-Yrelease supplements -release, allows access to additional JVM packages

src/compiler/scala/tools/nsc/Global.scala

@@ -146,9 +146,10 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
   def optimizerClassPath(base: ClassPath): ClassPath =
     base match {
       case AggregateClassPath(entries) if entries.head.isInstanceOf[CtSymClassPath] =>
-        JrtClassPath(release = None, closeableRegistry)
-          .map(jrt => AggregateClassPath(entries.drop(1).prepended(jrt)))
-          .getOrElse(base)
+        JrtClassPath(release = None, unsafe = None, closeableRegistry) match {
+          case jrt :: Nil => AggregateClassPath(entries.drop(1).prepended(jrt))
+          case _ => base
+        }
       case _ => base
     }
 

src/compiler/scala/tools/nsc/classpath/DirectoryClassPath.scala

@@ -14,14 +14,17 @@ package scala.tools.nsc.classpath
 
 import java.io.{Closeable, File}
 import java.net.{URI, URL}
+import java.nio.file._
 
-import scala.reflect.io.{AbstractFile, PlainFile, PlainNioFile}
-import scala.tools.nsc.util.{ClassPath, ClassRepresentation, EfficientClassPath}
-import FileUtils._
 import scala.jdk.CollectionConverters._
 import scala.reflect.internal.JDK9Reflectors
+import scala.reflect.io.{AbstractFile, PlainFile, PlainNioFile}
 import scala.tools.nsc.CloseableRegistry
 import scala.tools.nsc.classpath.PackageNameUtils.{packageContains, separatePkgAndClassNames}
+import scala.tools.nsc.util.{ClassPath, ClassRepresentation, EfficientClassPath}
+import scala.util.Properties.{isJavaAtLeast, javaHome}
+import scala.util.control.NonFatal
+import FileUtils._
 
 /**
  * A trait allowing to look for classpath entries in directories. It provides common logic for
@@ -129,12 +132,10 @@ trait JFileDirectoryLookup[FileEntryType <: ClassRepresentation] extends Directo
 }
 
 object JrtClassPath {
-  import java.nio.file._, java.net.URI
   private val jrtClassPathCache = new FileBasedCache[Unit, JrtClassPath]()
   private val ctSymClassPathCache = new FileBasedCache[String, CtSymClassPath]()
-  def apply(release: Option[String], closeableRegistry: CloseableRegistry): Option[ClassPath] = {
-    import scala.util.Properties._
-    if (!isJavaAtLeast("9")) None
+  def apply(release: Option[String], unsafe: Option[List[String]], closeableRegistry: CloseableRegistry): List[ClassPath] =
+    if (!isJavaAtLeast("9")) Nil
     else {
       // TODO escalate errors once we're sure they are fatal
       // I'm hesitant to do this immediately, because -release will still work for multi-release JARs
@@ -145,28 +146,52 @@ object JrtClassPath {
 
