[SPARK-22500][SQL] Fix 64KB JVM bytecode limit problem with cast

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

@@ -1039,13 +1039,19 @@ case class Cast(child: Expression, dataType: DataType, timeZoneId: Option[String
           }
         }
        """
-    }.mkString("\n")
+    }
+    val fieldsEvalCodes = if (ctx.INPUT_ROW != null && ctx.currentVars == null) {
+      ctx.splitExpressions(fieldsEvalCode, "castStruct",
+        ("InternalRow", tmpRow) :: (rowClass, result) :: Nil)
+    } else {
+      fieldsEvalCode.mkString("\n")
+    }
 
     (c, evPrim, evNull) =>
       s"""
         final $rowClass $result = new $rowClass(${fieldsCasts.length});
         final InternalRow $tmpRow = $c;
-        $fieldsEvalCode
+        $fieldsEvalCodes
         $evPrim = $result;
       """
   }

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

@@ -827,4 +827,49 @@ class CastSuite extends SparkFunSuite with ExpressionEvalHelper {
 
     checkEvaluation(cast(Literal.create(input, from), to), input)
   }
+
+  test("SPARK-22500: cast for struct should not generate codes beyond 64KB") {
+    val N = 1000
+    val M = 250
+
+    val from1 = new StructType(
+      (1 to N).map(i => StructField(s"s$i", StringType)).toArray)
+    val to1 = new StructType(
+      (1 to N).map(i => StructField(s"i$i", IntegerType)).toArray)
+    val input1 = Row.fromSeq((1 to N).map(i => i.toString))
+    val output1 = Row.fromSeq((1 to N))
+    checkEvaluation(cast(Literal.create(input1, from1), to1), output1)
+
+    val from2 = new StructType(
+      (1 to N).map(i => StructField(s"a$i", ArrayType(StringType, containsNull = false))).toArray)
+    val to2 = new StructType(
+      (1 to N).map(i => StructField(s"i$i", ArrayType(IntegerType, containsNull = true))).toArray)
+    val input2 = Row.fromSeq((1 to N).map(_ => Seq("456", "true", "78.9")))
+    val output2 = Row.fromSeq((1 to N).map(_ => Seq(456, null, 78)))
+    checkEvaluation(cast(Literal.create(input2, from2), to2), output2)
+
+    val from3 = new StructType(
+      (1 to N).map(i => StructField(s"s$i",
+        StructType(Seq(StructField("l$i", IntegerType, nullable = true))))).toArray)
+    val to3 = new StructType(
+      (1 to N).map(i => StructField(s"s$i",
+        StructType(Seq(StructField("l$i", LongType, nullable = true))))).toArray)
+    val input3 = Row.fromSeq((1 to N).map(i => Row(i)))
+    val output3 = Row.fromSeq((1 to N).map(i => Row(i.toLong)))
+    checkEvaluation(cast(Literal.create(input3, from3), to3), output3)
+
+    val fromInner = new StructType(
+      (1 to M).map(i => StructField(s"s$i", DoubleType)).toArray)
+    val toInner = new StructType(
+      (1 to M).map(i => StructField(s"i$i", IntegerType)).toArray)
+    val inputInner = Row.fromSeq((1 to M).map(i => i + 0.5))
+    val outputInner = Row.fromSeq((1 to M))
+    val fromOuter = new StructType(
+      (1 to M).map(i => StructField(s"s$i", fromInner)).toArray)
+    val toOuter = new StructType(
+      (1 to M).map(i => StructField(s"s$i", toInner)).toArray)
+    val inputOuter = Row.fromSeq((1 to M).map(_ => inputInner))
+    val outputOuter = Row.fromSeq((1 to M).map(_ => outputInner))
+    checkEvaluation(cast(Literal.create(inputOuter, fromOuter), toOuter), outputOuter)
+  }
 }