Add Event trait to FileCacheEntry

Rather than exposing the FileEventMonitor.Event types, which are under
active development in the io repo, I am adding a new event trait to
FileCacheEntry. This trait doesn't expose any internal implementation
details.

main-command/src/main/scala/sbt/Watched.scala

@@ -23,7 +23,6 @@ import sbt.internal.util.Types.const
 import sbt.internal.util.complete.{ DefaultParsers, Parser }
 import sbt.internal.util.{ AttributeKey, JLine }
 import sbt.internal.{ FileCacheEntry, LegacyWatched }
-import sbt.io.FileEventMonitor.{ Creation, Deletion, Event, Update }
 import sbt.io._
 import sbt.util.{ Level, Logger }
 
@@ -145,13 +144,14 @@ object Watched {
   private[sbt] def onEvent(
       sources: Seq[WatchSource],
       projectSources: Seq[WatchSource]
-  ): Event[FileCacheEntry] => Watched.Action =
+  ): FileCacheEntry.Event => Watched.Action =
     event =>
-      if (sources.exists(_.accept(event.entry.typedPath.toPath))) Watched.Trigger
+      if (sources.exists(_.accept(event.path))) Watched.Trigger
-      else if (projectSources.exists(_.accept(event.entry.typedPath.toPath))) event match {
+      else if (projectSources.exists(_.accept(event.path))) {
-        case Update(prev, cur, _) if prev.value != cur.value => Reload
+        (event.previous, event.current) match {
-        case _: Creation[_] | _: Deletion[_]                 => Reload
+          case (Some(p), Some(c)) => if (c == p) Watched.Ignore else Watched.Reload
-        case _                                               => Ignore
+          case _                  => Watched.Trigger
+        }
       } else Ignore
 
   private[this] val reRun = if (isWin) "" else " or 'r' to re-run the command"
@@ -333,7 +333,9 @@ object Watched {
           case action @ (CancelWatch | HandleError | Reload | _: Custom) => action
           case Trigger                                                   => Trigger
           case _ =>
-            val events = config.fileEventMonitor.poll(10.millis)
+            val events = config.fileEventMonitor
+              .poll(10.millis)
+              .map(new FileCacheEntry.EventImpl(_))
             val next = events match {
               case Seq()                => (Ignore, None)
               case Seq(head, tail @ _*) =>
@@ -362,14 +364,14 @@ object Watched {
                   if (action == HandleError) "error"
                   else if (action.isInstanceOf[Custom]) action.toString
                   else "cancellation"
-                logger.debug(s"Stopping watch due to $cause from ${event.entry.typedPath.toPath}")
+                logger.debug(s"Stopping watch due to $cause from ${event.path}")
                 action
               case (Trigger, Some(event)) =>
-                logger.debug(s"Triggered by ${event.entry.typedPath.toPath}")
+                logger.debug(s"Triggered by ${event.path}")
-                config.triggeredMessage(event.entry.typedPath.toPath, count).foreach(info)
+                config.triggeredMessage(event.path, count).foreach(info)
                 Trigger
               case (Reload, Some(event)) =>
-                logger.info(s"Reload triggered by ${event.entry.typedPath.toPath}")
+                logger.info(s"Reload triggered by ${event.path}")
                 Reload
               case _ =>
                 nextAction()
@@ -481,7 +483,7 @@ trait WatchConfig {
    * @param event the detected sbt.io.FileEventMonitor.Event.
    * @return the next [[Watched.Action Action]] to run.
    */
-  def onWatchEvent(event: Event[FileCacheEntry]): Watched.Action
+  def onWatchEvent(event: FileCacheEntry.Event): Watched.Action
 
   /**
    * Transforms the state after the watch terminates.
@@ -540,7 +542,7 @@ object WatchConfig {
       fileEventMonitor: FileEventMonitor[FileCacheEntry],
       handleInput: InputStream => Watched.Action,
       preWatch: (Int, Boolean) => Watched.Action,
-      onWatchEvent: Event[FileCacheEntry] => Watched.Action,
+      onWatchEvent: FileCacheEntry.Event => Watched.Action,
       onWatchTerminated: (Watched.Action, String, State) => State,
       triggeredMessage: (Path, Int) => Option[String],
       watchingMessage: Int => Option[String]
@@ -559,7 +561,7 @@ object WatchConfig {
       override def handleInput(inputStream: InputStream): Watched.Action = hi(inputStream)
       override def preWatch(count: Int, lastResult: Boolean): Watched.Action =
         pw(count, lastResult)
-      override def onWatchEvent(event: Event[FileCacheEntry]): Watched.Action = owe(event)
+      override def onWatchEvent(event: FileCacheEntry.Event): Watched.Action = owe(event)
       override def onWatchTerminated(action: Watched.Action, command: String, state: State): State =
         owt(action, command, state)
       override def triggeredMessage(path: Path, count: Int): Option[String] =

main-command/src/main/scala/sbt/internal/FileCacheEntry.scala

@@ -8,10 +8,12 @@
 package sbt
 package internal
 import java.lang
+import java.nio.file.Path
 import java.util.Optional
 
 import sbt.internal.inc.{ EmptyStamp, LastModified, Stamp }
-import sbt.io.TypedPath
+import sbt.io.FileEventMonitor.{ Creation, Deletion, Update }
+import sbt.io.{ FileEventMonitor, TypedPath }
 import xsbti.compile.analysis.{ Stamp => XStamp }
 
