Add JarArchive as a new kind of output directory

Author: allanrenucci

compiler/src/dotty/tools/backend/jvm/GenBCode.scala

@@ -49,18 +49,16 @@ class GenBCode extends Phase {
     superCallsMap.put(sym, old + calls)
   }
 
-  private[this] var jarFS: JarFS = _
-
-  def outputDir(implicit ctx: Context): AbstractFile = {
-    val path = Directory(ctx.settings.outputDir.value)
-    if (path.extension == "jar") {
-      if (jarFS == null) {
-        path.delete()
-        jarFS = JarFS.create(path)
-      }
-      jarFS.getRoot()
+  private[this] var myOutput: AbstractFile = _
+
+  protected def outputDir(implicit ctx: Context): AbstractFile = {
+    if (myOutput eq null) {
+      val path = Directory(ctx.settings.outputDir.value)
+      myOutput =
+        if (path.extension == "jar") JarArchive.create(path)
+        else new PlainDirectory(path)
     }
-    else new PlainDirectory(path)
+    myOutput
   }
 
   def run(implicit ctx: Context): Unit = {
@@ -71,9 +69,10 @@ class GenBCode extends Phase {
 
   override def runOn(units: List[CompilationUnit])(implicit ctx: Context) = {
     try super.runOn(units)
-    finally if (jarFS ne null) {
-      jarFS.close()
-      jarFS = null
+    finally myOutput match {
+      case jar: JarArchive => 
+        jar.close()
+      case _ =>
     }
   }
 }

compiler/src/dotty/tools/io/JarArchive.scala

@@ -0,0 +1,31 @@
+package dotty.tools.io
+
+import java.nio.file.{Files, FileSystem, FileSystems}
+
+import scala.collection.JavaConverters._
+
+/**
+ * This class implements an [[AbstractFile]] backed by a jar
+ * that be can used as the compiler's output directory.
+ */
+class JarArchive private (root: Directory) extends PlainDirectory(root) {
+  def close() = jpath.getFileSystem().close()
+}
+
+object JarArchive {
+  /** Create a new jar file. Overwrite if file already exists */
+  def create(path: Path): JarArchive = {
+    require(path.extension == "jar")
+
+    path.delete()
+
+    // creating a new zip file system by using the JAR URL syntax:
+    // https://docs.oracle.com/javase/7/docs/technotes/guides/io/fsp/zipfilesystemprovider.html
+    val env = Map("create" -> "true").asJava
+    val uri = java.net.URI.create("jar:file:" + path.toAbsolute.path)
+    val fs = FileSystems.newFileSystem(uri, env)
+
+    val root = fs.getRootDirectories().iterator.next()
+    new JarArchive(Directory(root))
+  }
+}