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Signed-off-by: Karen Feng <[email protected]>

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala

@@ -961,6 +961,8 @@ class Analyzer(override val catalogManager: CatalogManager)
       lazy val childMetadataOutput = plan.children.flatMap(_.metadataOutput)
       val hasMetaCol = plan.expressions.exists(_.find {
         case a: Attribute =>
+          // If an attribute is resolved before being labeled as metadata
+          // (i.e. from the originating Dataset), we check with expression ID
           a.isMetadataCol || childMetadataOutput.exists(_.exprId == a.exprId)
         case _ => false
       }.isDefined)

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

@@ -205,7 +205,7 @@ package object util extends Logging {
   val METADATA_COL_ATTR_KEY = "__metadata_col"
 
   /**
-   * Hidden columns are a type of metadata column that are not propagated through subquery aliases,
+   * Hidden columns are a type of metadata column that are propagated through Project
    * and are candidates during qualified star expansions.
    */
   val HIDDEN_COL_ATTR_KEY = "__hidden_col"