Position generated trees, allowing use under -Yrangepos / IDE

Fixes typelevel#7

build.sbt

@@ -25,6 +25,11 @@ scalacOptions in Test <+= (packageBin in Compile) map {
   pluginJar => "-Xplugin:" + pluginJar
 }
 
+scalacOptions in Test ++= Seq("-Yrangepos")
+
+// Useful for debugging:
+// scalacOptions in Test ++= Seq("-Xprint:typer", "-Xprint-pos")
+
 crossScalaVersions := Seq("2.10.5", "2.11.6", "2.12.0-M1")
 
 seq(bintrayPublishSettings: _*)

src/main/scala/KindProjector.scala

@@ -200,19 +200,19 @@ class KindRewriter(plugin: Plugin, val global: Global)
 
       tree match {
         case Template(parents, self, body) =>
-          Template(parents.map(transform), self, body.map(transform))
+          treeCopy.Template(tree, parents.map(transform), self, body.map(transform))
 
         // Lambda[A => Either[A, Int]] case.
         case AppliedTypeTree(Ident(TypeLambda1), AppliedTypeTree(_, a :: as) :: Nil) =>
-          handleLambda(a, as)
+          atPos(tree.pos.makeTransparent)(handleLambda(a, as))
 
         // λ[A => Either[A, Int]] case.
         case AppliedTypeTree(Ident(TypeLambda2), AppliedTypeTree(_, a :: as) :: Nil) =>
-          handleLambda(a, as)
+          atPos(tree.pos.makeTransparent)(handleLambda(a, as)) 
 
         // Either[?, Int] case (if no ? present this is a noop)
         case AppliedTypeTree(t, as) =>
-          handlePlaceholders(t, as)
+          atPos(tree.pos.makeTransparent)(handlePlaceholders(t, as))
 
         // Otherwise, carry on as normal.
         case _ =>