Replace sealed traits by abstract classes in order to generate less byte code

cache/src/main/scala/coursier/Cache.scala

@@ -571,31 +571,29 @@ object Cache {
 
 }
 
-sealed trait FileError extends Product with Serializable {
-  def message: String
-}
+sealed abstract class FileError(val message: String) extends Product with Serializable
 
 object FileError {
 
-  case class DownloadError(message0: String) extends FileError {
-    def message = s"Download error: $message0"
-  }
-  case class NotFound(file: String) extends FileError {
-    def message = s"Not found: $file"
-  }
-  case class ChecksumNotFound(sumType: String, file: String) extends FileError {
-    def message = s"$sumType checksum not found: $file"
-  }
-  case class WrongChecksum(sumType: String, got: String, expected: String, file: String, sumFile: String) extends FileError {
-    def message = s"$sumType checksum validation failed: $file"
-  }
+  final case class DownloadError(reason: String) extends FileError(s"Download error: $reason")
 
-  sealed trait Recoverable extends FileError
-  case class Locked(file: File) extends Recoverable {
-    def message = s"Locked: $file"
-  }
-  case class ConcurrentDownload(url: String) extends Recoverable {
-    def message = s"Concurrent download: $url"
-  }
+  final case class NotFound(file: String) extends FileError(s"Not found: $file")
+
+  final case class ChecksumNotFound(
+    sumType: String,
+    file: String
+  ) extends FileError(s"$sumType checksum not found: $file")
+
+  final case class WrongChecksum(
+    sumType: String,
+    got: String,
+    expected: String,
+    file: String,
+    sumFile: String
+  ) extends FileError(s"$sumType checksum validation failed: $file")
+
+  sealed abstract class Recoverable(message: String) extends FileError(message)
+  final case class Locked(file: File) extends Recoverable(s"Locked: $file")
+  final case class ConcurrentDownload(url: String) extends Recoverable(s"Concurrent download: $url")
 
 }

cache/src/main/scala/coursier/CachePolicy.scala

@@ -1,6 +1,6 @@
 package coursier
 
-sealed trait CachePolicy extends Product with Serializable
+sealed abstract class CachePolicy extends Product with Serializable
 
 object CachePolicy {
   case object LocalOnly extends CachePolicy

cli/src/main/scala-2.11/coursier/cli/Coursier.scala

@@ -62,7 +62,7 @@ case class CacheOptions(
     cache: String = Cache.defaultBase.toString
 )
 
-sealed trait CoursierCommand extends Command
+sealed abstract class CoursierCommand extends Command
 
 case class Resolve(
   @Recurse

core/shared/src/main/scala/coursier/core/ResolutionProcess.scala

@@ -5,7 +5,7 @@ import scalaz._
 import scala.annotation.tailrec
 
 
-sealed trait ResolutionProcess {
+sealed abstract class ResolutionProcess {
   def run[F[_]](
     fetch: Fetch.Metadata[F],
     maxIterations: Int = 50

core/shared/src/main/scala/coursier/core/Version.scala

@@ -20,7 +20,7 @@ case class Version(repr: String) extends Ordered[Version] {
 
 object Version {
 
-  sealed trait Item extends Ordered[Item] {
+  sealed abstract class Item extends Ordered[Item] {
     def compare(other: Item): Int =
       (this, other) match {
         case (Number(a), Number(b)) => a.compare(b)
@@ -43,7 +43,7 @@ object Version {
     def compareToEmpty: Int = 1
   }
 
-  sealed trait Numeric extends Item {
+  sealed abstract class Numeric extends Item {
     def repr: String
     def next: Numeric
   }
@@ -93,7 +93,7 @@ object Version {
   val qualifiersMap = qualifiers.map(q => q.value -> q).toMap
 
   object Tokenizer {
-    sealed trait Separator
+    sealed abstract class Separator
     case object Dot extends Separator
     case object Hyphen extends Separator
     case object Underscore extends Separator

core/shared/src/main/scala/coursier/core/Versions.scala

@@ -82,21 +82,23 @@ object VersionInterval {
   val zero = VersionInterval(None, None, fromIncluded = false, toIncluded = false)
 }
 
-sealed trait VersionConstraint {
-  def interval: VersionInterval
-  def repr: String
-}
+sealed abstract class VersionConstraint(
+  val interval: VersionInterval,
+  val repr: String
+)
+
 object VersionConstraint {
   /** Currently treated as minimum... */
-  final case class Preferred(version: Version) extends VersionConstraint {
-    def interval: VersionInterval = VersionInterval(Some(version), Option.empty, fromIncluded = true, toIncluded = false)
-    def repr: String = version.repr
-  }
-  final case class Interval(interval: VersionInterval) extends VersionConstraint {
-    def repr: String = interval.repr
-  }
-  case object None extends VersionConstraint {
-    val interval = VersionInterval.zero
-    def repr: String = "" // Once parsed, "(,)" becomes "" because of this
-  }
+  final case class Preferred(version: Version) extends VersionConstraint(
+    VersionInterval(Some(version), Option.empty, fromIncluded = true, toIncluded = false),
+    version.repr
+  )
+  final case class Interval(interval0: VersionInterval) extends VersionConstraint(
+    interval0,
+    interval0.repr
+  )
+  case object None extends VersionConstraint(
+    VersionInterval.zero,
+    "" // Once parsed, "(,)" becomes "" because of this
+  )
 }