Ensure unique project Id in composite projects

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

@@ -125,6 +125,27 @@ trait CompositeProject {
   def componentProjects: Seq[Project]
 }
 
+object CompositeProject {
+
+  /**
+   *  If two projects with the same id appear in `compositeProjects` and
+   *  in `compositeProjects.map(_.componentProjects)`, the one in
+   *  `compositeProjects` wins.
+   *  This is necessary for backward compatibility with the idiom:
+   *    lazy val foo = crossProject
+   *    lazy val fooJVM = foo.jvm.setting
+   */
+  def uniqueId(compositeProjects: Seq[Project]): Seq[Project] = {
+    for (p <- compositeProjects.flatMap(_.componentProjects)) yield {
+      compositeProjects.find(_.id == p.id) match {
+        case Some(overridingProject) => overridingProject
+        case None                    => p
+      }
+    }
+
+  }
+}
+
 sealed trait Project extends ProjectDefinition[ProjectReference] with CompositeProject {
   def componentProjects: Seq[Project] = this :: Nil
 

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

@@ -18,7 +18,9 @@ import sbt.internal.inc.ReflectUtilities
 trait BuildDef {
   def projectDefinitions(@deprecated("unused", "") baseDirectory: File): Seq[Project] = projects
   def projects: Seq[Project] =
-    ReflectUtilities.allVals[CompositeProject](this).values.toSeq.flatMap(_.componentProjects)
+    CompositeProject.uniqueId(
+      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

@@ -151,11 +151,13 @@ private[sbt] object EvaluateConfigurations {
     val allGeneratedFiles = (definitions.generated ++ dslEntries.flatMap(_.generated))
     loader =>
       {
-        val projects =
-          definitions.values(loader).flatMap {
+        val projects = {
+          val compositeProjects = definitions.values(loader).flatMap {
             case p: CompositeProject => p.componentProjects.map(resolveBase(file.getParentFile, _))
             case _                   => Nil
           }
+          CompositeProject.uniqueId(compositeProjects)
+        }
         val (settingsRaw, manipulationsRaw) =
           dslEntries map (_.result apply loader) partition {
             case DslEntry.ProjectSettings(_) => true

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

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

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

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

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

@@ -4,21 +4,29 @@ import sbt.CompositeProject
 lazy val check = taskKey[Unit]("check")
 
 // Based on sbt-file-projects test
-lazy val cross = new CompositeProject
+lazy val foo = 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 jvm = Project.apply("jvm", new File("jvm"))
+  val js = Project.apply("js", new File("js"))
+  def componentProjects: Seq[Project] = Seq(jvm, js)
 }
 
+lazy val fooJVM = foo.jvm
+
+lazy val bar = project
+  .dependsOn(foo.jvm)
+
 val g = taskKey[Unit]("A task in the root project")
 g := println("Hello.")
 
 
 check := {
-  val verP1 = (version in cross.p1).?.value
-  assert (verP1 == Some("0.1.0-SNAPSHOT"))
+  val verJvm = (version in foo.jvm).?.value
+  assert (verJvm == Some("0.1.0-SNAPSHOT"))
 
-  val verP2 = (version in cross.p2).?.value
-  assert (verP2 == Some("0.1.0-SNAPSHOT"))
+  val verFooJvm = (version in fooJVM).?.value
+  assert (verFooJvm == Some("0.1.0-SNAPSHOT"))
+
+  val verJs = (version in foo.js).?.value
+  assert (verJs == Some("0.1.0-SNAPSHOT"))
 }

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

@@ -3,38 +3,30 @@ import sbt.CompositeProject
 
 lazy val check = taskKey[Unit]("check")
 
-lazy val a = (project in file("a"))
-  .settings(
-    version := "0.2.0"
-  )
-
 // Based on sbt-file-projects test
-lazy val cross = new CompositeProject
+lazy val foo = 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 jvm = Project.apply("jvm", new File("jvm"))
+  val js = Project.apply("js", new File("js"))
+  def componentProjects: Seq[Project] = Seq(jvm, js)
 }
 
-lazy val b = (project in file("b"))
-  .settings(
-    version := "0.2.0"
-  )
+lazy val fooJVM = foo.jvm.settings(version := "0.2.0") // this one needs to win
+
+lazy val bar = project
+  .dependsOn(foo.jvm)
 
 val g = taskKey[Unit]("A task in the root project")
 g := println("Hello.")
 
 
 check := {
-  val verP1 = (version in cross.p1).?.value
-  assert (verP1 == Some("0.2.0"))//Some("0.1.0-SNAPSHOT"))
+  val verJvm = (version in foo.jvm).?.value
+  assert (verJvm == Some("0.2.0"))
 
-  val verP2 = (version in cross.p2).?.value
-  assert (verP2 == Some("0.1.0-SNAPSHOT"))
+  val verFooJvm = (version in fooJVM).?.value
+  assert (verFooJvm == Some("0.2.0"))
 
-  val verA = (version in a).?.value
-  assert (verA == Some("0.2.0"))
-
-  val verB = (version in b).?.value
-  assert (verA == Some("0.2.0"))
+  val verJs = (version in foo.js).?.value
+  assert (verJs == Some("0.1.0-SNAPSHOT"))
 }

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

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

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

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

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

@@ -1,22 +1,30 @@
 > g
 -> root/compile
-> a/compile
-> a/aa
-> b/compile
-> b/h
+> jvm/compile
+> jvm/aa
+> js/compile
+> js/h
 > c/compile
+> bar/compile
 
 $ copy-file changes/basic.sbt basic.sbt
 > reload
 > g
 > root/compile
-> a/compile
-> a/aa
-> b/compile
-> b/h
+> jvm/compile
+> jvm/aa
+> js/compile
+> js/h
 > c/compile
+> bar/compile
 > check
 
 $ copy-file changes/shadow.sbt build.sbt
 > reload
+> jvm/compile
+> jvm/aa
+> js/compile
+> js/h
+> c/compile
+> bar/compile
 > check