Added compiler crash recovery to the repl.

up it will issue some apologies and then replay the session up
to the crash line with a new compiler. If you combine this with
-Yrich-exceptions then you can induce a crash, see the exact path
through the code which led there, and then continue on your merry way as
if nothing happened.

// say ticket #4188 for example
% scala -Yrich-exceptions
scala> class A {
     |   object Ding
     |   class B {
     |     (null: Any) match { case _: Ding.type => () }
     |   }
     | }

assertion failed: Trying to access the this of another class: tree.symbol = class $read$$iw$$iw$A, ctx.clazz.symbol = class $read$$iw$$iw$A$B compilation unit:<console>
[searching for exception contexts...]
[GenICode.scala$tools$nsc$backend$icode$GenICode$ICodePhase$$genLoad]
 958:
 959:         case This(qual) =>
 960:           assert(tree.symbol == ctx.clazz.symbol || tree.symbol.isModuleClass,
*961:                  "Trying to access the this of another class: " +
 962:                  "tree.symbol = " + tree.symbol + ", ctx.clazz.symbol = " + ctx.clazz.symbol + " compilation unit:"+unit)
 963:           if (tree.symbol.isModuleClass && tree.symbol != ctx.clazz.symbol) {
 964:             if (settings.debug.value)

[GenICode.genLoadQualifier]
 1166:       tree match {
 1167:         case Select(qualifier, _) =>
 1168:           genLoad(qualifier, ctx, toTypeKind(qualifier.tpe))
*1169:         case _ =>
 1170:           abort("Unknown qualifier " + tree)
 1171:       }
 1172:
[...]
Attempting session recovery...

scala>

No review.

4 files changed, 113 insertions, 55 deletions

diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
index b1490e411a..6e15906b97 100644
--- a/src/compiler/scala/tools/nsc/Global.scala
+++ b/src/compiler/scala/tools/nsc/Global.scala
@@ -15,6 +15,7 @@ import io.{ SourceReader, AbstractFile, Path }
 import reporters.{ Reporter, ConsoleReporter }
 import util.{ Exceptional, ClassPath, SourceFile, Statistics, BatchSourceFile, ScriptSourceFile, ShowPickled, returning }
 import reflect.generic.{ PickleBuffer, PickleFormat }
+import settings.{ AestheticSettings }
 
 import symtab.{ Flags, SymbolTable, SymbolLoaders, SymbolTrackers }
 import symtab.classfile.Pickler
@@ -206,16 +207,13 @@ class Global(var settings: Settings, var reporter: Reporter) extends SymbolTable
     informComplete("[search path for class files: " + classPath.asClasspathString + "]")
   }
 
-  /** Taking flag checking to a somewhat higher level. */
-  object opt {
+  object opt extends AestheticSettings {
+    def settings = Global.this.settings
+
     // protected implicit lazy val globalPhaseOrdering: Ordering[Phase] = Ordering[Int] on (_.id)
     def isActive(ph: Settings#PhasesSetting)  = ph containsPhase globalPhase
     def wasActive(ph: Settings#PhasesSetting) = ph containsPhase globalPhase.prev
 
-    // Some(value) if setting has been set by user, None otherwise.
-    def optSetting[T](s: Settings#Setting): Option[T] =
-      if (s.isDefault) None else Some(s.value.asInstanceOf[T])
-
     // Allows for syntax like scalac -Xshow-class Random@erasure,typer
     private def splitClassAndPhase(str: String, term: Boolean): Name = {
       def mkName(s: String) = if (term) newTermName(s) else newTypeName(s)
@@ -228,52 +226,35 @@ class Global(var settings: Settings, var reporter: Reporter) extends SymbolTable
       }
     }
 
-    val showClass    = optSetting[String](settings.Xshowcls) map (x => splitClassAndPhase(x, false))
-    val showObject   = optSetting[String](settings.Xshowobj) map (x => splitClassAndPhase(x, true))
-    def script       = optSetting[String](settings.script)
-    def encoding     = optSetting[String](settings.encoding)
-    def sourceReader = optSetting[String](settings.sourceReader)
+    // debugging
+    def checkPhase = wasActive(settings.check)
+    def logPhase   = isActive(settings.log)
+    def typerDebug = settings.Ytyperdebug.value
+    def writeICode = settings.writeICode.value
 
