Change exceptions logging: Add logging of exceptions' causes

[dominh]

This pull request adds logging for Exception#cause

[iMacTia]

Hi @dominh and thank you for the contribution.
I really like the idea of exposing the cause from the exception as that can sometimes provide useful information about what happened. I have a few of concerns with the change as-is right now though:

1. The output structure is changed in a backwards-incompatible way: we're moving from a flat, 3-fields structure to a multi-level one. People might be relying on the older structure and have their observability platforms configured with monitors and alerts, so we can't just change it like that unfortunately. A few options on how we could address this:
   • Keep both the old and new structure, add a config setting to pick which one to use (defaults to OLD)
   • Add a new error_cause field to the payload alongside the 3 existing ones. Since this is an entirely new field, this CAN be multi-level so you could have the same recursive error_cause: { class:, message:, backtrace:, cause: }
2. The recursion is uncapped; this could have various unintended side-effects. Some observability systems may struggle with too many levels of data, and the log line size could go over the transfer/ingestion limit (e.g. Datadog has a hard limit of 1MB, but a suggested soft limit of 25KB).
   • My suggestion here would be to cap the recursion to 1-2 levels deep. I doubt you'll need more than that under normal circumstances. This could also be made into a setting later if we need to provide more flexibility.

[dominh]

Hi @iMacTia
I pushed new changes addressing your concerns.
I chose to keep both the old and new structure and added a config that allows user to chose one. The "hybrid" but backward compatible log seems to me more complex which is unnecessary I think.
I added causes_logging_max_depth config with 2 as default. Personally I'm going to set it to higher values in my projects as I like to have errors logged as verbosely as possible.

[iMacTia]

Thank you for addressing my comments @dominh 🙏
I also prefer the approach of having 2 separate but configurable behaviours.
I believe adding the exception_cause to the legacy behaviour would have also been a nice addition, but appreciate this is not a priority for you so I'll do it myself in a follow-up PR 🙂

[iMacTia]

Inspired by this change, I've opened #39 🙌