Initial infrastructure and hello world for the Scala.js back-end.

The Scala.js back-end can be enabled with the `-scalajs`
command-line option. Currently, it adds one phase to the pipeline,
which emits .sjsir files from trees.

A sandbox project `sjsSandbox`, in `sandbox/scalajs/`, can be used
to easily test Scala.js compilation. One can run the `main()`
method of the `hello.world` object with

  > sjsSandbox/run

The back-end only contains the bare mimimum to compile the hello
world application in the sandbox. Anything else will blow up
(for example, primitive method calls). It is a work-in-progress.

2 files changed, 13 insertions, 1 deletions

diff --git a/src/dotty/tools/dotc/Compiler.scala b/src/dotty/tools/dotc/Compiler.scala
index d526903b8..2a3346486 100644
--- a/src/dotty/tools/dotc/Compiler.scala
+++ b/src/dotty/tools/dotc/Compiler.scala
@@ -16,6 +16,7 @@ import core.DenotTransformers.DenotTransformer
 import core.Denotations.SingleDenotation
 
 import dotty.tools.backend.jvm.{LabelDefs, GenBCode}
+import dotty.tools.backend.sjs.GenSJSIR
 
 class Compiler {
 
@@ -83,6 +84,7 @@ class Compiler {
       List(new ExpandPrivate,
            new CollectEntryPoints,
            new LabelDefs),
+      List(new GenSJSIR),
       List(new GenBCode)
     )
 
@@ -101,7 +103,16 @@ class Compiler {
    */
   def rootContext(implicit ctx: Context): Context = {
     ctx.definitions.init(ctx)
-    ctx.setPhasePlan(phases)
+    val actualPhases = if (ctx.settings.scalajs.value) {
+      phases
+    } else {
+      // Remove Scala.js-related phases
+      phases.mapConserve(_.filter {
+        case _: GenSJSIR => false
+        case _ => true
+      }).filter(_.nonEmpty)
+    }
+    ctx.setPhasePlan(actualPhases)
     val rootScope = new MutableScope
     val bootstrap = ctx.fresh
       .setPeriod(Period(nextRunId, FirstPhaseId))
diff --git a/src/dotty/tools/dotc/config/ScalaSettings.scala b/src/dotty/tools/dotc/config/ScalaSettings.scala
index 65bc9ba23..aa264329c 100644
--- a/src/dotty/tools/dotc/config/ScalaSettings.scala
+++ b/src/dotty/tools/dotc/config/ScalaSettings.scala
@@ -29,6 +29,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val target = ChoiceSetting("-target", "target", "Target platform for object files. All JVM 1.5 targets are deprecated.",
     List("jvm-1.5", "jvm-1.5-fjbg", "jvm-1.5-asm", "jvm-1.6", "jvm-1.7", "jvm-1.8", "msil"),
     "jvm-1.8")
+  val scalajs = BooleanSetting("-scalajs", "Compile in Scala.js mode (requires scalajs-library.jar on the classpath).")
   val unchecked = BooleanSetting("-unchecked", "Enable additional warnings where generated code depends on assumptions.")
   val uniqid = BooleanSetting("-uniqid", "Uniquely tag all identifiers in debugging output.")
   val usejavacp = BooleanSetting("-usejavacp", "Utilize the java.class.path in classpath resolution.")