-    // XXX: short term, but I can't bear to add another option.
-    // scalac -Dscala.timings will make this true.
-    def timings       = sys.props contains "scala.timings"
+    // showing/printing things
+    def browsePhase   = isActive(settings.browse)
+    def echoFilenames = opt.debug && (opt.verbose || currentRun.size < 5)
+    def noShow        = settings.Yshow.isDefault
+    def printLate     = settings.printLate.value
+    def printPhase    = isActive(settings.Xprint)
+    def showNames     = List(showClass, showObject).flatten
+    def showPhase     = isActive(settings.Yshow)
+    def showSymbols   = settings.Yshowsyms.value
+    def showTrees     = settings.Xshowtrees.value
+    val showClass     = optSetting[String](settings.Xshowcls) map (x => splitClassAndPhase(x, false))
+    val showObject    = optSetting[String](settings.Xshowobj) map (x => splitClassAndPhase(x, true))
 
-    def debug           = settings.debug.value
-    def deprecation     = settings.deprecation.value
-    def experimental    = settings.Xexperimental.value
-    def fatalWarnings   = settings.Xwarnfatal.value
-    def logClasspath    = settings.Ylogcp.value
-    def printLate       = settings.printLate.value
-    def printStats      = settings.Ystatistics.value
-    def profileClass    = settings.YprofileClass.value
-    def profileMem      = settings.YprofileMem.value
-    def richExes        = settings.YrichExes.value
-    def showTrees       = settings.Xshowtrees.value
-    def showSymbols     = settings.Yshowsyms.value
-    def target          = settings.target.value
-    def typerDebug      = settings.Ytyperdebug.value
-    def unchecked       = settings.unchecked.value
-    def verbose         = settings.verbose.value
-    def writeICode      = settings.writeICode.value
-    def declsOnly       = false
-
-    /** Flags as applied to the current or previous phase */
-    def browsePhase  = isActive(settings.browse)
-    def checkPhase   = wasActive(settings.check)
-    def logPhase     = isActive(settings.log)
-    def printPhase   = isActive(settings.Xprint)
-    def showPhase    = isActive(settings.Yshow)
+    // profiling
     def profCPUPhase = isActive(settings.Yprofile) && !profileAll
+    def profileAll   = settings.Yprofile.doAllPhases
+    def profileAny   = !settings.Yprofile.isDefault || !settings.YprofileMem.isDefault
+    def profileClass = settings.YprofileClass.value
+    def profileMem   = settings.YprofileMem.value
 
-    /** Derived values */
-    def noShow        = settings.Yshow.isDefault
-    def showNames     = List(showClass, showObject).flatten
-    def profileAll    = settings.Yprofile.doAllPhases
-    def profileAny    = !settings.Yprofile.isDefault || !settings.YprofileMem.isDefault
-    def jvm           = target startsWith "jvm"
-    def msil          = target == "msil"
-    def verboseDebug  = debug && verbose
-    def echoFilenames = opt.debug && (opt.verbose || currentRun.size < 5)
+    // XXX: short term, but I can't bear to add another option.
+    // scalac -Dscala.timings will make this true.
+    def timings       = sys.props contains "scala.timings"
   }
 
   // True if -Xscript has been set, indicating a script run.
diff --git a/src/compiler/scala/tools/nsc/interpreter/ILoop.scala b/src/compiler/scala/tools/nsc/interpreter/ILoop.scala
index f663bfd1be..90346c480f 100644
--- a/src/compiler/scala/tools/nsc/interpreter/ILoop.scala
+++ b/src/compiler/scala/tools/nsc/interpreter/ILoop.scala
@@ -17,9 +17,9 @@ import scala.annotation.tailrec
 import scala.util.control.Exception.{ ignoring }
 import scala.collection.mutable.ListBuffer
 import scala.concurrent.ops
-import util.{ ClassPath, stringFromWriter, stringFromStream }
+import util.{ ClassPath, Exceptional, stringFromWriter, stringFromStream }
 import interpreter._
-import io.File
+import io.{ File, Sources }
 
 /** The Scala interactive shell.  It provides a read-eval-print loop
  *  around the Interpreter class.
@@ -45,6 +45,9 @@ class ILoop(in0: Option[BufferedReader], protected val out: PrintWriter)
   var intp: IMain = _
   var power: Power = _
 
+  // TODO
+  // object opt extends AestheticSettings
+
   @deprecated("Use `intp` instead.")
   def interpreter = intp
 
@@ -389,6 +392,25 @@ class ILoop(in0: Option[BufferedReader], protected val out: PrintWriter)
     else powerCommands
   )
 
