[SPARK-9268] [ML] Removed varargs annotation from Params.setDefault taking multiple params

Removed varargs annotation from Params.setDefault taking multiple params.

Though varargs is technically correct, it often requires that developers do clean assembly, rather than (not clean) assembly, which is a nuisance during development.

CC: mengxr

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #7604 from jkbradley/params-setdefault-varargs and squashes the following commits:

6016dc6 [Joseph K. Bradley] removed varargs annotation from Params.setDefault taking multiple params

mllib/src/main/scala/org/apache/spark/ml/param/params.scala

@@ -476,11 +476,14 @@ trait Params extends Identifiable with Serializable {
   /**
    * Sets default values for a list of params.
    *
+   * Note: Java developers should use the single-parameter [[setDefault()]].
+   *       Annotating this with varargs can cause compilation failures due to a Scala compiler bug.
+   *       See SPARK-9268.
+   *
    * @param paramPairs  a list of param pairs that specify params and their default values to set
    *                    respectively. Make sure that the params are initialized before this method
    *                    gets called.
    */
-  @varargs
   protected final def setDefault(paramPairs: ParamPair[_]*): this.type = {
     paramPairs.foreach { p =>
       setDefault(p.param.asInstanceOf[Param[Any]], p.value)

mllib/src/test/java/org/apache/spark/ml/param/JavaTestParams.java

@@ -96,11 +96,8 @@ public class JavaTestParams extends JavaParams {
       new DoubleArrayParam(this, "myDoubleArrayParam", "this is a double param");
 
     setDefault(myIntParam(), 1);
-    setDefault(myIntParam().w(1));
     setDefault(myDoubleParam(), 0.5);
-    setDefault(myIntParam().w(1), myDoubleParam().w(0.5));
     setDefault(myDoubleArrayParam(), new double[] {1.0, 2.0});
-    setDefault(myDoubleArrayParam().w(new double[] {1.0, 2.0}));
   }
 
   @Override