raise_single_exception_from_group causes SystemExit to have no exit status

[seowalex]

raise_single_exception_from_group was introduced as part of #3240 and #3197, but handles KeyboardInterrupt and SystemExit by wrapping the original exception in an exception of the same type:

# immediately bail out if there's any KI or SystemExit
for e in eg.exceptions:
    if isinstance(e, (KeyboardInterrupt, SystemExit)):
        raise type(e) from eg

Notably, this causes the resulting SystemExit to have no exit status, so system.exit(1) (or really any other exit status) does not properly set the exit status. I do not see a good reason why the exception should not be raised directly:

# immediately bail out if there's any KI or SystemExit
for e in eg.exceptions:
    if isinstance(e, (KeyboardInterrupt, SystemExit)):
        raise e from eg

Was there a reason for this handling?

[A5rocks]

I assume to ensure trackbacks in the exception group remain alright. But we can probably do some handling cause this is only for SystemExit and KeyboardInterrupt.

cc @jakkdl

[jakkdl]

yeah it's got special handling to bailout ASAP instead of doing special logic, but it should indeed preserve e.args. Feel free to contribute a PR, should be a simple one :)

[seowalex]

Sure, I can do that. I presume my suggested solution above works?

[CoolCat467]

I don't see any reason immediately why it wouldn't work, no.

[A5rocks]

raise e from eg might mutate the trace back of e in eg; just make sure it doesn't.

[jakkdl]

raise e from eg might mutate the trace back of e in eg; just make sure it doesn't.

oh yeah, the helper is in large part specifically to avoid this problem. See python-trio/trio-websocket#191 or HypothesisWorks/hypothesis#4115.

I think the better fix is to do something like

# immediately bail out if there's any KI or SystemExit
for e in eg.exceptions:
    if isinstance(e, (KeyboardInterrupt, SystemExit)):
        raise type(e)(e.args) from eg

[seowalex]

I don't think e.args works for SystemExit, but I will look at the issues and work something out.