From 4071691357394ba43a833537425e274d7ca3cd12 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 30 Oct 2023 19:01:03 +0200
Subject: [PATCH] gh-108082: C API: Add tests for PyErr_WriteUnraisable()
 (GH-111455)

Also document the behavior when called with NULL.
---
 Doc/c-api/exceptions.rst              |  8 +++++
 Lib/test/test_capi/test_exceptions.py | 45 +++++++++++++++++++++++++++
 Modules/_testcapi/exceptions.c        | 17 ++++++++++
 3 files changed, 70 insertions(+)

diff --git a/Doc/c-api/exceptions.rst b/Doc/c-api/exceptions.rst
index 2139da051e0193..f27e2bbfef05c5 100644
--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -88,9 +88,17 @@ Printing and clearing
    The function is called with a single argument *obj* that identifies the context
    in which the unraisable exception occurred. If possible,
    the repr of *obj* will be printed in the warning message.
+   If *obj* is ``NULL``, only the traceback is printed.
 
    An exception must be set when calling this function.
 
+   .. versionchanged:: 3.4
+      Print a traceback. Print only traceback if *obj* is ``NULL``.
+
+   .. versionchanged:: 3.8
+      Use :func:`sys.unraisablehook`.
+
+
 .. c:function:: void PyErr_DisplayException(PyObject *exc)
 
    Print the standard traceback display of ``exc`` to ``sys.stderr``, including
diff --git a/Lib/test/test_capi/test_exceptions.py b/Lib/test/test_capi/test_exceptions.py
index b96cc7922a0ee7..1bff65b6559f0b 100644
--- a/Lib/test/test_capi/test_exceptions.py
+++ b/Lib/test/test_capi/test_exceptions.py
@@ -17,6 +17,10 @@
 
 NULL = None
 
+class CustomError(Exception):
+    pass
+
+
 class Test_Exceptions(unittest.TestCase):
 
     def test_exception(self):
@@ -270,6 +274,47 @@ def test_setfromerrnowithfilename(self):
                          (ENOENT, 'No such file or directory', 'file'))
         # CRASHES setfromerrnowithfilename(ENOENT, NULL, b'error')
 
+    def test_err_writeunraisable(self):
+        # Test PyErr_WriteUnraisable()
+        writeunraisable = _testcapi.err_writeunraisable
+        firstline = self.test_err_writeunraisable.__code__.co_firstlineno
+
+        with support.catch_unraisable_exception() as cm:
+            writeunraisable(CustomError('oops!'), hex)
+            self.assertEqual(cm.unraisable.exc_type, CustomError)
+            self.assertEqual(str(cm.unraisable.exc_value), 'oops!')
+            self.assertEqual(cm.unraisable.exc_traceback.tb_lineno,
+                             firstline + 6)
+            self.assertIsNone(cm.unraisable.err_msg)
+            self.assertEqual(cm.unraisable.object, hex)
+
+        with support.catch_unraisable_exception() as cm:
+            writeunraisable(CustomError('oops!'), NULL)
+            self.assertEqual(cm.unraisable.exc_type, CustomError)
+            self.assertEqual(str(cm.unraisable.exc_value), 'oops!')
+            self.assertEqual(cm.unraisable.exc_traceback.tb_lineno,
+                             firstline + 15)
+            self.assertIsNone(cm.unraisable.err_msg)
+            self.assertIsNone(cm.unraisable.object)
+
+        with (support.swap_attr(sys, 'unraisablehook', None),
+              support.captured_stderr() as stderr):
+            writeunraisable(CustomError('oops!'), hex)
+        lines = stderr.getvalue().splitlines()
+        self.assertEqual(lines[0], f'Exception ignored in: {hex!r}')
+        self.assertEqual(lines[1], 'Traceback (most recent call last):')
+        self.assertEqual(lines[-1], f'{__name__}.CustomError: oops!')
+
+        with (support.swap_attr(sys, 'unraisablehook', None),
+              support.captured_stderr() as stderr):
+            writeunraisable(CustomError('oops!'), NULL)
+        lines = stderr.getvalue().splitlines()
+        self.assertEqual(lines[0], 'Traceback (most recent call last):')
+        self.assertEqual(lines[-1], f'{__name__}.CustomError: oops!')
+
+        # CRASHES writeunraisable(NULL, hex)
+        # CRASHES writeunraisable(NULL, NULL)
+
 
 class Test_PyUnstable_Exc_PrepReraiseStar(ExceptionIsLikeMixin, unittest.TestCase):
 
diff --git a/Modules/_testcapi/exceptions.c b/Modules/_testcapi/exceptions.c
index e463e6237099fe..aac672a3788ae1 100644
--- a/Modules/_testcapi/exceptions.c
+++ b/Modules/_testcapi/exceptions.c
@@ -303,6 +303,22 @@ _testcapi_traceback_print_impl(PyObject *module, PyObject *traceback,
     Py_RETURN_NONE;
 }
 
+static PyObject *
+err_writeunraisable(PyObject *Py_UNUSED(module), PyObject *args)
+{
+    PyObject *exc, *obj;
+    if (!PyArg_ParseTuple(args, "OO", &exc, &obj)) {
+        return NULL;
+    }
+    NULLABLE(exc);
+    NULLABLE(obj);
+    if (exc) {
+        PyErr_SetRaisedException(Py_NewRef(exc));
+    }
+    PyErr_WriteUnraisable(obj);
+    Py_RETURN_NONE;
+}
+
 /*[clinic input]
 _testcapi.unstable_exc_prep_reraise_star
     orig: object
@@ -347,6 +363,7 @@ static PyTypeObject PyRecursingInfinitelyError_Type = {
 
 static PyMethodDef test_methods[] = {
     {"err_restore",             err_restore,                     METH_VARARGS},
+    {"err_writeunraisable",     err_writeunraisable,             METH_VARARGS},
     _TESTCAPI_ERR_SET_RAISED_METHODDEF
     _TESTCAPI_EXCEPTION_PRINT_METHODDEF
     _TESTCAPI_FATAL_ERROR_METHODDEF