Replace OutputSetting by OutputGroup

`OutputSetting` is like `OutputGroup` by just returns strings instead of
files. I see no reason why `OutputGroup` should not be used instead,
therefore simplifying the Zinc API and allowing users to have access to
files and not mere strings. If they want strings, they always can do
`getAbsolutePath`.

N.B. This is good for machine independence.

internal/compiler-bridge/src/main/scala/xsbt/CallbackGlobal.scala

@@ -18,7 +18,8 @@ sealed abstract class CallbackGlobal(settings: Settings,
 
   lazy val outputDirs: Iterable[File] = {
     output match {
-      case single: SingleOutput  => List(single.outputDirectory)
+      case single: SingleOutput => List(single.outputDirectory)
+      // Use Stream instead of List because Analyzer maps intensively over the directories
       case multi: MultipleOutput => multi.outputGroups.toStream map (_.outputDirectory)
     }
   }

internal/compiler-interface/src/main/contraband/other.json

@@ -35,24 +35,14 @@
         { "name": "hash", "type": "int"    }
       ]
     },
-    {
-      "name": "OutputSetting",
-      "namespace": "xsbti.api",
-      "target": "Java",
-      "type": "record",
-      "fields": [
-        { "name": "sourceDirectory", "type": "String" },
-        { "name": "outputDirectory", "type": "String" }
-      ]
-    },
     {
       "name": "Compilation",
       "namespace": "xsbti.api",
       "target": "Java",
       "type": "record",
       "fields": [
         { "name": "startTime", "type": "long"           },
-        { "name": "outputs",   "type": "OutputSetting*" }
+        { "name": "outputs",   "type": "xsbti.compile.OutputGroup*" }
       ]
     },
     {

internal/compiler-interface/src/main/java/xsbti/compile/MultipleOutput.java

@@ -11,29 +11,6 @@
 
 /** Define the interface for several kind of output directories. */
 public interface MultipleOutput extends Output {
-
-	/** Define the interface of a group of outputs. */
-	interface OutputGroup {
-		/**
-		 * Return the directory where source files are stored for this group.
-         *
-		 * Note that source directories should uniquely identify the group
-		 * for a certain source file.
-         */
-		File sourceDirectory();
-
-		/**
-		 * Return the directory where class files should be generated.
-		 *
-		 * Incremental compilation manages the class files in this directory, so
-		 * don't play with this directory out of the Zinc API. Zinc already takes
-		 * care of deleting classes before every compilation run.
-		 *
-		 * This directory must be exclusively used for one set of sources.
-		 */
-		File outputDirectory();
-	}
-
 	/** Return an array of the existent output groups. */
 	OutputGroup[] outputGroups();
 }

internal/compiler-interface/src/main/java/xsbti/compile/OutputGroup.java

@@ -0,0 +1,25 @@
+package xsbti.compile;
+
+import java.io.File;
+
+/** Define the interface of a group of outputs. */
+public interface OutputGroup {
+    /**
+     * Return the directory where source files are stored for this group.
+     *
+     * Note that source directories should uniquely identify the group
+     * for a certain source file.
+     */
+    public File sourceDirectory();
+
+    /**
+     * Return the directory where class files should be generated.
+     *
+     * Incremental compilation manages the class files in this directory, so
+     * don't play with this directory out of the Zinc API. Zinc already takes
+     * care of deleting classes before every compilation run.
+     *
+     * This directory must be exclusively used for one set of sources.
+     */
+    public File outputDirectory();
+}

internal/zinc-compile-core/src/main/scala/sbt/internal/inc/CompileOutput.scala

@@ -9,7 +9,7 @@ package sbt
 package internal
 package inc
 
-import xsbti.compile.{ Output, SingleOutput, MultipleOutput }
+import xsbti.compile.{ MultipleOutput, Output, OutputGroup, SingleOutput }
 import java.io.File
 
