf?)""",
-
-    'vtodo_datesearch_nodtstart_task_is_skipped_in_closed_date_range':
-        """only open-ended date searches for todo-items will find tasks without a dtstart""",
-
-    'vtodo_datesearch_notime_task_is_skipped':
-        """date searches for todo-items will (only) find tasks that has either """
-        """a dtstart or due set""",
-
-    'vtodo_no_due_infinite_duration':
-        """date search will find todo-items without due if dtstart is """
-        """before the date search interval.  This is in breach of rfc4791"""
-        """section 9.9""",
-
-    'vtodo-cannot-be-uncompleted':
-        """If a VTODO object has been set with STATUS:COMPLETE, it's not possible to delete the COMPLTEDED attribute and change back to STATUS:IN-ACTION""",
-
-    'sticky_events':
-        """Events should be deleted before the calendar is deleted, """
-        """and/or deleting a calendar may not have immediate effect""",
-
-    'dav_not_supported':
-        """when asked, the server may claim it doesn't support the DAV protocol.  Observed by one baikal server, should be investigated more (TODO) and robur""",
-
-   'fastmail_buggy_noexpand_date_search':
-        """The 'blissful anniversary' recurrent example event is returned when asked for a no-expand date search for some timestamps covering a completely different date""",
-
-    'robur_rrule_freq_yearly_expands_monthly':
-        """Robur expands a yearly event into a monthly event.  I believe I've reported this one upstream at some point, but can't find back to it""",
-
-}
-
+## Server profiles.  Each dict below is a feature set (see
+## FeatureSet.FEATURES above) describing one server.  In addition there
+## are some hacks in the library code itself to work around some known
+## compatibility issues, like the caldav.lib.vcal.fix function.
 xandikos = {
     ## Probed 2026-10-11 on 0.4.8, unchanged on master (0.4.9): a token that
     ## isn't a hex SHA crashes the git store lookup, and a hex one is refused
@@ -1677,20 +1621,14 @@ def compare(self, observed):
     'save-load.icalendar.related-to': {'support': 'unsupported'},
     'search.time-range.open.start': {'support': 'broken'},
 
-    "old_flags": [
-    ## setting display name in zimbra does not work (display name,
-    ## calendar-ID and URL is the same, the display name cannot be
-    ## changed, it can only be given if no calendar-ID is given.  In
-    ## earlier versions of Zimbra display-name could be changed, but
-    ## then the calendar would not be available on the old URL
-    ## anymore)
-    ## 'event_by_url_is_broken' removed - works in zimbra/zcs-foss:latest
-    'vtodo_datesearch_notime_task_is_skipped',
+    ## Probed 2026-10-20: a task with DUE but no DTSTART is found by a
+    ## date search, one with neither is not
+    'search.time-range.todo.no-dtstart.no-due': {'support': 'unsupported'},
 
     ## TODO: I just discovered that when searching for a date some
     ## years after a recurring daily event was made, the event does
     ## not appear.
-    ],
+
     ## extra properties not specified in RFC4791/RFC5545.  Zimbra stores
     ## calendar-order, and stores calendar-color only when set as a hex value -
     ## it rejects/ignores a colour name like "blue".  (The old 'calendar_color'
@@ -2079,12 +2017,6 @@ def compare(self, observed):
     'principal-search': {'support': 'unsupported'},
     ## DAViCal skips VTODOs without DTSTART in date-range searches.
     'search.time-range.todo.no-dtstart': {'support': 'unsupported'},
-    "old_flags": [
-        #'no_journal', ## it threw a 500 internal server error! ## for old versions
-        #'nofreebusy', ## for old versions
-        ## 'fragile_sync_tokens' removed - covered by 'sync-token': {'support': 'fragile'}
-        'vtodo_datesearch_notime_task_is_skipped',
-    ],
     ## extra properties not specified in RFC4791/RFC5545
     "calendar-color": {"support": "full"},
     "calendar-order": {"support": "full"},
@@ -2184,7 +2116,10 @@ def compare(self, observed):
     'test-calendar': {'cleanup-regime': 'wipe-calendar'},
 
