Don't overwrite nio build settings with injected settings

The current injection of the new nio keys will overwrite any definitions
of those keys in a build source. This is undesirable. The fix is to
create a mapping of scoped keys to settings and for each inject setting
key, if there is a previous key, put that definition after the injected
definition so that it can override it.

main/src/main/scala/sbt/nio/Settings.scala

@@ -27,13 +27,26 @@ import scala.collection.immutable.VectorBuilder
 
 private[sbt] object Settings {
   private[sbt] def inject(transformed: Seq[Def.Setting[_]]): Seq[Def.Setting[_]] = {
-    val fileOutputScopes = transformed.collect {
-      case s if s.key.key == fileOutputs.key && s.key.scope.task.toOption.isDefined =>
-        s.key.scope
+    val definedSettings = new java.util.HashMap[Def.ScopedKey[_], VectorBuilder[Def.Setting[_]]]
+    val fileOutputScopes = transformed.flatMap { s =>
+      val list = new VectorBuilder[Def.Setting[_]]
+      definedSettings.putIfAbsent(s.key, list) match {
+        case null => list += s
+        case l    => l += s
+      }
+      if (s.key.key == fileOutputs.key && s.key.scope.task.toOption.isDefined) Some(s.key.scope)
+      else None
     }.toSet
-    transformed.flatMap {
-      case s if s.key.key == fileInputs.key => inputPathSettings(s)
-      case s                                => s :: maybeAddOutputsAndFileStamps(s, fileOutputScopes)
+    transformed.flatMap { s =>
+      val inject =
+        if (s.key.key == fileInputs.key) inputPathSettings(s)
+        else maybeAddOutputsAndFileStamps(s, fileOutputScopes)
+      s +: inject.flatMap { setting =>
+        (definedSettings.get(setting.key) match {
+          case null => Vector(setting)
+          case set  => setting +: set.result()
+        }): Seq[Def.Setting[_]]
+      }
     }
   }
 
@@ -126,7 +139,7 @@ private[sbt] object Settings {
   private[sbt] def inputPathSettings(setting: Def.Setting[_]): Seq[Def.Setting[_]] = {
     val scopedKey = setting.key
     val scope = scopedKey.scope
-    setting :: (Keys.allInputPathsAndAttributes in scope := {
+    (Keys.allInputPathsAndAttributes in scope := {
       val view = (fileTreeView in scope).value
       val inputs = (fileInputs in scope).value
       val stamper = (inputFileStamper in scope).value

sbt/src/sbt-test/nio/code-formatter/build.sbt

@@ -14,7 +14,7 @@ val compileAndCheckNoClassFileUpdates = taskKey[Unit]("Checks that there are no
 compileAndCheckNoClassFileUpdates := {
   val current = (classFiles / outputFileStamps).value.toSet
   val previous = (classFiles / outputFileStamps).previous.getOrElse(Nil).toSet
-  assert(current == previous)
+  assert(current == previous, s"$current did not equal $previous")
 }
 
 val checkLastModified = inputKey[Unit]("Check the last modified time for a file")
@@ -25,6 +25,7 @@ checkLastModified := {
     case (file, (negate, expectedLastModified)) =>
       val sourceFile = baseDirectory.value / "src" / "main" / "scala" / file
       val lastModified = IO.getModifiedTimeOrZero(sourceFile)
+      println(s"$lastModified $expectedLastModified")
       negate match {
         case Some(_) => assert(lastModified != expectedLastModified)
         case None    => assert(lastModified == expectedLastModified)

sbt/src/sbt-test/nio/overrides/build.sbt

@@ -0,0 +1,24 @@
+import java.nio.file.Path
+
+val foo = taskKey[Path]("foo")
+// Check a direct override
+foo / outputFileStamps := Nil
+foo := baseDirectory.value.toPath / "foo.txt"
+
+TaskKey[Unit]("checkFoo") := assert((foo / outputFileStamps).value == Nil)
+
+val bar = taskKey[Path]("bar")
+// Check an append
+bar / outputFileStamps ++= (baz / outputFileStamps).value
+bar / outputFileStamps ++= (baz / outputFileStamps).value
+bar := baseDirectory.value.toPath / "bar.txt"
+
+val baz = taskKey[Path]("baz")
+baz := baseDirectory.value.toPath / "baz.txt"
+
+TaskKey[Unit]("checkBar") := {
+  val stamps = (bar / outputFileStamps).value
+  assert(stamps.length == 3)
+  val fileNames = stamps.map(_._1.getFileName.toString).toSet
+  assert(fileNames == Set("bar.txt", "baz.txt"))
+}

sbt/src/sbt-test/nio/overrides/foo.txt

@@ -0,0 +1 @@
+foo

sbt/src/sbt-test/nio/overrides/test

@@ -0,0 +1,3 @@
+> checkBar
+
+> checkFoo