[issue44594] AsyncExitStack.enter_async_context() is mishandling exception __context__

[John Belmonte]

John Belmonte <john at neggie.net> added the comment:

demonstrating the difference for async case:

    import contextlib
    import trio
    
    async def background():
        assert False
    
    async def main1():
        async with trio.open_nursery() as nursery:
            nursery.start_soon(background)
            await trio.sleep_forever()
    
    async def main2():
        async with contextlib.AsyncExitStack() as stack:
            nursery = await stack.enter_async_context(trio.open_nursery())
            nursery.start_soon(background)
            await trio.sleep_forever()
    
    try:
        trio.run(main1)
    except BaseException as e:
        print('main1, context:', e.__context__)
    
    try:
        trio.run(main2)
    except BaseException as e:
        print('main2, context:', e.__context__)


----
main1, context: None
main2, context: Cancelled

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44594>
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