[7.x] Add scala docs to javadocs (#1368) (#1382)

This commit introduces a 3rd party plugin to co-locate
scala docs with java docs. https://github.com/lightbend/genjavadoc

Fixes: #1363

Author: jakelandis

spark/sql-13/build.gradle

@@ -12,6 +12,14 @@ variants {
     targetVersions '2.10.7', '2.11.12'
 }
 
+configurations {
+    scalaCompilerPlugin {
+        defaultDependencies { dependencies ->
+            dependencies.add(project.dependencies.create( "com.typesafe.genjavadoc:genjavadoc-plugin_${scalaVersion}:0.13"))
+        }
+    }
+}
+
 println "Compiled using Scala ${project.ext.scalaMajorVersion} [${project.ext.scalaVersion}]"
 String sparkVersion = spark13Version
 
@@ -111,7 +119,9 @@ jar {
 }
 
 javadoc {
+    dependsOn compileScala
     source += project(":elasticsearch-hadoop-mr").sourceSets.main.allJava
+    source += "$buildDir/generated/java"
     classpath += files(project(":elasticsearch-hadoop-mr").sourceSets.main.compileClasspath)
 }
 
@@ -137,3 +147,12 @@ configurations.all { Configuration conf ->
 
     conf.exclude group: "org.mortbay.jetty"
 }
+
+tasks.withType(ScalaCompile) {
+    scalaCompileOptions.with {
+        additionalParameters = [
+                "-Xplugin:" + configurations.scalaCompilerPlugin.asPath,
+                "-P:genjavadoc:out=$buildDir/generated/java".toString()
+        ]
+    }
+}

spark/sql-20/build.gradle

@@ -12,6 +12,14 @@ variants {
     targetVersions '2.10.7', '2.11.12'
 }
 
+configurations {
+    scalaCompilerPlugin {
+        defaultDependencies { dependencies ->
+            dependencies.add(project.dependencies.create( "com.typesafe.genjavadoc:genjavadoc-plugin_${scalaVersion}:0.13"))
+        }
+    }
+}
+
 println "Compiled using Scala ${project.ext.scalaMajorVersion} [${project.ext.scalaVersion}]"
 String sparkVersion = spark20Version
 
@@ -124,7 +132,9 @@ jar {
 }
 
 javadoc {
+    dependsOn compileScala
     source += project(":elasticsearch-hadoop-mr").sourceSets.main.allJava
+    source += "$buildDir/generated/java"
     classpath += files(project(":elasticsearch-hadoop-mr").sourceSets.main.compileClasspath)
 }
 
@@ -135,3 +145,12 @@ sourcesJar {
 scaladoc {
     title = "${rootProject.description} ${version} API"
 }
+
+tasks.withType(ScalaCompile) {
+    scalaCompileOptions.with {
+        additionalParameters = [
+                "-Xplugin:" + configurations.scalaCompilerPlugin.asPath,
+                "-P:genjavadoc:out=$buildDir/generated/java".toString()
+        ]
+    }
+}