add missing file

compile/inc/FileValueCache.scala

@@ -0,0 +1,49 @@
+package sbt
+package inc
+
+	import java.io.File
+	import java.util.concurrent.ConcurrentHashMap
+
+sealed trait FileValueCache[T]
+{
+	def clear(): Unit
+	def get: File => T
+}
+
+private[this] final class FileValueCache0[T](getStamp: File => Stamp, make: File => T)(implicit equiv: Equiv[Stamp]) extends FileValueCache[T]
+{
+	private[this] val backing = new ConcurrentHashMap[File, FileCache]
+
+	def clear(): Unit = backing.clear()
+	def get = file => {
+		val ifAbsent = new FileCache(file)
+		val cache = backing.putIfAbsent(file, ifAbsent)
+		(if(cache eq null) ifAbsent else cache).get()
+	}
+
+	private[this] final class FileCache(file: File)
+	{
+		private[this] var stampedValue: Option[(Stamp,T)] = None
+		def get(): T = synchronized
+		{
+			val latest = getStamp(file)
+			stampedValue match
+			{
+				case Some( (stamp, value) ) if(equiv.equiv(latest, stamp)) => value
+				case _ => update(latest)
+			}
+		}
+
+		private[this] def update(stamp: Stamp): T =
+		{
+			val value = make(file)
+			stampedValue = Some((stamp, value))
+			value
+		}
+	}
+}
+object FileValueCache
+{
+	def apply[T](f: File => T): FileValueCache[T] = make(Stamp.lastModified)(f)
+	def make[T](stamp: File => Stamp)(f: File => T): FileValueCache[T] = new FileValueCache0[T](stamp, f)
+}