Add Scala API completeness Test

This is very naive right now, just checks whether a function of the same
name is available. There are lists and regex patterns of excluded
functions since not all functions in the Java API need to be available
in the Scala API.

flink-scala/src/main/scala/org/apache/flink/api/scala/DataSet.scala

@@ -826,6 +826,21 @@ class DataSet[T: ClassTag](private[flink] val set: JavaDataSet[T]) {
     wrap(result)
   }
 
+  // -------------------------------------------------------------------------------------------
+  //  Custom Operators
+  // -------------------------------------------------------------------------------------------
+
+  // Keep it out until we have an actual use case for this.
+//  /**
+//   * Runs a [[CustomUnaryOperation]] on the data set. Custom operations are typically complex
+//   * operators that are composed of multiple steps.
+//   */
+//  def runOperation[R: ClassTag](operation: CustomUnaryOperation[T, R]): DataSet[R] = {
+//    Validate.notNull(operation, "The custom operator must not be null.")
+//    operation.setInput(this.set)
+//    wrap(operation.createResult)
+//  }
+
   // --------------------------------------------------------------------------------------------
   //  Union
   // --------------------------------------------------------------------------------------------

flink-scala/src/test/scala/org/apache/flink/api/scala/ScalaAPICompletenessTest.scala

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.api.scala
+
+import java.lang.reflect.Method
+
+import org.apache.flink.api.java.operators._
+import org.apache.flink.api.java.{DataSet => JavaDataSet}
+
+import scala.language.existentials
+
+import org.junit.Assert._
+import org.junit.Test
+
+/**
+ * This checks whether the Scala API is up to feature parity with the Java API. Right now is very
+ * simple, it is only checked whether a method with the same name exists.
+ *
+ * When adding excluded methods to the lists you should give a good reason in a comment.
+ *
+ * Note: This is inspired by the JavaAPICompletenessChecker from Spark.
+ */
+class ScalaAPICompletenessTest {
+
+  private def isExcludedByName(method: Method): Boolean = {
+    val name = method.getDeclaringClass.getName + "." + method.getName
+    val excludedNames = Seq(
+      // These are only used internally. Should be internal API but Java doesn't have
+      // private[flink].
+      "org.apache.flink.api.java.DataSet.getExecutionEnvironment",
+      "org.apache.flink.api.java.DataSet.getType",
+      "org.apache.flink.api.java.operators.Operator.getResultType",
+      "org.apache.flink.api.java.operators.Operator.getName",
+      "org.apache.flink.api.java.operators.Grouping.getDataSet",
+      "org.apache.flink.api.java.operators.Grouping.getKeys",
+      "org.apache.flink.api.java.operators.SingleInputOperator.getInput",
+      "org.apache.flink.api.java.operators.SingleInputOperator.getInputType",
+      "org.apache.flink.api.java.operators.TwoInputOperator.getInput1",
+      "org.apache.flink.api.java.operators.TwoInputOperator.getInput2",
+      "org.apache.flink.api.java.operators.TwoInputOperator.getInput1Type",
+      "org.apache.flink.api.java.operators.TwoInputOperator.getInput2Type",
+
+      // This is really just a mapper, which in Scala can easily expressed as a map lambda
+      "org.apache.flink.api.java.DataSet.writeAsFormattedText",
+
+      // Exclude minBy and maxBy for now, since there is some discussion about our aggregator
+      // semantics
+      "org.apache.flink.api.java.DataSet.minBy",
+      "org.apache.flink.api.java.DataSet.maxBy",
