Exception.__context__ circular reference to containing ExceptionGroup

[Arnatious]

I'm running into an issue using python 3.12, starlette 0.46.2 and rich 14 where exceptions raised in a route, when the asgi app has middleware, are causing rich to enter an infinite recursion when generating the traceback for logging.

Rich tries to follow the __context__ of the exception, which points to the ExceptionGroup that contains it, causing an infinite loop.

This #2893 bug seems to cover something similar, but it claims to be fixed. I have also reported it to rich at Textualize/rich#3682 but it seems hyper specific to starlette, and I don't think the context should be set this way but I'm having trouble following the exception in the debugger.

Here's a minimal example that produces this error

import anyio

import logging.config
import uvicorn
import fastapi
import httpx

from starlette.middleware.base import BaseHTTPMiddleware

logger = logging.getLogger(__name__)

app = fastapi.FastAPI()


@app.get("/api/v1/foo")
async def root():
    raise Exception("original exception")


async def call_api():
    await anyio.sleep(2) # wait for the server to start
    async with httpx.AsyncClient() as client:
        await client.get("http://localhost:12345/api/v1/foo")


async def run():
    async with anyio.create_task_group() as tg:
        app.add_middleware(BaseHTTPMiddleware)
        server = uvicorn.Server(uvicorn.Config(app, host="0.0.0.0", port=12345, log_config=None, log_level=None))
        tg.start_soon(server.serve)
        tg.start_soon(call_api)


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


if __name__ == "__main__":
    # Configure logging with RichHandler
    logging.config.dictConfig({
        "version": 1,
        "disable_existing_loggers": False,
        "handlers": {
            "console": {
                "class": "rich.logging.RichHandler",
                "level": "INFO",
                "rich_tracebacks": True,
            }
        },
        "root": {"handlers": ["console"], "level": "INFO"},
        "incremental": False,
    })
    main()

The logging of Exception("original exception") leads to an infinite loop as the __context__ of Exception("original exception") is ExceptionGroup('unhandled errors in a TaskGroup', [Exception('original exception')]).

The middleware is important for some reason, it doesn't occur when there is no middleware. Note the fact that this middleware is essentially no-op. A middleware added with the @app,middleware('http') decorator also triggers it. Anyio is not required, it also occurs with pure asyncio.