[GitHub] spark pull request #22544: [SPARK-25522][SQL] Improve type promotion for inp...

[viirya <gi...@git.apache.org>]

Github user viirya commented on a diff in the pull request:

    https://github.com/apache/spark/pull/22544#discussion_r220147139
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala ---
    @@ -971,9 +971,36 @@ object TypeCoercion {
             case (ArrayType(fromType, true), ArrayType(toType: DataType, false)) => null
     
             case (ArrayType(fromType, false), ArrayType(toType: DataType, false))
    -            if !Cast.forceNullable(fromType, toType) =>
    +          if !Cast.forceNullable(fromType, toType) =>
               implicitCast(fromType, toType).map(ArrayType(_, false)).orNull
     
    +        // Implicit cast between Map types.
    +        // Follows the same semantics of implicit casting between two array types.
    +        // Refer to documentation above.
    +        case (MapType(fromKeyType, fromValueType, fn), MapType(toKeyType, toValueType, true)) =>
    +          val newFromType = implicitCast(fromKeyType, toKeyType).orNull
    +          val newValueType = implicitCast(fromValueType, toValueType).orNull
    +          if (newFromType != null && newValueType != null
    --- End diff --
    
    Don't we need to verify `!Cast.forceNullable(fromKeyType, toKeyType)`


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