       val currentMajorVersion: Int = JDK9Reflectors.runtimeVersionMajor(JDK9Reflectors.runtimeVersion()).intValue()
       release match {
-        case Some(v) if v.toInt < currentMajorVersion =>
-          try {
-            val ctSym = Paths.get(javaHome).resolve("lib").resolve("ct.sym")
-            if (Files.notExists(ctSym)) None
-            else {
-              val classPath = ctSymClassPathCache.getOrCreate(v, ctSym :: Nil, () => new CtSymClassPath(ctSym, v.toInt), closeableRegistry, checkStamps = true)
-              Some(classPath)
-            }
-          } catch {
-            case _: Throwable => None
+        case Some(version) if version.toInt < currentMajorVersion =>
+          val ct = createCt(version, closeableRegistry)
+          unsafe match {
+            case Some(pkgs) if pkgs.nonEmpty =>
+              createJrt(closeableRegistry) match {
+                case Nil  => ct
+                case jrts => ct.appended(new FilteringJrtClassPath(jrts.head, pkgs: _*))
+              }
+            case _ => ct
           }
         case _ =>
-          try {
-            val fs = FileSystems.getFileSystem(URI.create("jrt:/"))
-            val classPath = jrtClassPathCache.getOrCreate((), Nil, () => new JrtClassPath(fs), closeableRegistry, checkStamps = false)
-            Some(classPath)
-          } catch {
-            case _: ProviderNotFoundException | _: FileSystemNotFoundException => None
-          }
+          createJrt(closeableRegistry)
       }
     }
-  }
+  private def createCt(v: String, closeableRegistry: CloseableRegistry): List[ClassPath] =
+    try {
+      val ctSym = Paths.get(javaHome).resolve("lib").resolve("ct.sym")
+      if (Files.notExists(ctSym)) Nil
+      else {
+        val classPath = ctSymClassPathCache.getOrCreate(v, ctSym :: Nil, () => new CtSymClassPath(ctSym, v.toInt), closeableRegistry, checkStamps = true)
+        List(classPath)
+      }
+    } catch {
+      case NonFatal(_) => Nil
+    }
+  private def createJrt(closeableRegistry: CloseableRegistry): List[JrtClassPath] =
+    try {
+      val fs = FileSystems.getFileSystem(URI.create("jrt:/"))
+      val classPath = jrtClassPathCache.getOrCreate((), Nil, () => new JrtClassPath(fs), closeableRegistry, checkStamps = false)
+      List(classPath)
+    } catch {
+      case _: ProviderNotFoundException | _: FileSystemNotFoundException => Nil
+    }
+}
+
+final class FilteringJrtClassPath(delegate: JrtClassPath, allowed: String*) extends ClassPath with NoSourcePaths {
+  private val allowedPackages = allowed
+  private def packagePrefix(p: String, q: String) = p.startsWith(q) && (p.length == q.length || p.charAt(q.length) == '.')
+  private def ok(pkg: PackageName) = pkg.dottedString.isEmpty || allowedPackages.exists(packagePrefix(_, pkg.dottedString))
+  def asClassPathStrings: Seq[String] = delegate.asClassPathStrings
+  def asURLs: Seq[java.net.URL] = delegate.asURLs
+  private[nsc] def classes(inPackage: PackageName) = if (ok(inPackage)) delegate.classes(inPackage) else Nil
+  def findClassFile(className: String) = if (ok(PackageName(separatePkgAndClassNames(className)._1))) delegate.findClassFile(className) else None
+  private[nsc] def hasPackage(pkg: PackageName) = ok(pkg) && delegate.hasPackage(pkg)
+  private[nsc] def list(inPackage: PackageName) = if (ok(inPackage)) delegate.list(inPackage) else ClassPathEntries(Nil, Nil)
+  private[nsc] def packages(inPackage: PackageName) = if (ok(inPackage)) delegate.packages(inPackage) else Nil
 }
 
 /**
@@ -177,8 +202,7 @@ object JrtClassPath {
   *
   * The implementation assumes that no classes exist in the empty package.
   */
-final class JrtClassPath(fs: java.nio.file.FileSystem) extends ClassPath with NoSourcePaths {
-  import java.nio.file.Path, java.nio.file._
+final class JrtClassPath(fs: FileSystem) extends ClassPath with NoSourcePaths {
   type F = Path
   private val dir: Path = fs.getPath("/packages")
 
@@ -246,7 +270,7 @@ final class CtSymClassPath(ctSym: java.nio.file.Path, release: Int) extends Clas
   // e.g. "java.lang" -> Seq(/876/java/lang, /87/java/lang, /8/java/lang))
   private val packageIndex: scala.collection.Map[String, scala.collection.Seq[Path]] = {
     val index = collection.mutable.AnyRefMap[String, collection.mutable.ListBuffer[Path]]()
-    val isJava12OrHigher = scala.util.Properties.isJavaAtLeast("12")
+    val isJava12OrHigher = isJavaAtLeast("12")
     rootsForRelease.foreach(root => Files.walk(root).iterator().asScala.filter(Files.isDirectory(_)).foreach { p =>
       val moduleNamePathElementCount = if (isJava12OrHigher) 1 else 0
       if (p.getNameCount > root.getNameCount + moduleNamePathElementCount) {

src/compiler/scala/tools/nsc/settings/ScalaSettings.scala

@@ -264,6 +264,7 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
 
   val Youtline        = BooleanSetting    ("-Youtline", "Don't compile method bodies. Use together with `-Ystop-after:pickler` to generate the pickled signatures for all source files.").internalOnly()
 
