Interesting implications of supporting Scala 2.13

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Interesting implications of supporting Scala 2.13

Sean Owen-2
While that's not happening soon (2.13 isn't out), note that some of
the changes to collections will be fairly breaking changes.

https://issues.apache.org/jira/browse/SPARK-25075
https://docs.scala-lang.org/overviews/core/collections-migration-213.html

Some of this may impact a public API, so may need to start proactively
fixing stuff for 2.13 before 3.0 comes out where possible.

Here's an example: Traversable goes away. We have a method
SparkConf.setAll(Traversable). We can't support 2.13 while that still
exists. Of course, we can decide to deprecate it with replacement (use
Iterable) and remove it in the version that supports 2.13. But that
would mean a little breaking change, and we either have to accept that
for a future 3.x release, or it waits until 4.x.

I wanted to put that on the radar now to gather opinions about whether
this will probably be acceptable, or whether we really need to get
methods like that changed before 3.0.

Also: there's plenty of straightforward but medium-sized changes we
can make now in anticipation of 2.13 support, like, make the type of
Seq we use everywhere explicit (will be good for a like 1000 file
change I'm sure). Or see if we can swap out Traversable everywhere.
Remove MutableList, etc.

I was going to start fiddling with that unless it just sounds too disruptive.

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Re: Interesting implications of supporting Scala 2.13

rxin
Looks like a great idea to make changes in Spark 3.0 to prepare for Scala 2.13 upgrade.

Are there breaking changes that would require us to have two different source code for 2.12 vs 2.13?


On Fri, May 10, 2019 at 11:41 AM, Sean Owen <[hidden email]> wrote:

While that's not happening soon (2.13 isn't out), note that some of the changes to collections will be fairly breaking changes.

https://issues.apache.org/jira/browse/SPARK-25075
https://docs.scala-lang.org/overviews/core/collections-migration-213.html

Some of this may impact a public API, so may need to start proactively fixing stuff for 2.13 before 3.0 comes out where possible.

Here's an example: Traversable goes away. We have a method SparkConf.setAll(Traversable). We can't support 2.13 while that still exists. Of course, we can decide to deprecate it with replacement (use Iterable) and remove it in the version that supports 2.13. But that would mean a little breaking change, and we either have to accept that for a future 3.x release, or it waits until 4.x.

I wanted to put that on the radar now to gather opinions about whether this will probably be acceptable, or whether we really need to get methods like that changed before 3.0.

Also: there's plenty of straightforward but medium-sized changes we can make now in anticipation of 2.13 support, like, make the type of Seq we use everywhere explicit (will be good for a like 1000 file change I'm sure). Or see if we can swap out Traversable everywhere. Remove MutableList, etc.

I was going to start fiddling with that unless it just sounds too disruptive.

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Re: Interesting implications of supporting Scala 2.13

Sean Owen-2
I really hope we don't have to have separate source trees for some files, but yeah it's an option too. OK, will start looking into changes we can make now that don't break things now, and deprecations we need to make now proactively.

I should also say that supporting Scala 2.13 will mean dependencies have to support Scala 2.13, and that could take a while, because there are a lot.
In particular, I think we'll find our SBT 0.13 build won't make it, perhaps just because of the plugins it needs. I tried updating to SBT 1.x and it seemed to need quite a lot of rewrite, again in part due to how newer plugin versions changed. I failed and gave up.

At some point maybe we figure out whether we can remove the SBT-based build if it's super painful, but only if there's not much other choice. That is for a future thread.


On Fri, May 10, 2019 at 1:51 PM Reynold Xin <[hidden email]> wrote:
Looks like a great idea to make changes in Spark 3.0 to prepare for Scala 2.13 upgrade.

Are there breaking changes that would require us to have two different source code for 2.12 vs 2.13?


On Fri, May 10, 2019 at 11:41 AM, Sean Owen <[hidden email]> wrote:

While that's not happening soon (2.13 isn't out), note that some of the changes to collections will be fairly breaking changes.

https://issues.apache.org/jira/browse/SPARK-25075
https://docs.scala-lang.org/overviews/core/collections-migration-213.html

Some of this may impact a public API, so may need to start proactively fixing stuff for 2.13 before 3.0 comes out where possible.

Here's an example: Traversable goes away. We have a method SparkConf.setAll(Traversable). We can't support 2.13 while that still exists. Of course, we can decide to deprecate it with replacement (use Iterable) and remove it in the version that supports 2.13. But that would mean a little breaking change, and we either have to accept that for a future 3.x release, or it waits until 4.x.

I wanted to put that on the radar now to gather opinions about whether this will probably be acceptable, or whether we really need to get methods like that changed before 3.0.

