Support Java 9 modular runtime images

http://openjdk.java.net/jeps/220 changes the layout of the
JDK to encapsulate the provided libraries with the new module
system.

This commit modifies the compiler's classpath implementation
to scan the new location of these, the `jrt://` virtual filesystem.

This might need to be adjusted once we provide a means for
users to specify the subset of modules that they want to
depend on, but for now reclaims the ground we lost.

```
⚡ (java_use 9-ea; qscala)
Welcome to Scala 2.12.0-20160908-223617-7e4ebda (Java HotSpot(TM) 64-Bit Server VM, Java 9-ea).
Type in expressions for evaluation. Or try :help.

scala> import StackWalker._, java.util.stream._, scala.collection.JavaConverters._
import StackWalker._
import java.util.stream._
import scala.collection.JavaConverters._

scala> (() => StackWalker.getInstance(java.util.EnumSet.of(Option.RETAIN_CLASS_REFERENCE)).walk[Seq[String]]((s: java.util.stream.Stream[StackFrame]) => s.iterator.asScala.take(3).map(_.toString).toList)).apply().mkString("\n")
res0: String =
.$anonfun$res0$1(<console>:21)
.<init>(<console>:21)
.<clinit>(<console>)

scala>
```

I've marked the new class, `NioFile` as `private[scala]` to justify
the forward compatibility whitelist entry.

In principle we could use NioFile more widely rather than `PlainFile`
I tried this out in https://github.com/retronym/scala/commit/b2d0a17a
which passed CI. But to be conservative, I'm not submitting that change
at this point.

1 files changed, 79 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/io/PlainFile.scala b/src/reflect/scala/reflect/io/PlainFile.scala
index eb0940e703..989081ebe0 100644
--- a/src/reflect/scala/reflect/io/PlainFile.scala
+++ b/src/reflect/scala/reflect/io/PlainFile.scala
@@ -40,7 +40,6 @@ class PlainFile(val givenPath: Path) extends AbstractFile {
   override def output = givenPath.toFile.outputStream()
   override def sizeOption = Some(givenPath.length.toInt)
 
-  override def toString = path
   override def hashCode(): Int = fpath.hashCode()
   override def equals(that: Any): Boolean = that match {
     case x: PlainFile => fpath == x.fpath
@@ -91,3 +90,82 @@ class PlainFile(val givenPath: Path) extends AbstractFile {
   def lookupNameUnchecked(name: String, directory: Boolean): AbstractFile =
     new PlainFile(givenPath / name)
 }
+
+private[scala] class PlainNioFile(nioPath: java.nio.file.Path) extends AbstractFile {
+  import java.nio.file._
+
+  assert(nioPath ne null)
+
+  /** Returns the underlying File if any and null otherwise. */
+  override def file: java.io.File = try {
+    nioPath.toFile
+  } catch {
+    case _: UnsupportedOperationException => null
+  }
+
+  override def underlyingSource  = Some(this)
+
+  private val fpath = nioPath.toAbsolutePath.toString
+
+  /** Returns the name of this abstract file. */
+  def name = nioPath.getFileName.toString
+
+  /** Returns the path of this abstract file. */
+  def path = nioPath.toString
+
+  /** The absolute file. */
+  def absolute = new PlainNioFile(nioPath.toAbsolutePath)
+
+  override def container: AbstractFile = new PlainNioFile(nioPath.getParent)
+  override def input = Files.newInputStream(nioPath)
+  override def output = Files.newOutputStream(nioPath)
+  override def sizeOption = Some(Files.size(nioPath).toInt)
+  override def hashCode(): Int = fpath.hashCode()
+  override def equals(that: Any): Boolean = that match {
+    case x: PlainNioFile => fpath == x.fpath
+    case _               => false
+  }
+
+  /** Is this abstract file a directory? */
+  def isDirectory: Boolean = Files.isDirectory(nioPath)
+
+  /** Returns the time that this abstract file was last modified. */
+  def lastModified: Long = Files.getLastModifiedTime(nioPath).toMillis
+
+  /** Returns all abstract subfiles of this abstract directory. */
+  def iterator: Iterator[AbstractFile] = {
+    try {
+      import scala.collection.JavaConverters._
+      val it = Files.newDirectoryStream(nioPath).iterator()
+      it.asScala.map(new PlainNioFile(_))
+    } catch {
+      case _: NotDirectoryException => Iterator.empty
+    }
+  }
+
+  /**
+    * Returns the abstract file in this abstract directory with the
+    * specified name. If there is no such file, returns null. The
+    * argument "directory" tells whether to look for a directory or
+    * or a regular file.
+    */
+  def lookupName(name: String, directory: Boolean): AbstractFile = {
+    val child = nioPath.resolve(name)
+    if ((Files.isDirectory(child) && directory) || (Files.isRegularFile(child) && !directory)) new PlainNioFile(child)
+    else null
+  }
+
+  /** Does this abstract file denote an existing file? */
+  def create(): Unit = if (!exists)  Files.createFile(nioPath)
+
+  /** Delete the underlying file or directory (recursively). */
+  def delete(): Unit =
+    if (Files.isRegularFile(nioPath)) Files.deleteIfExists(nioPath)
+    else if (Files.isDirectory(nioPath)) new Directory(nioPath.toFile).deleteRecursively()
+
+  /** Returns a plain file with the given name. It does not
+    *  check that it exists.
+    */
+  def lookupNameUnchecked(name: String, directory: Boolean): AbstractFile =
+    new PlainNioFile(nioPath.resolve(name))
+}