[SPARK-5038] Add explicit return type for implicit functions.

As we learned in #3580, not explicitly typing implicit functions can lead to compiler bugs and potentially unexpected runtime behavior.

This is a follow up PR for rest of Spark (outside Spark SQL). The original PR for Spark SQL can be found at https://github.com/apache/spark/pull/3859

Author: Reynold Xin <rxin@databricks.com>

Closes #3860 from rxin/implicit and squashes the following commits:

73702f9 [Reynold Xin] [SPARK-5038] Add explicit return type for implicit functions.

4 files changed, 38 insertions, 37 deletions

diff --git a/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartitionBuilder.scala b/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartitionBuilder.scala
index 409cf60977..906d42328f 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartitionBuilder.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartitionBuilder.scala
@@ -129,44 +129,45 @@ private[impl] case class EdgeWithLocalIds[@specialized ED](
     srcId: VertexId, dstId: VertexId, localSrcId: Int, localDstId: Int, attr: ED)
 
 private[impl] object EdgeWithLocalIds {
-  implicit def lexicographicOrdering[ED] = new Ordering[EdgeWithLocalIds[ED]] {
-    override def compare(a: EdgeWithLocalIds[ED], b: EdgeWithLocalIds[ED]): Int = {
-      if (a.srcId == b.srcId) {
-        if (a.dstId == b.dstId) 0
-        else if (a.dstId < b.dstId) -1
+  implicit def lexicographicOrdering[ED]: Ordering[EdgeWithLocalIds[ED]] =
+    new Ordering[EdgeWithLocalIds[ED]] {
+      override def compare(a: EdgeWithLocalIds[ED], b: EdgeWithLocalIds[ED]): Int = {
+        if (a.srcId == b.srcId) {
+          if (a.dstId == b.dstId) 0
+          else if (a.dstId < b.dstId) -1
+          else 1
+        } else if (a.srcId < b.srcId) -1
         else 1
-      } else if (a.srcId < b.srcId) -1
-      else 1
+      }
     }
-  }
 
-  private[graphx] def edgeArraySortDataFormat[ED]
-      = new SortDataFormat[EdgeWithLocalIds[ED], Array[EdgeWithLocalIds[ED]]] {
-    override def getKey(
-        data: Array[EdgeWithLocalIds[ED]], pos: Int): EdgeWithLocalIds[ED] = {
-      data(pos)
-    }
+  private[graphx] def edgeArraySortDataFormat[ED] = {
+    new SortDataFormat[EdgeWithLocalIds[ED], Array[EdgeWithLocalIds[ED]]] {
+      override def getKey(data: Array[EdgeWithLocalIds[ED]], pos: Int): EdgeWithLocalIds[ED] = {
+        data(pos)
+      }
 
-    override def swap(data: Array[EdgeWithLocalIds[ED]], pos0: Int, pos1: Int): Unit = {
-      val tmp = data(pos0)
-      data(pos0) = data(pos1)
-      data(pos1) = tmp
-    }
+      override def swap(data: Array[EdgeWithLocalIds[ED]], pos0: Int, pos1: Int): Unit = {
+        val tmp = data(pos0)
+        data(pos0) = data(pos1)
+        data(pos1) = tmp
+      }
 
-    override def copyElement(
-        src: Array[EdgeWithLocalIds[ED]], srcPos: Int,
-        dst: Array[EdgeWithLocalIds[ED]], dstPos: Int) {
-      dst(dstPos) = src(srcPos)
-    }
+      override def copyElement(
+          src: Array[EdgeWithLocalIds[ED]], srcPos: Int,
+          dst: Array[EdgeWithLocalIds[ED]], dstPos: Int) {
+        dst(dstPos) = src(srcPos)
+      }
 
-    override def copyRange(
-        src: Array[EdgeWithLocalIds[ED]], srcPos: Int,
-        dst: Array[EdgeWithLocalIds[ED]], dstPos: Int, length: Int) {
-      System.arraycopy(src, srcPos, dst, dstPos, length)
-    }
+      override def copyRange(
+          src: Array[EdgeWithLocalIds[ED]], srcPos: Int,
+          dst: Array[EdgeWithLocalIds[ED]], dstPos: Int, length: Int) {
+        System.arraycopy(src, srcPos, dst, dstPos, length)
+      }
 
-    override def allocate(length: Int): Array[EdgeWithLocalIds[ED]] = {
-      new Array[EdgeWithLocalIds[ED]](length)
+      override def allocate(length: Int): Array[EdgeWithLocalIds[ED]] = {
+        new Array[EdgeWithLocalIds[ED]](length)
+      }
     }
   }
 }
diff --git a/graphx/src/main/scala/org/apache/spark/graphx/impl/ShippableVertexPartition.scala b/graphx/src/main/scala/org/apache/spark/graphx/impl/ShippableVertexPartition.scala
index 5412d72047..aa320088f2 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/impl/ShippableVertexPartition.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/impl/ShippableVertexPartition.scala
@@ -74,8 +74,8 @@ object ShippableVertexPartition {
    * Implicit conversion to allow invoking `VertexPartitionBase` operations directly on a
    * `ShippableVertexPartition`.
    */
-  implicit def shippablePartitionToOps[VD: ClassTag](partition: ShippableVertexPartition[VD]) =
-    new ShippableVertexPartitionOps(partition)
+  implicit def shippablePartitionToOps[VD: ClassTag](partition: ShippableVertexPartition[VD])
+    : ShippableVertexPartitionOps[VD] = new ShippableVertexPartitionOps(partition)
 
   /**
    * Implicit evidence that `ShippableVertexPartition` is a member of the
diff --git a/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartition.scala b/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartition.scala
index 55c7a19d1b..fbe53acfc3 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartition.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartition.scala
@@ -38,8 +38,8 @@ private[graphx] object VertexPartition {
    * Implicit conversion to allow invoking `VertexPartitionBase` operations directly on a
    * `VertexPartition`.
    */
-  implicit def partitionToOps[VD: ClassTag](partition: VertexPartition[VD]) =
-    new VertexPartitionOps(partition)
+  implicit def partitionToOps[VD: ClassTag](partition: VertexPartition[VD])
+    : VertexPartitionOps[VD] = new VertexPartitionOps(partition)
 
   /**
    * Implicit evidence that `VertexPartition` is a member of the `VertexPartitionBaseOpsConstructor`
diff --git a/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartitionBaseOps.scala b/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartitionBaseOps.scala
index b40aa1b417..4fd2548b7f 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartitionBaseOps.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/impl/VertexPartitionBaseOps.scala
@@ -238,8 +238,8 @@ private[graphx] abstract class VertexPartitionBaseOps
    * because these methods return a `Self` and this implicit conversion re-wraps that in a
    * `VertexPartitionBaseOps`. This relies on the context bound on `Self`.
    */
-  private implicit def toOps[VD2: ClassTag](
-      partition: Self[VD2]): VertexPartitionBaseOps[VD2, Self] = {
+  private implicit def toOps[VD2: ClassTag](partition: Self[VD2])
+    : VertexPartitionBaseOps[VD2, Self] = {
     implicitly[VertexPartitionBaseOpsConstructor[Self]].toOps(partition)
   }
 }