TopLevelExceptionHandler: if exception is AssertionError and no java stack trace: print info helper message to use WithJavaStackTrace

Author: cosminbasca

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/exception/TopLevelExceptionHandler.java

@@ -43,6 +43,7 @@
 import static com.oracle.graal.python.builtins.PythonBuiltinClassType.RecursionError;
 import static com.oracle.graal.python.builtins.modules.io.IONodes.T_WRITE;
 import static com.oracle.graal.python.nodes.BuiltinNames.T_SYS;
+import static com.oracle.graal.python.runtime.exception.ExceptionUtils.printToStdErr;
 import static com.oracle.graal.python.runtime.exception.PythonErrorType.SystemExit;
 import static com.oracle.graal.python.util.PythonUtils.toTruffleStringUncached;
 
@@ -219,7 +220,11 @@ private void handleJavaException(Throwable e) {
             boolean exitException = InteropLibrary.getUncached().isException(e) && InteropLibrary.getUncached().getExceptionType(e) == ExceptionType.EXIT;
             if (!exitException) {
                 ExceptionUtils.printPythonLikeStackTrace(getContext(), e);
-                if (PythonOptions.isWithJavaStacktrace(getPythonLanguage())) {
+                boolean withJavaStacktrace = PythonOptions.isWithJavaStacktrace(getPythonLanguage());
+                if (e instanceof AssertionError && !withJavaStacktrace) {
+                    printToStdErr("To get more information about the failed assertion rerun with --python.WithJavaStacktrace=3\n");
+                }
+                if (withJavaStacktrace) {
                     e.printStackTrace();
                 }
             }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/exception/ExceptionUtils.java

@@ -113,6 +113,12 @@ private static int getLineno(Frame frame) {
         return lineno;
     }
 
+    @TruffleBoundary
+    public static void printToStdErr(String message, Object... args) {
+        PrintWriter printWriter = new PrintWriter(System.err, true);
+        printWriter.printf(message, args);
+    }
+
     /**
      * this method is similar to 'PyErr_WriteUnraisable' and may be used when the context is not
      * available.
@@ -151,7 +157,8 @@ public static void printPythonLikeStackTrace(PrintWriter p, Throwable e) {
                 throw CompilerDirectives.shouldNotReachHere();
             }
         } else {
-            p.println(e.getMessage());
+            String message = e.getMessage();
+            p.println(message == null ? e.getClass().getSimpleName() : message);
         }
     }