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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2021/10/20 18:19:26 UTC

[GitHub] [spark] sarutak opened a new pull request #34341: [SPARK-37076][SQL] Implement StructType.toString explicitly for Scala 2.13

sarutak opened a new pull request #34341:
URL: https://github.com/apache/spark/pull/34341

### What changes were proposed in this pull request?

This PR fixes an issue that the string returned by `StructType.toString` is different between Scala 2.12 and 2.13.

* Scala 2.12
```
val st = StructType(StructField("a", IntegerType) :: Nil)
st.toString
res0: String = StructType(StructField(a,IntegerType,true)
```

* Scala 2.13
```
val st = StructType(StructField("a", IntegerType) :: Nil)
st.toString
val res0: String = Seq(StructField(a,IntegerType,true))
```

It's because the logic to make the prefix of the string was changed from Scala 2.13.

Scala 2.12: https://github.com/scala/scala/blob/v2.12.15/src/library/scala/collection/TraversableLike.scala#L804
Scala 2:13:https://github.com/scala/scala/blob/v2.13.5/src/library/scala/collection/Seq.scala#L46

One option which solves this issue would be to override `className` because it's used as the prefix of the string returned by `toString`.
https://github.com/scala/scala/blob/v2.13.5/src/library/scala/collection/Iterable.scala#L76

But it doesn't works with Scala 2.12 because `className` was introduced from Scala 2.12.
Another option would be to override `stringPrefix` and this should work with both Scala 2.12 and 2.13.
https://github.com/scala/scala/blob/v2.12.15/src/library/scala/collection/TraversableLike.scala#L796
https://github.com/scala/scala/blob/v2.13.5/src/library/scala/collection/Iterable.scala#L56

But we need to make the method `public` though it is expected to be used only from `toString` for Scala 2.12, while the method is `private[this]` for Scala 2.13.

So, rather than exposing a new public method, this PR proposes to implement `Struct.toString` explicitly.

### Why are the changes needed?

To fix a kind of compatibility issue.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

New test is added and confirmed it passed with the following command.
```
build/sbt -Pscala-2.13 "testOnly org.apache.spark.sql.types.StructTypeSuite -- -z SPARK-37076"
```

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