Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/22544#discussion_r220531899
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -974,6 +974,33 @@ object TypeCoercion {
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))
+ if !Cast.forceNullable(fromKeyType, toKeyType) =>
+ val newKeyType = implicitCast(fromKeyType, toKeyType).orNull
+ val newValueType = implicitCast(fromValueType,
toValueType).orNull
+ if (newKeyType != null && newValueType != null) {
+ MapType(newKeyType, 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(fromKeyType, toKeyType) ||
+ Cast.forceNullable(fromValueType, toValueType))) =>
+ val newKeyType = implicitCast(fromKeyType, toKeyType).orNull
+ val newValueType = implicitCast(fromValueType,
toValueType).orNull
+ if (newKeyType != null && newValueType != null) {
+ MapType(newKeyType, newValueType, false)
+ } else {
+ null
+ }
+
--- End diff --
nit:
```
case (MapType(fromKeyType, fromValueType, fromNullable), MapType(toKeyType,
toValueType, toNullable))
if !Cast.forceNullable(fromKeyType, toKeyType) &&
Cast.resolvableNullability(fromNullable, toNullable)
....
if (Cast.forceNullable(fromValueType, toValueType) $$ !toNullable) {
null
} else {
MapType(newKeyType, newValueType, toNullable)
}
```
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