Handle control flow exceptions when assigning span status

[alexander-alderman-webb]

We have a few cases of libraries using custom exception types as control flow signals, e.g.:

• HueyControlFlowExceptions
• LangGraph's GraphInterrupt and GraphBubbleUp: LangchainIntegration reports GraphInterrupt / GraphBubbleUp as errors via on_tool_error #6384

The should_be_treated_as_error() function is currently used to determine whether a transaction or span is assigned the internal_error or error status in Span.__exit__() and in StreamedSpan.__exit__(), respectively. As should_be_treated_as_error() currently holds an ever-expanding number of special cases, code is added that does not apply in the majority of cases (dead code if the relevant integrations did not create the span).

Proposal

Add a parameter to Span.__init__(), start_span(), start_transaction() and start_child() (and equivalent span streaming APIs) that accepts a set or tuple of control flow exceptions. Special case against the exceptions in the set on __exit__(). The parameter can be called control_flow_exceptions.

For example, in the AIOHTTP integration, the parameter would be set to control_flow_exceptions=(AIOHttpHttpException, ).

[linear-code]

PY-2492

[alexander-alderman-webb]

Adding a private instance variable could be a good first step before we agree to increase API surface.

[sentrivana]

I wouldn't add this to start_span because that API should be kept minimal and it feels like this is a global ignore list rather than something that needs tailoring per start_span call.

What I'd suggest is a global list somewhere that can be added to via a util function, and should_be_treated_as_error then checks this list. Integrations themselves would be responsible for adding known control flow exceptions to the list.

The serializer uses a similar pattern here: global list of sequences we'll try to iterate through, small func to add a type to that list, and in the Django integration we use it to register a Django-specific sequence.

[sentrivana]

Something like this: https://github.com/getsentry/sentry-python/pull/6425/changes

If we want to be fancy at some point later the list/function can also accept callbacks (e.g. if we need additional checks to decide whether an exception is an error, like for instance checking the status code)