Github user srowen commented on the issue:
https://github.com/apache/spark/pull/18645
That's not an upgrade. spark_2.11 2.2.0 to spark_2.11 2.3.0 is an upgrade,
and that can't break, and doesn't with this change.
Or: Scala itself has never been source- or binary-compatible across Scala
minor releases, and neither has Spark across Scala versions. Compiling vs
spark_2.10 and running on spark_2.11 doesn't work; cross compiling I don't
think even works in all cases. I don't follow why that's an issue here.
In fact, we already know it can't be source compatible, for _Java_ callers:
https://issues.apache.org/jira/browse/SPARK-14643 That may well be the
argument that this can't happen until 3.0. Check in with @JoshRosen for more
context.
However, I am not suggesting creating any Scala 2.12 release at all anytime
soon here, so I don't think that's worth debating. The question of whether's
it's source compatible is moot because this creates no new type of release to
be compatible or not. I don't even disagree with someone who argues that Scala
2.12 support can't happen before 3.0.
It does make a lot of the changes that will have to be made for 2.12
though, without disrupting the current 2.11 build. The question is really
whether that statement is true -- the Jackson thing is the problem right now.
Why would we bother implementing most of the groundwork for 2.12 without
making an official 2.12 build? generally, to break down the problem and address
this incrementally rather than in one huge change. But also to make it possible
for a brave soul out there, like maybe the folks at Twitter, to run their own
2.12 build if they wanted to self-support.
More concretely, if this went in to a 2.3.0 release tomorrow, what goes
wrong?
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