cloud-fan commented on code in PR #53164:
URL: https://github.com/apache/spark/pull/53164#discussion_r2559749409
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala:
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@@ -360,6 +360,35 @@ object Cast extends QueryErrorsBase {
*/
def canUpCast(from: DataType, to: DataType): Boolean =
UpCastRule.canUpCast(from, to)
+ /**
+ * Returns true iff it is safe to provide a default value of `from` type
typically defined in the
+ * data source metadata to the `to` type typically in the read schema of a
query.
+ */
+ def canAssignDefaultValue(from: DataType, to: DataType): Boolean = {
+ def isVariantStruct(dt: DataType): Boolean = {
+ dt match {
+ case s: StructType =>
+ s.fields.length > 0 &&
s.fields.forall(_.metadata.contains("__VARIANT_METADATA_KEY"))
+ case _ => false
+ }
+ }
+ (from, to) match {
+ case (s1: StructType, s2: StructType) =>
+ s1.length == s2.length && s1.fields.zip(s2.fields).forall {
+ case (f1, f2) => resolvableNullability(f1.nullable, f2.nullable) &&
+ canAssignDefaultValue(f1.dataType, f2.dataType)
+ }
+ case (ArrayType(fromType, fn), ArrayType(toType, tn)) =>
+ resolvableNullability(fn, tn) && canAssignDefaultValue(fromType,
toType)
+ case (MapType(fromKey, fromValue, fn), MapType(toKey, toValue, tn)) =>
+ resolvableNullability(fn, tn) && canAssignDefaultValue(fromKey, toKey)
&&
+ canAssignDefaultValue(fromValue, toValue)
+ // A VARIANT field can be read as StructType due to shredding.
+ case (_: VariantType, s: StructType) => isVariantStruct(s)
+ case (k, v) => canUpCast(k, v)
Review Comment:
```suggestion
case _ => canUpCast(from, to)
```
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