From fbab57e9c75751cd489bf36eb20078711bf6c6e1 Mon Sep 17 00:00:00 2001
From: Patrick Ribbsaeter <patrickswedish@gmail.com>
Date: Sat, 17 Oct 2026 21:27:03 +0200
Subject: [PATCH] Fix TaskGroup.start() losing child exception during
 cancellation on asyncio

---
 changelog.d/1356.fixed.rst      |  3 +++
 src/anyio/_backends/_asyncio.py |  9 ++++++++-
 tests/test_taskgroups.py        | 16 ++++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/1356.fixed.rst

diff --git a/changelog.d/1356.fixed.rst b/changelog.d/1356.fixed.rst
new file mode 100644
index 0000000..dd37230
--- /dev/null
+++ b/changelog.d/1356.fixed.rst
@@ -0,0 +1,3 @@
+Fixed ``TaskGroup.start()`` on the asyncio backend discarding a non-cancellation
+exception raised by the child task during cleanup when ``start()`` was cancelled
+before ``task_status.started()`` was called
diff --git a/src/anyio/_backends/_asyncio.py b/src/anyio/_backends/_asyncio.py
index 874374a..3e6fcac 100644
--- a/src/anyio/_backends/_asyncio.py
+++ b/src/anyio/_backends/_asyncio.py
@@ -1040,6 +1040,7 @@ class TaskGroup(abc.TaskGroup):
         # point between, the task group is cancelled and this method never proceeds to
         # process the completed future. That's why we have to have a shielded cancel
         # scope here.
+        exc_to_raise: BaseException | None = None
         try:
             await future
         except BaseException:
@@ -1049,7 +1050,13 @@ class TaskGroup(abc.TaskGroup):
                 with CancelScope(shield=True):
                     await handle.wait()
 
-            raise
+            if handle.status is TaskHandle.Status.FAILED:
+                exc_to_raise = handle._exception
+            else:
+                raise
+
+        if exc_to_raise is not None:
+            raise exc_to_raise
 
         if return_handle:
             handle._start_value = future.result()
diff --git a/tests/test_taskgroups.py b/tests/test_taskgroups.py
index 109d279..5241999 100644
--- a/tests/test_taskgroups.py
+++ b/tests/test_taskgroups.py
@@ -308,6 +308,22 @@ async def test_start_cancelled() -> None:
     assert not finished
 
 
+async def test_start_cancelled_child_raises() -> None:
+    """Regression test for #1356."""
+
+    async def taskfunc(*, task_status: TaskStatus) -> None:
+        try:
+            await sleep_forever()
+        finally:
+            raise RuntimeError("cleanup failed")
+
+    async with create_task_group() as tg:
+        with CancelScope() as scope:
+            scope.cancel()
+            with pytest.raises(RuntimeError, match="cleanup failed"):
+                await tg.start(taskfunc)
+
+
 @pytest.mark.parametrize("anyio_backend", asyncio_params)
 async def test_start_native_host_cancelled() -> None:
     started = finished = False
-- 
2.55.0.windows.3