Also: there's plenty of straightforward but medium-sized changes we can make now in anticipation of 2.13 support, like, make the type of Seq we use everywhere explicit (will be good for a like 1000 file change I'm sure). Or see if we can swap out Traversable everywhere. Remove MutableList, etc.

I was going to start fiddling with that unless it just sounds too disruptive.

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Re: Interesting implications of supporting Scala 2.13

Imran Rashid-4
+1 on making whatever api changes we can now for 3.0.

I don't think that is making any commitments to supporting scala 2.13 in any specific version.  We'll have to deal with all the other points you raised when we do cross that bridge, but hopefully those are things we can cover in a minor release.

On Fri, May 10, 2019 at 2:31 PM Sean Owen <[hidden email]> wrote:
I really hope we don't have to have separate source trees for some files, but yeah it's an option too. OK, will start looking into changes we can make now that don't break things now, and deprecations we need to make now proactively.

I should also say that supporting Scala 2.13 will mean dependencies have to support Scala 2.13, and that could take a while, because there are a lot.
In particular, I think we'll find our SBT 0.13 build won't make it, perhaps just because of the plugins it needs. I tried updating to SBT 1.x and it seemed to need quite a lot of rewrite, again in part due to how newer plugin versions changed. I failed and gave up.

At some point maybe we figure out whether we can remove the SBT-based build if it's super painful, but only if there's not much other choice. That is for a future thread.


On Fri, May 10, 2019 at 1:51 PM Reynold Xin <[hidden email]> wrote:
Looks like a great idea to make changes in Spark 3.0 to prepare for Scala 2.13 upgrade.

Are there breaking changes that would require us to have two different source code for 2.12 vs 2.13?


On Fri, May 10, 2019 at 11:41 AM, Sean Owen <[hidden email]> wrote:

While that's not happening soon (2.13 isn't out), note that some of the changes to collections will be fairly breaking changes.

https://issues.apache.org/jira/browse/SPARK-25075
https://docs.scala-lang.org/overviews/core/collections-migration-213.html

Some of this may impact a public API, so may need to start proactively fixing stuff for 2.13 before 3.0 comes out where possible.

Here's an example: Traversable goes away. We have a method SparkConf.setAll(Traversable). We can't support 2.13 while that still exists. Of course, we can decide to deprecate it with replacement (use Iterable) and remove it in the version that supports 2.13. But that would mean a little breaking change, and we either have to accept that for a future 3.x release, or it waits until 4.x.

I wanted to put that on the radar now to gather opinions about whether this will probably be acceptable, or whether we really need to get methods like that changed before 3.0.

Also: there's plenty of straightforward but medium-sized changes we can make now in anticipation of 2.13 support, like, make the type of Seq we use everywhere explicit (will be good for a like 1000 file change I'm sure). Or see if we can swap out Traversable everywhere. Remove MutableList, etc.

I was going to start fiddling with that unless it just sounds too disruptive.

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Re: Interesting implications of supporting Scala 2.13

rxin
Yea my main point is when we do support 2.13, it'd be great if we don't have to break APIs. That's why doing the prep work in 3.0 would be great.


On Fri, May 10, 2019 at 1:30 PM, Imran Rashid <[hidden email]> wrote:
+1 on making whatever api changes we can now for 3.0.

I don't think that is making any commitments to supporting scala 2.13 in any specific version.  We'll have to deal with all the other points you raised when we do cross that bridge, but hopefully those are things we can cover in a minor release.

On Fri, May 10, 2019 at 2:31 PM Sean Owen <[hidden email]> wrote:
I really hope we don't have to have separate source trees for some files, but yeah it's an option too. OK, will start looking into changes we can make now that don't break things now, and deprecations we need to make now proactively.

I should also say that supporting Scala 2.13 will mean dependencies have to support Scala 2.13, and that could take a while, because there are a lot.
In particular, I think we'll find our SBT 0.13 build won't make it, perhaps just because of the plugins it needs. I tried updating to SBT 1.x and it seemed to need quite a lot of rewrite, again in part due to how newer plugin versions changed. I failed and gave up.

At some point maybe we figure out whether we can remove the SBT-based build if it's super painful, but only if there's not much other choice. That is for a future thread.


On Fri, May 10, 2019 at 1:51 PM Reynold Xin <[hidden email]> wrote:
Looks like a great idea to make changes in Spark 3.0 to prepare for Scala 2.13 upgrade.

Are there breaking changes that would require us to have two different source code for 2.12 vs 2.13?


