Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/22544#discussion_r220140660
--- 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
+ && (!newFromType.sameType(fromKeyType) ||
!newValueType.sameType(fromValueType))) {
+ MapType(newFromType, newValueType, true)
+ } else {
+ null
+ }
+
+ case (MapType(fromKeyType, fromValueType, true),
MapType(toKeyType, toValueType, false)) =>
+ null
+
+ case (MapType(fromKeyType, fromValueType, false),
MapType(toKeyType, toValueType, false))
+ if !Cast.forceNullable(fromValueType, toValueType) =>
+ val newFromType = implicitCast(fromKeyType, toKeyType).orNull
--- End diff --
ditto, `newKeyType`.
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