gh-148722: Make code objects support cyclic GC

Author: iamrajhans

Lib/test/test_code.py

@@ -1282,6 +1282,19 @@ def callback(code):
         self.assertFalse(bool(coderef()))
         self.assertTrue(self.called)
 
+    def test_code_const_reference_cycle_collected(self):
+        def f():
+            return 1234.5
+
+        a = []
+        code = f.__code__.replace(co_consts=f.__code__.co_consts + (a,))
+        coderef = weakref.ref(code)
+        a.append(code)
+
+        del code, a
+        gc_collect()
+        self.assertIsNone(coderef())
+
 # Python implementation of location table parsing algorithm
 def read(it):
     return next(it)

Lib/test/test_marshal.py

@@ -357,8 +357,7 @@ def f():
         code = f.__code__
         a = []
         code = code.replace(co_consts=code.co_consts + (a,))
-        # This test creates a reference loop which leads to reference leaks,
-        # so we need to break the loop manually. See gh-148722.
+        # Break the cycle without relying on cyclic GC after the test.
         self.addCleanup(a.clear)
         a.append(code)
         for v in range(marshal.version + 1):

Misc/NEWS.d/next/Core_and_Builtins/2026-06-05-14-45-00.gh-issue-148722.A7mV9e.rst

@@ -0,0 +1,2 @@
+Fix a reference leak when a code object's constants contain a reference cycle
+back to the code object.

Objects/codeobject.c

@@ -731,12 +731,7 @@ _PyCode_New(struct _PyCodeConstructor *con)
     }
 
     Py_ssize_t size = PyBytes_GET_SIZE(con->code) / sizeof(_Py_CODEUNIT);
-    PyCodeObject *co;
-#ifdef Py_GIL_DISABLED
-    co = PyObject_GC_NewVar(PyCodeObject, &PyCode_Type, size);
-#else
-    co = PyObject_NewVar(PyCodeObject, &PyCode_Type, size);
-#endif
+    PyCodeObject *co = PyObject_GC_NewVar(PyCodeObject, &PyCode_Type, size);
     if (co == NULL) {
         Py_XDECREF(replacement_locations);
         PyErr_NoMemory();
@@ -750,8 +745,8 @@ _PyCode_New(struct _PyCodeConstructor *con)
 
 #ifdef Py_GIL_DISABLED
     co->_co_unique_id = _PyObject_AssignUniqueId((PyObject *)co);
-    _PyObject_GC_TRACK(co);
 #endif
+    _PyObject_GC_TRACK(co);
     Py_XDECREF(replacement_locations);
     return co;
 }
@@ -2402,9 +2397,7 @@ code_dealloc(PyObject *self)
         return;
     }
 
-#ifdef Py_GIL_DISABLED
     PyObject_GC_UnTrack(co);
-#endif
 
     _PyFunction_ClearCodeByVersion(co->co_version);
     if (co->co_extra != NULL) {
@@ -2459,18 +2452,16 @@ code_dealloc(PyObject *self)
     }
     PyMem_Free(co->co_tlbc);
 #endif
-    PyObject_Free(co);
+    PyObject_GC_Del(co);
 }
 
-#ifdef Py_GIL_DISABLED
 static int
 code_traverse(PyObject *self, visitproc visit, void *arg)
 {
     PyCodeObject *co = _PyCodeObject_CAST(self);
     Py_VISIT(co->co_consts);
     return 0;
 }
-#endif
 
 static PyObject *
 code_repr(PyObject *self)
@@ -2890,17 +2881,9 @@ PyTypeObject PyCode_Type = {
     PyObject_GenericGetAttr,            /* tp_getattro */
     0,                                  /* tp_setattro */
     0,                                  /* tp_as_buffer */
-#ifdef Py_GIL_DISABLED
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
-#else
-    Py_TPFLAGS_DEFAULT,                 /* tp_flags */
-#endif
     code_new__doc__,                    /* tp_doc */
-#ifdef Py_GIL_DISABLED
     code_traverse,                      /* tp_traverse */
-#else
-    0,                                  /* tp_traverse */
-#endif
     0,                                  /* tp_clear */
     code_richcompare,                   /* tp_richcompare */
     offsetof(PyCodeObject, co_weakreflist),     /* tp_weaklistoffset */