+  private val crashRecovery: PartialFunction[Throwable, Unit] = {
+    case ex: Throwable =>
+      if (settings.YrichExes.value) {
+        val sources = implicitly[Sources]
+        out.println("\n" + ex.getMessage)
+        out.println(
+          if (isReplDebug) "[searching " + sources.path + " for exception contexts...]"
+          else "[searching for exception contexts...]"
+        )
+        out.println(Exceptional(ex).force().context())
+      }
+      else {
+        out.println(util.stackTraceString(ex))
+      }
+      out.println("Attempting session recovery...")
+
+      replay()
+  }
+
   /** The main read-eval-print loop for the repl.  It calls
    *  command() for each line of input, and stops when
    *  command() returns false.
@@ -407,7 +429,10 @@ class ILoop(in0: Option[BufferedReader], protected val out: PrintWriter)
         case _                          => true
       }
 
-    while (processLine(readOneLine)) { }
+    while (true) {
+      try if (!processLine(readOneLine)) return
+      catch crashRecovery
+    }
   }
 
   /** interpret all lines from a specified file */
diff --git a/src/compiler/scala/tools/nsc/io/Sources.scala b/src/compiler/scala/tools/nsc/io/Sources.scala
index a3f0e09bb2..317701b3c4 100644
--- a/src/compiler/scala/tools/nsc/io/Sources.scala
+++ b/src/compiler/scala/tools/nsc/io/Sources.scala
@@ -64,10 +64,25 @@ trait LowPrioritySourcesImplicits {
 
 
 object Sources extends LowPrioritySourcesImplicits {
-  val scalaSourceJars     = List("scala-library-src.jar", "scala-compiler-src.jar")
-  val sourcePathEnv       = envOrElse("SOURCEPATH", "")
-  val scalaLibraryJarPath = (scalaSourceJars map locateJarByName).flatten map (_.path)
-  val defaultSources      = apply(scalaLibraryJarPath :+ sourcePathEnv: _*)
+  // Examples of what libraryJar might be, each of which we'd like to find
+  // the source files automatically:
+  //
+  // /scala/trunk/build/pack/lib/scala-library.jar
+  // /scala/trunk/build/quick/classes/library
+  // /scala/inst/scala-2.9.0.r24213-b20110206233447/lib/scala-library.jar
+  private def libraryJar = Path.locateJarByClass(classOf[ScalaObject]) map (_.toAbsolute.path)
+  private def autoSourcePaths: List[String] = libraryJar.toList flatMap { lib =>
+    val markers = List("build/pack/lib", "build/quick/classes", "scala-library.jar")
+    markers filter (lib contains _) flatMap { m =>
+      val dir = Path(lib take lib.indexOf(m)) / "src"
+
+      if (dir.exists) ClassPath.expandDir(dir.path)
+      else Nil
+    }
+  }
+
+  val sourcePathEnv   = envOrElse("SOURCEPATH", "")
+  val defaultSources  = apply(autoSourcePaths :+ sourcePathEnv: _*)
 
   def apply(paths: String*): Sources = new Sources(ClassPath.join(paths: _*))
 }
diff --git a/src/compiler/scala/tools/nsc/settings/AestheticSettings.scala b/src/compiler/scala/tools/nsc/settings/AestheticSettings.scala
new file mode 100644
index 0000000000..d7bec764b3
--- /dev/null
+++ b/src/compiler/scala/tools/nsc/settings/AestheticSettings.scala
@@ -0,0 +1,37 @@
+/* NSC -- new Scala compiler
+ * Copyright 2005-2011 LAMP/EPFL
+ * @author  Paul Phillips
+ */
+
+package scala.tools.nsc
+package settings
+
+/** Taking flag checking to a somewhat higher level. */
+trait AestheticSettings {
+  def settings: Settings
+
+  // Some(value) if setting has been set by user, None otherwise.
+  def optSetting[T](s: Settings#Setting): Option[T] =
+    if (s.isDefault) None else Some(s.value.asInstanceOf[T])
+
+  def script       = optSetting[String](settings.script)
+  def encoding     = optSetting[String](settings.encoding)
+  def sourceReader = optSetting[String](settings.sourceReader)
+
+  def debug           = settings.debug.value
+  def declsOnly       = false
+  def deprecation     = settings.deprecation.value
+  def experimental    = settings.Xexperimental.value
+  def fatalWarnings   = settings.Xwarnfatal.value
+  def logClasspath    = settings.Ylogcp.value
+  def printStats      = settings.Ystatistics.value
+  def richExes        = settings.YrichExes.value
+  def target          = settings.target.value
+  def unchecked       = settings.unchecked.value
+  def verbose         = settings.verbose.value
+
+  /** Derived values */
+  def jvm           = target startsWith "jvm"
+  def msil          = target == "msil"
+  def verboseDebug  = debug && verbose
+}