Use pickler to cache UpdateReport for update task. #1763

build.sbt

@@ -305,7 +305,7 @@ lazy val cacheProj = (project in cachePath).
   settings(baseSettings: _*).
   settings(
     name := "Cache",
-    libraryDependencies ++= Seq(sbinary) ++ scalaXml.value
+    libraryDependencies ++= Seq(sbinary, sbtSerialization) ++ scalaXml.value
   )
 
 // Builds on cache to provide caching for filesystem-related operations

cache/tracking/src/main/scala/sbt/Tracked.scala

@@ -9,6 +9,7 @@ import sbinary.Format
 import scala.reflect.Manifest
 import scala.collection.mutable
 import IO.{ delete, read, write }
+import sbt.serialization._
 
 object Tracked {
   /**
@@ -36,6 +37,25 @@ object Tracked {
       toFile(next)(cacheFile)
       next
     }
+  private[sbt] def lastOuputWithJson[I, O: Pickler: Unpickler](cacheFile: File)(f: (I, Option[O]) => O): I => O = in =>
+    {
+      val previous: Option[O] = fromJsonFile[O](cacheFile)
+      val next = f(in, previous)
+      toJsonFile(next)(cacheFile)
+      next
+    }
+  private[sbt] def fromJsonFile[A: Unpickler](file: File): Option[A] =
+    try {
+      val s = IO.read(file, IO.utf8)
+      fromJsonString[A](s).toOption
+    } catch {
+      case e: Throwable => None
+    }
+  private[sbt] def toJsonFile[A: Pickler](a: A)(file: File): Unit =
+    {
+      val str = toJsonString(a)
+      IO.write(file, str, IO.utf8)
+    }
 
   def inputChanged[I, O](cacheFile: File)(f: (Boolean, I) => O)(implicit ic: InputCache[I]): I => O = in =>
     {
@@ -44,6 +64,18 @@ object Tracked {
       val changed = help.changed(cacheFile, conv)
       val result = f(changed, in)
 
+      if (changed)
+        help.save(cacheFile, conv)
+
+      result
+    }
+  private[sbt] def inputChangedWithJson[I: Pickler: Unpickler, O](cacheFile: File)(f: (Boolean, I) => O): I => O = in =>
+    {
+      val help = new JsonCacheHelp[I]
+      val conv = help.convert(in)
+      val changed = help.changed(cacheFile, conv)
+      val result = f(changed, in)
+
       if (changed)
         help.save(cacheFile, conv)
 
@@ -56,6 +88,18 @@ object Tracked {
       val changed = help.changed(cacheFile, help.convert(initial))
       val result = f(changed, initial)
 
+      if (changed)
+        help.save(cacheFile, help.convert(in()))
+
+      result
+    }
+  private[sbt] def outputChangedWithJson[I: Pickler, O](cacheFile: File)(f: (Boolean, I) => O): (() => I) => O = in =>
+    {
+      val initial = in()
+      val help = new JsonCacheHelp[I]
+      val changed = help.changed(cacheFile, help.convert(initial))
+      val result = f(changed, initial)
+
       if (changed)
         help.save(cacheFile, help.convert(in()))
 
@@ -71,6 +115,16 @@ object Tracked {
         !ic.equiv.equiv(converted, prev)
       } catch { case e: Exception => true }
   }
+  private[sbt] final class JsonCacheHelp[I: Pickler] {
+    def convert(i: I): String = toJsonString(i)
+    def save(cacheFile: File, value: String): Unit =
+      IO.write(cacheFile, value, IO.utf8)
+    def changed(cacheFile: File, converted: String): Boolean =
+      try {
+        val prev = IO.read(cacheFile, IO.utf8)
+        converted != prev
+      } catch { case e: Exception => true }
+  }
 }
 
 trait Tracked {

main/src/main/scala/sbt/Defaults.scala

@@ -1388,13 +1388,13 @@ object Classpaths {
 
       val outCacheFile = cacheFile / "output"
       def skipWork: In => UpdateReport =
-        Tracked.lastOutput[In, UpdateReport](outCacheFile) {
+        Tracked.lastOuputWithJson[In, UpdateReport](outCacheFile) {
           case (_, Some(out)) => out
           case _              => sys.error("Skipping update requested, but update has not previously run successfully.")
         }
       def doWork: In => UpdateReport =
         Tracked.inputChanged(cacheFile / "inputs") { (inChanged: Boolean, in: In) =>
-          val outCache = Tracked.lastOutput[In, UpdateReport](outCacheFile) {
+          val outCache = Tracked.lastOuputWithJson[In, UpdateReport](outCacheFile) {
             case (_, Some(out)) if uptodate(inChanged, out) => out
             case _ => work(in)
           }