Anyio

- **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)
- 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
- Ensured that exiting a ``TaskGroup`` always hits a yield point, regardless of
whether there are running child tasks to be waited on
- On asyncio, cancel scopes will defer cancelling tasks that are scheduled to resume
with a finished future
- On asyncio and Python 3.9/3.10, cancel scopes now only suppress cancellation
exceptions if the cancel message matches the scope
- Task groups on all backends now raise a single cancellation exception when an outer
cancel scope is cancelled, and no exceptions other than cancellation exceptions are
raised in the group
- **BACKWARDS INCOMPATIBLE** Changes the pytest plugin to run all tests and fixtures in
the same task, allowing fixtures to set context variables for tests and other fixtures
- **BACKWARDS INCOMPATIBLE** Changed ``anyio.Path.relative_to()`` and
``anyio.Path.is_relative_to()`` to only accept one argument, as passing multiple
arguments is deprecated as of Python 3.12
- **BACKWARDS INCOMPATIBLE** Dropped support for spawning tasks from old-style coroutine
functions (``asyncio.coroutine``)
- **BACKWARDS INCOMPATIBLE** The ``policy`` option on the ``asyncio`` backend was
changed to ``loop_factory`` to accommodate ``asyncio.Runner``
- Changed ``anyio.run()`` to use ``asyncio.Runner`` (or a back-ported version of it on
Pythons older than 3.11) on the ``asyncio`` backend
- Dropped support for Python 3.7
- Added support for Python 3.12
- Bumped minimum version of trio to v0.22
- Added the ``anyio.Path.is_junction()`` and ``anyio.Path.walk()`` methods
- Added ``create_unix_datagram_socket`` and ``create_connected_unix_datagram_socket`` to
create UNIX datagram sockets (PR by Jean Hominal)
- Fixed ``from_thread.run`` and ``from_thread.run_sync`` not setting sniffio on asyncio.
As a result:

- Fixed ``from_thread.run_sync`` failing when used to call sniffio-dependent functions
on asyncio
- Fixed ``from_thread.run`` failing when used to call sniffio-dependent functions on
asyncio from a thread running trio or curio
- Fixed deadlock when using ``from_thread.start_blocking_portal(backend="asyncio")``
in a thread running trio or curio (PR by Ganden Schaffner)
- Improved type annotations:

- The ``item_type`` argument of ``create_memory_object_stream`` was deprecated.
To indicate the item type handled by the stream, use
``create_memory_object_stream[T_Item]()`` instead. Type checking should no longer
fail when annotating memory object streams with uninstantiable item types (PR by
Ganden Schaffner)
- Added the ``CancelScope.cancelled_caught`` property which tells users if the cancel
scope suppressed a cancellation exception
- Fixed ``fail_after()`` raising an unwarranted ``TimeoutError`` when the cancel scope
was cancelled before reaching its deadline
- Fixed ``MemoryObjectReceiveStream.receive()`` causing the receiving task on asyncio to
remain in a cancelled state if the operation was cancelled after an item was queued to
be received by the task (but before the task could actually receive the item)
- Fixed ``TaskGroup.start()`` on asyncio not responding to cancellation from the outside
- Fixed tasks started from ``BlockingPortal`` not notifying synchronous listeners
(``concurrent.futures.wait()``) when they're cancelled
- Removed unnecessary extra waiting cycle in ``Event.wait()`` on asyncio in the case
where the event was not yet set
- Fixed processes spawned by ``anyio.to_process()`` being "lost" as unusable to the
process pool when processes that have idled over 5 minutes are pruned at part of the
``to_process.run_sync()`` call, leading to increased memory consumption
(PR by Anael Gorfinkel)

