Issue #28843: Fix asyncio C Task to handle exceptions __traceback__.

Lib/test/test_asyncio/test_tasks.py

@@ -1952,6 +1952,21 @@ class BaseTaskTests:
         self.assertFalse(gather_task.cancelled())
         self.assertEqual(gather_task.result(), [42])
 
+    def test_exception_traceback(self):
+        # See http://bugs.python.org/issue28843
+
+        @asyncio.coroutine
+        def foo():
+            1 / 0
+
+        @asyncio.coroutine
+        def main():
+            task = self.new_task(self.loop, foo())
+            yield  # skip one loop iteration
+            self.assertIsNotNone(task.exception().__traceback__)
+
+        self.loop.run_until_complete(main())
+
     @mock.patch('asyncio.base_events.logger')
     def test_error_in_call_soon(self, m_log):
         def call_soon(callback, *args):

Misc/NEWS

@@ -24,6 +24,8 @@ Library
 - Issue #24142: Reading a corrupt config file left configparser in an
   invalid state.  Original patch by Florian Höch.
 
+- Issue #28843: Fix asyncio C Task to handle exceptions __traceback__.
+
 Tools/Demos
 -----------
 

Modules/_asynciomodule.c

@@ -1042,6 +1042,8 @@ FutureIter_throw(futureiterobject *self, PyObject *args)
 
     if (PyExceptionClass_Check(type)) {
         PyErr_NormalizeException(&type, &val, &tb);
+        /* No need to call PyException_SetTraceback since we'll be calling
+           PyErr_Restore for `type`, `val`, and `tb`. */
     } else if (PyExceptionInstance_Check(type)) {
         if (val) {
             PyErr_SetString(PyExc_TypeError,
@@ -2003,6 +2005,9 @@ task_step_impl(TaskObj *task, PyObject *exc)
         if (!ev || !PyObject_TypeCheck(ev, (PyTypeObject *) et)) {
             PyErr_NormalizeException(&et, &ev, &tb);
         }
+        if (tb != NULL) {
+            PyException_SetTraceback(ev, tb);
+        }
         o = future_set_exception((FutureObj*)task, ev);
         if (!o) {
             /* An exception in Task.set_exception() */