[SPARK-22855][BUILD] Add -no-java-comments to sbt docs/scalacOptions …

…on scala 2.12

Prevents Scala 2.12 scaladoc from blowing up attempting to parse java comments. Also
moves scaladoc configs out of the TestSettings and into the standard sharedSettings
section in SparkBuild.scala.

project/SparkBuild.scala

@@ -254,6 +254,21 @@ object SparkBuild extends PomBuild {
       "-sourcepath", (baseDirectory in ThisBuild).value.getAbsolutePath  // Required for relative source links in scaladoc
     ),
 
+    // Remove certain packages from Scaladoc
+    scalacOptions in (Compile, doc) := Seq(
+      "-groups",
+      "-skip-packages", Seq(
+        "org.apache.spark.api.python",
+        "org.apache.spark.network",
+        "org.apache.spark.deploy",
+        "org.apache.spark.util.collection"
+      ).mkString(":"),
+      "-doc-title", "Spark " + version.value.replaceAll("-SNAPSHOT", "") + " ScalaDoc"
+    ) ++ {
+      // Do not attempt to scaladoc javadoc comments under 2.12 since it can't handle inner classes
+      if (scalaBinaryVersion.value == "2.12") Seq("-no-java-comments") else Seq.empty
+    },
+
     // Implements -Xfatal-warnings, ignoring deprecation warnings.
     // Code snippet taken from https://issues.scala-lang.org/browse/SI-8410.
     compile in Compile := {
@@ -828,18 +843,7 @@ object TestSettings {
       }
       Seq.empty[File]
     }).value,
-    concurrentRestrictions in Global += Tags.limit(Tags.Test, 1),
-    // Remove certain packages from Scaladoc
-    scalacOptions in (Compile, doc) := Seq(
-      "-groups",
-      "-skip-packages", Seq(
-        "org.apache.spark.api.python",
-        "org.apache.spark.network",
-        "org.apache.spark.deploy",
-        "org.apache.spark.util.collection"
-      ).mkString(":"),
-      "-doc-title", "Spark " + version.value.replaceAll("-SNAPSHOT", "") + " ScalaDoc"
-    )
+    concurrentRestrictions in Global += Tags.limit(Tags.Test, 1)
   )
 
 }