Suppress GeneratorExit from .aclose() for as_safe_channel

src/trio/_channel.py

@@ -590,7 +590,31 @@ async def _move_elems_to_channel(
                 try:
                     await agen.aclose()
                 except BaseExceptionGroup as exceptions:
-                    _, narrowed_exceptions = exceptions.split(GeneratorExit)
+                    removed, narrowed_exceptions = exceptions.split(GeneratorExit)
+
+                    # TODO: extract a helper to flatten exception groups
+                    removed_exceptions = [removed]
+                    for e in removed_exceptions:
+                        if isinstance(e, BaseExceptionGroup):
+                            removed_exceptions.extend(e.exceptions)  # noqa: B909
+
+                    if (
+                        len(
+                            [
+                                e
+                                for e in removed_exceptions
+                                if isinstance(e, GeneratorExit)
+                            ]
+                        )
+                        > 1
+                    ):
+                        exc = AssertionError("More than one GeneratorExit found.")
+                        if narrowed_exceptions is None:
+                            narrowed_exceptions = exceptions.derive([exc])
+                        else:
+                            narrowed_exceptions = narrowed_exceptions.derive(
+                                [*narrowed_exceptions.exceptions, exc]
+                            )
                     if narrowed_exceptions is not None:
                         raise narrowed_exceptions from None
 

src/trio/_tests/test_channel.py

@@ -11,7 +11,7 @@
 from ..testing import Matcher, RaisesGroup, assert_checkpoints, wait_all_tasks_blocked
 
 if sys.version_info < (3, 11):
-    from exceptiongroup import BaseExceptionGroup, ExceptionGroup
+    from exceptiongroup import ExceptionGroup
 
 if TYPE_CHECKING:
     from collections.abc import AsyncGenerator
@@ -634,7 +634,7 @@ async def agen() -> AsyncGenerator[None]:
             async with trio.open_nursery():
                 yield
         except BaseException as e:
-            assert isinstance(e, BaseExceptionGroup)  # noqa: PT017  # we reraise
+            assert pytest.RaisesGroup(GeneratorExit).matches(e)  # noqa: PT017
             raise
 
     async with agen() as g:
@@ -670,3 +670,22 @@ async def agen() -> AsyncGenerator[None]:
         async with agen() as g:
             async for _ in g:
                 break
+
+
+async def test_as_safe_channel_swallowing_extra_exceptions() -> None:
+    async def wait_then_raise() -> None:
+        try:
+            await trio.sleep_forever()
+        except trio.Cancelled:
+            raise GeneratorExit from None
+
+    @as_safe_channel
+    async def agen() -> AsyncGenerator[None]:
+        async with trio.open_nursery() as nursery:
+            nursery.start_soon(wait_then_raise)
+            yield
+
+    with pytest.RaisesGroup(AssertionError):
+        async with agen() as g:
+            async for _ in g:
+                break