- Fixed the type annotation of ``TaskGroup.start_soon()`` to accept any awaitables
(already in v3.7.0 but was missing from 4.0.0rc1)
- Changed ``CancelScope`` to also consider the cancellation count (in addition to the
cancel message) on asyncio to determine if a cancellation exception should be
swallowed on scope exit, to combat issues where third party libraries catch the
``CancelledError`` and raise another, thus erasing the original cancel message
- Worked around a `CPython bug <https://github.com/python/cpython/issues/108668>`_ that
caused ``TLSListener.handle_handshake_error()`` on asyncio to log ``"NoneType: None"``
instead of the error (PR by Ganden Schaffner)
- Re-added the ``item_type`` argument to ``create_memory_object_stream()`` (but using it
raises a deprecation warning and does nothing with regards to the static types of the
returned streams)
- Fixed processes spawned by ``anyio.to_process()`` being "lost" as unusable to the
process pool when processes that have idled over 5 minutes are pruned at part of the
``to_process.run_sync()`` call, leading to increased memory consumption
(PR by Anael Gorfinkel)

- Fixed sending large buffers via UNIX stream sockets on asyncio
- Fixed several minor documentation issues (broken links to classes, missing classes or
attributes)

- Dropped support for Python 3.6
- Improved type annotations:

- Several functions and methods that were previously annotated as accepting
``Coroutine[Any, Any, Any]`` as the return type of the callable have been amended to
accept ``Awaitable[Any]`` instead, to allow a slightly broader set of coroutine-like
inputs, like ``async_generator_asend`` objects returned from the ``asend()`` method
of async generators, and to match the ``trio`` annotations:

- ``anyio.run()``
- ``anyio.from_thread.run()``
- ``TaskGroup.start_soon()``
- ``TaskGroup.start()``
- ``BlockingPortal.call()``
- ``BlockingPortal.start_task_soon()``
- ``BlockingPortal.start_task()``

Note that this change involved only changing the type annotations; run-time
functionality was not altered.

- The ``TaskStatus`` class is now a generic protocol, and should be parametrized to
indicate the type of the value passed to ``task_status.started()``
- The ``Listener`` class is now covariant in its stream type
- ``create_memory_object_stream()`` now allows passing only ``item_type``
- Object receive streams are now covariant and object send streams are correspondingly
contravariant
- Changed ``TLSAttribute.shared_ciphers`` to match the documented semantics of
``SSLSocket.shared_ciphers`` of always returning ``None`` for client-side streams
- Fixed ``CapacityLimiter`` on the asyncio backend to order waiting tasks in the FIFO
order (instead of LIFO) (PR by Conor Stevenson)
- Fixed ``CancelScope.cancel()`` not working on asyncio if called before entering the
scope
- Fixed ``open_signal_receiver()`` inconsistently yielding integers instead of
``signal.Signals`` instances on the ``trio`` backend
- Fixed ``to_thread.run_sync()`` hanging on asyncio if the target callable raises
``StopIteration``
- Fixed ``start_blocking_portal()`` raising an unwarranted
``RuntimeError: This portal is not running`` if a task raises an exception that causes
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 the ``OP_IGNORE_UNEXPECTED_EOF`` flag in an SSL context created by default in
``TLSStream.wrap()`` being inadvertently set on Python 3.11.3 and 3.10.11
- Fixed ``CancelScope`` to properly handle asyncio task uncancellation on Python 3.11
(PR by Nikolay Bryskin)
- Fixed ``OSError`` when trying to use ``create_tcp_listener()`` to bind to a link-local
IPv6 address (and worked around related bugs in ``uvloop``)
- Worked around a `PyPy bug <https://foss.heptapod.net/pypy/pypy/-/issues/3938>`_
when using ``anyio.getaddrinfo()`` with for IPv6 link-local addresses containing
interface names

- Pinned Trio to < 0.22 to avoid incompatibility with AnyIO's ``ExceptionGroup`` class
causing ``AttributeError: 'NonBaseMultiError' object has no attribute '_exceptions'``

- Fixed exception handler in the asyncio test runner not properly handling a context
that does not contain the ``exception`` key