 }
-## Old notes for sogo (todo - incorporate them in the structure above)
+## Old notes for sogo (todo - incorporate them in the structure above).
+## The commented-out lists here and below name flags of the old-style
+## system, removed in https://github.com/python-caldav/caldav/issues/585 -
+## kept only as a record of what was once observed on those servers.
 ## https://www.sogo.nu/bugs/view.php?id=3065
 ## left a note about time-based sync tokens on https://www.sogo.nu/bugs/view.php?id=5163
 ## https://www.sogo.nu/bugs/view.php?id=5282
@@ -2606,10 +2541,11 @@ def compare(self, observed):
     ## Open-start searches used to work (no hint, so full), but were
     ## rejected with 403 Forbidden 2026-10-11
     'search.time-range.open.start': {'support': 'fragile'},
-    "old_flags":  [
-        #"text_search_is_case_insensitive",
-        "vtodo-cannot-be-uncompleted",
-    ]
+    ## Probed 2026-10-20
+    "save-load.todo.uncomplete": {
+        "support": "unsupported",
+        "behaviour": "the task is saved as pending, but loads back with STATUS:COMPLETED",
+    },
 }
 
 ## https://ox.io/

changes/585.added.md

@@ -0,0 +1 @@
+Compatibility features `save-load.todo.uncomplete` (a completed task can be made pending again with `Todo.uncomplete()`; GMX keeps it completed) and `search.time-range.todo.no-dtstart.no-due` (a date search finds a task with neither DTSTART nor DUE, as RFC 4791 section 9.9 says it should; Zimbra does not).  They replace the last two old-style flags in the Zimbra and GMX profiles.

changes/585.removed.md

@@ -0,0 +1 @@
+The old-style compatibility flags are gone: `caldav.compatibility_hints.incompatibility_description`, and the `old_flags` key in a feature set.  They were only ever used by the test suite to skip or adjust tests, and every flag still in use is now a compatibility feature.

docs/design/FEATURE_COMPLETE_ROADMAP.md

@@ -535,7 +535,7 @@ Also related: [#697](https://github.com/python-caldav/caldav/issues/697) - smart
 - **Related issues:** [#585](https://github.com/python-caldav/caldav/issues/585), [#482](https://github.com/python-caldav/caldav/issues/482), [#128](https://github.com/python-caldav/caldav/issues/128), [#619](https://github.com/python-caldav/caldav/issues/619), [#515](https://github.com/python-caldav/caldav/issues/515)
 
 **Tasks:**
-- [ ] Remove old incompatibility flags ([#585](https://github.com/python-caldav/caldav/issues/585))
+- [x] Remove old incompatibility flags ([#585](https://github.com/python-caldav/caldav/issues/585))
 - [ ] Obsolete `get_duration`, `get_due`, `get_dtend` ([#482](https://github.com/python-caldav/caldav/issues/482))
 - [ ] v4.0: remove everything that raises a `DeprecationWarning`, and add the
       warning to methods deprecated without one ([#619](https://github.com/python-caldav/caldav/issues/619))

docs/design/TODO_COMPATIBILITY_HINTS.md

@@ -44,26 +44,13 @@ and once in the post-loop block (line 606).  The second call (line 606) uses the
 Needs careful review; may be an off-by-one in the loop termination logic, or the two
 conditions are truly independent and the second call is simply redundant.
 