On Fri, May 10, 2019 at 11:41 AM, Sean Owen <[hidden email]> wrote:

While that's not happening soon (2.13 isn't out), note that some of the changes to collections will be fairly breaking changes.

https://issues.apache.org/jira/browse/SPARK-25075
https://docs.scala-lang.org/overviews/core/collections-migration-213.html

Some of this may impact a public API, so may need to start proactively fixing stuff for 2.13 before 3.0 comes out where possible.

Here's an example: Traversable goes away. We have a method SparkConf.setAll(Traversable). We can't support 2.13 while that still exists. Of course, we can decide to deprecate it with replacement (use Iterable) and remove it in the version that supports 2.13. But that would mean a little breaking change, and we either have to accept that for a future 3.x release, or it waits until 4.x.

I wanted to put that on the radar now to gather opinions about whether this will probably be acceptable, or whether we really need to get methods like that changed before 3.0.

Also: there's plenty of straightforward but medium-sized changes we can make now in anticipation of 2.13 support, like, make the type of Seq we use everywhere explicit (will be good for a like 1000 file change I'm sure). Or see if we can swap out Traversable everywhere. Remove MutableList, etc.

I was going to start fiddling with that unless it just sounds too disruptive.

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Re: Interesting implications of supporting Scala 2.13

Sean Owen-2
For those interested, here's the first significant problem I see that
will require separate source trees or a breaking change:
https://issues.apache.org/jira/browse/SPARK-27683?focusedCommentId=16837967&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16837967

Interested in thoughts on how to proceed on something like this, as
there will probably be a few more similar issues.

On Fri, May 10, 2019 at 3:32 PM Reynold Xin <[hidden email]> wrote:

>
> Yea my main point is when we do support 2.13, it'd be great if we don't have to break APIs. That's why doing the prep work in 3.0 would be great.
>
>
> On Fri, May 10, 2019 at 1:30 PM, Imran Rashid <[hidden email]> wrote:
>>
>> +1 on making whatever api changes we can now for 3.0.
>>
>> I don't think that is making any commitments to supporting scala 2.13 in any specific version.  We'll have to deal with all the other points you raised when we do cross that bridge, but hopefully those are things we can cover in a minor release.
>>
>> On Fri, May 10, 2019 at 2:31 PM Sean Owen <[hidden email]> wrote:
>>>
>>> I really hope we don't have to have separate source trees for some files, but yeah it's an option too. OK, will start looking into changes we can make now that don't break things now, and deprecations we need to make now proactively.
>>>
>>> I should also say that supporting Scala 2.13 will mean dependencies have to support Scala 2.13, and that could take a while, because there are a lot.
>>> In particular, I think we'll find our SBT 0.13 build won't make it, perhaps just because of the plugins it needs. I tried updating to SBT 1.x and it seemed to need quite a lot of rewrite, again in part due to how newer plugin versions changed. I failed and gave up.
>>>
>>> At some point maybe we figure out whether we can remove the SBT-based build if it's super painful, but only if there's not much other choice. That is for a future thread.
>>>
>>>
>>> On Fri, May 10, 2019 at 1:51 PM Reynold Xin <[hidden email]> wrote:
>>>>
>>>> Looks like a great idea to make changes in Spark 3.0 to prepare for Scala 2.13 upgrade.
>>>>
>>>> Are there breaking changes that would require us to have two different source code for 2.12 vs 2.13?
>>>>
>>>>
>>>> On Fri, May 10, 2019 at 11:41 AM, Sean Owen <[hidden email]> wrote:
>>>>>
>>>>> While that's not happening soon (2.13 isn't out), note that some of the changes to collections will be fairly breaking changes.
>>>>>
>>>>> https://issues.apache.org/jira/browse/SPARK-25075
>>>>> https://docs.scala-lang.org/overviews/core/collections-migration-213.html
>>>>>
>>>>> Some of this may impact a public API, so may need to start proactively fixing stuff for 2.13 before 3.0 comes out where possible.
>>>>>
>>>>> Here's an example: Traversable goes away. We have a method SparkConf.setAll(Traversable). We can't support 2.13 while that still exists. Of course, we can decide to deprecate it with replacement (use Iterable) and remove it in the version that supports 2.13. But that would mean a little breaking change, and we either have to accept that for a future 3.x release, or it waits until 4.x.
>>>>>
>>>>> I wanted to put that on the radar now to gather opinions about whether this will probably be acceptable, or whether we really need to get methods like that changed before 3.0.
>>>>>
>>>>> Also: there's plenty of straightforward but medium-sized changes we can make now in anticipation of 2.13 support, like, make the type of Seq we use everywhere explicit (will be good for a like 1000 file change I'm sure). Or see if we can swap out Traversable everywhere. Remove MutableList, etc.
>>>>>
>>>>> I was going to start fiddling with that unless it just sounds too disruptive.
>>>>>
>>>>> --------------------------------------------------------------------- To unsubscribe e-mail: [hidden email]
>
>

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Re: Interesting implications of supporting Scala 2.13

rxin
If the number of changes that would require two source trees are small, another thing we can do is to reach out to the Scala team and kindly ask them whether they could change Scala 2.13 itself so it'd be easier to maintain compatibility with Scala 2.12.



