Treat the the last Backtrace as the Ruby exception's Backtrace

* Show the Java-level stacktrace for non-TruffleException to help debugging

Author: eregon

src/main/java/org/truffleruby/core/exception/CoreExceptions.java

@@ -246,6 +246,13 @@ public DynamicObject runtimeError(String fullMessage, Node currentNode, Throwabl
         return ExceptionOperations.createRubyException(context, exceptionClass, errorMessage, currentNode, javaThrowable);
     }
 
+    @TruffleBoundary
+    public DynamicObject runtimeError(String fullMessage, Backtrace backtrace) {
+        DynamicObject exceptionClass = context.getCoreLibrary().getRuntimeErrorClass();
+        DynamicObject errorMessage = StringOperations.createString(context, StringOperations.encodeRope(fullMessage, UTF8Encoding.INSTANCE));
+        return ExceptionOperations.createRubyException(context, exceptionClass, errorMessage, backtrace);
+    }
+
     // SystemStackError
 
     @TruffleBoundary

src/main/java/org/truffleruby/core/exception/ExceptionOperations.java

@@ -71,7 +71,7 @@ public static DynamicObject createSystemCallError(RubyContext context, DynamicOb
 
     // because the factory is not constant
     @TruffleBoundary
-    private static DynamicObject createRubyException(RubyContext context, DynamicObject rubyClass, Object message, Backtrace backtrace) {
+    public static DynamicObject createRubyException(RubyContext context, DynamicObject rubyClass, Object message, Backtrace backtrace) {
         final DynamicObject cause = ThreadGetExceptionNode.getLastException(context);
         context.getCoreExceptions().showExceptionIfDebug(rubyClass, message, backtrace);
         return Layouts.CLASS.getInstanceFactory(rubyClass).newInstance(Layouts.EXCEPTION.build(message, null, backtrace, cause));

src/main/java/org/truffleruby/language/methods/ExceptionTranslatingNode.java

@@ -263,13 +263,19 @@ private DynamicObject translateThrowable(Throwable throwable) {
 
         final StringBuilder builder = new StringBuilder();
         boolean firstException = true;
+        Backtrace lastBacktrace = null;
 
         while (t != null) {
             if (t.getClass().getSimpleName().equals("LazyStackTrace")) {
                 // Truffle's lazy stracktrace support, not a real exception
                 break;
             }
 
+            if (lastBacktrace != null) {
+                appendTruffleStackTrace(builder, lastBacktrace);
+                lastBacktrace = null;
+            }
+
             if (!firstException) {
                 builder.append("Caused by:\n");
             }
@@ -290,15 +296,13 @@ private DynamicObject translateThrowable(Throwable throwable) {
                 builder.append(" (").append(t.getClass().getSimpleName()).append(")\n");
 
                 if (t instanceof TruffleException) {
-                    final Backtrace backtrace = new Backtrace((TruffleException) t);
-                    appendTruffleStackTrace(builder, backtrace);
+                    lastBacktrace = new Backtrace((TruffleException) t);
                 } else {
+                    // Print the first 10 lines of the Java stacktrace
+                    appendJavaStackTrace(t, builder, 10);
+
                     if (TruffleStackTrace.getStackTrace(t) != null) {
-                        final Backtrace backtrace = new Backtrace(t);
-                        appendTruffleStackTrace(builder, backtrace);
-                    } else {
-                        // Print the first 10 lines of the Java stacktrace
-                        appendJavaStackTrace(t, builder, 10);
+                        lastBacktrace = new Backtrace(t);
                     }
                 }
             }
@@ -310,7 +314,11 @@ private DynamicObject translateThrowable(Throwable throwable) {
         // When printing the backtrace of the exception, make it clear it's not a cause
         builder.append("Translated to internal error");
 
-        return coreExceptions().runtimeError(builder.toString(), this, throwable);
+        if (lastBacktrace != null) {
+            return coreExceptions().runtimeError(builder.toString(), lastBacktrace);
+        } else {
+            return coreExceptions().runtimeError(builder.toString(), this, throwable);
+        }
     }
 
     private void appendTruffleStackTrace(StringBuilder builder, Backtrace backtrace) {