From 09668664af1fe3f828c20ffd859d3a7c08b0527f Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Sat, 10 Jun 2017 09:56:01 +0300
Subject: [PATCH 1/2] bpo-28994: Chain exceptions rather than dropping the old
 exception.

---
 Modules/_ctypes/callproc.c | 18 +++++++++++-------
 Objects/genobject.c        | 16 +++++-----------
 Python/ceval.c             | 31 +++++++------------------------
 Python/traceback.c         |  4 +---
 4 files changed, 24 insertions(+), 45 deletions(-)

diff --git a/Modules/_ctypes/callproc.c b/Modules/_ctypes/callproc.c
index 3a6ad86e87e79d..1189a1d9ad457f 100644
--- a/Modules/_ctypes/callproc.c
+++ b/Modules/_ctypes/callproc.c
@@ -924,14 +924,17 @@ void _ctypes_extend_error(PyObject *exc_class, const char *fmt, ...)
     va_list vargs;
     PyObject *tp, *v, *tb, *s, *cls_str, *msg_str;
 
+    PyErr_Fetch(&tp, &v, &tb);
+    assert(tp != NULL);
+    PyErr_NormalizeException(&tp, &v, &tb);
+
     va_start(vargs, fmt);
     s = PyUnicode_FromFormatV(fmt, vargs);
     va_end(vargs);
-    if (!s)
-        return;
+    if (s == NULL) {
+        goto error;
+    }
 
-    PyErr_Fetch(&tp, &v, &tb);
-    PyErr_NormalizeException(&tp, &v, &tb);
     cls_str = PyObject_Str(tp);
     if (cls_str) {
         PyUnicode_AppendAndDel(&s, cls_str);
@@ -950,10 +953,11 @@ void _ctypes_extend_error(PyObject *exc_class, const char *fmt, ...)
     if (s == NULL)
         goto error;
     PyErr_SetObject(exc_class, s);
+    Py_DECREF(s);
+    return;
+
 error:
-    Py_XDECREF(tp);
-    Py_XDECREF(v);
-    Py_XDECREF(tb);
+    _PyErr_ChainExceptions(tp, v, tb);
     Py_XDECREF(s);
 }
 
diff --git a/Objects/genobject.c b/Objects/genobject.c
index 7793a54fb3d682..ec9544af1b34df 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -284,17 +284,11 @@ gen_send_ex(PyGenObject *gen, PyObject *arg, int exc, int closing)
             /* Pop the exception before issuing a warning. */
             PyErr_Fetch(&exc, &val, &tb);
 
-            if (PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
-                                 "generator '%.50S' raised StopIteration",
-                                 gen->gi_qualname)) {
-                /* Warning was converted to an error. */
-                Py_XDECREF(exc);
-                Py_XDECREF(val);
-                Py_XDECREF(tb);
-            }
-            else {
-                PyErr_Restore(exc, val, tb);
-            }
+            (void)PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
+                                   "generator '%.50S' raised StopIteration",
+                                   gen->gi_qualname);
+            /* Warning can be converted to an error. */
+            _PyErr_ChainExceptions(exc, val, tb);
         }
     }
     else if (PyAsyncGen_CheckExact(gen) && !result &&
diff --git a/Python/ceval.c b/Python/ceval.c
index f6519cff590fe1..dc17276632177d 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -4224,8 +4224,8 @@ call_exc_trace(Py_tracefunc func, PyObject *self,
                PyThreadState *tstate, PyFrameObject *f)
 {
     PyObject *type, *value, *traceback, *orig_traceback, *arg;
-    int err;
     PyErr_Fetch(&type, &value, &orig_traceback);
+    assert(type != NULL);
     if (value == NULL) {
         value = Py_None;
         Py_INCREF(value);
@@ -4233,19 +4233,11 @@ call_exc_trace(Py_tracefunc func, PyObject *self,
     PyErr_NormalizeException(&type, &value, &orig_traceback);
     traceback = (orig_traceback != NULL) ? orig_traceback : Py_None;
     arg = PyTuple_Pack(3, type, value, traceback);
-    if (arg == NULL) {
-        PyErr_Restore(type, value, orig_traceback);
-        return;
-    }
-    err = call_trace(func, self, tstate, f, PyTrace_EXCEPTION, arg);
-    Py_DECREF(arg);
-    if (err == 0)
-        PyErr_Restore(type, value, orig_traceback);
-    else {
-        Py_XDECREF(type);
-        Py_XDECREF(value);
-        Py_XDECREF(orig_traceback);
+    if (arg != NULL) {
+        (void)call_trace(func, self, tstate, f, PyTrace_EXCEPTION, arg);
+        Py_DECREF(arg);
     }
+    _PyErr_ChainExceptions(type, value, orig_traceback);
 }
 
 static int
@@ -4257,17 +4249,8 @@ call_trace_protected(Py_tracefunc func, PyObject *obj,
     int err;
     PyErr_Fetch(&type, &value, &traceback);
     err = call_trace(func, obj, tstate, frame, what, arg);
-    if (err == 0)
-    {
-        PyErr_Restore(type, value, traceback);
-        return 0;
-    }
-    else {
-        Py_XDECREF(type);
-        Py_XDECREF(value);
-        Py_XDECREF(traceback);
-        return -1;
-    }
+    _PyErr_ChainExceptions(type, value, traceback);
+    return err;
 }
 
 static int
diff --git a/Python/traceback.c b/Python/traceback.c
index 21b36b1471935c..36094d95de9cef 100644
--- a/Python/traceback.c
+++ b/Python/traceback.c
@@ -495,9 +495,7 @@ PyTraceBack_Print(PyObject *v, PyObject *f)
                 limit = PyTraceBack_LIMIT;
             }
             else {
-                Py_XDECREF(exc_type);
-                Py_XDECREF(exc_value);
-                Py_XDECREF(exc_tb);
+                _PyErr_ChainExceptions(exc_type, exc_value, exc_tb);
                 return 0;
             }
         }

From d69a99622e1c5b515cca6bb9da8bbdf760606dec Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 6 Nov 2017 18:39:06 +0200
Subject: [PATCH 2/2] Withdraw changes in Python/traceback.c.

---
 Python/traceback.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Python/traceback.c b/Python/traceback.c
index 36094d95de9cef..21b36b1471935c 100644
--- a/Python/traceback.c
+++ b/Python/traceback.c
@@ -495,7 +495,9 @@ PyTraceBack_Print(PyObject *v, PyObject *f)
                 limit = PyTraceBack_LIMIT;
             }
             else {
-                _PyErr_ChainExceptions(exc_type, exc_value, exc_tb);
+                Py_XDECREF(exc_type);
+                Py_XDECREF(exc_value);
+                Py_XDECREF(exc_tb);
                 return 0;
             }
         }