Implement Scala.js support

src/main/scala/sbt/ProjectMatrix.scala

@@ -67,6 +67,10 @@ sealed trait ProjectMatrix extends CompositeProject {
 
   def jvm: ProjectFinder
 
+  def jsPlatform(settings: Setting[_]*): ProjectMatrix
+
+  def js: ProjectFinder
+
   def projectRefs: Seq[ProjectReference]
 }
 
@@ -86,6 +90,8 @@ object ProjectMatrix {
 
   val jvmIdSuffix: String = "JVM"
   val jvmDirectorySuffix: String = "-jvm"
+  val jsIdSuffix: String = "JS"
+  val jsDirectorySuffix: String = "-js"
 
   /** A row in the project matrix, typically representing a platform.
    */
@@ -199,19 +205,26 @@ object ProjectMatrix {
     override def jvmPlatform(settings: Setting[_]*): ProjectMatrix =
       custom(jvmIdSuffix, jvmDirectorySuffix, Nil, { _.settings(settings) })
 
-    override def jvm: ProjectFinder = new ProjectFinder {
+    override def jsPlatform(settings: Setting[_]*): ProjectMatrix =
-      def get: Seq[Project] = projectMatrix.toSeq collect {
+      custom(jsIdSuffix, jsDirectorySuffix, Nil, { _.settings(settings) })
-        case ((r, sv), v) if r.idSuffix == jvmIdSuffix => v
+
-      }
+    override def jvm: ProjectFinder = new SuffixBaseProjectFinder(jvmIdSuffix)
-      def apply(sv: String): Project =
+
-        (projectMatrix.toSeq collect {
+    override def js: ProjectFinder = new SuffixBaseProjectFinder(jsIdSuffix)
-          case ((r, `sv`), v) if r.idSuffix == jvmIdSuffix => v
-        }).headOption.getOrElse(sys.error(s"$sv was not found"))
-    }
 
     override def projectRefs: Seq[ProjectReference] =
       componentProjects map { case p => (p: ProjectReference) }
 
+    private final class SuffixBaseProjectFinder(idSuffix: String) extends ProjectFinder {
+      def get: Seq[Project] = projectMatrix.toSeq collect {
+        case ((r, sv), v) if r.idSuffix == idSuffix => v
+      }
+      def apply(sv: String): Project =
+        (projectMatrix.toSeq collectFirst {
+          case ((r, `sv`), v) if r.idSuffix == idSuffix => v
+        }).getOrElse(sys.error(s"$sv was not found"))
+    }
+
     override def custom(
         idSuffix: String,
         directorySuffix: String,

src/sbt-test/projectMatrix/js/build.sbt

@@ -0,0 +1,19 @@
+// lazy val root = (project in file("."))
+//   .aggregate(core.projectRefs ++ app.projectRefs: _*)
+//   .settings(
+//   )
+
+lazy val core = (projectMatrix in file("core"))
+  .scalaVersions("2.12.6", "2.11.12")
+  .settings(
+    name := "core"
+  )
+  .jsPlatform()
+
+lazy val app = (projectMatrix in file("app"))
+  .dependsOn(core)
+  .scalaVersions("2.12.6")
+  .settings(
+    name := "app"
+  )
+  .jsPlatform()

src/sbt-test/projectMatrix/js/core/src/main/scala/Core.scala

@@ -0,0 +1,6 @@
+package a
+
+class Core {
+}
+
+object Core extends Core

src/sbt-test/projectMatrix/js/project/plugins.sbt

@@ -0,0 +1,5 @@
+sys.props.get("plugin.version") match {
+  case Some(x) => addSbtPlugin("com.eed3si9n" % "sbt-projectmatrix" % x)
+  case _ => sys.error("""|The system property 'plugin.version' is not defined.
+                         |Specify this property using the scriptedLaunchOpts -D.""".stripMargin)
+}

src/sbt-test/projectMatrix/js/test

@@ -0,0 +1,4 @@
+> compile
+
+$ exists core/target/js-2.12/classes/a/Core.class
+$ exists core/target/js-2.11/classes/a/Core.class