merge 3.4-slp (Stackless python#115)

Author: Anselm Kruis

Python/ceval.c

@@ -1788,22 +1788,10 @@ slp_eval_frame_value(PyFrameObject *f, int throwflag, PyObject *retval)
                     err = 0;
                 Py_DECREF(retval);
 
-                if (err >= 0) {
-                    if (err > 0) {
-                        /* There was an exception and a true return */
-                        PyObject *v = SECOND();
-                        PyObject *w = THIRD();
-                        err = 0;
-                        STACKADJ(-2);
-                        Py_INCREF(Py_None);
-                        SET_TOP(Py_None);
-                        Py_DECREF(u);
-                        Py_DECREF(v);
-                        Py_DECREF(w);
-                    } else {
-                        /* The stack was rearranged to remove EXIT
-                           above. Let END_FINALLY do its thing */
-                    }
+                if (err > 0) {
+                    err = 0;
+                    /* There was an exception and a True return */
+                    PUSH(PyLong_FromLong((long) WHY_SILENCED));
                 }
                 /* XXX: The main loop contains a PREDICT(END_FINALLY).
                  * I wonder, if we must use it here?

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/115
+  Fix an unlikely crash caused by an context manager, which silences an
+  exception.
+
 - https://bitbucket.org/stackless-dev/stackless/issues/117
   Fix various reference leaks:
   - Leak of a reference to Py_None in generator.throw()

Stackless/unittests/test_defects.py

@@ -505,6 +505,42 @@ def generator():
         frame.clear()  # causes the failure
 
 
+class TestContextManager(StacklessTestCase):
+    def test_crash_on_WHY_SILENCED(self):
+        current_switch = stackless.current.switch
+        steps = []
+
+        class CtxManager:
+            def __enter__(self):
+                steps.append(2)
+
+            def __exit__(self, exc_type, exc_val, exc_tb):
+                steps.append(4)
+                current_switch()  # causes a stack corruption upon resuming __exit__
+                steps.append(5)
+                return True  # silence the exception
+
+        def task():
+            try:
+                steps.append(1)
+                return "OK"
+            finally:
+                with CtxManager():
+                    steps.append(3)
+                    1 // 0
+                steps.append(6)
+                # Stackless issue #115 ()
+                # Leaving this finally block crashes Python,
+                # because the interpreter stack is corrupt.
+
+        t = stackless.tasklet(task)()
+        t.run()
+        self.assertListEqual(steps, [1, 2, 3, 4])
+        t.run()
+        r = t.tempval
+        self.assertListEqual(steps, [1, 2, 3, 4, 5, 6])
+
+
 if __name__ == '__main__':
     if not sys.argv[1:]:
         sys.argv.append('-v')