[SPARK-32167][SQL] Fix GetArrayStructFields to respect inner field's nullability together

### What changes were proposed in this pull request?

Fix nullability of `GetArrayStructFields`. It should consider both the original array's `containsNull` and the inner field's nullability.

### Why are the changes needed?

Fix a correctness issue.

### Does this PR introduce _any_ user-facing change?

Yes. See the added test.

### How was this patch tested?

a new UT and end-to-end test

Closes apache#28992 from cloud-fan/bug.

Authored-by: Wenchen Fan <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: cloud-fan

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

@@ -57,7 +57,7 @@ object ExtractValue {
         val fieldName = v.toString
         val ordinal = findField(fields, fieldName, resolver)
         GetArrayStructFields(child, fields(ordinal).copy(name = fieldName),
-          ordinal, fields.length, containsNull)
+          ordinal, fields.length, containsNull || fields(ordinal).nullable)
 
       case (_: ArrayType, _) => GetArrayItem(child, extraction)
 

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

@@ -18,6 +18,7 @@
 package org.apache.spark.sql.catalyst.expressions
 
 import org.apache.spark.SparkFunSuite
+import org.apache.spark.sql.Row
 import org.apache.spark.sql.catalyst.analysis.{TypeCheckResult, UnresolvedExtractValue}
 import org.apache.spark.sql.catalyst.dsl.expressions._
 import org.apache.spark.sql.catalyst.expressions.codegen.CodegenContext
@@ -159,6 +160,31 @@ class ComplexTypeSuite extends SparkFunSuite with ExpressionEvalHelper {
     checkEvaluation(getArrayStructFields(nullArrayStruct, "a"), null)
   }
 
+  test("SPARK-32167: nullability of GetArrayStructFields") {
+    val resolver = SQLConf.get.resolver
+
+    val array1 = ArrayType(
+      new StructType().add("a", "int", nullable = true),
+      containsNull = false)
+    val data1 = Literal.create(Seq(Row(null)), array1)
+    val get1 = ExtractValue(data1, Literal("a"), resolver).asInstanceOf[GetArrayStructFields]
+    assert(get1.containsNull)
+
+    val array2 = ArrayType(
+      new StructType().add("a", "int", nullable = false),
+      containsNull = true)
+    val data2 = Literal.create(Seq(null), array2)
+    val get2 = ExtractValue(data2, Literal("a"), resolver).asInstanceOf[GetArrayStructFields]
+    assert(get2.containsNull)
+
+    val array3 = ArrayType(
+      new StructType().add("a", "int", nullable = false),
+      containsNull = false)
+    val data3 = Literal.create(Seq(Row(1)), array3)
+    val get3 = ExtractValue(data3, Literal("a"), resolver).asInstanceOf[GetArrayStructFields]
+    assert(!get3.containsNull)
+  }
+
   test("CreateArray") {
     val intSeq = Seq(5, 10, 15, 20, 25)
     val longSeq = intSeq.map(_.toLong)

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

@@ -254,13 +254,13 @@ class SelectedFieldSuite extends AnalysisTest {
     StructField("col3", ArrayType(StructType(
       StructField("field1", StructType(
         StructField("subfield1", IntegerType, nullable = false) :: Nil))
-        :: Nil), containsNull = false), nullable = false)
+        :: Nil), containsNull = true), nullable = false)
   }
 
   testSelect(arrayWithStructAndMap, "col3.field2['foo'] as foo") {
     StructField("col3", ArrayType(StructType(
       StructField("field2", MapType(StringType, IntegerType, valueContainsNull = false))
-        :: Nil), containsNull = false), nullable = false)
+        :: Nil), containsNull = true), nullable = false)
   }
 
   //  |-- col1: string (nullable = false)
@@ -471,7 +471,7 @@ class SelectedFieldSuite extends AnalysisTest {
   testSelect(mapWithArrayOfStructKey, "map_keys(col2)[0].field1 as foo") {
     StructField("col2", MapType(
       ArrayType(StructType(
-        StructField("field1", StringType) :: Nil), containsNull = false),
+        StructField("field1", StringType) :: Nil), containsNull = true),
       ArrayType(StructType(
         StructField("field3", StructType(
           StructField("subfield3", IntegerType) ::
@@ -482,7 +482,7 @@ class SelectedFieldSuite extends AnalysisTest {
     StructField("col2", MapType(
       ArrayType(StructType(
         StructField("field2", StructType(
-          StructField("subfield1", IntegerType) :: Nil)) :: Nil), containsNull = false),
+          StructField("subfield1", IntegerType) :: Nil)) :: Nil), containsNull = true),
       ArrayType(StructType(
         StructField("field3", StructType(
           StructField("subfield3", IntegerType) ::

sql/core/src/test/scala/org/apache/spark/sql/ComplexTypesSuite.scala

@@ -17,11 +17,15 @@
 
 package org.apache.spark.sql
 
+import scala.collection.JavaConverters._
+
 import org.apache.spark.sql.catalyst.expressions.CreateNamedStruct
 import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
 import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types.{ArrayType, StructType}
 
 class ComplexTypesSuite extends QueryTest with SharedSparkSession {
+  import testImplicits._
 
   override def beforeAll(): Unit = {
     super.beforeAll()
@@ -106,4 +110,11 @@ class ComplexTypesSuite extends QueryTest with SharedSparkSession {
     checkAnswer(df1, Row(10, 12) :: Row(11, 13) :: Nil)
     checkNamedStruct(df.queryExecution.optimizedPlan, expectedCount = 0)
   }
+
+  test("SPARK-32167: get field from an array of struct") {
+    val innerStruct = new StructType().add("i", "int", nullable = true)
+    val schema = new StructType().add("arr", ArrayType(innerStruct, containsNull = false))
+    val df = spark.createDataFrame(List(Row(Seq(Row(1), Row(null)))).asJava, schema)
+    checkAnswer(df.select($"arr".getField("i")), Row(Seq(1, null)))
+  }
 }