Add Scala 2.12.0-M2 as a cross build

 - Disable genjavadoc for this variation for now.
 - Avoid inheritance from DefaultPromise, which is final in 2.12

Author: retronym

.travis.yml

@@ -12,6 +12,7 @@ script:
   - admin/build.sh
 scala:
   - 2.11.6
+  - 2.12.0-M2
 jdk:
   - oraclejdk8
 notifications:

build.sbt

@@ -2,6 +2,8 @@ scalaModuleSettings
 
 scalaVersion := "2.11.6"
 
+crossScalaVersions := List("2.11.6", "2.12.0-M2")
+
 organization := "org.scala-lang.modules"
 
 name := "scala-java8-compat"
@@ -76,8 +78,16 @@ inConfig(JavaDoc)(Defaults.configSettings) ++ (if (disableDocs) Nil else Seq(
   },
   javacOptions in JavaDoc := Seq(),
   artifactName in packageDoc in JavaDoc := ((sv, mod, art) => "" + mod.name + "_" + sv.binary + "-" + mod.revision + "-javadoc.jar"),
-  libraryDependencies += compilerPlugin("com.typesafe.genjavadoc" % "genjavadoc-plugin" % "0.8" cross CrossVersion.full),
-  scalacOptions in Compile <+= target map (t => "-P:genjavadoc:out=" + (t / "java"))
+  libraryDependencies ++= (
+    if (scalaBinaryVersion.value == "2.11")
+      compilerPlugin("com.typesafe.genjavadoc" % "genjavadoc-plugin" % "0.8" cross CrossVersion.full) :: Nil
+    else Nil
+  ),
+  scalacOptions in Compile ++= (
+    if (scalaBinaryVersion.value == "2.11")
+      ("-P:genjavadoc:out=" + (target.value / "java")) :: Nil
+    else Nil
+  )
 ))
 
 initialCommands :=

src/main/scala/scala/compat/java8/FutureConverters.scala

@@ -71,8 +71,14 @@ object FutureConverters {
    * @return a Scala Future that represents the CompletionStage's completion
    */
   def toScala[T](cs: CompletionStage[T]): Future[T] = {
-    val p = new P[T]
-    cs whenComplete p
+    val p = Promise[T]()
+    val bc = new BiConsumer[T, Throwable] {
+      override def accept(v: T, e: Throwable): Unit = {
+        if (e == null) p.complete(Success(v))
+        else p.complete(Failure(e))
+      }
+    }
+    cs whenComplete bc
     p.future
   }
 

src/main/scala/scala/concurrent/java8/FutureConvertersImpl.scala

@@ -71,11 +71,4 @@ object FuturesConvertersImpl {
 
     override def toString: String = super[CompletableFuture].toString
   }
-
-  class P[T] extends impl.Promise.DefaultPromise[T] with BiConsumer[T, Throwable] {
-    override def accept(v: T, e: Throwable): Unit = {
-      if (e == null) complete(Success(v))
-      else complete(Failure(e))
-    }
-  }
 }