On Sat, May 11, 2019 at 4:25 PM, Sean Owen <[hidden email]> wrote:

For those interested, here's the first significant problem I see that will require separate source trees or a breaking change: https://issues.apache.org/jira/browse/SPARK-27683?focusedCommentId=16837967&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16837967

Interested in thoughts on how to proceed on something like this, as there will probably be a few more similar issues.

On Fri, May 10, 2019 at 3:32 PM Reynold Xin <[hidden email]> wrote:

Yea my main point is when we do support 2.13, it'd be great if we don't have to break APIs. That's why doing the prep work in 3.0 would be great.

On Fri, May 10, 2019 at 1:30 PM, Imran Rashid <[hidden email]> wrote:

+1 on making whatever api changes we can now for 3.0.

I don't think that is making any commitments to supporting scala 2.13 in any specific version. We'll have to deal with all the other points you raised when we do cross that bridge, but hopefully those are things we can cover in a minor release.

On Fri, May 10, 2019 at 2:31 PM Sean Owen <[hidden email]> wrote:

I really hope we don't have to have separate source trees for some files, but yeah it's an option too. OK, will start looking into changes we can make now that don't break things now, and deprecations we need to make now proactively.

I should also say that supporting Scala 2.13 will mean dependencies have to support Scala 2.13, and that could take a while, because there are a lot. In particular, I think we'll find our SBT 0.13 build won't make it, perhaps just because of the plugins it needs. I tried updating to SBT 1.x and it seemed to need quite a lot of rewrite, again in part due to how newer plugin versions changed. I failed and gave up.

At some point maybe we figure out whether we can remove the SBT-based build if it's super painful, but only if there's not much other choice. That is for a future thread.

On Fri, May 10, 2019 at 1:51 PM Reynold Xin <[hidden email]> wrote:

Looks like a great idea to make changes in Spark 3.0 to prepare for Scala 2.13 upgrade.

Are there breaking changes that would require us to have two different source code for 2.12 vs 2.13?

On Fri, May 10, 2019 at 11:41 AM, Sean Owen <[hidden email]> wrote:

While that's not happening soon (2.13 isn't out), note that some of the changes to collections will be fairly breaking changes.

https://issues.apache.org/jira/browse/SPARK-25075
https://docs.scala-lang.org/overviews/core/collections-migration-213.html

Some of this may impact a public API, so may need to start proactively fixing stuff for 2.13 before 3.0 comes out where possible.

Here's an example: Traversable goes away. We have a method SparkConf.setAll(Traversable). We can't support 2.13 while that still exists. Of course, we can decide to deprecate it with replacement (use Iterable) and remove it in the version that supports 2.13. But that would mean a little breaking change, and we either have to accept that for a future 3.x release, or it waits until 4.x.

I wanted to put that on the radar now to gather opinions about whether this will probably be acceptable, or whether we really need to get methods like that changed before 3.0.

Also: there's plenty of straightforward but medium-sized changes we can make now in anticipation of 2.13 support, like, make the type of Seq we use everywhere explicit (will be good for a like 1000 file change I'm sure). Or see if we can swap out Traversable everywhere. Remove MutableList, etc.

I was going to start fiddling with that unless it just sounds too disruptive.

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Re: Interesting implications of supporting Scala 2.13

antonkulaga
In reply to this post by Sean Owen-2
There is https://github.com/scala/scala-collection-compat to enable 2.13
collections in Scala 2.12, so probably you can use it to avoid having
separate source trees for 2.12 and 2.13



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Re: Interesting implications of supporting Scala 2.13

Sean Owen-2
I think the particular issue here isn't resolved by
scala-collection-compat: TraversableOnce goes away. However I hear
that maybe Scala 2.13 retains it as a deprecated alias, which might
help.

On Wed, May 29, 2019 at 4:59 PM antonkulaga <[hidden email]> wrote:

>
> There is https://github.com/scala/scala-collection-compat to enable 2.13
> collections in Scala 2.12, so probably you can use it to avoid having
> separate source trees for 2.12 and 2.13
>
>
>
> --
> Sent from: http://apache-spark-developers-list.1001551.n3.nabble.com/
>
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