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From DB Tsai <d_t...@apple.com>
Subject Re: Scala 2.12 support
Date Thu, 07 Jun 2018 23:27:01 GMT
Thanks Felix for bringing this up.

Currently, in Scala 2.11.8, we initialize the Spark by overriding loadFIles() before REPL
sees any file since there is no good hook in Scala to load our initialization code.

In Scala 2.11.12 and newer version of the Scala 2.12.x, loadFIles() method was removed.

Alternatively, one way we can do in the newer version of Scala is by overriding initializeSynchronous()
suggested by Som Snytt; I have a working PR with this approach,
https://github.com/apache/spark/pull/21495 , and this approach should work for older version
of Scala too. 

However, in the newer version of Scala, the first thing that the REPL calls is printWelcome,
so in the newer version of Scala, welcome message will be shown and then the URL of the SparkUI
in this approach. This will cause UI inconsistencies between different versions of Scala.

We can also initialize the Spark in the printWelcome which I feel more hacky. It will only
work for newer version of Scala since in order version of Scala, printWelcome is called in
the end of the initialization process. If we decide to go this route, basically users can
not use Scala older than 2.11.9.

I think this is also a blocker for us to move to newer version of Scala 2.12.x since the newer
version of Scala 2.12.x has the same issue.

In my opinion, Scala should fix the root cause and provide a stable hook for 3rd party developers
to initialize their custom code.

DB Tsai  |  Siri Open Source Technologies [not a contribution]  |   Apple, Inc

> On Jun 7, 2018, at 6:43 AM, Felix Cheung <felixcheung_m@hotmail.com> wrote:
> 
> +1
> 
> Spoke to Dean as well and mentioned the problem with 2.11.12 https://github.com/scala/bug/issues/10913
> 
> _____________________________
> From: Sean Owen <srowen@gmail.com>
> Sent: Wednesday, June 6, 2018 12:23 PM
> Subject: Re: Scala 2.12 support
> To: Holden Karau <holden@pigscanfly.ca>
> Cc: Dean Wampler <deanwampler@gmail.com>, Reynold Xin <rxin@databricks.com>,
dev <dev@spark.apache.org>
> 
> 
> If it means no change to 2.11 support, seems OK to me for Spark 2.4.0. The 2.12 support
is separate and has never been mutually compatible with 2.11 builds anyway. (I also hope,
suspect that the changes are minimal; tests are already almost entirely passing with no change
to the closure cleaner when built for 2.12)
> 
> On Wed, Jun 6, 2018 at 1:33 PM Holden Karau <holden@pigscanfly.ca> wrote:
> Just chatted with Dean @ the summit and it sounds like from Adriaan there is a fix in
2.13 for the API change issue that could be back ported to 2.12 so how about we try and get
this ball rolling?
> 
> It sounds like it would also need a closure cleaner change, which could be backwards
compatible but since it’s such a core component and we might want to be cautious with it,
we could when building for 2.11 use the old cleaner code and for 2.12 use the new code so
we don’t break anyone.
> 
> How do folks feel about this?
> 
> 
> 


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