[SPARK-38030][SQL] Canonicalization should not remove nullability of AttributeReference dataType

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala

@@ -294,7 +294,7 @@ case class AttributeReference(
   }
 
   override lazy val preCanonicalized: Expression = {
-    AttributeReference("none", dataType.asNullable)(exprId)
+    AttributeReference("none", dataType)(exprId)
   }
 
   override def newInstance(): AttributeReference =

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CanonicalizeSuite.scala

@@ -23,7 +23,7 @@ import org.apache.spark.SparkFunSuite
 import org.apache.spark.sql.catalyst.dsl.expressions._
 import org.apache.spark.sql.catalyst.dsl.plans._
 import org.apache.spark.sql.catalyst.plans.logical.Range
-import org.apache.spark.sql.types.{IntegerType, LongType, StructField, StructType}
+import org.apache.spark.sql.types.{IntegerType, LongType, StringType, StructField, StructType}
 
 class CanonicalizeSuite extends SparkFunSuite {
 
@@ -177,4 +177,17 @@ class CanonicalizeSuite extends SparkFunSuite {
     assert(expr.semanticEquals(attr))
     assert(attr.semanticEquals(expr))
   }
+
+  test("SPARK-38030: Canonicalization should not remove nullability of AttributeReference" +
+    " dataType") {
+    val structType = StructType(Seq(StructField("name", StringType, nullable = false)))
+    val attr = AttributeReference("col", structType)()
+    // AttributeReference dataType should not be converted to nullable
+    assert(attr.canonicalized.dataType === structType)
+
+    val cast = Cast(attr, structType)
+    assert(cast.resolved)
+    // canonicalization should not converted resolved cast to unresolved
+    assert(cast.canonicalized.resolved)
+  }
 }