+      "org.apache.flink.api.java.operators.UnsortedGrouping.minBy",
+      "org.apache.flink.api.java.operators.UnsortedGrouping.maxBy"
+
+    )
+    val excludedPatterns = Seq(
+      // We don't have project on tuples in the Scala API
+      """^org\.apache\.flink\.api.java.*project""",
+
+      // I don't want to have withParameters in the API since I consider Configuration to be
+      // deprecated. But maybe thats just me ...
+      """^org\.apache\.flink\.api.java.*withParameters""",
+
+      // These are only used internally. Should be internal API but Java doesn't have
+      // private[flink].
+      """^org\.apache\.flink\.api.java.*getBroadcastSets""",
+      """^org\.apache\.flink\.api.java.*setSemanticProperties""",
+      """^org\.apache\.flink\.api.java.*getSemanticProperties""",
+      """^org\.apache\.flink\.api.java.*getParameters""",
+
+      // Commented out for now until we have a use case for this.
+      """^org\.apache\.flink\.api.java.*runOperation""",
+
+      // Object methods
+      """^.*notify""",
+      """^.*wait""",
+      """^.*notifyAll""",
+      """^.*equals""",
+      """^.*toString""",
+      """^.*getClass""",
+      """^.*hashCode"""
+    ).map(_.r)
+    lazy val excludedByPattern =
+      excludedPatterns.map(_.findFirstIn(name)).filter(_.isDefined).nonEmpty
+    name.contains("$") || excludedNames.contains(name) || excludedByPattern
+  }
+
+  private def isExcludedByInterface(method: Method): Boolean = {
+    val excludedInterfaces =
+      Set("org.apache.spark.Logging", "org.apache.hadoop.mapreduce.HadoopMapReduceUtil")
+    def toComparisionKey(method: Method) =
+      (method.getReturnType, method.getName, method.getGenericReturnType)
+    val interfaces = method.getDeclaringClass.getInterfaces.filter { i =>
+      excludedInterfaces.contains(i.getName)
+    }
+    val excludedMethods = interfaces.flatMap(_.getMethods.map(toComparisionKey))
+    excludedMethods.contains(toComparisionKey(method))
+  }
+
+  private def checkMethods(
+      javaClassName: String,
+      scalaClassName: String,
+      javaClass: Class[_],
+      scalaClass: Class[_]) {
+    val javaMethods = javaClass.getMethods
+      .filterNot(_.isAccessible)
+      .filterNot(isExcludedByName)
+      .filterNot(isExcludedByInterface)
+      .map(m => m.getName).toSet
+
+    val scalaMethods = scalaClass.getMethods
+      .filterNot(_.isAccessible)
+      .filterNot(isExcludedByName)
+      .filterNot(isExcludedByInterface)
+      .map(m => m.getName).toSet
+
+    val missingMethods = javaMethods -- scalaMethods
+
+    for (method <- missingMethods) {
+      fail("Method " + method + " from " + javaClass + " is missing from " + scalaClassName + ".")
+    }
+  }
+
+  @Test
+  def testCompleteness(): Unit = {
+    checkMethods("DataSet", "DataSet", classOf[JavaDataSet[_]], classOf[DataSet[_]])
+
+    checkMethods("Operator", "DataSet", classOf[Operator[_, _]], classOf[DataSet[_]])
+
+    checkMethods("UnsortedGrouping", "GroupedDataSet",
+      classOf[UnsortedGrouping[_]], classOf[GroupedDataSet[_]])
+
+    checkMethods("SortedGrouping", "GroupedDataSet",
+      classOf[SortedGrouping[_]], classOf[GroupedDataSet[_]])
+
+    checkMethods("SingleInputOperator", "DataSet",
+      classOf[SingleInputOperator[_, _, _]], classOf[DataSet[_]])
+
+    checkMethods("TwoInputOperator", "DataSet", classOf[TwoInputOperator[_, _, _, _]], classOf[DataSet[_]])
+
+    checkMethods("SingleInputUdfOperator", "DataSet",
+      classOf[SingleInputUdfOperator[_, _, _]], classOf[DataSet[_]])
+
+    checkMethods("TwoInputUdfOperator", "DataSet",
+      classOf[TwoInputUdfOperator[_, _, _, _]], classOf[DataSet[_]])
+  }
+}