Prevent possible infinite recursion

[JonRowe]

Fixes #2127

[seanwalbran]

@JonRowe Just a note that this doesn't catch cause loops of more than one exception (e.g. when error.cause != error, but error.cause.cause == error), which I happened to run into with rails+haml: https://gist.github.com/seanwalbran/b63fbe7117645c5ddef1#file-gistfile1-txt-L26

[myronmarston]

Thanks for reporting that, @seanwalbran!

It sounds like the fix needs to be more sophisticated -- either it needs to keep track of all exceptions seen so far (e.g. via an extra arg passed as part of the recursion) so it can notice when it's seeing one it has already seeing, or maybe we should just put a hard limit on the max depth (e.g. 10 or 20 or something) and give up when we've followed Exception#cause that many times.

[JonRowe]

I've reworked this to take @seanwalbran's issue into account

[myronmarston]

It'll probably be slightly faster if you call cause only once:

def final_exception(exception, previous=[])
  cause = exception.cause
  return exception unless cause
  return exception if previous.include?(cause)

  previous << cause
  final_exception(cause, previous)
end

Not a merge blocker, though.

[myronmarston]

LGTM otherwise.

[joeletizia]

Any chance of a 3.5 release for this this?

[JonRowe]

We could put out a patch release of 3.4 (@samphippen might need your help)

[taylorzr]

I ran into this issue as well, any chance this will be released as a patch to 3.4?

[JonRowe]

Hmm apparently I forgot to backport this so it was never released in recent patch versions, something I've just rectified with 3.4.3.

[dgilperez]

I just got hit by this at 3.4.4 - expected?

[JonRowe]

This should have been rectified in 3.4.4 can you provide more details?

[dgilperez]

I'm sorry, I somehow worked around it and can't reproduce it now.