-## 3. `_old_flags` — in-progress migration, clear removal path
+## 3. `_old_flags` (fixed)
 
-**Location**: `FeatureSet.__init__`, `FeatureSet.copy_feature_set`, and ~12 server config
-dicts in `compatibility_hints.py`
-
-`_old_flags` is explicitly marked `## TODO: remove this when it can be removed`.  It is
-a shim that carries forward the legacy flat-list quirk system while server configs are
-being migrated to the new dotted-feature style.
-
-`test_caldav.py:1006` still reads `self.caldav.features._old_flags` to validate that old
-flags are known strings.  The test at line 1015-1016 confirms all flags are present in
-`incompatibility_description`.
-
-**Fix**: For each server dict that still has `'old_flags': [...]`, translate the listed
-flags into equivalent new-style features and remove the `old_flags` key.  Once all server
-dicts are migrated:
-- Remove the `if feature == 'old_flags':` special-case in `copy_feature_set`
-- Remove `self._old_flags = []` from `__init__`
-- Remove the `_old_flags` copy in the copy-constructor branch
-- Remove the validation in `test_caldav.py`
+The last old-style flags are gone (https://github.com/python-caldav/caldav/issues/585):
+the two still set by a server profile became `save-load.todo.uncomplete` and
+`search.time-range.todo.no-dtstart.no-due`, each probed by caldav-server-tester, and the
+rest were set by no profile.  `incompatibility_description`, the `old_flags` key and the
+test helpers reading them are removed.
 
 ## 4. `feature_tree` / `_dots_to_tree` — internal detail that can be simplified
 
@@ -104,8 +91,7 @@ return (
 
 The `enable`, `value` and `observed` slots exist to correctly compare `client-feature` and
 `server-observation` nodes during collapse.  In practice, collapse is only ever invoked
-on server-feature nodes (the only type that appears in the server config dicts, aside
-from `old_flags`).  The extra slots add noise without effect.
+on server-feature nodes (the only type that appears in the server config dicts).  The extra slots add noise without effect.
 
 **Fix**: Simplify to `return feature_dict.get('support')` once the broader type-system
 simplification is settled.
@@ -150,5 +136,5 @@ want a second look at the same time.
 
 ## Ordering / dependencies
 
-Items 3 (old_flags) and 6 (rename) are independent and safe to do first.  Items 1, 2,
+Items 3 (old_flags) and 6 (rename) are done.  Items 1, 2,
 4, 5 are interrelated around the type-system simplification and are best tackled together.

tests/test_async_integration.py

@@ -192,9 +192,6 @@ def skip_unless_support(self, feature):
             msg = self._features.find_feature(feature).get("description", feature)
             pytest.skip("Test skipped due to server incompatibility issue: " + msg)
 
-    def check_compatibility_flag(self, flag: str) -> bool:
-        return flag in getattr(self._features, "_old_flags", [])
-
     @pytest.fixture(scope="class")
     @classmethod
     def test_server(cls) -> TestServer:
@@ -1740,13 +1737,10 @@ async def test_todo_datesearch(self, async_task_list: Any) -> None:
         foo = 5
         if not self.is_supported("search.recurrences.includes-implicit.todo"):
             foo -= 1
-        if not self.is_supported(
-            "search.time-range.todo.no-dtstart"
-        ) or self.check_compatibility_flag(
-            "vtodo_datesearch_nodtstart_task_is_skipped_in_closed_date_range"
-        ):
-            foo -= 2
-        elif self.check_compatibility_flag("vtodo_datesearch_notime_task_is_skipped"):
+        if not self.is_supported("search.time-range.todo.no-dtstart"):
+            foo -= 1
+        ## follows no-dtstart unless set
+        if not self.is_supported("search.time-range.todo.no-dtstart.no-due"):
             foo -= 1
 
         if implicit_fragile:
@@ -1779,14 +1773,9 @@ async def test_create_journal_list_and_journal_entry(self, async_journal_list: A
 
     # ==================== Group E – Properties & Meta ====================
 
-    def _skip_on_compatibility_flag(self, flag: str) -> None:
-        if self.check_compatibility_flag(flag):
-            pytest.skip(f"Test skipped due to compatibility flag: {flag}")
-
     @pytest.mark.asyncio
     async def test_support(self, async_client: Any) -> None:
         """check_dav_support / check_cdav_support / check_scheduling_support."""
-        self._skip_on_compatibility_flag("dav_not_supported")
         assert await async_client.check_dav_support()
         assert await async_client.check_cdav_support()
         if self.is_supported("scheduling", return_type=str) != "unknown":