__cause__ and __context__ on user exceptions are lost when running with exception groups #191
Description
This code will fully lose the TypeError as the __context__ from the exception, due to python-trio/flake8-async#298
async def test_user_exception_cause(nursery) -> None:
async def handler(request):
await request.accept()
server = await nursery.start(serve_websocket, handler, HOST, 0, None)
async with open_websocket(HOST, server.port, RESOURCE, use_ssl=False):
try:
raise TypeError
except TypeError:
raise ValueErrorThe offending code for this example is
trio-websocket/trio_websocket/_impl.py
Lines 205 to 208 in f5fd6d7
which implicitly sets
__context__ to the caught group, and the user exception inside the group is the same exception, so it simultaneously loses its old __context__.
The fix is to sprinkle a bunch of copy.copy() calls. Given that we have a finally it's not an alternative to raise the exception outside of the exception handler.