From 1dbd492b16212883ffd324ae7830217cbd8324ab Mon Sep 17 00:00:00 2001
From: pteromys <pteromys@gmail.com>
Date: Mon, 3 Aug 2026 22:41:40 -0400
Subject: [PATCH] Fix asyncio.shield leaking tasks via await-graph.

There were two places where `cur_task` could live until `inner` ended:

1. `inner._asyncio_awaited_by`, and
2. as a capture in `_clear_awaited_by_callback` in `inner._callbacks`.
---
 Lib/asyncio/tasks.py                            |  3 +++
 Lib/test/test_asyncio/test_tasks.py             | 17 +++++++++++++++++
 ...26-08-03-22-46-07.gh-issue-155143.9-byZp.rst |  2 ++
 3 files changed, 22 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-08-03-22-46-07.gh-issue-155143.9-byZp.rst

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 9d20930dc300c67..7889d4793a5dec3 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -997,6 +997,9 @@ def _outer_done_callback(outer):
             # Keep only one callback to log on cancel
             inner.remove_done_callback(_log_on_exception)
             inner.add_done_callback(_log_on_exception)
+            if cur_task is not None:
+                inner.remove_done_callback(_clear_awaited_by_callback)
+                futures.future_discard_from_awaited_by(inner, cur_task)
 
     if cur_task is not None:
         inner.add_done_callback(_clear_awaited_by_callback)
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index ad9b09857f8fd2b..1bb8d3090531dc0 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -2109,6 +2109,8 @@ def test_shield_cancel_outer(self):
         test_utils.run_briefly(self.loop)
         self.assertTrue(outer.cancelled())
         self.assertEqual(0, 0 if outer._callbacks is None else len(outer._callbacks))
+        self.assertEqual(0, 0 if inner._asyncio_awaited_by is None else len(inner._asyncio_awaited_by))
+        self.assertTrue({f for f, _ctx in inner._callbacks or []} <= {asyncio.tasks._log_on_exception})
 
     def test_shield_cancel_outer_result(self):
         mock_handler = mock.Mock()
@@ -2134,6 +2136,21 @@ def test_shield_cancel_outer_exception(self):
         test_utils.run_briefly(self.loop)
         mock_handler.assert_called_once()
 
+    def test_shield_cancel_outer_in_task(self):
+        inner = self.new_future(self.loop)
+
+        async def coro():
+            outer = asyncio.shield(inner)
+            self.assertNotEqual(0, len(inner._callbacks))
+            outer.cancel()
+            await asyncio.sleep(0)
+            self.assertTrue(outer.cancelled())
+
+        task = self.new_task(self.loop, coro())
+        self.loop.run_until_complete(task)
+        self.assertEqual(0, 0 if inner._asyncio_awaited_by is None else len(inner._asyncio_awaited_by))
+        self.assertTrue({f for f, _ctx in inner._callbacks or []} <= {asyncio.tasks._log_on_exception})
+
     def test_shield_duplicate_log_once(self):
         mock_handler = mock.Mock()
         self.loop.set_exception_handler(mock_handler)
diff --git a/Misc/NEWS.d/next/Library/2026-08-03-22-46-07.gh-issue-155143.9-byZp.rst b/Misc/NEWS.d/next/Library/2026-08-03-22-46-07.gh-issue-155143.9-byZp.rst
new file mode 100644
index 000000000000000..ae39b30e40a643e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-03-22-46-07.gh-issue-155143.9-byZp.rst
@@ -0,0 +1,2 @@
+Fix :func:`asyncio.shield` leaking the calling task via the await-graph and
+callbacks when called on a future that never resolves.