[SPARK-58043][SQL] Use explicit .apply instead of a case class companion as a function for Scala 3 compatibility#57129
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…anion as a function for Scala 3 compatibility ### What changes were proposed in this pull request? Replace bare case class companions used as function values with an explicit `.apply` method reference across `catalyst`, `sql-core`, `hive`, and `sql-api` (190 call sites), e.g.: - `xs.reduceLeft(And)` -> `xs.reduceLeft(And.apply)` - `convertUnaryExpr(expr, IsNull)` -> `convertUnaryExpr(expr, IsNull.apply)` - `.map(sources.Not)` -> `.map(sources.Not.apply)` Two lines are reflowed to stay within the 100-character limit. ### Why are the changes needed? In Scala 2 a case class's companion object automatically extends `FunctionN`, so the bare companion can be passed wherever a function is expected. Scala 3 removed this (case companions no longer extend `FunctionN`), so these call sites fail to compile. Referencing `Foo.apply` -- the method the synthetic `FunctionN.apply` forwarded to -- restores the explicit form. This is part of the incremental Scala 3 readiness tracked in SPARK-54150. ### Does this PR introduce _any_ user-facing change? No. `Foo.apply` is the exact method the synthetic `FunctionN.apply` delegated to, so the change is behavior- and byte-identical on Scala 2.13. ### How was this patch tested? Existing tests. The `catalyst`, `sql-core`, `hive`, and `sql-api` modules compile under both the default build and `-Xsource:3`, `scalastyle` passes, and no `case-companion-function` migration warnings remain in these modules. ### Was this patch authored or co-authored using generative AI tooling? Generated-by: Claude Code (Claude Opus 4.8) Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
…nion-function # Conflicts: # sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/V2ExpressionUtils.scala
… count for eta-expansion The case-companion -> .apply change in QueryStartedEvent's jobTags serialization eta-expands to a lambda, which the Scala 2.13 compiler lifts to a synthetic public $anonfun method on the class. Reflection-based test_number_of_public_methods sees it via getMethods(), so bump the expected count from 16 to 17. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
| @@ -122,15 +122,15 @@ object StructFilters { | |||
| case sources.Or(left, right) => | |||
| zip(translate(left), translate(right)).map(Or.tupled) | |||
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.tupled / .curried on case companions are left untouched - the modules still won't compile under real Scala 3. The same Scala 3 change (case companions no longer extend FunctionN) also breaks Foo.tupled, since tupled is a FunctionN member. These remain in bare form in the touched modules. There are also remaining .tupled uses in NaturalAndUsingJoinResolution.scala, windowExpressions.scala, and subquery.scala.
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@fangchenli My question is: if we do not have an explicit plan to support Scala 3 in any major Spark release, what is the value of these changes? @HyukjinKwon has already provided a Spark Connect client for Scala 3, and I have also developed an implementation myself. Can’t these clients solve the problem? |
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I am not against this idea but I think we should make a proper consensus, create an umbrella JIRA, and do it incrementally. We should also know that if it is possible at all to support both Scala 2 and 3 in the same source base |
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Sorry for the response from Claude. It misunderstood my instruction. We do have an umbrella JIRA that tracks Scala 3 support https://issues.apache.org/jira/browse/SPARK-54150. #50474 was an attempt to do all the
Those changes don't have much value if Spark won't support Scala 3 in the future. But if we do want Scala 3 support at some point, those changes are mandatory.
I think we can. It might be similar to the 2.12-2.13 transition. |
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@fangchenli IIRC, https://lists.apache.org/thread/60sjx0sh525rsl1j0z4g1jsrdrs2sg96 this email is earlier discussion regarding Scala 3 on the dev mailing list. |
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I agree with @HyukjinKwon |
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Yea we need a full design of supporting both scala 2 and 3, instead of merging partial fixes without knowing what the full fix looks like. |
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What changes were proposed in this pull request?
In Scala 2 a case class's companion object automatically extends FunctionN, so the bare companion can be passed wherever a function is expected. Scala 3 removed this (case companions no longer extend FunctionN), so these call sites fail to compile. Referencing Foo.apply, the method the synthetic FunctionN.apply forwarded to, restores the explicit form.
Why are the changes needed?
It's required for Scala 3 compatibility.
Does this PR introduce any user-facing change?
No
How was this patch tested?
Compiled with -Xsource:3
Was this patch authored or co-authored using generative AI tooling?
Generated-by: Claude Code (Claude Opus 4.8)