Wrap exception groups less when raising in as_safe_channel

newsfragments/3332.misc.rst

@@ -0,0 +1 @@
+Decrease indentation for exception groups raised in `trio.as_safe_channel`.

src/trio/_channel.py

@@ -556,10 +556,13 @@ async def context_manager(
             except MultipleExceptionError:
                 # In case user has except* we make it possible for them to handle the
                 # exceptions.
-                raise BaseExceptionGroup(
-                    "Encountered exception during cleanup of generator object, as well as exception in the contextmanager body - unable to unwrap.",
-                    [eg],
-                ) from None
+                if sys.version_info >= (3, 11):
+                    eg.add_note(
+                        "Encountered exception during cleanup of generator object, as "
+                        "well as exception in the contextmanager body - unable to unwrap."
+                    )
+
+                raise eg from None
 
     async def _move_elems_to_channel(
         agen: AsyncGenerator[T, None],

src/trio/_tests/test_channel.py

@@ -519,17 +519,20 @@ async def agen(events: list[str]) -> AsyncGenerator[int]:
 
     events: list[str] = []
     with RaisesGroup(
-        RaisesGroup(
-            Matcher(ValueError, match="^agen$"),
-            Matcher(TypeError, match="^iterator$"),
-        ),
-        match=r"^Encountered exception during cleanup of generator object, as well as exception in the contextmanager body - unable to unwrap.$",
-    ):
+        Matcher(ValueError, match="^agen$"),
+        Matcher(TypeError, match="^iterator$"),
+    ) as g:
         async with agen(events) as recv_chan:
             async for i in recv_chan:  # pragma: no branch
                 assert i == 1
                 raise TypeError("iterator")
 
+    if sys.version_info >= (3, 11):
+        assert g.value.__notes__ == [
+            "Encountered exception during cleanup of generator object, as "
+            "well as exception in the contextmanager body - unable to unwrap."
+        ]
+
     assert events == ["GeneratorExit()", "finally"]
 
 
@@ -734,8 +737,12 @@ async def agen() -> AsyncGenerator[None]:
         while True:
             yield
 
-    for _ in range(10):  # 20% missed-alarm rate, so run ten times
-        async with agen() as chan:
-            with pytest.raises(trio.ClosedResourceError):
-                async for _ in chan:
-                    pass
+    async with agen() as chan:
+        with pytest.raises(trio.ClosedResourceError):
+            async for _ in chan:
+                pass
+
+        # This is necessary to ensure that `chan` has been sent
+        # to. Otherwise, this test sometimes passes on a broken
+        # version of trio.
+        await trio.testing.wait_all_tasks_blocked()