dongjoon-hyun opened a new pull request, #59241:
URL: https://github.com/apache/spark/pull/59241
### What changes were proposed in this pull request?
This PR aims to fix `ToStringSQLBuilder` to render a
`GeneralScalarExpression` with an unknown name as a function call, e.g.,
`DATE_TRUNC('MONTH', ts)`.
### Why are the changes needed?
Currently, `toString` and `describe` of a V2 expression with an unknown name
fail with `StackOverflowError`, because
`V2ExpressionSQLBuilder.visitUnexpectedExpr` builds its error message with
`toString` of the same expression.
```scala
import org.apache.spark.sql.connector.expressions.{Expression, Expressions,
GeneralScalarExpression}
val e = new GeneralScalarExpression("DATE_TRUNC",
Array[Expression](Expressions.literal("MONTH"), Expressions.column("ts")))
e.toString // java.lang.StackOverflowError
```
This is a regression since Apache Spark
[v3.4.0](https://github.com/apache/spark/releases/tag/v3.4.0) (2023-04-07) by
[SPARK-39139](https://issues.apache.org/jira/browse/SPARK-39139).
### Does this PR introduce _any_ user-facing change?
Yes. `toString` and `describe` return a string like `DATE_TRUNC('MONTH',
ts)` instead of throwing `StackOverflowError`. Known names are rendered as
before, and the SQL builders for pushdown still reject such expressions with
`UNEXPECTED_V2_EXPRESSION`.
### How was this patch tested?
Pass the CIs with the newly added test case.
### Was this patch authored or co-authored using generative AI tooling?
Generated-by: Claude Opus 5.5
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