[GitHub] [spark] gengliangwang commented on a change in pull request #25242: [SPARK-28497][SQL] Disallow upcasting complex data types to string type

[GitBox <gi...@apache.org>]

gengliangwang commented on a change in pull request #25242: [SPARK-28497][SQL] Disallow upcasting complex data types to string type
URL: https://github.com/apache/spark/pull/25242#discussion_r306836526
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
 ##########
 @@ -131,7 +131,8 @@ object Cast {
     case (from: DecimalType, to: NumericType) if from.isTighterThan(to) => true
     case (f, t) if legalNumericPrecedence(f, t) => true
     case (DateType, TimestampType) => true
-    case (_, StringType) => true
+    case (_: AtomicType, StringType) => true
+    case (_: CalendarIntervalType, StringType) => true
 
 Review comment:
   I don't think it is valid up-cast.
   Even in `Cast`, Spark only allows casting to the same udt.
   ```
   case udt: UserDefinedType[_]
             if udt.userClass == from.asInstanceOf[UserDefinedType[_]].userClass =>
             identity[Any]
   case _: UserDefinedType[_] =>
             throw new SparkException(s"Cannot cast $from to $to.")
   ```

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