Make the dotty-bridge sbt project a subproject of dotty

Note that the dotty-bridge tests will not be run automatically by `test`
which is short for `dotty/test`, to run the dotty-bridge tests, do in sbt:
> dotty-bridge/test
> dotty-bridge/scripted

Original history: https://github.com/smarter/dotty-bridge/commits/master

4 files changed, 178 insertions, 0 deletions

diff --git a/bridge/src/main/scala/xsbt/CompilerClassLoader.scala b/bridge/src/main/scala/xsbt/CompilerClassLoader.scala
new file mode 100644
index 000000000..3cb3f344f
--- /dev/null
+++ b/bridge/src/main/scala/xsbt/CompilerClassLoader.scala
@@ -0,0 +1,90 @@
+package xsbt
+
+import java.net.{URL, URLClassLoader}
+
+/**  A classloader to run the compiler
+ *
+ *   A CompilerClassLoader is constructed from a list of `urls` that need to be on
+ *   the classpath to run the compiler and the classloader used by sbt.
+ *
+ *   To understand why a custom classloader is needed for the compiler, let us
+ *   describe some alternatives that wouldn't work.
+ *   - `new URLClassLoader(urls)`:
+ *     The compiler contains sbt phases that callback to sbt using the `xsbti.*`
+ *     interfaces. If `urls` does not contain the sbt interfaces we'll get a
+ *     `ClassNotFoundException` in the compiler when we try to use them, if
+ *     `urls` does contain the interfaces we'll get a `ClassCastException` or a
+ *     `LinkageError` because if the same class is loaded by two different
+ *     classloaders, they are considered distinct by the JVM.
+ *    - `new URLClassLoader(urls, sbtLoader)`:
+ *      Because of the JVM delegation model, this means that we will only load
+ *      a class from `urls` if it's not present in the parent `sbtLoader`, but
+ *      sbt uses its own version of the scala compiler and scala library which
+ *      is not the one we need to run the compiler.
+ *
+ *  Our solution is to implement a subclass of URLClassLoader with no parent, instead
+ *  we override `loadClass` to load the `xsbti.*` interfaces from `sbtLoader`.
+ */
+class CompilerClassLoader(urls: Array[URL], sbtLoader: ClassLoader)
+    extends URLClassLoader(urls, null) {
+  override def loadClass(className: String, resolve: Boolean): Class[_] =
+    if (className.startsWith("xsbti.")) {
+      // We can't use the loadClass overload with two arguments because it's
+      // protected, but we can do the same by hand (the classloader instance
+      // from which we call resolveClass does not matter).
+      val c = sbtLoader.loadClass(className)
+      if (resolve)
+        resolveClass(c)
+      c
+    } else {
+      super.loadClass(className, resolve)
+    }
+}
+
+object CompilerClassLoader {
+  /** Fix the compiler bridge ClassLoader
+   *
+   *  Soundtrack: https://www.youtube.com/watch?v=imamcajBEJs
+   *
+   *  The classloader that we get from sbt looks like:
+   *
+   *    URLClassLoader(bridgeURLs,
+   *      DualLoader(scalaLoader, notXsbtiFilter, sbtLoader, xsbtiFilter))
+   *
+   *  DualLoader will load the `xsbti.*` interfaces using `sbtLoader` and
+   *  everything else with `scalaLoader`. Once we have loaded the dotty Main
+   *  class using `scalaLoader`, subsequent classes in the dotty compiler will
+   *  also be loaded by `scalaLoader` and _not_ by the DualLoader. But the sbt
+   *  compiler phases are part of dotty and still need access to the `xsbti.*`
+   *  interfaces in `sbtLoader`, therefore DualLoader does not work for us
+   *  (this issue is not present with scalac because the sbt phases are
+   *  currently defined in the compiler bridge itself, not in scalac).
+   *
+   *  CompilerClassLoader is a replacement for DualLoader. Until we can fix
+   *  this in sbt proper, we need to use reflection to construct our own
+   *  fixed classloader:
+   *
+   *    URLClassLoader(bridgeURLs,
+   *      CompilerClassLoader(scalaLoader.getURLs, sbtLoader))
+   *
+   *  @param bridgeLoader  The classloader that sbt uses to load the compiler bridge
+   *  @return A fixed classloader that works with dotty
+   */
+  def fixBridgeLoader(bridgeLoader: ClassLoader) = bridgeLoader match {
+    case bridgeLoader: URLClassLoader =>
+      val dualLoader = bridgeLoader.getParent
+      val dualLoaderClass = dualLoader.getClass
+
+      // DualLoader#parentA and DualLoader#parentB are private
+      val parentAField = dualLoaderClass.getDeclaredField("parentA")
+      parentAField.setAccessible(true)
+      val parentBField = dualLoaderClass.getDeclaredField("parentB")
+      parentBField.setAccessible(true)
