big fat error message for default mirror failures

2 files changed, 83 insertions, 6 deletions

diff --git a/src/library/scala/reflect/ReflectionUtils.scala b/src/library/scala/reflect/ReflectionUtils.scala
index 1be46eac55..79a42f6ec4 100644
--- a/src/library/scala/reflect/ReflectionUtils.scala
+++ b/src/library/scala/reflect/ReflectionUtils.scala
@@ -27,6 +27,28 @@ object ReflectionUtils {
     case ex if pf isDefinedAt unwrapThrowable(ex)   => pf(unwrapThrowable(ex))
   }
 
+  private def systemProperties: Iterator[(String, String)] = {
+    import scala.collection.JavaConverters._
+    System.getProperties.asScala.iterator
+  }
+
+  private def searchForBootClasspath = (
+    systemProperties find (_._1 endsWith ".boot.class.path") map (_._2) getOrElse ""
+  )
+
+  def show(cl: ClassLoader) = {
+    def inferClasspath(cl: ClassLoader) = cl match {
+      case cl: java.net.URLClassLoader => "[" + (cl.getURLs mkString ",") + "]"
+      case _ => "<unknown>"
+    }
+    cl match {
+      case cl if cl != null =>
+        "%s of type %s with classpath %s".format(cl, cl.getClass, inferClasspath(cl))
+      case null =>
+        "primordial classloader with boot classpath [%s]".format(searchForBootClasspath)
+    }
+  }
+
   def defaultReflectionClassLoader() = {
     // say no to non-determinism of mirror classloaders
     // default classloader will be instantiated using current system classloader
diff --git a/src/library/scala/reflect/package.scala b/src/library/scala/reflect/package.scala
index 1738642932..6f40a3ac3e 100644
--- a/src/library/scala/reflect/package.scala
+++ b/src/library/scala/reflect/package.scala
@@ -3,6 +3,7 @@ package scala
 package object reflect {
 
   import ReflectionUtils._
+  import scala.compat.Platform.EOL
 
   // !!! This was a val; we can't throw exceptions that aggressively without breaking
   // non-standard environments, e.g. google app engine.  I made it a lazy val, but
@@ -12,15 +13,69 @@ package object reflect {
   // todo. default mirror (a static object) might become a source for memory leaks (because it holds a strong reference to a classloader)!
   lazy val mirror: api.Mirror = mkMirror(defaultReflectionClassLoader)
 
+  private def mirrorDiagnostics(cl: ClassLoader): String = """
+    |
+    | This error has happened because `scala.reflect.runtime.package` located in
+    | scala-compiler.jar cannot be loaded. Classloader you are using is:
+    | %s.
+    |
+    | In Scala 2.10.0 M3, scala-compiler.jar is required to be on the classpath
+    | for manifests and type tags to function. This will change in the final release,
+    | but for now you need to adjust your scripts or build system to proceed.
+    | Here are the instructions for some of the situations that might be relevant.
+    |
+    | If you compile your application directly from the command line
+    | or a hand-rolled script, this is a bug. Please, report it.
+    |
+    | If you compile your application with Maven using the maven-scala plugin,
+    | set its "fork" configuration entry to "false:
+    |
+    |   <plugin>
+    |     <groupId>org.scala-tools</groupId>
+    |     <artifactId>maven-scala-plugin</artifactId>
+    |     <version>2.15.0</version>
+    |     <executions>
+    |       <execution>
+    |         <goals>
+    |           ...
+    |         </goals>
+    |         <configuration>
+    |          <fork>false</fork>
+    |          ...
+    |        </configuration>
+    |      </execution>
+    |    </executions>
+    |  </plugin>
+    |
+    | If you compile your application with SBT,
+    | <to be implemented: release SBT for 2.10.0 M3>
+    |
+    | If you compile your application in Scala IDE,
+    | <to be implemented: release Scala IDE for 2.10.0 M3>.
+    |
+    | If you launch your application directly from the command line
+    | or a hand-rolled script, add `scala-compiler.jar` to the classpath:
+    |
+    |   scalac HelloWorld.scala
+    |   scala HelloWorld -cp path/to/scala-compiler.jar
+    |
+    | If you launch your application with Maven using the maven-scala plugin,
+    | set its "fork" configuration entry to "false as shown above.
+    |
+    | If you launch your application with SBT, make sure that you use
+    | <to be implemented: release SBT for 2.10.0 M3>
+    |
+    | If you launch your application in Scala IDE, make sure that both scala-library.jar and scala-compiler.jar
+    | are in bootstrap entries on the classpath of your launch configuration.
+  """.stripMargin('|').format(show(cl))
+
   def mkMirror(classLoader: ClassLoader): api.Mirror = {
-    // we use (Java) reflection here so that we can keep reflect.runtime and reflect.internals in a seperate jar
-    // note that we must instantiate the mirror with current classloader, otherwise we won't be able to cast it to api.Mirror
-    // that's not a problem, though, because mirror can service classes from arbitrary classloaders
-    val instance = invokeFactoryOpt(getClass.getClassLoader, "scala.reflect.runtime.package", "mkMirror", classLoader)
+    val coreClassLoader = getClass.getClassLoader
+    val instance = invokeFactoryOpt(coreClassLoader, "scala.reflect.runtime.package", "mkMirror", classLoader)
     instance match {
       case Some(x: api.Mirror) => x
-      case Some(_) => throw new UnsupportedOperationException("Available scala reflection implementation is incompatible with this interface")
-      case None => throw new UnsupportedOperationException("Scala reflection not available on this platform")
+      case Some(_) => throw new UnsupportedOperationException("Available scala reflection implementation is incompatible with this interface." + mirrorDiagnostics(coreClassLoader))
+      case None => throw new UnsupportedOperationException("Scala reflection not available on this platform." + mirrorDiagnostics(coreClassLoader))
     }
   }