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Discussion on: Should behavioural changes be considered breaking changes under SemVer?

turnerj profile image
James Turner Author

What makes it hard is that fixing any bug would change the behaviour as the code goes from bug to bug free. If it had no behavioural change, the bug couldn't be fixed.

It is totally a trade off though as it would get ridiculous jumping major versions for every bug fix. I guess the intention of SemVer isn't to be that pedantic though.

I have written code before where I captured exceptions to look at the specific exception message to perform an action. I'm sure the developers would have never considered the exception message a breaking change. I consider this now bad code but it does show how we can depend on the unintentional.

dmfay profile image
Dian Fay

The difference is that the behavior of a bug is unanticipated. If I call your encodeText function, it's because I want to transform 'abbreviate' into 'xyzbbrevixyzte'. If it throws when I pass in 'abbŗévīaţè' and you fix it to handle expanded character sets, you're not interfering with existing usages so there's no reason for it to be more than a semver-patch bump. If, however, the fix means that the function no longer works for length-1 strings for arcane Unicode reasons, it's still a bugfix but one with a breaking change involved which requires a semver-major bump.

If encodeText suddenly turns 'abbreviate' into 'xyzfoofoorevixyzte' instead, that's either a breaking change (semver-major) or a bug which should be fixed with a semver-patch bump.

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rhymes profile image
rhymes • Edited

I just read this old issue report that might be relevant. Sometimes backports introduce breaking changes that aren't foreseen :D

Consider defaulting Application.confidential to false #1142

rhymes avatar
rhymes commented on Sep 10, 2018

Recently we had an app break because of the following reasons:

  • version 4.4.0 was released with the following changelog message: Backport security fix from 5.x for token revocation when using public clients
  • we applied the security fix knowing revocation wasn't an issue for our use case
  • the security fix went to production without deep testing
  • Android users started complaining, iOS users were fine
  • after reverting and debugging we noticed a difference between the two: Android clients didn't send the client secret, iOS did
  • the security fix set confidential to true which seems to disable clients without client secret

Setting it to false fixed the issue.

My question is: shouldn't a breaking change like this be clearer?

The changelog doesn't mention it, the upgrade guide says to add the migration but it doesn't clearly state: "hey, the default will break clients without client secret key"

Expected behavior

Either the default should change or the documentation should be clearer about this change.

Thank you

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turnerj profile image
James Turner Author

Wow, that is a subtle breaking change!

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