 /**
@@ -23,7 +25,33 @@ trait FileCacheEntry {
   def lastModified: Option[Long]
 }
 object FileCacheEntry {
-  def default(typedPath: TypedPath): FileCacheEntry =
+  trait Event {
+    def path: Path
+    def previous: Option[FileCacheEntry]
+    def current: Option[FileCacheEntry]
+  }
+  private[sbt] class EventImpl(event: FileEventMonitor.Event[FileCacheEntry]) extends Event {
+    override def path: Path = event.entry.typedPath.toPath
+    override def previous: Option[FileCacheEntry] = event match {
+      case Deletion(entry, _)     => entry.value.toOption
+      case Update(previous, _, _) => previous.value.toOption
+      case _                      => None
+    }
+    override def current: Option[FileCacheEntry] = event match {
+      case Creation(entry, _)    => entry.value.toOption
+      case Update(_, current, _) => current.value.toOption
+      case _                     => None
+    }
+    override def equals(o: Any): Boolean = o match {
+      case that: Event =>
+        this.path == that.path && this.previous == that.previous && this.current == that.current
+      case _ => false
+    }
+    override def hashCode(): Int =
+      ((path.hashCode * 31) ^ previous.hashCode() * 31) ^ current.hashCode()
+    override def toString: String = s"Event($path, $previous, $current)"
+  }
+  private[sbt] def default(typedPath: TypedPath): FileCacheEntry =
     DelegateFileCacheEntry(Stamped.converter(typedPath))
   private[sbt] implicit class FileCacheEntryOps(val e: FileCacheEntry) extends AnyVal {
     private[sbt] def stamp: XStamp = e match {

main-command/src/test/scala/sbt/WatchedSpec.scala

@@ -15,7 +15,6 @@ import org.scalatest.{ FlatSpec, Matchers }
 import sbt.Watched._
 import sbt.WatchedSpec._
 import sbt.internal.FileCacheEntry
-import sbt.io.FileEventMonitor.Event
 import sbt.io._
 import sbt.io.syntax._
 import sbt.util.Logger
@@ -31,7 +30,7 @@ class WatchedSpec extends FlatSpec with Matchers {
         logger: Logger = NullLogger,
         handleInput: InputStream => Action = _ => Ignore,
         preWatch: (Int, Boolean) => Action = (_, _) => CancelWatch,
-        onWatchEvent: Event[FileCacheEntry] => Action = _ => Ignore,
+        onWatchEvent: FileCacheEntry.Event => Action = _ => Ignore,
         triggeredMessage: (Path, Int) => Option[String] = (_, _) => None,
         watchingMessage: Int => Option[String] = _ => None
     ): WatchConfig = {
@@ -87,7 +86,7 @@ class WatchedSpec extends FlatSpec with Matchers {
     val config = Defaults.config(
       globs = Seq(realDir ** AllPassFilter),
       preWatch = (count, _) => if (count == 2) CancelWatch else Ignore,
-      onWatchEvent = e => if (e.entry.typedPath.toPath == foo) Trigger else Ignore,
+      onWatchEvent = e => if (e.path == foo) Trigger else Ignore,
       triggeredMessage = (tp, _) => { queue += tp; None },
       watchingMessage = _ => { Files.createFile(bar); Thread.sleep(5); Files.createFile(foo); None }
     )

main/src/main/scala/sbt/Keys.scala

@@ -23,7 +23,6 @@ import sbt.internal.io.WatchState
 import sbt.internal.librarymanagement.{ CompatibilityWarningOptions, IvySbt }
 import sbt.internal.server.ServerHandler
 import sbt.internal.util.{ AttributeKey, SourcePosition }
-import sbt.io.FileEventMonitor.Event
 import sbt.io._
 import sbt.librarymanagement.Configurations.CompilerPlugin
 import sbt.librarymanagement.LibraryManagementCodec._
@@ -102,7 +101,7 @@ object Keys {
   val watchConfig = taskKey[WatchConfig]("The configuration for continuous execution.").withRank(BMinusSetting)
   val watchLogger = taskKey[Logger]("A logger that reports watch events.").withRank(DSetting)
   val watchHandleInput = settingKey[InputStream => Watched.Action]("Function that is periodically invoked to determine if the continous build should be stopped or if a build should be triggered. It will usually read from stdin to respond to user commands.").withRank(BMinusSetting)
-  val watchOnEvent = taskKey[Event[FileCacheEntry] => Watched.Action]("Determines how to handle a file event").withRank(BMinusSetting)
+  val watchOnEvent = taskKey[FileCacheEntry.Event => Watched.Action]("Determines how to handle a file event").withRank(BMinusSetting)
   val watchOnTermination = taskKey[(Watched.Action, String, State) => State]("Transforms the input state after the continuous build completes.").withRank(BMinusSetting)
   val watchService = settingKey[() => WatchService]("Service to use to monitor file system changes.").withRank(BMinusSetting)
   val watchProjectSources = taskKey[Seq[Watched.WatchSource]]("Defines the sources for the sbt meta project to watch to trigger a reload.").withRank(CSetting)