Issue 5794: fix cPickle's unpickling of recursive tuples.

Lib/test/pickletester.py

@@ -463,6 +463,16 @@ class AbstractPickleTests(unittest.TestCase):
             self.assertEqual(len(x), 1)
             self.assert_(x is x[0])
 
+    def test_recursive_tuple(self):
+        t = ([],)
+        t[0].append(t)
+        for proto in protocols:
+            s = self.dumps(t, proto)
+            x = self.loads(s)
+            self.assertEqual(len(x), 1)
+            self.assertEqual(len(x[0]), 1)
+            self.assert_(x is x[0][0])
+
     def test_recursive_dict(self):
         d = {}
         d[1] = d

Lib/test/test_cpickle.py

@@ -65,6 +65,11 @@ class cPickleFastPicklerTests(AbstractPickleTests):
                           AbstractPickleTests.test_recursive_list,
                           self)
 
+    def test_recursive_tuple(self):
+        self.assertRaises(ValueError,
+                          AbstractPickleTests.test_recursive_tuple,
+                          self)
+
     def test_recursive_inst(self):
         self.assertRaises(ValueError,
                           AbstractPickleTests.test_recursive_inst,

Modules/cPickle.c

@@ -4086,25 +4086,24 @@ load_binpersid(Unpicklerobject *self)
 static int
 load_pop(Unpicklerobject *self)
 {
-	int len;
-
-	if (!( (len=self->stack->length) > 0 ))  return stackUnderflow();
+	int len = self->stack->length;
 
 	/* Note that we split the (pickle.py) stack into two stacks,
 	   an object stack and a mark stack. We have to be clever and
 	   pop the right one. We do this by looking at the top of the
-	   mark stack.
+	   mark stack first, and only signalling a stack underflow if
+	   the object stack is empty and the mark stack doesn't match
+	   our expectations.
 	*/
-
-	if ((self->num_marks > 0) &&
-	    (self->marks[self->num_marks - 1] == len))
+	if (self->num_marks > 0 && self->marks[self->num_marks - 1] == len) {
 		self->num_marks--;
-	else {
+	} else if (len >= 0) {
 		len--;
 		Py_DECREF(self->stack->data[len]);
-		self->stack->length=len;
+		self->stack->length = len;
+	} else {
+		return stackUnderflow();
 	}
-
 	return 0;
 }