turn back syntax classes into traits

core/src/main/scala/sbt/librarymanagement/DependencyBuilders.scala

@@ -8,7 +8,12 @@ import sbt.internal.librarymanagement.StringUtilities.nonEmpty
 /**
  * DependencyBuilders implements the implicits for % and %% DSL.
  */
-abstract class DependencyBuilders {
+trait DependencyBuilders {
+  // See http://www.scala-lang.org/news/2.12.0#traits-compile-to-interfaces
+  // Avoid defining fields (val or var, but a constant is ok – final val without result type)
+  // Avoid calling super
+  // Avoid initializer statements in the body
+
   import DependencyBuilders._
 
   implicit def stringToOrganization(organization: String): Organization = {

core/src/main/scala/sbt/librarymanagement/DependencyFilter.scala

@@ -6,6 +6,11 @@ package sbt.librarymanagement
 import sbt.io.{ AllPassFilter, NameFilter }
 
 trait DependencyFilterExtra {
+  // See http://www.scala-lang.org/news/2.12.0#traits-compile-to-interfaces
+  // Avoid defining fields (val or var, but a constant is ok – final val without result type)
+  // Avoid calling super
+  // Avoid initializer statements in the body
+
   def moduleFilter(
       organization: NameFilter = AllPassFilter,
       name: NameFilter = AllPassFilter,
@@ -15,6 +20,7 @@ trait DependencyFilterExtra {
       def apply(m: ModuleID): Boolean =
         organization.accept(m.organization) && name.accept(m.name) && revision.accept(m.revision)
     }
+
   def artifactFilter(
       name: NameFilter = AllPassFilter,
       `type`: NameFilter = AllPassFilter,
@@ -26,11 +32,13 @@ trait DependencyFilterExtra {
         name.accept(a.name) && `type`.accept(a.`type`) && extension.accept(a.extension) && classifier
           .accept(a.classifier getOrElse "")
     }
+
   def configurationFilter(name: NameFilter = AllPassFilter): ConfigurationFilter =
     new ConfigurationFilter {
       def apply(c: ConfigRef): Boolean = name.accept(c.name)
     }
 }
+
 object DependencyFilter extends DependencyFilterExtra {
   def make(
       configuration: ConfigurationFilter = configurationFilter(),

core/src/main/scala/sbt/librarymanagement/LibraryManagementSyntax.scala

@@ -1,13 +1,28 @@
 package sbt.librarymanagement
 
-abstract class LibraryManagementSyntax extends DependencyBuilders {
-  type ExclusionRule = InclExclRule
-  val ExclusionRule = InclExclRule
-
-  type InclusionRule = InclExclRule
-  val InclusionRule = InclExclRule
+trait LibraryManagementSyntax0 {
+  // See http://www.scala-lang.org/news/2.12.0#traits-compile-to-interfaces
+  // Avoid defining fields (val or var, but a constant is ok – final val without result type)
+  // Avoid calling super
+  // Avoid initializer statements in the body
 
   implicit def richUpdateReport(ur: UpdateReport): RichUpdateReport = new RichUpdateReport(ur)
+}
+
+trait LibraryManagementSyntax
+    extends LibraryManagementSyntax0
+    with DependencyBuilders
+    with DependencyFilterExtra {
+  // See http://www.scala-lang.org/news/2.12.0#traits-compile-to-interfaces
+  // Avoid defining fields (val or var, but a constant is ok – final val without result type)
+  // Avoid calling super
+  // Avoid initializer statements in the body
+
+  type ExclusionRule = InclExclRule
+  final val ExclusionRule = InclExclRule
+
+  type InclusionRule = InclExclRule
+  final val InclusionRule = InclExclRule
 
   import sbt.librarymanagement.{ Configurations => C }
   final val Compile = C.Compile