From: Alexander Shadchin <shadchin@yandex-team.com>
Date: Fri, 3 Jan 2025 18:47:58 +0000 (+0300)
Subject: gh-127903: Fix a crash on debug builds when calling `Objects/unicodeobject::_copy_cha... 
X-Git-Tag: v3.14.0a4~126
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=46cb6340d7bad955edfc0a20f6a52dabc03b0932;p=thirdparty%2FPython%2Fcpython.git

gh-127903: Fix a crash on debug builds when calling `Objects/unicodeobject::_copy_characters`` (#127876)
---

diff --git a/Lib/test/test_str.py b/Lib/test/test_str.py
index 4de6c1cba152..d1c9542c7d13 100644
--- a/Lib/test/test_str.py
+++ b/Lib/test/test_str.py
@@ -7,6 +7,7 @@ Written by Marc-Andre Lemburg (mal@lemburg.com).
 """
 import _string
 import codecs
+import datetime
 import itertools
 import operator
 import pickle
@@ -1908,6 +1909,12 @@ class StrTest(string_tests.StringLikeTest,
             self.assertRaises(UnicodeDecodeError,
                               (b'\xF4'+cb+b'\xBF\xBF').decode, 'utf-8')
 
+    def test_issue127903(self):
+        # gh-127903: ``_copy_characters`` crashes on DEBUG builds when
+        # there is nothing to copy.
+        d = datetime.datetime(2013, 11, 10, 14, 20, 59)
+        self.assertEqual(d.strftime('%z'), '')
+
     def test_issue8271(self):
         # Issue #8271: during the decoding of an invalid UTF-8 byte sequence,
         # only the start byte and the continuation byte(s) are now considered
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-12-13-14-17-24.gh-issue-127903.vemHSl.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-12-13-14-17-24.gh-issue-127903.vemHSl.rst
new file mode 100644
index 000000000000..ad479b52d167
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-12-13-14-17-24.gh-issue-127903.vemHSl.rst
@@ -0,0 +1,2 @@
+``Objects/unicodeobject.c``: fix a crash on DEBUG builds in ``_copy_characters``
+when there is nothing to copy.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 9f0a4d4785ed..5e532ce0f348 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1463,11 +1463,14 @@ _copy_characters(PyObject *to, Py_ssize_t to_start,
     assert(PyUnicode_Check(from));
     assert(from_start + how_many <= PyUnicode_GET_LENGTH(from));
 
-    assert(PyUnicode_Check(to));
-    assert(to_start + how_many <= PyUnicode_GET_LENGTH(to));
+    assert(to == NULL || PyUnicode_Check(to));
 
-    if (how_many == 0)
+    if (how_many == 0) {
         return 0;
+    }
+
+    assert(to != NULL);
+    assert(to_start + how_many <= PyUnicode_GET_LENGTH(to));
 
     from_kind = PyUnicode_KIND(from);
     from_data = PyUnicode_DATA(from);