andygrove opened a new issue, #4490:
URL: https://github.com/apache/datafusion-comet/issues/4490
## Describe the bug
Spark 4.1 introduced `TimeType` (HH:mm:ss). Spark 4.1's `Cast.scala` adds
many `TimeType` arms (`StringType <-> TimeType`, `TimeType <-> TimeType`,
`TimeType -> IntegralType / DecimalType`, etc.). `CometCast.isSupported` has no
`TimeType` arm at all, so every TimeType-involving cast falls into the default
`case _ => unsupported(fromType, toType)` and falls back to Spark.
The fallback is correct, but it is implicit, and `getUnsupportedReasons()`
on `CometCast` does not enumerate `TimeType` as one of the unsupported
branches, so the auto-generated compatibility guide doesn't mention it.
Surfaced by the cast audit (collection PR queue).
## Expected behavior
Either:
1. Add an explicit `TimeType` arm to `CometCast.isSupported` that returns
`Unsupported(Some("Cast to/from TimeType is not yet supported"))`, OR
2. Implement native `TimeType` cast (depends on `TimeType` being supported
broadly across Comet, tracked by the broader date/time epic #4418).
The minimum here is the explicit `Unsupported` arm so the compatibility
guide reflects it.
## Additional context
- Spark reference: `Cast.scala` in
`/tmp/spark-v4.1.1/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/`.
- Comet matrix: `CometCast.scala`.
- Related: #4418 (EPIC for date/time expressions on Spark 4.x).
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