 /**
@@ -39,7 +39,7 @@ object CompileOutput {
   def apply(groups: (File, File)*): Output = new MultipleOutput {
     def outputGroups = groups.toArray map {
       case (src, out) =>
-        new MultipleOutput.OutputGroup {
+        new OutputGroup {
           def sourceDirectory = src
           def outputDirectory = out
           override def toString = s"OutputGroup($src -> $out)"

internal/zinc-core/src/main/scala/sbt/internal/inc/Compile.scala

@@ -13,11 +13,13 @@ import sbt.internal.inc.Analysis.{ LocalProduct, NonLocalProduct }
 import xsbt.api.{ APIUtil, HashAPI, NameHashing }
 import xsbti.api._
 import xsbti.compile.{
+  ClassFileManager,
   CompileAnalysis,
   DependencyChanges,
   IncOptions,
   MultipleOutput,
   Output,
+  OutputGroup,
   SingleOutput
 }
 import xsbti.{ Position, Problem, Severity, UseScope }
@@ -27,7 +29,6 @@ import java.io.File
 import java.util
 
 import xsbti.api.DependencyContext
-import xsbti.compile.ClassFileManager
 import xsbti.compile.analysis.ReadStamps
 
 /**
@@ -133,14 +134,14 @@ private final class AnalysisCallback(
   private[this] val compilation: Compilation = {
     val outputSettings = output match {
       case single: SingleOutput =>
-        Array(new OutputSetting("/", single.outputDirectory.getAbsolutePath))
+        // TODO: Why are we using the root as the file with all the sources? Smell.
+        val rootFile = new java.io.File("/")
+        List(new SimpleOutputGroup(rootFile, single.outputDirectory))
       case multi: MultipleOutput =>
-        multi.outputGroups.map(
-          out =>
-            new OutputSetting(out.sourceDirectory.getAbsolutePath,
-                              out.outputDirectory.getAbsolutePath))
+        multi.outputGroups.toList.map(out =>
+          new SimpleOutputGroup(out.sourceDirectory, out.outputDirectory))
     }
-    new Compilation(System.currentTimeMillis, outputSettings)
+    new Compilation(System.currentTimeMillis, outputSettings.toArray)
   }
 
   override def toString =

internal/zinc-core/src/main/scala/sbt/internal/inc/MiniSetupUtil.scala

@@ -13,12 +13,13 @@ import java.io.File
 
 import xsbti.T2
 import xsbti.compile.{
-  MiniSetup,
   CompileOrder,
-  Output => APIOutput,
-  SingleOutput,
+  MiniOptions,
+  MiniSetup,
   MultipleOutput,
-  MiniOptions
+  OutputGroup,
+  SingleOutput,
+  Output => APIOutput
 }
 
 /**
@@ -87,7 +88,7 @@ object MiniSetupUtil {
   implicit val equivOutput: Equiv[APIOutput] = {
     new Equiv[APIOutput] {
       implicit val outputGroupsOrdering =
-        Ordering.by((og: MultipleOutput.OutputGroup) => og.sourceDirectory)
+        Ordering.by((og: OutputGroup) => og.sourceDirectory)
 
       def equiv(out1: APIOutput, out2: APIOutput) = (out1, out2) match {
         case (m1: MultipleOutput, m2: MultipleOutput) =>

internal/zinc-core/src/main/scala/sbt/internal/inc/OutputGroup.scala

@@ -0,0 +1,7 @@
+package sbt.internal.inc
+
+import java.io.File
+
+import xsbti.compile.OutputGroup
+
+case class SimpleOutputGroup(sourceDirectory: File, outputDirectory: File) extends OutputGroup

internal/zinc-persist/src/main/scala/sbt/internal/inc/TextAnalysisFormat.scala

@@ -369,9 +369,9 @@ class TextAnalysisFormat(override val mappers: AnalysisMappers)
               }
             case `multipleOutputMode` =>
               new MultipleOutput {
-                val outputGroups: Array[MultipleOutput.OutputGroup] = outputAsMap.toArray.map {
+                val outputGroups: Array[OutputGroup] = outputAsMap.toArray.map {
                   case (src: File, out: File) =>
-                    new MultipleOutput.OutputGroup {
+                    new OutputGroup {
                       val sourceDirectory = src
                       val outputDirectory = out
                       override def toString = s"OutputGroup($src -> $out)"