+      val scalaLoader = parentAField.get(dualLoader).asInstanceOf[URLClassLoader]
+      val sbtLoader = parentBField.get(dualLoader).asInstanceOf[URLClassLoader]
+
+      val bridgeURLs = bridgeLoader.getURLs
+      new URLClassLoader(bridgeURLs,
+        new CompilerClassLoader(scalaLoader.getURLs, sbtLoader))
+  }
+}
diff --git a/bridge/src/main/scala/xsbt/CompilerInterface.scala b/bridge/src/main/scala/xsbt/CompilerInterface.scala
new file mode 100644
index 000000000..ee272b8b1
--- /dev/null
+++ b/bridge/src/main/scala/xsbt/CompilerInterface.scala
@@ -0,0 +1,70 @@
+/* sbt -- Simple Build Tool
+ * Copyright 2008, 2009 Mark Harrah
+ */
+package xsbt
+
+import xsbti.{ AnalysisCallback, Logger, Problem, Reporter, Severity, DependencyContext }
+import xsbti.api.SourceAPI
+import xsbti.compile._
+import Log.debug
+import java.io.File
+
+import dotty.tools.dotc.core.Contexts.ContextBase
+import dotty.tools.dotc.{ Main => DottyMain }
+import dotty.tools.dotc.interfaces._
+
+import java.net.URLClassLoader
+
+final class CompilerInterface {
+  def newCompiler(options: Array[String], output: Output, initialLog: Logger,
+                  initialDelegate: Reporter, resident: Boolean): CachedCompiler = {
+    // The classloader that sbt uses to load the compiler bridge is broken
+    // (see CompilerClassLoader#fixBridgeLoader for details). To workaround
+    // this we construct our own ClassLoader and then run the following code
+    // with it:
+    //   new CachedCompilerImpl(options, output, resident)
+
+    val bridgeLoader = getClass.getClassLoader
+    val fixedLoader = CompilerClassLoader.fixBridgeLoader(bridgeLoader)
+    val cciClass = fixedLoader.loadClass("xsbt.CachedCompilerImpl")
+    cciClass.getConstructors.head
+      .newInstance(options, output, resident: java.lang.Boolean)
+      .asInstanceOf[CachedCompiler]
+  }
+
+  def run(sources: Array[File], changes: DependencyChanges, callback: AnalysisCallback, log: Logger,
+          delegate: Reporter, progress: CompileProgress, cached: CachedCompiler): Unit =
+    cached.run(sources, changes, callback, log, delegate, progress)
+}
+
+class CachedCompilerImpl(args: Array[String], output: Output, resident: Boolean) extends CachedCompiler {
+  val outputArgs =
+    output match {
+      case multi: MultipleOutput =>
+        ???
+      case single: SingleOutput =>
+        List("-d", single.outputDirectory.getAbsolutePath.toString)
+    }
+
+  def commandArguments(sources: Array[File]): Array[String] =
+    (outputArgs ++ args.toList ++ sources.map(_.getAbsolutePath).sortWith(_ < _)).toArray[String]
+
+  def run(sources: Array[File], changes: DependencyChanges, callback: AnalysisCallback, log: Logger, delegate: Reporter, progress: CompileProgress): Unit = synchronized {
+    run(sources.toList, changes, callback, log, progress)
+  }
+  private[this] def run(sources: List[File], changes: DependencyChanges, callback: AnalysisCallback, log: Logger, compileProgress: CompileProgress): Unit = {
+    debug(log, args.mkString("Calling Dotty compiler with arguments  (CompilerInterface):\n\t", "\n\t", ""))
+    val ctx = (new ContextBase).initialCtx.fresh
+      .setSbtCallback(callback)
+    val cl = getClass.getClassLoader.asInstanceOf[URLClassLoader]
+
+    val reporter = DottyMain.process(commandArguments(sources.toArray), ctx)
+    if (reporter.hasErrors) {
+      throw new InterfaceCompileFailed(args, Array())
+    }
+  }
+}
+
+class InterfaceCompileFailed(override val arguments: Array[String], override val problems: Array[Problem]) extends xsbti.CompileFailed {
+  override val toString = "Compilation failed"
+}
diff --git a/bridge/src/main/scala/xsbt/Log.scala b/bridge/src/main/scala/xsbt/Log.scala
new file mode 100644
index 000000000..e514d7abb
--- /dev/null
+++ b/bridge/src/main/scala/xsbt/Log.scala
@@ -0,0 +1,10 @@
+/* sbt -- Simple Build Tool
+ * Copyright 2008, 2009 Mark Harrah
+ */
+package xsbt
+
+object Log {
+  def debug(log: xsbti.Logger, msg: => String) = log.debug(Message(msg))
+  def settingsError(log: xsbti.Logger): String => Unit =
+    s => log.error(Message(s))
+}
diff --git a/bridge/src/main/scala/xsbt/Message.scala b/bridge/src/main/scala/xsbt/Message.scala
new file mode 100644
index 000000000..48f24f533
--- /dev/null
+++ b/bridge/src/main/scala/xsbt/Message.scala
@@ -0,0 +1,8 @@
+/* sbt -- Simple Build Tool
+ * Copyright 2008, 2009 Mark Harrah
+ */
+package xsbt
+
+object Message {
+  def apply[T](s: => T) = new xsbti.F0[T] { def apply() = s }
+}