SI-8415 Exception handling in REPL init

Incremental robustness, and probe for typer phase.

The probe would be unnecessary if repl contributed a
terminal phase that "requires" whatever it needs; that
is checked when the Run is built.

3 files changed, 15 insertions, 4 deletions

diff --git a/src/repl/scala/tools/nsc/interpreter/ILoop.scala b/src/repl/scala/tools/nsc/interpreter/ILoop.scala
index a96bed4696..ce0eadc04f 100644
--- a/src/repl/scala/tools/nsc/interpreter/ILoop.scala
+++ b/src/repl/scala/tools/nsc/interpreter/ILoop.scala
@@ -402,7 +402,13 @@ class ILoop(in0: Option[BufferedReader], protected val out: JPrintWriter)
 
   private val crashRecovery: PartialFunction[Throwable, Boolean] = {
     case ex: Throwable =>
-      echo(intp.global.throwableAsString(ex))
+      val (err, explain) = (
+        if (intp.isInitializeComplete)
+          (intp.global.throwableAsString(ex), "")
+        else
+          (ex.getMessage, "The compiler did not initialize.\n")
+      )
+      echo(err)
 
       ex match {
         case _: NoSuchMethodError | _: NoClassDefFoundError =>
@@ -410,7 +416,7 @@ class ILoop(in0: Option[BufferedReader], protected val out: JPrintWriter)
           throw ex
         case _  =>
           def fn(): Boolean =
-            try in.readYesOrNo(replayQuestionMessage, { echo("\nYou must enter y or n.") ; fn() })
+            try in.readYesOrNo(explain + replayQuestionMessage, { echo("\nYou must enter y or n.") ; fn() })
             catch { case _: RuntimeException => false }
 
           if (fn()) replay()
diff --git a/src/repl/scala/tools/nsc/interpreter/IMain.scala b/src/repl/scala/tools/nsc/interpreter/IMain.scala
index 9c853fb514..47d97dd4dd 100644
--- a/src/repl/scala/tools/nsc/interpreter/IMain.scala
+++ b/src/repl/scala/tools/nsc/interpreter/IMain.scala
@@ -117,8 +117,10 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
   private def _initSources = List(new BatchSourceFile("<init>", "class $repl_$init { }"))
   private def _initialize() = {
     try {
-      // todo. if this crashes, REPL will hang
-      new _compiler.Run() compileSources _initSources
+      // if this crashes, REPL will hang its head in shame
+      val run = new _compiler.Run()
+      assert(run.typerPhase != NoPhase, "REPL requires a typer phase.")
+      run compileSources _initSources
       _initializeComplete = true
       true
     }
@@ -384,6 +386,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
 
   def compileSourcesKeepingRun(sources: SourceFile*) = {
     val run = new Run()
+    assert(run.typerPhase != NoPhase, "REPL requires a typer phase.")
     reporter.reset()
     run compileSources sources.toList
     (!reporter.hasErrors, run)
diff --git a/src/repl/scala/tools/nsc/interpreter/ReplGlobal.scala b/src/repl/scala/tools/nsc/interpreter/ReplGlobal.scala
index 51fab3082e..07d619bca5 100644
--- a/src/repl/scala/tools/nsc/interpreter/ReplGlobal.scala
+++ b/src/repl/scala/tools/nsc/interpreter/ReplGlobal.scala
@@ -55,6 +55,8 @@ trait ReplGlobal extends Global {
         // newNamer(rootContext(unit)).enterSym(unit.body)
       }
     }
+    // add to initial or terminal phase to sanity check Run at construction
+    override val requires = List("typer")  // ensure they didn't -Ystop-after:parser
   }
 
   override protected def computePhaseDescriptors: List[SubComponent] = {