GH-94597: add deprecation warnings for subclassing AbstractChildWatcher (#99386)

Author: kumaraditya303

Doc/library/asyncio-policy.rst

@@ -222,6 +222,9 @@ implementation used by the asyncio event loop:
  This method has to be called to ensure that underlying
  resources are cleaned-up.
 
+ .. deprecated:: 3.12
+
+
 .. class:: ThreadedChildWatcher
 
  This implementation starts a new waiting thread for every subprocess spawn.

Doc/whatsnew/3.12.rst

@@ -203,8 +203,8 @@ asyncio
  (Contributed by Kumar Aditya in :gh:`98024`.)
 
 * The child watcher classes :class:`~asyncio.MultiLoopChildWatcher`,
- :class:`~asyncio.FastChildWatcher` and
- :class:`~asyncio.SafeChildWatcher` are deprecated and
+ :class:`~asyncio.FastChildWatcher`, :class:`~asyncio.AbstractChildWatcher`
+ and :class:`~asyncio.SafeChildWatcher` are deprecated and
  will be removed in Python 3.14. It is recommended to not manually
  configure a child watcher as the event loop now uses the best available
  child watcher for each platform (:class:`~asyncio.PidfdChildWatcher`

Lib/asyncio/unix_events.py

@@ -846,6 +846,13 @@ class AbstractChildWatcher:
  waitpid(-1), there should be only one active object per process.
  """
 
+ def __init_subclass__(cls) -> None:
+ if cls.__module__ != __name__:
+ warnings._deprecated("AbstractChildWatcher",
+ "{name!r} is deprecated as of Python 3.12 and will be "
+ "removed in Python {remove}.",
+ remove=(3, 14))
+
  def add_child_handler(self, pid, callback, *args):
  """Register a new child handler.
 

Lib/test/test_asyncio/test_unix_events.py

@@ -1108,6 +1108,11 @@ def test_write_eof_pending(self):
 
 class AbstractChildWatcherTests(unittest.TestCase):
 
+ def test_warns_on_subclassing(self):
+ with self.assertWarns(DeprecationWarning):
+ class MyWatcher(asyncio.AbstractChildWatcher):
+ pass
+
  def test_not_implemented(self):
  f = mock.Mock()
  watcher = asyncio.AbstractChildWatcher()
@@ -1747,7 +1752,9 @@ def f():
 
  self.assertIsInstance(policy.get_event_loop(),
  asyncio.AbstractEventLoop)
- watcher = policy.get_child_watcher()
+ with warnings.catch_warnings():
+ warnings.simplefilter("ignore", DeprecationWarning)
+ watcher = policy.get_child_watcher()
 
  self.assertIsInstance(watcher, asyncio.SafeChildWatcher)
  self.assertIsNone(watcher._loop)

Misc/NEWS.d/next/Library/2022-11-11-18-23-41.gh-issue-94597.m6vMDK.rst

@@ -0,0 +1 @@
+Deprecate :class:`asyncio.AbstractChildWatcher` to be removed in Python 3.14. Patch by Kumar Aditya.