[GitHub] [spark] rednaxelafx opened a new pull request #24392: [SPARK-27423][SQL][FOLLOWUP] Minor polishes to Cast codegen templates for Date <-> Timestamp

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rednaxelafx opened a new pull request #24392: [SPARK-27423][SQL][FOLLOWUP] Minor polishes to Cast codegen templates for Date <-> Timestamp 
URL: https://github.com/apache/spark/pull/24392
 
 
   ## What changes were proposed in this pull request?
   
   https://github.com/apache/spark/pull/24332 introduced an unnecessary `import` statement and two slight issues in the codegen templates in `Cast` for `Date` <-> `Timestamp`.
   This PR removes the unused import statement and fixes the slight codegen issue.
   
   The issue in those two codegen templates is this pattern:
   ```scala
   val zid = JavaCode.global(
     ctx.addReferenceObj("zoneId", zoneId, "java.time.ZoneId"),
     zoneId.getClass)
   ```
   `zoneId` can refer to an instance of a non-public class, e.g. `java.time.ZoneRegion`, and while this code correctly puts in the 3rd argument to `ctx.addReferenceObj()`, it's still passing `zoneId.getClass` to `JavaCode.global()` which is not desirable, but doesn't cause any immediate bugs in this particular case, because `zid` is used in an expression immediately afterwards.
   If this `zid` ever needs to spill to any explicitly typed variables, e.g. a local variable, and if the spill handling uses the `javaType` on this `GlobalVariable`, it'd generate code that looks like:
   ```java
   java.time.ZoneRegion value1 = ((java.time.ZoneId) references[2] /* literal */);
   ```
   which would then be a real bug:
   - a non-accessible type `java.time.ZoneRegion` is referenced in the generated code, and
   - `ZoneId` -> `ZoneRegion` requires an explicit downcast.
   
   ## How was this patch tested?
   
   Existing tests. This PR does not change behavior, and the original PR won't cause any real behavior bug to begin with.

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