[SPARK-16294][SQL] Labelling support for the include_example Jekyll plugin

## What changes were proposed in this pull request?

This PR adds labelling support for the `include_example` Jekyll plugin, so that we may split a single source file into multiple line blocks with different labels, and include them in multiple code snippets in the generated HTML page.

## How was this patch tested?

Manually tested.

<img width="923" alt="screenshot at jun 29 19-53-21" src="https://cloud.githubusercontent.com/assets/230655/16451099/66a76db2-3e33-11e6-84fb-63104c2f0688.png">

Author: Cheng Lian <lian@databricks.com>

Closes #13972 from liancheng/include-example-with-labels.

2 files changed, 25 insertions, 41 deletions

diff --git a/docs/_plugins/include_example.rb b/docs/_plugins/include_example.rb
index f7485826a7..306888801d 100644
--- a/docs/_plugins/include_example.rb
+++ b/docs/_plugins/include_example.rb
@@ -32,8 +32,18 @@ module Jekyll
       @code_dir = File.join(site.source, config_dir)
 
       clean_markup = @markup.strip
-      @file = File.join(@code_dir, clean_markup)
-      @lang = clean_markup.split('.').last
+
+      parts = clean_markup.strip.split(' ')
+      if parts.length > 1 then
+        @snippet_label = ':' + parts[0]
+        snippet_file = parts[1]
+      else
+        @snippet_label = ''
+        snippet_file = parts[0]
+      end
+
+      @file = File.join(@code_dir, snippet_file)
+      @lang = snippet_file.split('.').last
 
       code = File.open(@file).read.encode("UTF-8")
       code = select_lines(code)
@@ -41,7 +51,7 @@ module Jekyll
       rendered_code = Pygments.highlight(code, :lexer => @lang)
 
       hint = "<div><small>Find full example code at " \
-        "\"examples/src/main/#{clean_markup}\" in the Spark repo.</small></div>"
+        "\"examples/src/main/#{snippet_file}\" in the Spark repo.</small></div>"
 
       rendered_code + hint
     end
@@ -66,13 +76,13 @@ module Jekyll
       # Select the array of start labels from code.
       startIndices = lines
         .each_with_index
-        .select { |l, i| l.include? "$example on$" }
+        .select { |l, i| l.include? "$example on#{@snippet_label}$" }
         .map { |l, i| i }
 
       # Select the array of end labels from code.
       endIndices = lines
         .each_with_index
-        .select { |l, i| l.include? "$example off$" }
+        .select { |l, i| l.include? "$example off#{@snippet_label}$" }
         .map { |l, i| i }
 
       raise "Start indices amount is not equal to end indices amount, see #{@file}." \
@@ -92,7 +102,10 @@ module Jekyll
             if start == endline
         lastIndex = endline
         range = Range.new(start + 1, endline - 1)
-        result += trim_codeblock(lines[range]).join
+        trimmed = trim_codeblock(lines[range])
+        # Filter out possible example tags of overlapped labels.
+        taggs_filtered = trimmed.select { |l| !l.include? '$example ' }
+        result += taggs_filtered.join
         result += "\n"
       end
       result
diff --git a/docs/sql-programming-guide.md b/docs/sql-programming-guide.md
index 6c6bc8db6a..68419e1331 100644
--- a/docs/sql-programming-guide.md
+++ b/docs/sql-programming-guide.md
@@ -63,52 +63,23 @@ Throughout this document, we will often refer to Scala/Java Datasets of `Row`s a
 <div class="codetabs">
 <div data-lang="scala"  markdown="1">
 
-The entry point into all functionality in Spark is the [`SparkSession`](api/scala/index.html#org.apache.spark.sql.SparkSession) class. To create a basic `SparkSession`, just use `SparkSession.build()`:
-
-{% highlight scala %}
-import org.apache.spark.sql.SparkSession
-
-val spark = SparkSession.build()
-  .master("local")
-  .appName("Word Count")
-  .config("spark.some.config.option", "some-value")
-  .getOrCreate()
-
-// this is used to implicitly convert an RDD to a DataFrame.
-import spark.implicits._
-{% endhighlight %}
+The entry point into all functionality in Spark is the [`SparkSession`](api/scala/index.html#org.apache.spark.sql.SparkSession) class. To create a basic `SparkSession`, just use `SparkSession.builder()`:
 
+{% include_example init_session scala/org/apache/spark/examples/sql/RDDRelation.scala %}
 </div>
 
 <div data-lang="java" markdown="1">
 
-The entry point into all functionality in Spark is the [`SparkSession`](api/java/index.html#org.apache.spark.sql.SparkSession) class. To create a basic `SparkSession`, just use `SparkSession.build()`:
+The entry point into all functionality in Spark is the [`SparkSession`](api/java/index.html#org.apache.spark.sql.SparkSession) class. To create a basic `SparkSession`, just use `SparkSession.builder()`:
 
-{% highlight java %}
-import org.apache.spark.sql.SparkSession
-
-SparkSession spark = SparkSession.build()
-  .master("local")
-  .appName("Word Count")
-  .config("spark.some.config.option", "some-value")
-  .getOrCreate();
-{% endhighlight %}
+{% include_example init_session java/org/apache/spark/examples/sql/JavaSparkSQL.java %}
 </div>
 
 <div data-lang="python"  markdown="1">
 
-The entry point into all functionality in Spark is the [`SparkSession`](api/python/pyspark.sql.html#pyspark.sql.SparkSession) class. To create a basic `SparkSession`, just use `SparkSession.build`:
-
-{% highlight python %}
-from pyspark.sql import SparkSession
-
-spark = SparkSession.build \
-  .master("local") \
-  .appName("Word Count") \
-  .config("spark.some.config.option", "some-value") \
-  .getOrCreate()
-{% endhighlight %}
+The entry point into all functionality in Spark is the [`SparkSession`](api/python/pyspark.sql.html#pyspark.sql.SparkSession) class. To create a basic `SparkSession`, just use `SparkSession.builder`:
 
+{% include_example init_session python/sql.py %}
 </div>
 
 <div data-lang="r"  markdown="1">