bpo-36829: Add _PyErr_WriteUnraisableMsg() (GH-13488)

* sys.unraisablehook: add 'err_msg' field to UnraisableHookArgs.
* Use _PyErr_WriteUnraisableMsg() in _ctypes _DictRemover_call()
  and gc delete_garbage().

3 files changed, 19 insertions, 9 deletions

diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index f4eb536..21b08f8 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -150,9 +150,9 @@ _DictRemover_call(PyObject *myself, PyObject *args, PyObject *kw)
 {
     DictRemoverObject *self = (DictRemoverObject *)myself;
     if (self->key && self->dict) {
-        if (-1 == PyDict_DelItem(self->dict, self->key))
-            /* XXX Error context */
-            PyErr_WriteUnraisable(Py_None);
+        if (-1 == PyDict_DelItem(self->dict, self->key)) {
+            _PyErr_WriteUnraisableMsg("on calling _ctypes.DictRemover", NULL);
+        }
         Py_CLEAR(self->key);
         Py_CLEAR(self->dict);
     }
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 7945f49..51e5d80 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -4985,13 +4985,24 @@ negative_refcount(PyObject *self, PyObject *Py_UNUSED(args))
 static PyObject*
 test_write_unraisable_exc(PyObject *self, PyObject *args)
 {
-    PyObject *exc, *obj;
-    if (!PyArg_ParseTuple(args, "OO", &exc, &obj)) {
+    PyObject *exc, *err_msg, *obj;
+    if (!PyArg_ParseTuple(args, "OOO", &exc, &err_msg, &obj)) {
         return NULL;
     }
 
+    const char *err_msg_utf8;
+    if (err_msg != Py_None) {
+        err_msg_utf8 = PyUnicode_AsUTF8(err_msg);
+        if (err_msg_utf8 == NULL) {
+            return NULL;
+        }
+    }
+    else {
+        err_msg_utf8 = NULL;
+    }
+
     PyErr_SetObject((PyObject *)Py_TYPE(exc), exc);
-    PyErr_WriteUnraisable(obj);
+    _PyErr_WriteUnraisableMsg(err_msg_utf8, obj);
     Py_RETURN_NONE;
 }
 
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index be9b73a..3b15c7b 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -929,9 +929,8 @@ delete_garbage(struct _gc_runtime_state *state,
                 Py_INCREF(op);
                 (void) clear(op);
                 if (PyErr_Occurred()) {
-                    PySys_WriteStderr("Exception ignored in tp_clear of "
-                                      "%.50s\n", Py_TYPE(op)->tp_name);
-                    PyErr_WriteUnraisable(NULL);
+                    _PyErr_WriteUnraisableMsg("in tp_clear of",
+                                              (PyObject*)Py_TYPE(op));
                 }
                 Py_DECREF(op);
             }