Handling unintended breaking changes #1156

I think we should talk about breaking changes and deprecation cycles, specifically around accidental or unforeseen breaking changes and how to handle those when they end up in a release. nodejs/node#38924 didn't undergo a deprecation cycle, but it was an accidental breaking change as per our contributing guidelines. This particular case was aggravated by a few factors:

• The breaking change never went through a deprecation cycle
• We didn't revert it once we found out it was breaking certain packages
• Because of tooling issues, the breaking change is not present on changelogs
• The documentation is still describing the previous behavior

We have a section about unintended breaking changes, but it doesn't go into what should be done when one of those breaking changes lands on a release (it's also only implicit that As an alternative to reverting, the TSC can apply the semver-major label after-the-fact means we're granting a one-time exception for the breaking change to happen). I think we need to clarify what should be done in those scenarios. IMO it's not just about reverting or not, but also taking action to reduce the chances of it happening again in the future (be it adding more tests or adding affected projects to CITGM) as well as ensuring documentations and changelogs reflect the breaking change accordingly. It probably will be a case-by-case thing where the TSC choses from a list of potential actions which one should be taken for each specific breaking change. Furthermore, IMO if the actions cannot be completed in a timely manner, revert should be considered.

I want to hear others thoughts on this, and it doesn't have to be specific to the issue linked. Also, if folks remember other unintentional breaking changes that have landed in the past, please link here so we can inform out decision based on past experiences.