From 6530243a52b05007e566d458cd8f075e851e91f1 Mon Sep 17 00:00:00 2001
From: zsxwing <zsxwing@gmail.com>
Date: Tue, 16 Dec 2014 14:13:40 -0800
Subject: [SPARK-4812][SQL] Fix the initialization issue of 'codegenEnabled'

The problem is `codegenEnabled` is `val`, but it uses a `val` `sqlContext`, which can be override by subclasses. Here is a simple example to show this issue.

```Scala
scala> :paste
// Entering paste mode (ctrl-D to finish)

abstract class Foo {

  protected val sqlContext = "Foo"

  val codegenEnabled: Boolean = {
    println(sqlContext) // it will call subclass's `sqlContext` which has not yet been initialized.
    if (sqlContext != null) {
      true
    } else {
      false
    }
  }
}

class Bar extends Foo {
  override val sqlContext = "Bar"
}

println(new Bar().codegenEnabled)

// Exiting paste mode, now interpreting.

null
false
defined class Foo
defined class Bar
```

We should make `sqlContext` `final` to prevent subclasses from overriding it incorrectly.

Author: zsxwing <zsxwing@gmail.com>

Closes #3660 from zsxwing/SPARK-4812 and squashes the following commits:

1cbb623 [zsxwing] Make `sqlContext` final to prevent subclasses from overriding it incorrectly
---
 .../scala/org/apache/spark/sql/columnar/InMemoryColumnarTableScan.scala | 2 --
 sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala  | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/columnar/InMemoryColumnarTableScan.scala b/sql/core/src/main/scala/org/apache/spark/sql/columnar/InMemoryColumnarTableScan.scala
index 0cebe823b2..1e432485c4 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/columnar/InMemoryColumnarTableScan.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/columnar/InMemoryColumnarTableScan.scala
@@ -175,8 +175,6 @@ private[sql] case class InMemoryColumnarTableScan(
     relation: InMemoryRelation)
   extends LeafNode {
 
-  @transient override val sqlContext = relation.child.sqlContext
-
   override def output: Seq[Attribute] = attributes
 
   private def statsFor(a: Attribute) = relation.partitionStatistics.forAttribute(a)
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala
index 4cd8e7d657..017c78d2c6 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala
@@ -44,7 +44,7 @@ abstract class SparkPlan extends QueryPlan[SparkPlan] with Logging with Serializ
    * populated by the query planning infrastructure.
    */
   @transient
-  protected[spark] val sqlContext = SparkPlan.currentContext.get()
+  protected[spark] final val sqlContext = SparkPlan.currentContext.get()
 
   protected def sparkContext = sqlContext.sparkContext
 
-- 
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