[SPARK-18138][DOCS] Document that Java 7, Python 2.6, Scala 2.10, Hadoop < 2.6...

[SPARK-18138][DOCS] Document that Java 7, Python 2.6, Scala 2.10, Hadoop < 2.6 are deprecated in Spark 2.1.0

## What changes were proposed in this pull request?

Document that Java 7, Python 2.6, Scala 2.10, Hadoop < 2.6 are deprecated in Spark 2.1.0. This does not actually implement any of the change in SPARK-18138, just peppers the documentation with notices about it.

## How was this patch tested?

Doc build

Author: Sean Owen <sowen@cloudera.com>

Closes #15733 from srowen/SPARK-18138.

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -183,6 +183,8 @@ class SparkContext(config: SparkConf) extends Logging {
   // log out Spark Version in Spark driver log
   logInfo(s"Running Spark version $SPARK_VERSION")
 
+  warnDeprecatedVersions()
+
   /* ------------------------------------------------------------------------------------- *
    | Private variables. These variables keep the internal state of the context, and are    |
    | not accessible by the outside world. They're mutable since we want to initialize all  |
@@ -346,6 +348,16 @@ class SparkContext(config: SparkConf) extends Logging {
     value
   }
 
+  private def warnDeprecatedVersions(): Unit = {
+    val javaVersion = System.getProperty("java.version").split("[+.\\-]+", 3)
+    if (javaVersion.length >= 2 && javaVersion(1).toInt == 7) {
+      logWarning("Support for Java 7 is deprecated as of Spark 2.0.0")
+    }
+    if (scala.util.Properties.releaseVersion.exists(_.startsWith("2.10"))) {
+      logWarning("Support for Scala 2.10 is deprecated as of Spark 2.1.0")
+    }
+  }
+
   /** Control our logLevel. This overrides any user-defined log settings.
    * @param logLevel The desired log level as a string.
    * Valid log levels include: ALL, DEBUG, ERROR, FATAL, INFO, OFF, TRACE, WARN

docs/building-spark.md

@@ -13,6 +13,7 @@ redirect_from: "building-with-maven.html"
 
 The Maven-based build is the build of reference for Apache Spark.
 Building Spark using Maven requires Maven 3.3.9 or newer and Java 7+.
+Note that support for Java 7 is deprecated as of Spark 2.0.0 and may be removed in Spark 2.2.0.
 
 ### Setting up Maven's Memory Usage
 
@@ -79,6 +80,9 @@ Because HDFS is not protocol-compatible across versions, if you want to read fro
   </tbody>
 </table>
 
+Note that support for versions of Hadoop before 2.6 are deprecated as of Spark 2.1.0 and may be 
+removed in Spark 2.2.0.
+
 
 You can enable the `yarn` profile and optionally set the `yarn.version` property if it is different from `hadoop.version`. Spark only supports YARN versions 2.2.0 and later.
 
@@ -129,6 +133,8 @@ To produce a Spark package compiled with Scala 2.10, use the `-Dscala-2.10` prop
 
     ./dev/change-scala-version.sh 2.10
     ./build/mvn -Pyarn -Phadoop-2.4 -Dscala-2.10 -DskipTests clean package
+    
+Note that support for Scala 2.10 is deprecated as of Spark 2.1.0 and may be removed in Spark 2.2.0.
 
 ## Building submodules individually
 

docs/index.md

@@ -28,6 +28,10 @@ Spark runs on Java 7+, Python 2.6+/3.4+ and R 3.1+. For the Scala API, Spark {{s
 uses Scala {{site.SCALA_BINARY_VERSION}}. You will need to use a compatible Scala version
 ({{site.SCALA_BINARY_VERSION}}.x).
 
+Note that support for Java 7 and Python 2.6 are deprecated as of Spark 2.0.0, and support for 
+Scala 2.10 and versions of Hadoop before 2.6 are deprecated as of Spark 2.1.0, and may be 
+removed in Spark 2.2.0.
+
 # Running the Examples and Shell
 
 Spark comes with several sample programs.  Scala, Java, Python and R examples are in the

docs/programming-guide.md

@@ -59,6 +59,8 @@ Spark {{site.SPARK_VERSION}} works with Java 7 and higher. If you are using Java
 for concisely writing functions, otherwise you can use the classes in the
 [org.apache.spark.api.java.function](api/java/index.html?org/apache/spark/api/java/function/package-summary.html) package.
 
+Note that support for Java 7 is deprecated as of Spark 2.0.0 and may be removed in Spark 2.2.0.
+
 To write a Spark application in Java, you need to add a dependency on Spark. Spark is available through Maven Central at:
 
     groupId = org.apache.spark
@@ -87,6 +89,8 @@ import org.apache.spark.SparkConf
 Spark {{site.SPARK_VERSION}} works with Python 2.6+ or Python 3.4+. It can use the standard CPython interpreter,
 so C libraries like NumPy can be used. It also works with PyPy 2.3+.
 
+Note that support for Python 2.6 is deprecated as of Spark 2.0.0, and may be removed in Spark 2.2.0.
+
 To run Spark applications in Python, use the `bin/spark-submit` script located in the Spark directory.
 This script will load Spark's Java/Scala libraries and allow you to submit applications to a cluster.
 You can also use `bin/pyspark` to launch an interactive Python shell.

python/pyspark/context.py

@@ -22,6 +22,7 @@ import shutil
 import signal
 import sys
 import threading
+import warnings
 from threading import RLock
 from tempfile import NamedTemporaryFile
 
@@ -187,6 +188,9 @@ class SparkContext(object):
         self.pythonExec = os.environ.get("PYSPARK_PYTHON", 'python')
         self.pythonVer = "%d.%d" % sys.version_info[:2]
 
+        if sys.version_info < (2, 7):
+            warnings.warn("Support for Python 2.6 is deprecated as of Spark 2.0.0")
+
         # Broadcast's __reduce__ method stores Broadcast instances here.
         # This allows other code to determine which Broadcast instances have
         # been pickled, so it can determine which Java broadcast objects to