tobixen · Oct 22, 2026 · Oct 20, 2026 · Oct 20, 2026 · Oct 20, 2026 · Oct 20, 2026
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
@@ -66,3 +66,29 @@ jobs:
 
       - name: Run tests
         run: pytest
+
+  suite-coverage:
+    name: Branch coverage of the conformance suite
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+          fetch-depth: 0
+
+      - name: Set up Python
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
+        with:
+          python-version: "3.13"
+
+      - name: Install dependencies
+        run: pip install -e ".[dev]"
+
+      # A branch of a capability-aware test that no memory profile reaches
+      # tests nothing; the profiles in tests/_async/test_memory_conformance.py
+      # are there to reach them.
+      - name: Measure
+        run: |
+          coverage run --branch --source=calendaring -m pytest -q tests/_async/test_memory_conformance.py
+          coverage report -m --include='*/_async/conformance.py' --fail-under=95
diff --git a/.gitignore b/.gitignore
@@ -17,3 +17,4 @@ build/
 *.egg-info/
 .ruff_cache/
 .lycheecache
+.coverage
diff --git a/docs/design/API_DESIGN.md b/docs/design/API_DESIGN.md
@@ -1049,14 +1049,22 @@ initial set:
 | `identity.client-uid`, `identity.foreign-id` | [§3.2 Identity](#32-identity) |
 | `identity.client-native-id` | `add(native_id=...)`: the caller may name the stored object (CalDAV href, vdir file name) |
 | `properties.passthrough` | unknown properties and components survive a round trip |
-| `recurrence`, `recurrence.edit-this-and-future` | stores `RRULE`; [§3.7 Recurrence](#37-recurrence) |
+| `recurrence`, `recurrence.edit-this-and-future` | stores a recurrence set: `RRULE`, `RDATE`, `EXDATE` and the overrides (`RECURRENCE-ID`); `UNSUPPORTED` drops all four, overrides included; [§3.7 Recurrence](#37-recurrence) |
 | `recurrence.edit-occurrence` | `save(occurrence)` merges it into the stored object ([§3.7](#37-recurrence)); `UNSUPPORTED` where the merge is not available yet (Q3) |
 | `task.complete-recurring` | `complete()` on a recurring task or one occurrence of it ([§3.7](#37-recurrence)) |
 | `move` | [§2.3 Collection](#23-collection) |
 | `task.status`, `task.priority`, `task.percent-complete` | `LOSSY` when values are mapped |
 | `task.start`, `task.due`, `task.completed`, `task.planned`, `task.estimate` | |
 | `task.relations.parent`, `task.relations.depends-on` | |
 | `categories`, `attendees` | for every component; on a task, attendees are its assignees |
+| `alarms` | `VALARM` components survive; `UNSUPPORTED` drops them |
+| `timezones` | a time with a `TZID` keeps it (with its `VTIMEZONE`), a floating time stays floating; `LOSSY` stores both in UTC, a floating time read as local time ([§4](#4-search)) |
+| `dates` | a `DATE` value stays a date; `LOSSY` stores midnight UTC |
+
+Text is not a feature: non-ASCII, escaped and multi-line text, and every
+value of a property with several, round-trip on every backend.  The
+conformance suite stores a corpus of real-world objects and lets `verify`
+compare what comes back; only what the declaration says may differ.
 
 Feature names are identifiers, not attribute paths: `task.due` means "stores a
 task's `DUE`", which is read as `task.component.DUE`, and `task.estimate`
@@ -1165,6 +1173,7 @@ CalendaringError
 ├── UnsupportedError              # carries .feature
 │   └── LossyWriteError           # carries .losses; raised before anything is sent
 ├── InvalidDataError              # the backend rejected the data, or it does not parse; also a ValueError
+│   └── PartialResultError        # a read left out stored objects it could not use; .results, .broken
 ├── RateLimitError                # carries .retry_after: float | None
 ├── VerificationError             # verify=True: written, but stored differently; carries .differences
 └── BackendError                  # anything else from the backend or transport
@@ -1197,7 +1206,23 @@ CalendaringWarning
   reload the item. It is still a `ConflictError`, as `AlreadyExistsError`
   is, because all three are a failed precondition; a handler that reloads
   on `ConflictError` should catch the subclasses first.
-- Fan-out ([§2.1 Workspace](#21-workspace)) does not raise; `MultiResult.raise_for_errors()` raises an `ExceptionGroup` of these.
+- **One bad stored object does not hide the rest.** A read that lists
+  (`search()`, `iter_search()` once exhausted, the listing shorthands,
+  `changes()`, `relatives()`, and `get(uid)` where the UID is not found)
+  leaves out an
+  object that does not parse, or that the searcher cannot match (two
+  masters for one UID), and then raises `PartialResultError`.  `.results`
+  is what the call would have returned from the rest (for `changes()` the
+  `ChangeSet`, whose token is good; for `iter_search()` nothing, since it
+  yielded them already), and `.broken` lists the objects left
+  out (`BrokenObject`: native id, etag, error, and the bytes as read where
+  the backend has them, to repair the object from).  A broken object is
+  never reported as deleted.  `get_by_native_id()` of one raises
+  `InvalidDataError`.  Raising rather than warning means no caller misses
+  it; a caller that can live with the gap takes `.results`.  The listing
+  primitives return a `BrokenObject` in place of a `StoredObject` rather
+  than raising, so the backend decides per object.
+- Fan-out ([§2.1 Workspace](#21-workspace)) does not raise; `MultiResult.raise_for_errors()` raises an `ExceptionGroup` of these.  `Workspace.search()` keeps a `PartialResultError`'s `.results` among the items, and the error among the errors.
 
