From 919295b3884d471249e13278420c7d21b54f2917 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Fri, 9 Jan 2026 17:50:38 +0200
Subject: [PATCH 1/2] gh-143196: Fix crash in non-standard use of internal JSON
 encoder object

The internal encoder object returned by undocumented function
json.encoder.c_make_encoder() (aka _json.make_encoder()) crashed
when it was called with non-zero second argument.
---
 Lib/test/test_json/test_speedups.py           | 35 +++++++++++++++++++
 ...-01-09-17-50-26.gh-issue-143196.WxKxzU.rst |  3 ++
 Modules/_json.c                               |  1 +
 3 files changed, 39 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst

diff --git a/Lib/test/test_json/test_speedups.py b/Lib/test/test_json/test_speedups.py
index 682014cfd5b344..4eeb7b002b4415 100644
--- a/Lib/test/test_json/test_speedups.py
+++ b/Lib/test/test_json/test_speedups.py
@@ -80,3 +80,38 @@ def test(name):
     def test_unsortable_keys(self):
         with self.assertRaises(TypeError):
             self.json.encoder.JSONEncoder(sort_keys=True).encode({'a': 1, 1: 'a'})
+
+    def test_current_indent_level(self):
+        enc = self.json.encoder.c_make_encoder(
+            markers=None,
+            default=str,
+            encoder=self.json.encoder.c_encode_basestring,
+            indent='\t',
+            key_separator=': ',
+            item_separator=', ',
+            sort_keys=False,
+            skipkeys=False,
+            allow_nan=False)
+        self.assertEqual(enc(['spam', {'ham': 'eggs'}], 0)[0],
+                         '[\n'
+                         '\t"spam", \n'
+                         '\t{\n'
+                         '\t\t"ham": "eggs"\n'
+                         '\t}\n'
+                         ']')
+        self.assertEqual(enc(['spam', {'ham': 'eggs'}], 3)[0],
+                         '[\n'
+                         '\t\t\t\t"spam", \n'
+                         '\t\t\t\t{\n'
+                         '\t\t\t\t\t"ham": "eggs"\n'
+                         '\t\t\t\t}\n'
+                         '\t\t\t]')
+        self.assertEqual(enc(['spam', {'ham': 'eggs'}], -3)[0],
+                         '[\n'
+                         '\t"spam", \n'
+                         '\t{\n'
+                         '\t\t"ham": "eggs"\n'
+                         '\t}\n'
+                         ']')
+        self.assertRaises(TypeError, enc, ['spam', {'ham': 'eggs'}], 3.0)
+        self.assertRaises(TypeError, enc, ['spam', {'ham': 'eggs'}])
diff --git a/Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst b/Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst
new file mode 100644
index 00000000000000..a9e5997ffaf4ab
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst
@@ -0,0 +1,3 @@
+Fix crash when the internal encoder object returned by undocumented function
+:func:`json.encoder.c_make_encoder` was called with non-zero second
+(*_current_indent_level*) argument.
diff --git a/Modules/_json.c b/Modules/_json.c
index 14714d4b346546..e2ee96ba39fe03 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -1459,6 +1459,7 @@ encoder_call(PyObject *op, PyObject *args, PyObject *kwds)
             return NULL;
         }
     }
+    indent_level = 0;
     if (encoder_listencode_obj(self, writer, obj, indent_level, indent_cache)) {
         PyUnicodeWriter_Discard(writer);
         Py_XDECREF(indent_cache);

From 4d0d3bb6a084b8487528433183aa57a4393c1d1b Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Fri, 9 Jan 2026 18:47:12 +0200
Subject: [PATCH 2/2] Fix documentation for json.encoder.c_make_encoder

---
 .../next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst b/Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst
index a9e5997ffaf4ab..9143cf2aeccc9e 100644
--- a/Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst
+++ b/Misc/NEWS.d/next/Library/2026-01-09-17-50-26.gh-issue-143196.WxKxzU.rst
@@ -1,3 +1,3 @@
 Fix crash when the internal encoder object returned by undocumented function
-:func:`json.encoder.c_make_encoder` was called with non-zero second
+:func:`!json.encoder.c_make_encoder` was called with non-zero second
 (*_current_indent_level*) argument.