Changes to cross-compile with the 2.13 collections

Author: lrytz

build.sbt

@@ -23,6 +23,16 @@ lazy val xml = crossProject(JSPlatform, JVMPlatform)
       else Some("1.1.0")
     },
 
+    unmanagedSourceDirectories in Compile ++= {
+      (unmanagedSourceDirectories in Compile).value.map { dir =>
+        val sv = scalaVersion.value
+        CrossVersion.partialVersion(sv) match {
+          case Some((2, 13)) if !sv.startsWith("2.13.0-M3") => file(dir.getPath ++ "-2.13") // TODO: remove M3 guard once M4 is out.
+          case _             => file(dir.getPath ++ "-2.11-2.12")
+        }
+      }
+    },
+
     apiMappings ++= Map(
       scalaInstance.value.libraryJar
         -> url(s"http://www.scala-lang.org/api/${scalaVersion.value}/")

shared/src/main/scala-2.11-2.12/scala/xml/ScalaVersionSpecific.scala

@@ -0,0 +1,22 @@
+package scala.xml
+
+import scala.collection.SeqLike
+import scala.collection.generic.CanBuildFrom
+
+object ScalaVersionSpecific {
+  import NodeSeq.Coll
+  type CBF[-From, -A, +C] = CanBuildFrom[From, A, C]
+  object NodeSeqCBF extends CanBuildFrom[Coll, Node, NodeSeq] {
+    def apply(from: Coll) = NodeSeq.newBuilder
+    def apply() = NodeSeq.newBuilder
+  }
+}
+
+trait ScalaVersionSpecificNodeSeq extends SeqLike[Node, NodeSeq] { self: NodeSeq =>
+  /** Creates a list buffer as builder for this class */
+  override protected[this] def newBuilder = NodeSeq.newBuilder
+}
+
+trait ScalaVersionSpecificNodeBuffer { self: NodeBuffer =>
+  override def stringPrefix: String = "NodeBuffer"
+}

shared/src/main/scala-2.13/scala/xml/ScalaVersionSpecific.scala

@@ -0,0 +1,27 @@
+package scala.xml
+
+import scala.collection.immutable.StrictOptimizedSeqOps
+import scala.collection.{SeqOps, immutable, mutable}
+import scala.collection.BuildFrom
+import scala.collection.mutable.Builder
+
+object ScalaVersionSpecific {
+  import NodeSeq.Coll
+  type CBF[-From, -A, +C] = BuildFrom[From, A, C]
+  object NodeSeqCBF extends BuildFrom[Coll, Node, NodeSeq] {
+    def newBuilder(from: Coll): Builder[Node, NodeSeq] = NodeSeq.newBuilder
+    def fromSpecificIterable(from: Coll)(it: Iterable[Node]): NodeSeq = (NodeSeq.newBuilder ++= from).result()
+  }
+}
+
+trait ScalaVersionSpecificNodeSeq
+  extends SeqOps[Node, immutable.Seq, NodeSeq]
+    with StrictOptimizedSeqOps[Node, immutable.Seq, NodeSeq] { self: NodeSeq =>
+  override def fromSpecificIterable(coll: Iterable[Node]): NodeSeq = (NodeSeq.newBuilder ++= coll).result()
+
+  override def newSpecificBuilder(): mutable.Builder[Node, NodeSeq] = NodeSeq.newBuilder
+}
+
+trait ScalaVersionSpecificNodeBuffer { self: NodeBuffer =>
+  override def className: String = "NodeBuffer"
+}

shared/src/main/scala/scala/xml/NodeBuffer.scala

@@ -19,10 +19,7 @@ package xml
  *
  * @author  Burak Emir
  */
-class NodeBuffer extends scala.collection.mutable.ArrayBuffer[Node] {
-
-  override def stringPrefix: String = "NodeBuffer"
-
+class NodeBuffer extends scala.collection.mutable.ArrayBuffer[Node] with ScalaVersionSpecificNodeBuffer {
   /**
    * Append given object to this buffer, returns reference on this
    * `NodeBuffer` for convenience. Some rules apply:

shared/src/main/scala/scala/xml/NodeSeq.scala

@@ -9,9 +9,9 @@
 package scala
 package xml
 
-import scala.collection.{ mutable, immutable, generic, SeqLike, AbstractSeq }
+import scala.collection.{ mutable, immutable, AbstractSeq }
 import mutable.{ Builder, ListBuffer }
-import generic.{ CanBuildFrom }
+import ScalaVersionSpecific.CBF
 import scala.language.implicitConversions
 import scala.collection.Seq
 
@@ -25,12 +25,15 @@ object NodeSeq {
   def fromSeq(s: Seq[Node]): NodeSeq = new NodeSeq {
     def theSeq = s
   }
+
+  // ---
+  // For 2.11 / 2.12 only. Moving the implicit to a parent trait of `object NodeSeq` and keeping it
+  // in ScalaVersionSpecific doesn't work because the implicit becomes less specific, which leads to
+  // ambiguities.
   type Coll = NodeSeq
-  implicit def canBuildFrom: CanBuildFrom[Coll, Node, NodeSeq] =
-    new CanBuildFrom[Coll, Node, NodeSeq] {
-      def apply(from: Coll) = newBuilder
-      def apply() = newBuilder
-    }
+  implicit def canBuildFrom: CBF[Coll, Node, NodeSeq] = ScalaVersionSpecific.NodeSeqCBF
+  // ---
+
   def newBuilder: Builder[Node, NodeSeq] = new ListBuffer[Node] mapResult fromSeq
   implicit def seqToNodeSeq(s: Seq[Node]): NodeSeq = fromSeq(s)
 }
@@ -41,11 +44,7 @@ object NodeSeq {
  *
  *  @author  Burak Emir
  */
-abstract class NodeSeq extends AbstractSeq[Node] with immutable.Seq[Node] with SeqLike[Node, NodeSeq] with Equality with Serializable {
-
-  /** Creates a list buffer as builder for this class */
-  override protected[this] def newBuilder = NodeSeq.newBuilder
-
+abstract class NodeSeq extends AbstractSeq[Node] with immutable.Seq[Node] with ScalaVersionSpecificNodeSeq with Equality with Serializable {
   def theSeq: Seq[Node]
   def length = theSeq.length
   override def iterator = theSeq.iterator