[SPARK-51119][SQL][FOLLOW-UP] Fix missing fallback case for parsing corrupt exists_default value

### What changes were proposed in this pull request?
Add another fallback for broken (non-resolved) exists_default values for SPARK-51119 original fix.

### Why are the changes needed?
#49962 added a fallback in case there were already broken (ie, non-resolved) persisted default values in catalogs.  A broken one is something like 'current_database, current_user, current_timestamp' , these are non-deterministic and will bring wrong results in EXISTS_DEFAULT, where user expects the value resolved when they set the default.

However, this fallback missed one case when the current_xxx is in a cast.  This fixes it.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
Add to existing unit test in StructTypeSuite

### Was this patch authored or co-authored using generative AI tooling?
No

Closes #50685 from szehon-ho/SPARK-51119-follow-3.

Authored-by: Szehon Ho <[email protected]>
Signed-off-by: Wenchen Fan <[email protected]>
(cherry picked from commit 516859f)
Signed-off-by: Wenchen Fan <[email protected]>

Author: szehon-ho

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/ResolveDefaultColumnsUtil.scala

@@ -371,7 +371,7 @@ object ResolveDefaultColumns extends QueryErrorsBase
     val expr = Literal.fromSQL(defaultSQL) match {
       // EXISTS_DEFAULT will have a cast from analyze() due to coerceDefaultValue
       // hence we need to add timezone to the cast if necessary
-      case c: Cast if c.needsTimeZone =>
+      case c: Cast if c.child.resolved && c.needsTimeZone =>
         c.withTimeZone(SQLConf.get.sessionLocalTimeZone)
       case e: Expression => e
     }

sql/catalyst/src/test/scala/org/apache/spark/sql/types/StructTypeSuite.scala

@@ -35,6 +35,7 @@ import org.apache.spark.sql.types.DayTimeIntervalType._
 import org.apache.spark.sql.types.StructType.fromDDL
 import org.apache.spark.sql.types.YearMonthIntervalType._
 import org.apache.spark.unsafe.types.UTF8String
+import org.apache.spark.unsafe.types.UTF8String.LongWrapper
 
 class StructTypeSuite extends SparkFunSuite with SQLHelper {
 
@@ -835,18 +836,33 @@ class StructTypeSuite extends SparkFunSuite with SQLHelper {
   test("SPARK-51119: Add fallback to process unresolved EXISTS_DEFAULT") {
     val source = StructType(
       Array(
-      StructField("c1", VariantType, true,
-        new MetadataBuilder()
-          .putString(ResolveDefaultColumns.EXISTS_DEFAULT_COLUMN_METADATA_KEY, "parse_json(null)")
-          .putString(ResolveDefaultColumns.CURRENT_DEFAULT_COLUMN_METADATA_KEY, "parse_json(null)")
-          .build()),
-      StructField("c0", StringType, true,
-        new MetadataBuilder()
-          .putString(ResolveDefaultColumns.EXISTS_DEFAULT_COLUMN_METADATA_KEY, "current_catalog()")
-          .putString(ResolveDefaultColumns.CURRENT_DEFAULT_COLUMN_METADATA_KEY, "current_catalog()")
-          .build())))
+        StructField("c0", VariantType, true,
+          new MetadataBuilder()
+            .putString(ResolveDefaultColumns.EXISTS_DEFAULT_COLUMN_METADATA_KEY,
+              "parse_json(null)")
+            .putString(ResolveDefaultColumns.CURRENT_DEFAULT_COLUMN_METADATA_KEY,
+              "parse_json(null)")
+            .build()),
+        StructField("c1", StringType, true,
+          new MetadataBuilder()
+            .putString(ResolveDefaultColumns.EXISTS_DEFAULT_COLUMN_METADATA_KEY,
+              "current_catalog()")
+            .putString(ResolveDefaultColumns.CURRENT_DEFAULT_COLUMN_METADATA_KEY,
+              "current_catalog()")
+            .build()),
+        StructField("c2", StringType, true,
+          new MetadataBuilder()
+            .putString(ResolveDefaultColumns.EXISTS_DEFAULT_COLUMN_METADATA_KEY,
+              "CAST(CURRENT_TIMESTAMP AS BIGINT)")
+            .putString(ResolveDefaultColumns.CURRENT_DEFAULT_COLUMN_METADATA_KEY,
+              "CAST(CURRENT_TIMESTAMP AS BIGINT)")
+            .build())))
     val res = ResolveDefaultColumns.existenceDefaultValues(source)
     assert(res(0) == null)
     assert(res(1) == UTF8String.fromString("spark_catalog"))
+
+    val res2Wrapper = new LongWrapper
+    assert(res(2).asInstanceOf[UTF8String].toLong(res2Wrapper))
+    assert(res2Wrapper.value > 0)
   }
 }