Github user pwendell commented on the pull request:
https://github.com/apache/spark/pull/2216#issuecomment-57060715
Ah I see - I thought this was an abstract class instead of a trait being
modified in this patch.
This is not an error with the compatibility checker - it's a legitimate
break. Because of the way traits work in Scala, you cannot add a new method
even if it has a default implementation. It's more like an interface in that
regard. For this reason we usually try to avoid traits for public-facing things
that could be implemented as abstract classes.
However, it will only break if someone outside of Spark has written a class
that extends this trait directly or indirectly. @JoshRosen is the design here
that this trait should ever be used outside of Spark?
You can look on Slide 10 here to see why:
http://www.slideshare.net/mircodotta/managing-binary-compatibility-in-scala
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