 caldav's errors map one to one where they overlap:
 `NotFoundError` → `NotFoundError`, `ETagMismatchError` and

diff --git a/docs/design/ROADMAP.md b/docs/design/ROADMAP.md
@@ -278,11 +278,15 @@ Notes from doing it:
   the suite: `FULL`, `TRACKER` (tasks only, mapped status and priority,
   assigned UIDs), `MINIMAL` (writable, most optional features left out, no
   collections of its own, so the suite borrows one that already holds an
-  item) and `FEED` (read-only). Between them the capability-aware tests run
-  both branches, except the supported branches of
-  `recurrence.edit-occurrence` and `task.complete-recurring` (below). Every
-  skip says why: a write test on the read-only profile after the write was
-  checked to raise, or a recurrence test where nothing recurs.
+  item) and `FEED` (read-only). Three more in the test module (events
+  only, tasks without a status, and a feed of tasks) reach the branches
+  these four left out, which a review found
+  ([issue 21](https://github.com/pycalendar/calendaring/issues/21)); CI
+  fails below 95 % branch coverage of the suite. The supported branches of
+  `recurrence.edit-occurrence`, `recurrence.edit-this-and-future` and
+  `task.complete-recurring` (below) are still not run. Every skip says why:
+  a write test on the read-only profile after the write was checked to
+  raise, or a recurrence test where nothing recurs.
 - A backend implements a handful of primitives (`_query`, `_fetch`,
   `_create`, `_update`, `_delete`); capability checks, loss policies,
   client-side filtering, change emulation, `move` emulation, `relatives` and

diff --git a/news/15.feature.rst b/news/15.feature.rst
@@ -0,0 +1 @@
+Three new capability features, ``alarms``, ``timezones`` and ``dates``, let a backend say honestly that it cannot keep alarms, time zones or all-day dates; what it would lose is then reported before writing, as for any other loss.  The conformance suite now checks that real-world objects (time zones, alarms, recurrence exceptions, non-ASCII and multi-line text) come back as they were stored.
diff --git a/news/22.feature.rst b/news/22.feature.rst
@@ -0,0 +1 @@
+One stored item that cannot be read no longer makes a whole collection unreadable.  A search, ``get()``, ``relatives()`` or ``changes()`` that has to leave items out raises ``PartialResultError``, which carries what could be read and the raw data of what could not, so it can be repaired.
diff --git a/pyproject.toml b/pyproject.toml
@@ -40,6 +40,7 @@ dev = [
   "mypy==2.4.0",
   "pre-commit>=4.0",
   "towncrier>=25.8",
+  "coverage>=7.6",
 ]
 
 [project.urls]

diff --git a/src/calendaring/__init__.py b/src/calendaring/__init__.py
@@ -39,6 +39,7 @@
     LossyWriteError,
     LossyWriteWarning,
     NotFoundError,
+    PartialResultError,
     RateLimitError,
     SyncTokenError,
     TransportError,
@@ -47,7 +48,7 @@
 )
 from .items import Event, Item, Journal, Task, TaskStatus
 from .loss import Loss, LossPolicy
-from .types import ChangeSet, Component, MultiResult, Scope, StoredObject, SyncToken
+from .types import BrokenObject, ChangeSet, Component, MultiResult, Scope, StoredObject, SyncToken
 
 # Register the reference backend's kind ("memory") in both modes.
 from . import memory as _memory  # noqa: E402, F401  isort: skip
@@ -86,8 +87,10 @@
     "LossyWriteWarning",
     "MultiResult",
     "NotFoundError",
+    "PartialResultError",
     "RateLimitError",
     "Scope",
+    "BrokenObject",
     "StoredObject",
     "Support",
     "SyncEvent",
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Three new capability features, ``alarms``, ``timezones`` and ``dates``, let a backend say honestly that it cannot keep alarms, time zones or all-day dates; what it would lose is then reported before writing, as for any other loss. The conformance suite now checks that real-world objects (time zones, alarms, recurrence exceptions, non-ASCII and multi-line text) come back as they were stored.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		One stored item that cannot be read no longer makes a whole collection unreadable. A search, ``get()``, ``relatives()`` or ``changes()`` that has to leave items out raises ``PartialResultError``, which carries what could be read and the raw data of what could not, so it can be repaired.