Fix #3305: Handle exceptions in REPL

The new REPL did not catch exceptions. We now handle exceptions but
there is a lot of room for improvement when reporting an exception.

Author: allanrenucci

compiler/src/dotty/tools/repl/Rendering.scala

@@ -1,7 +1,9 @@
 package dotty.tools
 package repl
 
-import java.lang.ClassLoader
+import java.io.{ StringWriter, PrintWriter }
+import java.lang.{ ClassLoader, ExceptionInInitializerError }
+import java.lang.reflect.InvocationTargetException
 
 import scala.util.control.NonFatal
 
@@ -70,10 +72,26 @@ private[repl] class Rendering(compiler: ReplCompiler,
   /** Render value definition result */
   def renderVal(d: Denotation)(implicit ctx: Context): Option[String] = {
     val dcl = d.symbol.showUser
-    val resultValue =
-      if (d.symbol.is(Flags.Lazy)) Some("<lazy>")
-      else valueOf(d.symbol)
 
-    resultValue.map(value => s"$dcl = $value")
+    try {
+      val resultValue =
+        if (d.symbol.is(Flags.Lazy)) Some("<lazy>")
+        else valueOf(d.symbol)
+
+      resultValue.map(value => s"$dcl = $value")
+    }
+    catch { case ex: InvocationTargetException => Some(renderError(ex)) }
+  }
+
+  /** Render the stack trace of the underlying exception */
+  private def renderError(ex: InvocationTargetException): String = {
+    val cause = ex.getCause match {
+      case ex: ExceptionInInitializerError => ex.getCause
+      case ex => ex
+    }
+    val sw = new StringWriter()
+    val pw = new PrintWriter(sw)
+    cause.printStackTrace(pw)
+    sw.toString
   }
 }

compiler/test/dotty/tools/repl/CompilerTests.scala

@@ -92,4 +92,27 @@ class ReplCompilerTests extends ReplTest {
         storedOutput()
       )
     }
+
+  @Test def i3305: Unit = {
+    fromInitialState { implicit s =>
+      compile("null.toString")
+      storedOutput().startsWith("java.lang.NullPointerException")
+    }
+
+    fromInitialState { implicit s =>
+      compile("def foo: Int = 1 + foo; foo")
+      storedOutput().startsWith("def foo: Int\njava.lang.StackOverflowError")
+    }
+
+    fromInitialState { implicit s =>
+      compile("""throw new IllegalArgumentException("Hello")""")
+      storedOutput().startsWith("java.lang.IllegalArgumentException: Hello")
+    }
+
+    // FIXME
+    // fromInitialState { implicit s =>
+    //   compile("val (x, y) = null")
+    //   storedOutput().startsWith("scala.MatchError: null")
+    // }
+  }
 }

compiler/test/dotty/tools/repl/ScriptedTests.scala

@@ -11,7 +11,7 @@ import scala.io.Source
 
 import dotc.reporting.MessageRendering
 
-/** Runs all tests contained in `/repl/test-resources/scripts` */
+/** Runs all tests contained in `compiler/test-resources/repl/` */
 class ScriptedTests extends ReplTest with MessageRendering {
 
   private def scripts(path: String): Array[JFile] = {