[I] [Doc] CAST has no explicit TimeType branch (Spark 4.1) [datafusion-comet]

["andygrove (via GitHub)" <gi...@apache.org>]

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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