sarutak opened a new pull request #34341:
URL: https://github.com/apache/spark/pull/34341
### What changes were proposed in this pull request?
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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?
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1. If you propose a new API, clarify the use case for a new API.
2. If you fix a bug, you can clarify why it is a bug.
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To fix a kind of compatibility issue.
### Does this PR introduce _any_ user-facing change?
<!--
Note that it means *any* user-facing change including all aspects such as
the documentation fix.
If yes, please clarify the previous behavior and the change this PR proposes
- provide the console output, description and/or an example to show the
behavior difference if possible.
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the released Spark versions or within the unreleased branches such as master.
If no, write 'No'.
-->
No.
### How was this patch tested?
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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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