+  val unsafe = MultiStringSetting("-Yrelease", "packages", "Expose platform packages hidden under --release")
   val exposeEmptyPackage = BooleanSetting ("-Yexpose-empty-package", "Internal only: expose the empty package.").internalOnly()
   val Ydelambdafy        = ChoiceSetting  ("-Ydelambdafy", "strategy", "Strategy used for translating lambdas into JVM code.", List("inline", "method"), "method")
 

src/compiler/scala/tools/util/PathResolver.scala

@@ -257,8 +257,9 @@ final class PathResolver(settings: Settings, closeableRegistry: CloseableRegistr
 
     // Assemble the elements!
     def basis = List[Iterable[ClassPath]](
-      jrt                                           // 0. The Java 9+ classpath (backed by the ct.sym or jrt:/ virtual system, if available)
-        .filter(_ => !settings.javabootclasspath.isSetByUser), // respect explicit `-javabootclasspath rt.jar`
+      if (settings.javabootclasspath.isSetByUser)   // respect explicit `-javabootclasspath rt.jar`
+        Nil
+      else jrt,                                     // 0. The Java 9+ classpath (backed by the ct.sym or jrt:/ virtual system, if available)
       classesInPath(javaBootClassPath),             // 1. The Java bootstrap class path.
       contentsOfDirsInPath(javaExtDirs),            // 2. The Java extension class path.
       classesInExpandedPath(javaUserClassPath),     // 3. The Java application class path.
@@ -269,7 +270,7 @@ final class PathResolver(settings: Settings, closeableRegistry: CloseableRegistr
       sourcesInPath(sourcePath)                     // 7. The Scala source path.
     )
 
-    private def jrt: Option[ClassPath] = JrtClassPath.apply(settings.releaseValue, closeableRegistry)
+    private def jrt: List[ClassPath] = JrtClassPath.apply(settings.releaseValue, settings.unsafe.valueSetByUser, closeableRegistry)
 
     lazy val containers = basis.flatten.distinct
 

test/files/neg/unsafe.check

@@ -0,0 +1,4 @@
+unsafe.scala:9: error: value threadId is not a member of Thread
+  def f(t: Thread) = t.threadId
+                       ^
+1 error

test/files/neg/unsafe.scala

@@ -0,0 +1,10 @@
+
+// scalac: --release:8 -Yrelease:java.lang
+// javaVersion: 19+
+
+// -Yrelease opens packages but does not override class definitions
+// because ct.sym comes first
+
+class C {
+  def f(t: Thread) = t.threadId
+}

test/files/pos/unsafe.scala

@@ -0,0 +1,21 @@
+
+// scalac: --release:8 -Yrelease:sun.misc
+
+import sun.misc.Unsafe
+
+class C {
+  val f = classOf[Unsafe].getDeclaredField("theUnsafe")
+  f.setAccessible(true)
+  val unsafe = f.get(null).asInstanceOf[Unsafe]
+
+  val k = unsafe.allocateInstance(classOf[K]).asInstanceOf[K]
+  assert(k.value == 0)
+}
+
+class K {
+  val value = 42
+}
+
+object Test extends App {
+  new C
+}

test/junit/scala/tools/nsc/classpath/JrtClassPathTest.scala

@@ -27,7 +27,7 @@ class JrtClassPathTest {
         val elements = new ClassPathFactory(settings, closeableRegistry).classesInPath(resolver.Calculated.javaBootClassPath)
         AggregateClassPath(elements)
       }
-      else JrtClassPath(None, closeableRegistry).get
+      else JrtClassPath(None, None, closeableRegistry).head
 
     assertEquals(Nil, cp.classes(""))
     assertTrue(cp.packages("java").toString, cp.packages("java").exists(_.name == "java.lang"))