[SPARK-18016][SQL][FOLLOWUP] merge declareAddedFunctions, initNestedClasses and declareNestedClasses

## What changes were proposed in this pull request?

These 3 methods have to be used together, so it makes more sense to merge them into one method and then the caller side only need to call one method.

## How was this patch tested?

existing tests.

Author: Wenchen Fan <wenchen@databricks.com>

Closes #18579 from cloud-fan/minor.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala

@@ -302,29 +302,20 @@ class CodegenContext {
   }
 
   /**
-   * Instantiates all nested, private sub-classes as objects to the `OuterClass`
+   * Declares all function code. If the added functions are too many, split them into nested
+   * sub-classes to avoid hitting Java compiler constant pool limitation.
    */
-  private[sql] def initNestedClasses(): String = {
+  def declareAddedFunctions(): String = {
+    val inlinedFunctions = classFunctions(outerClassName).values
+
     // Nested, private sub-classes have no mutable state (though they do reference the outer class'
     // mutable state), so we declare and initialize them inline to the OuterClass.
-    classes.filter(_._1 != outerClassName).map {
+    val initNestedClasses = classes.filter(_._1 != outerClassName).map {
       case (className, classInstance) =>
         s"private $className $classInstance = new $className();"
-    }.mkString("\n")
     }
 
-  /**
-   * Declares all function code that should be inlined to the `OuterClass`.
-   */
-  private[sql] def declareAddedFunctions(): String = {
-    classFunctions(outerClassName).values.mkString("\n")
-  }
-
-  /**
-   * Declares all nested, private sub-classes and the function code that should be inlined to them.
-   */
-  private[sql] def declareNestedClasses(): String = {
-    classFunctions.filterKeys(_ != outerClassName).map {
+    val declareNestedClasses = classFunctions.filterKeys(_ != outerClassName).map {
       case (className, functions) =>
         s"""
            |private class $className {
@@ -332,7 +323,9 @@ class CodegenContext {
            |}
            """.stripMargin
     }
-  }.mkString("\n")
+
+    (inlinedFunctions ++ initNestedClasses ++ declareNestedClasses).mkString("\n")
+  }
 
   final val JAVA_BOOLEAN = "boolean"
   final val JAVA_BYTE = "byte"

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateMutableProjection.scala

@@ -115,8 +115,6 @@ object GenerateMutableProjection extends CodeGenerator[Seq[Expression], MutableP
           ${ctx.initPartition()}
         }
 
-        ${ctx.declareAddedFunctions()}
-
         public ${classOf[BaseMutableProjection].getName} target(InternalRow row) {
           mutableRow = row;
           return this;
@@ -136,8 +134,7 @@ object GenerateMutableProjection extends CodeGenerator[Seq[Expression], MutableP
           return mutableRow;
         }
 
-        ${ctx.initNestedClasses()}
-        ${ctx.declareNestedClasses()}
+        ${ctx.declareAddedFunctions()}
       }
     """
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateOrdering.scala

@@ -173,15 +173,12 @@ object GenerateOrdering extends CodeGenerator[Seq[SortOrder], Ordering[InternalR
           ${ctx.initMutableStates()}
         }
 
-        ${ctx.declareAddedFunctions()}
-
         public int compare(InternalRow a, InternalRow b) {
           $comparisons
           return 0;
         }
 
-        ${ctx.initNestedClasses()}
-        ${ctx.declareNestedClasses()}
+        ${ctx.declareAddedFunctions()}
       }"""
 
     val code = CodeFormatter.stripOverlappingComments(

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GeneratePredicate.scala

@@ -66,15 +66,12 @@ object GeneratePredicate extends CodeGenerator[Expression, Predicate] {
           ${ctx.initPartition()}
         }
 
-        ${ctx.declareAddedFunctions()}
-
         public boolean eval(InternalRow ${ctx.INPUT_ROW}) {
           ${eval.code}
           return !${eval.isNull} && ${eval.value};
         }
 
-        ${ctx.initNestedClasses()}
-        ${ctx.declareNestedClasses()}
+        ${ctx.declareAddedFunctions()}
       }"""
 
     val code = CodeFormatter.stripOverlappingComments(

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateSafeProjection.scala

@@ -175,16 +175,13 @@ object GenerateSafeProjection extends CodeGenerator[Seq[Expression], Projection]
           ${ctx.initPartition()}
         }
 
-        ${ctx.declareAddedFunctions()}
-
         public java.lang.Object apply(java.lang.Object _i) {
           InternalRow ${ctx.INPUT_ROW} = (InternalRow) _i;
           $allExpressions
           return mutableRow;
         }
 
-        ${ctx.initNestedClasses()}
-        ${ctx.declareNestedClasses()}
+        ${ctx.declareAddedFunctions()}
       }
     """
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateUnsafeProjection.scala

@@ -391,8 +391,6 @@ object GenerateUnsafeProjection extends CodeGenerator[Seq[Expression], UnsafePro
           ${ctx.initPartition()}
         }
 
-        ${ctx.declareAddedFunctions()}
-
         // Scala.Function1 need this
         public java.lang.Object apply(java.lang.Object row) {
           return apply((InternalRow) row);
@@ -403,8 +401,7 @@ object GenerateUnsafeProjection extends CodeGenerator[Seq[Expression], UnsafePro
           return ${eval.value};
         }
 
-        ${ctx.initNestedClasses()}
-        ${ctx.declareNestedClasses()}
+        ${ctx.declareAddedFunctions()}
       }
       """
 

sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegenExec.scala

@@ -352,14 +352,11 @@ case class WholeStageCodegenExec(child: SparkPlan) extends UnaryExecNode with Co
           ${ctx.initPartition()}
         }
 
-        ${ctx.declareAddedFunctions()}
-
         protected void processNext() throws java.io.IOException {
           ${code.trim}
         }
 
-        ${ctx.initNestedClasses()}
-        ${ctx.declareNestedClasses()}
+        ${ctx.declareAddedFunctions()}
       }
       """.trim
 

sql/core/src/main/scala/org/apache/spark/sql/execution/columnar/GenerateColumnAccessor.scala

@@ -192,8 +192,6 @@ object GenerateColumnAccessor extends CodeGenerator[Seq[DataType], ColumnarItera
           this.columnIndexes = columnIndexes;
         }
 
-        ${ctx.declareAddedFunctions()}
-
         public boolean hasNext() {
           if (currentRow < numRowsInBatch) {
             return true;
@@ -222,8 +220,7 @@ object GenerateColumnAccessor extends CodeGenerator[Seq[DataType], ColumnarItera
           return unsafeRow;
         }
 
-        ${ctx.initNestedClasses()}
-        ${ctx.declareNestedClasses()}
+        ${ctx.declareAddedFunctions()}
       }"""
 
     val code = CodeFormatter.stripOverlappingComments(