raising a custom ExceptionGroup subclass from a TaskGroup gets replaced with a regular TaskGroup

[graingert]

Things to check first

• I have searched the existing issues and didn't find my bug already reported there

• I have checked that my bug is still present in the latest release

AnyIO version

4.7.0

Python version

3.12

What happened?

see repro

How can we reproduce the bug?

import anyio

class MyExceptionGroup(ExceptionGroup):
    pass


async def main():
    async with anyio.create_task_group() as tg:
        raise MyExceptionGroup("hello", [ValueError("bad")])

anyio.run(main, backend="asyncio")

I get the expected output on 3.12:

  + Exception Group Traceback (most recent call last):
  |   File "/home/graingert/projects/demo.py", line 9, in main
  |     raise MyExceptionGroup("hello", [ValueError("bad")])
  | MyExceptionGroup: hello (1 sub-exception)
  +-+---------------- 1 ----------------
    | ValueError: bad
    +------------------------------------

During handling of the above exception, another exception occurred:

  + Exception Group Traceback (most recent call last):
  |   File "/home/graingert/projects/demo.py", line 11, in <module>
  |     anyio.run(main, backend="asyncio")
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/anyio/_core/_eventloop.py", line 74, in run
  |     return async_backend.run(func, args, {}, backend_options)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 2347, in run
  |     return runner.run(wrapper())
  |            ^^^^^^^^^^^^^^^^^^^^^
  |   File "/usr/lib/python3.12/asyncio/runners.py", line 118, in run
  |     return self._loop.run_until_complete(task)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/usr/lib/python3.12/asyncio/base_events.py", line 687, in run_until_complete
  |     return future.result()
  |            ^^^^^^^^^^^^^^^
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 2335, in wrapper
  |     return await func(*args)
  |            ^^^^^^^^^^^^^^^^^
  |   File "/home/graingert/projects/demo.py", line 8, in main
  |     async with anyio.create_task_group() as tg:
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 815, in __aexit__
  |     raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/home/graingert/projects/demo.py", line 9, in main
    |     raise MyExceptionGroup("hello", [ValueError("bad")])
    | MyExceptionGroup: hello (1 sub-exception)
    +-+---------------- 1 ----------------
      | ValueError: bad
      +------------------------------------

I get a different output on trio:

  + Exception Group Traceback (most recent call last):
  |   File "/home/graingert/projects/demo.py", line 11, in <module>
  |     anyio.run(main, backend="trio")
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/anyio/_core/_eventloop.py", line 74, in run
  |     return async_backend.run(func, args, {}, backend_options)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/anyio/_backends/_trio.py", line 1000, in run
  |     return trio.run(func, *args)
  |            ^^^^^^^^^^^^^^^^^^^^^
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/trio/_core/_run.py", line 2306, in run
  |     raise runner.main_task_outcome.error
  |   File "/home/graingert/projects/demo.py", line 8, in main
  |     async with anyio.create_task_group() as tg:
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/anyio/_backends/_trio.py", line 191, in __aexit__
  |     return await self._nursery_manager.__aexit__(exc_type, exc_val, exc_tb)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/trio/_core/_run.py", line 959, in __aexit__
  |     raise combined_error_from_nursery
  | ExceptionGroup: Exceptions from Trio nursery (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/home/graingert/projects/demo.py", line 9, in main
    |     raise MyExceptionGroup("hello", [ValueError("bad")])
    | ExceptionGroup: hello (1 sub-exception)
    +-+---------------- 1 ----------------
      | ValueError: bad
      +------------------------------------

[graingert]

looks like this is a bug in trio python-trio/trio#3175, sorry:

import trio

class MyExceptionGroup(ExceptionGroup):
    pass


async def main():
    async with trio.open_nursery():
        raise MyExceptionGroup("hello", [ValueError("bad")])

trio.run(main)

 + Exception Group Traceback (most recent call last):
  |   File "/home/graingert/projects/demo.py", line 11, in <module>
  |     trio.run(main)
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/trio/_core/_run.py", line 2306, in run
  |     raise runner.main_task_outcome.error
  |   File "/home/graingert/projects/demo.py", line 8, in main
  |     async with trio.open_nursery():
  |   File "/home/graingert/.virtualenvs/anyio_fixture_methods/lib/python3.12/site-packages/trio/_core/_run.py", line 959, in __aexit__
  |     raise combined_error_from_nursery
  | ExceptionGroup: Exceptions from Trio nursery (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/home/graingert/projects/demo.py", line 9, in main
    |     raise MyExceptionGroup("hello", [ValueError("bad")])
    | ExceptionGroup: hello (1 sub-exception)
    +-+---------------- 1 ----------------
      | ValueError: bad
      +------------------------------------