Improved cancellation semantics

docs/tasks.rst

@@ -142,3 +142,21 @@ host task that will be copied, but the context of the task that calls
     support for this only landed in v3.7.
 
 .. _context: https://docs.python.org/3/library/contextvars.html
+
+Differences with asyncio.TaskGroup
+----------------------------------
+
+The :class:`asyncio.TaskGroup` class, added in Python 3.11, is very similar in design to
+the AnyIO :class:`~TaskGroup` class. The asyncio counterpart has some important
+differences in its semantics, however:
+
+* Tasks are spawned solely through :meth:`~asyncio.TaskGroup.create_task`; there is no
+  ``start()`` or ``start_soon()`` method
+* The :meth:`~asyncio.TaskGroup.create_task` method returns a task object which can be
+  awaited on (or cancelled)
+* Tasks can only be cancelled individually (there is no ``cancel()`` method or similar
+  in the task group)
+* When a task is cancelled before its coroutine has started running, it will not get a
+  chance to handle the cancellation exception
+* New tasks cannot be started after an exception in one of the tasks has triggered a
+  shutdown

docs/versionhistory.rst

@@ -7,6 +7,15 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 
 - **BACKWARDS INCOMPATIBLE** Replaced AnyIO's own ``ExceptionGroup`` class with the PEP
   654 ``BaseExceptionGroup`` and ``ExceptionGroup``
+- **BACKWARDS INCOMPATIBLE** Changes to cancellation semantics:
+
+  - Any exceptions raising out of a task groups are now nested inside an
+    ``ExceptionGroup`` (or ``BaseExceptionGroup`` if one or more ``BaseException`` were
+    included), except when all the exceptions are cancellation exceptions. In that case,
+    a single cancellation exception is raised instead.
+  - ``CancelScope`` now un-cancels its host task on Python 3.11 + asyncio when
+    appropriate, for compatibility with ``asyncio.timeout`` and other context managers
+    that swallow exceptions
 - Bumped minimum version of trio to v0.22
 - Added ``create_unix_datagram_socket`` and ``create_connected_unix_datagram_socket`` to
   create UNIX datagram sockets (PR by Jean Hominal)
@@ -42,6 +51,8 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
   the event loop to be closed
 - Fixed ``current_effective_deadline()`` not returning ``-inf`` on asyncio when the
   currently active cancel scope has been cancelled (PR by Ganden Schaffner)
+- Fixed task group not raising a cancellation exception on asyncio at exit if no child
+  tasks were spawned and an outer cancellation scope had been cancelled before
 
 **3.6.1**
 

pyproject.toml

@@ -26,7 +26,7 @@ classifiers = [
 ]
 requires-python = ">= 3.7"
 dependencies = [
-    "exceptiongroup; python_version < '3.11'",
+    "exceptiongroup >= 1.0.2; python_version < '3.11'",
     "idna >= 2.8",
     "sniffio >= 1.1",
     "typing_extensions; python_version < '3.8'",