Fix publishing akka-stream_2.12 with jdk8 and jdk9 classes (#25341)

* Fix publishing akka-stream_2.12 with jdk8 and jdk9 classes

* Only build jdk9 classes on jdk9+

* Avoid -release on jdk8

project/AkkaBuild.scala

@@ -97,7 +97,7 @@ object AkkaBuild {
       // methods not found in jdk8. To test whether this has the desired effect, compile akka-remote and check the
       // invocation of 'ByteBuffer.clear()' in EnvelopeBuffer.class with 'javap -c': it should refer to
       // "java/nio/ByteBuffer.clear:()Ljava/nio/Buffer" and not "java/nio/ByteBuffer.clear:()Ljava/nio/ByteBuffer":
-      scalacOptions in Compile ++= (if (scalaBinaryVersion.value == "2.11") Seq("-target:jvm-1.8", "-javabootclasspath", CrossJava.Keys.fullJavaHomes.value("8") + "/jre/lib/rt.jar") else Seq("-release", "8")),
+      scalacOptions in Compile ++= (if (scalaBinaryVersion.value == "2.11" || System.getProperty("java.version").startsWith("1.")) Seq("-target:jvm-1.8", "-javabootclasspath", CrossJava.Keys.fullJavaHomes.value("8") + "/jre/lib/rt.jar") else Seq("-release", "8")),
       scalacOptions in Compile ++= (if (allWarnings) Seq("-deprecation") else Nil),
       scalacOptions in Test := (scalacOptions in Test).value.filterNot(opt ⇒
         opt == "-Xlog-reflective-calls" || opt.contains("genjavadoc")),

project/Jdk9.scala

@@ -11,19 +11,31 @@ object Jdk9 extends AutoPlugin {
 
   lazy val CompileJdk9 = config("CompileJdk9").extend(Compile)
 
+  def notOnScala211[T](scalaBinaryVersion: String, values: Seq[T]): Seq[T] = scalaBinaryVersion match {
+    case "2.11" => Seq()
+    case _ => values
+  }
+
+  def notOnJdk8[T](values: Seq[T]): Seq[T] =
+    if (System.getProperty("java.version").startsWith("1.")) Seq()
+    else values
+
   val compileJdk9Settings = Seq(
     // following the scala-2.12, scala-sbt-1.0, ... convention
-    unmanagedSourceDirectories := Seq(
+    unmanagedSourceDirectories := notOnJdk8(notOnScala211(scalaBinaryVersion.value, Seq(
       (Compile / sourceDirectory).value / "scala-jdk-9",
       (Compile / sourceDirectory).value / "java-jdk-9"
-    ),
-    scalacOptions := AkkaBuild.DefaultScalacOptions ++ Seq("-release", "9"),
-    javacOptions := AkkaBuild.DefaultJavacOptions ++ Seq("--release", "9")
+    ))),
+    scalacOptions := AkkaBuild.DefaultScalacOptions ++ notOnJdk8(notOnScala211(scalaBinaryVersion.value, Seq("-release", "9"))),
+    javacOptions := AkkaBuild.DefaultJavacOptions ++ notOnJdk8(notOnScala211(scalaBinaryVersion.value, Seq("--release", "9")))
   )
 
   val compileSettings = Seq(
-    Compile / packageBin / mappings ++=
-      (CompileJdk9 / products).value.flatMap(Path.allSubpaths)
+    // It might have been more 'neat' to add the jdk9 products to the jar via packageBin/mappings, but that doesn't work with the OSGi plugin,
+    // so we add them to the fullClasspath instead.
+    //    Compile / packageBin / mappings
+    //      ++= (CompileJdk9 / products).value.flatMap(Path.allSubpaths),
+    Compile / fullClasspath ++= (CompileJdk9 / exportedProducts).value
   )
 
   override def trigger = noTrigger

project/OSGi.scala

@@ -16,7 +16,7 @@ object OSGi {
   // in the .../bundles directory which makes testing locally published artifacts
   // a pain. Create bundles but publish them to the normal .../jars directory.
   def osgiSettings = defaultOsgiSettings ++ Seq(
-    packagedArtifact in (Compile, packageBin) := ((artifact in (Compile, packageBin)).value, OsgiKeys.bundle.value),
+    Compile / packageBin := OsgiKeys.bundle.value,
     // This will fail the build instead of accidentally removing classes from the resulting artifact.
     // Each package contained in a project MUST be known to be private or exported, if it's undecided we MUST resolve this
     OsgiKeys.failOnUndecidedPackage := true,