implement tb_lineno of Traceback

src/runtime/traceback.cpp

@@ -145,7 +145,9 @@ void setupTraceback() {
     NULL));
     */
     traceback_cls->giveAttrDescriptor("tb_next", traceback_tb_next, NULL);
-
+    traceback_cls->giveAttr("tb_lineno",
+                            new BoxedMemberDescriptor(BoxedMemberDescriptor::INT,
+                                                      offsetof(BoxedTraceback, line) + offsetof(LineInfo, line)));
     traceback_cls->freeze();
 }
 }

src/runtime/traceback.h

@@ -30,7 +30,6 @@ public:
     Box* tb_next;
     LineInfo line;
     Box* py_lines;
-
     BoxedTraceback(LineInfo line, Box* tb_next) : tb_next(tb_next), line(std::move(line)), py_lines(NULL) {}
 
     DEFAULT_CLASS(traceback_cls);

test/tests/traceback_test2.py

+import sys, traceback
+
+def lumberjack():
+    bright_side_of_death()
+
+def bright_side_of_death():
+    return tuple()[0]
+
+try:
+    lumberjack()
+except IndexError:
+    exc_type, exc_value, exc_traceback = sys.exc_info()
+    print "*** print_tb:"
+    traceback.print_tb(exc_traceback, limit=1, file=sys.stdout)
+    print "*** print_exception:"
+    traceback.print_exception(exc_type, exc_value, exc_traceback,
+                              limit=2, file=sys.stdout)
+    print "*** print_exc:"
+    traceback.print_exc()
+    print "*** format_exc, first and last line:"
+    formatted_lines = traceback.format_exc().splitlines()
+    print formatted_lines[0]
+    print formatted_lines[-1]
+    print "*** format_exception:"
+    print repr(traceback.format_exception(exc_type, exc_value,
+                                          exc_traceback))
+    print "*** extract_tb:"
+    print repr(traceback.extract_tb(exc_traceback))
+    print "*** format_tb:"
+    print repr(traceback.format_tb(exc_traceback))
+    print "*** tb_lineno:", exc_traceback.tb_lineno
+    assert exc_traceback.tb_lineno == 10