Simplify operations on collections

util/collection/src/main/scala/sbt/Settings.scala

@@ -296,7 +296,7 @@ trait Init[Scope] {
   def definedAtString(settings: Seq[Setting[_]]): String =
     {
       val posDefined = settings.flatMap(_.positionString.toList)
-      if (posDefined.size > 0) {
+      if (posDefined.nonEmpty) {
         val header = if (posDefined.size == settings.size) "defined at:" else
           "some of the defining occurrences:"
         header + (posDefined.distinct mkString ("\n\t", "\n\t", "\n"))

util/complete/src/main/scala/sbt/LineReader.scala

@@ -45,7 +45,7 @@ abstract class JLine extends LineReader {
 
   private[this] def handleMultilinePrompt(prompt: String): String = {
     val lines = """\r?\n""".r.split(prompt)
-    lines.size match {
+    lines.length match {
       case 0 | 1 => prompt
       case _     => reader.print(lines.init.mkString("\n") + "\n"); lines.last;
     }

util/log/src/main/scala/sbt/LoggerWriter.scala

@@ -17,7 +17,7 @@ class LoggerWriter(delegate: Logger, unbufferedLevel: Option[Level.Value], nl: S
   override def close() = flush()
   override def flush(): Unit =
     synchronized {
-      if (buffer.length > 0) {
+      if (buffer.nonEmpty) {
         log(buffer.toString)
         buffer.clear()
       }

util/relation/src/main/scala/sbt/Relation.scala

@@ -123,7 +123,7 @@ private final class MRelation[A, B](fwd: Map[A, Set[B]], rev: Map[B, Set[A]]) ex
   def _1s = fwd.keySet
   def _2s = rev.keySet
 
-  def size = (fwd.valuesIterator map { _.size }).foldLeft(0)(_ + _)
+  def size = (fwd.valuesIterator map (_.size)).sum
 
   def all: Traversable[(A, B)] = fwd.iterator.flatMap { case (a, bs) => bs.iterator.map(b => (a, b)) }.toTraversable