Intial implementation of CompositeProject

main/src/main/scala/sbt/Project.scala

@@ -119,7 +119,13 @@ sealed trait ProjectDefinition[PR <: ProjectReference] {
     if (ts.isEmpty) Nil else s"$label: $ts" :: Nil
 }
 
-sealed trait Project extends ProjectDefinition[ProjectReference] {
+trait CompositeProject {
+  def componentProjects: Seq[Project]
+}
+
+sealed trait Project extends ProjectDefinition[ProjectReference] with CompositeProject {
+  def componentProjects: Seq[Project] = this :: Nil
+
   private[sbt] def copy(
       id: String = id,
       base: File = base,

main/src/main/scala/sbt/internal/BuildDef.scala

@@ -17,7 +17,8 @@ import sbt.internal.inc.ReflectUtilities
 
 trait BuildDef {
   def projectDefinitions(baseDirectory: File): Seq[Project] = projects
-  def projects: Seq[Project] = ReflectUtilities.allVals[Project](this).values.toSeq
+  def projects: Seq[Project] =
+    ReflectUtilities.allVals[CompositeProject](this).values.toSeq.flatMap(_.componentProjects)
   // TODO: Should we grab the build core settings here or in a plugin?
   def settings: Seq[Setting[_]] = Defaults.buildCore
   def buildLoaders: Seq[BuildLoader.Components] = Nil

main/src/main/scala/sbt/internal/EvaluateConfigurations.scala

@@ -123,10 +123,10 @@ private[sbt] object EvaluateConfigurations {
       // Tracks all the files we generated from evaluating the sbt file.
       val allGeneratedFiles = (definitions.generated ++ dslEntries.flatMap(_.generated))
       loader => {
-        val projects =
-          definitions.values(loader).collect {
-            case p: Project => resolveBase(file.getParentFile, p)
-          }
+        val projects = definitions.values(loader).flatMap {
+          case p: CompositeProject => p.componentProjects.map(resolveBase(file.getParentFile, _))
+          case _                   => Nil
+        }
         val (settingsRaw, manipulationsRaw) =
           dslEntries map (_.result apply loader) partition {
             case DslEntry.ProjectSettings(_) => true
@@ -234,7 +234,7 @@ private[sbt] object EvaluateConfigurations {
     }
 
   private[this] def extractedValTypes: Seq[String] =
-    Seq(classOf[Project], classOf[InputKey[_]], classOf[TaskKey[_]], classOf[SettingKey[_]]).map(_.getName)
+    Seq(classOf[CompositeProject], classOf[InputKey[_]], classOf[TaskKey[_]], classOf[SettingKey[_]]).map(_.getName)
 
   private[this] def evaluateDefinitions(eval: Eval, name: String, imports: Seq[(String, Int)], definitions: Seq[(String, LineRange)], file: Option[File]): compiler.EvalDefinitions =
     {

sbt/src/sbt-test/project/sbt-composite-projects/a/A.scala

@@ -0,0 +1 @@
+object A

sbt/src/sbt-test/project/sbt-composite-projects/a/a.sbt

@@ -0,0 +1,2 @@
+val aa = taskKey[Unit]("A task in the 'a' project")
+aa := println("Hello.")

sbt/src/sbt-test/project/sbt-composite-projects/b/build.sbt

@@ -0,0 +1,2 @@
+val h = taskKey[Unit]("A task in project 'b'")
+h := println("Hello.")

sbt/src/sbt-test/project/sbt-composite-projects/build.sbt

@@ -0,0 +1,13 @@
+import sbt.internal.AddSettings
+import sbt.CompositeProject
+
+// Based on sbt-file-projects test
+val cross = new CompositeProject
+{
+  val p1 = Project.apply("a", new File("a"))
+  val p2 = Project.apply("b", new File("b"))
+  def componentProjects: Seq[Project] = Seq(p1, p2)
+}
+
+val g = taskKey[Unit]("A task in the root project")
+g := println("Hello.")

sbt/src/sbt-test/project/sbt-composite-projects/changes/basic.sbt

@@ -0,0 +1 @@
+lazy val root = (project in file("."))

sbt/src/sbt-test/project/sbt-composite-projects/other.sbt

@@ -0,0 +1 @@
+val c = project

sbt/src/sbt-test/project/sbt-composite-projects/test

@@ -0,0 +1,17 @@
+> g
+-> root/compile
+> a/compile
+> a/aa
+> b/compile
+> b/h
+> c/compile
+
+$ copy-file changes/basic.sbt basic.sbt
+> reload
+> g
+> root/compile
+> a/compile
+> a/aa
+> b/compile
+> b/h
+> c/compile