Issue python#107: reconstruct the frame.f_back linkage in unpickled t…

…racebacks.

This is part 1 of issue python#107. If you unpickle a traceback object, Stackless now reconstructs the f_back links of the assorted frame objects.
There is also a new test case in test_pickle.py.
Manually grafted from pull request python#22.

https://bitbucket.org/stackless-dev/stackless/issues/107
(grafted from 3719f4e0d4371b941777f423941bfe5e875f9cf6)

Stackless/changelog.txt

@@ -9,6 +9,10 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://bitbucket.org/stackless-dev/stackless/issues/107
+  Improve unpickling of traceback objects. Stackless now reconstructs the
+  frame.f_back linkage in frames directly referenced by traceback objects.
+
 - https://bitbucket.org/stackless-dev/stackless/issues/110
   Remove the already non functional remains of psyco support.
 

Stackless/pickling/prickelpit.c

@@ -1206,6 +1206,14 @@ tb_setstate(PyObject *self, PyObject *args)
     tb->tb_lineno = lineno;
     Py_TYPE(tb) = Py_TYPE(tb)->tp_base;
 
+    if (frame != NULL && next != NULL && next->tb_frame != NULL &&
+        (PyObject *)(next->tb_frame->f_back) == Py_None) {
+        /* Reconstruct the f_back chain as far as possible. */
+        next->tb_frame->f_back = frame;
+        Py_INCREF(frame);
+        Py_DECREF(Py_None);
+    }
+
     Py_INCREF(self);
     return self;
 }

Stackless/unittests/test_pickle.py

@@ -4,6 +4,7 @@
 import pickle
 import gc
 import io
+import inspect
 
 from stackless import schedule, tasklet, stackless
 
@@ -611,6 +612,50 @@ class TestDictViewPicklingPy(AbstractTestPickledTasklets, DictViewPicklingTestCa
 class TestDictViewPicklingC(AbstractTestPickledTasklets, DictViewPicklingTestCases, CPickleMixin):
     pass
 
+
+class Traceback_TestCases(object):
+    def testTracebackFrameLinkage(self):
+        def a():
+            # raise an exception
+            1 // 0
+
+        def b():
+            return a()
+
+        def c():
+            return b()
+
+        try:
+            c()
+        except ZeroDivisionError:
+            tb = sys.exc_info()[2]
+
+        innerframes_orig = inspect.getinnerframes(tb)
+        p = self.dumps(tb)
+        tb2 = self.loads(p)
+        # basics
+        self.assertIs(type(tb), type(tb2))
+        self.assertIsNot(tb, tb2)
+        innerframes = inspect.getinnerframes(tb2)
+        # compare the content
+        self.assertListEqual([i[1:] for i in innerframes_orig], [i[1:] for i in innerframes])
+        # check linkage
+        all_outerframes_orig = inspect.getouterframes(innerframes_orig[-1][0])
+        all_outerframes = inspect.getouterframes(innerframes[-1][0])
+        l = len(innerframes_orig)
+        self.assertGreater(len(all_outerframes_orig), l)
+        self.assertGreaterEqual(len(all_outerframes), l)
+        # compare the content
+        self.assertListEqual([i[1:] for i in all_outerframes_orig[:l - 1]], [i[1:] for i in all_outerframes[:l - 1]])
+
+
+class TestTracebackPy(StacklessTestCase, Traceback_TestCases, PyPickleMixin):
+    pass
+
+
+class TestTracebackC(StacklessTestCase, Traceback_TestCases, CPickleMixin):
+    pass
+
 if __name__ == '__main__':
     if not sys.argv[1:]:
         sys.argv.append('-v')