gh-158095: Fix reference cycles in re scanners (#158100)

* Fix reference cycles in re scanners

* 📜🤖 Added by blurb_it.

* gh-158095: Normalize NEWS line endings

* gh-158095: Clear input references in re scanners

* ci: rerun checks

Assisted-by: Codex:GPT-6

---------

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Author: YangSiJun528

Lib/test/test_re.py

@@ -9,6 +9,7 @@
 import sys
 import unittest
 import warnings
+import weakref
 from re import Scanner
 from weakref import proxy
 
@@ -1940,6 +1941,27 @@ def test_finditer(self):
         self.assertEqual([item.group(0) for item in iter],
                          ["::", "::"])
 
+    def test_finditer_gc(self):
+        class Text(str):
+            pass
+
+        class Buffer(bytearray):
+            pass
+
+        text = Text('a')
+        text.iterator = re.finditer('a', text)
+        ref = weakref.ref(text)
+        del text
+        gc_collect()
+        self.assertIsNone(ref())
+
+        buffer = Buffer(b'a')
+        buffer.iterator = re.finditer(b'a', buffer)
+        ref = weakref.ref(buffer)
+        del buffer
+        gc_collect()
+        self.assertIsNone(ref())
+
     def test_bug_926075(self):
         self.assertIsNot(re.compile('bug_926075'),
                          re.compile(b'bug_926075'))

Misc/NEWS.d/next/Library/2026-09-24-14-59-08.gh-issue-158095.lcKOT4.rst

@@ -0,0 +1,2 @@
+Fix a memory leak in :func:`re.finditer` and regular expression scanners when
+their input participates in a reference cycle.

Modules/_sre/sre.c

@@ -3023,14 +3023,19 @@ scanner_traverse(PyObject *op, visitproc visit, void *arg)
     ScannerObject *self = _ScannerObject_CAST(op);
     Py_VISIT(Py_TYPE(self));
     Py_VISIT(self->pattern);
+    Py_VISIT(self->state.string);
+    Py_VISIT(self->state.buffer.obj);
     return 0;
 }
 
 static int
 scanner_clear(PyObject *op)
 {
     ScannerObject *self = _ScannerObject_CAST(op);
+    self->state.start = NULL;
     Py_CLEAR(self->pattern);
+    Py_CLEAR(self->state.string);
+    PyBuffer_Release(&self->state.buffer);
     return 0;
 }
 
@@ -3040,8 +3045,8 @@ scanner_dealloc(PyObject *self)
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
     ScannerObject *scanner = _ScannerObject_CAST(self);
-    state_fini(&scanner->state);
     (void)scanner_clear(self);
+    state_fini(&scanner->state);
     tp->tp_free(self);
     Py_DECREF(tp);
 }