[WIP] Full bootstrap: Use Dotty as the reference compiler

Before merging this I'd like to:

- Wait for 0.13.0-RC1 to be released.
- Change the nomenclature used in the build ("non-bootstrapped dotty"
  and "bootstrapped dotty" are not descriptive enough when the reference
  compiler is also dotty).
- Cross-compile the build with 2.12 on the CI so that we don't
  accidentally start using Dotty features in case we need to revert this
  PR (we'll start usin Dotty features eventually, but let's wait
  until we're confident that this setup works well enough).

Author: smarter

project/Build.scala

@@ -30,6 +30,7 @@ import scala.util.Properties.isJavaAtLeast
 
 object Build {
   val scalacVersion = "2.12.8"
+  val referenceVersion = "0.14.0-bin-20190321-bb0a1ed-NIGHTLY"
 
   val baseVersion = "0.14.0"
   val baseSbtDottyVersion = "0.3.2"
@@ -182,21 +183,27 @@ object Build {
   // Settings used for projects compiled only with Java
   lazy val commonJavaSettings = commonSettings ++ Seq(
     version := dottyVersion,
-    scalaVersion := scalacVersion,
+    scalaVersion := referenceVersion,
     // Do not append Scala versions to the generated artifacts
     crossPaths := false,
     // Do not depend on the Scala library
     autoScalaLibrary := false
   )
 
-  // Settings used when compiling dotty using Scala 2
-  lazy val commonNonBootstrappedSettings = commonSettings ++ Seq(
+  // Settings used when compiling dotty (both non-boostrapped and bootstrapped)
+  lazy val commonDottySettings = commonSettings ++ Seq(
+    // Manually set the standard library to use
+    autoScalaLibrary := false
+  )
+
+  // Settings used when compiling dotty with the reference compiler
+  lazy val commonNonBootstrappedSettings = commonDottySettings ++ Seq(
     version := dottyNonBootstrappedVersion,
-    scalaVersion := scalacVersion
+    scalaVersion := referenceVersion
   )
 
   // Settings used when compiling dotty with a non-bootstrapped dotty
-  lazy val commonBootstrappedSettings = commonSettings ++ Seq(
+  lazy val commonBootstrappedSettings = commonDottySettings ++ Seq(
     version := dottyVersion,
     scalaVersion := dottyNonBootstrappedVersion,
 
@@ -219,11 +226,6 @@ object Build {
     // sbt gets very unhappy if two projects use the same target
     target := baseDirectory.value / ".." / "out" / "bootstrap" / name.value,
 
-    // The non-bootstrapped dotty-library is not necessary when bootstrapping dotty
-    autoScalaLibrary := false,
-    // ...but scala-library is
-    libraryDependencies += "org.scala-lang" % "scala-library" % scalacVersion,
-
     // Compile using the non-bootstrapped and non-published dotty
     managedScalaInstance := false,
     scalaInstance := {
@@ -466,7 +468,7 @@ object Build {
           "-Ddotty.tests.classes.dottyLibrary=" + jars("dotty-library"),
           "-Ddotty.tests.classes.dottyCompiler=" + jars("dotty-compiler"),
           "-Ddotty.tests.classes.compilerInterface=" + findLib(attList, "compiler-interface"),
-          "-Ddotty.tests.classes.scalaLibrary=" + findLib(attList, "scala-library"),
+          "-Ddotty.tests.classes.scalaLibrary=" + findLib(attList, "scala-library-"),
           "-Ddotty.tests.classes.scalaAsm=" + findLib(attList, "scala-asm"),
           "-Ddotty.tests.classes.scalaXml=" + findLib(attList, "scala-xml"),
           "-Ddotty.tests.classes.jlineTerminal=" + findLib(attList, "jline-terminal"),
@@ -506,9 +508,6 @@ object Build {
         } else if (scalaLib == "") {
           println("Couldn't find scala-library on classpath, please run using script in bin dir instead")
         } else if (args.contains("-with-compiler")) {
-          if (!isDotty.value) {
-            throw new MessageOnlyException("-with-compiler can only be used with a bootstrapped compiler")
-          }
           val args1 = args.filter(_ != "-with-compiler")
           val asm = findLib(attList, "scala-asm")
           val dottyCompiler = jars("dotty-compiler")
@@ -558,7 +557,7 @@ object Build {
   def runCompilerMain(repl: Boolean = false) = Def.inputTaskDyn {
     val attList = (dependencyClasspath in Runtime).value
     val jars = packageAll.value
-    val scalaLib = findLib(attList, "scala-library")
+    val scalaLib = findLib(attList, "scala-library-")
     val dottyLib = jars("dotty-library")
     val dottyCompiler = jars("dotty-compiler")
     val args0: List[String] = spaceDelimited("<arg>").parsed.toList
@@ -576,12 +575,8 @@ object Build {
 
     var extraClasspath = s"$scalaLib${File.pathSeparator}$dottyLib"
     if ((decompile || printTasty) && !args.contains("-classpath")) extraClasspath += s"${File.pathSeparator}."
-    if (args0.contains("-with-compiler")) {
-      if (!isDotty.value) {
-        throw new MessageOnlyException("-with-compiler can only be used with a bootstrapped compiler")
-      }
+    if (args0.contains("-with-compiler"))
       extraClasspath += s"${File.pathSeparator}$dottyCompiler"
-    }
 
     val fullArgs = main :: insertClasspathInArgs(args, extraClasspath)
 
@@ -642,8 +637,12 @@ object Build {
   // Settings shared between dotty-library and dotty-library-bootstrapped
   lazy val dottyLibrarySettings = Seq(
     libraryDependencies += "org.scala-lang" % "scala-library" % scalacVersion,
+
+    // Needed so that the library sources are visible when `dotty.tools.dotc.core.Definitions#init` is called
+    scalacOptions in Compile ++= Seq("-sourcepath", (scalaSource in Compile).value.getAbsolutePath),
+
     // Add version-specific source directories:
-    // - files in src-non-bootstrapped will only be compiled by the reference compiler (scalac)
+    // - files in src-non-bootstrapped will only be compiled by the reference compiler
     // - files in src-bootstrapped will only be compiled by the current dotty compiler (non-bootstrapped and bootstrapped)
     unmanagedSourceDirectories in Compile += {
       val baseDir = baseDirectory.value
@@ -1149,11 +1148,7 @@ object Build {
       settings(dottyCompilerSettings)
 
     def asDottyLibrary(implicit mode: Mode): Project = project.withCommonSettings.
-      settings(dottyLibrarySettings).
-      bootstrappedSettings(
-        // Needed so that the library sources are visible when `dotty.tools.dotc.core.Definitions#init` is called.
-        scalacOptions in Compile ++= Seq("-sourcepath", (scalaSource in Compile).value.getAbsolutePath)
-      )
+      settings(dottyLibrarySettings)
 
     def asDottyDoc(implicit mode: Mode): Project = project.withCommonSettings.
       dependsOn(dottyCompiler, dottyCompiler % "test->test").