fix(time): make struct_time type immutable

Author: ashm-dev

Doc/c-api/tuple.rst

@@ -232,10 +232,6 @@ type.
    Creates an instance of *type*, which must have been created with
    :c:func:`PyStructSequence_NewType`.
 
-   The returned instance is not tracked by the garbage collector. If the
-   instance can contain objects that participate in reference cycles, call
-   :c:func:`PyObject_GC_Track` after populating its fields.
-
    Return ``NULL`` with an exception set on failure.
 
 

Lib/test/test_structseq.py

@@ -351,9 +351,9 @@ def test_reference_cycle(self):
         # was cleared first, the structseq instance would crash in the
         # destructor.
         script_helper.assert_python_ok("-c", textwrap.dedent(r"""
-            import time
-            t = time.gmtime()
-            type(t).refcyle = t
+            import os
+            t = os.stat('.')
+            type(t).refcycle = t
         """))
 
     def test_replace_gc_tracked(self):
@@ -365,12 +365,10 @@ def test_replace_gc_tracked(self):
 
         self.assertTrue(gc.is_tracked(replaced_struct))
 
-    def test_gc_tracked(self):
-        # Instances created via Python or stdlib callers that may participate
-        # in cycles are GC-tracked; simple instances like os.stat_result are not.
-        self.assertTrue(gc.is_tracked(time.gmtime()))
-        self.assertTrue(gc.is_tracked(time.struct_time((2020, 1, 1, 0, 0, 0, 0, 1, 0))))
-        self.assertFalse(gc.is_tracked(os.stat(__file__)))
+    def test_struct_time_type_immutable(self):
+        t = time.gmtime()
+        with self.assertRaisesRegex(TypeError, "immutable type"):
+            type(t).refcycle = t
 
 if __name__ == "__main__":
     unittest.main()

Lib/test/test_sys.py

@@ -1969,7 +1969,6 @@ def test_asyncgen_hooks(self):
 
         sys.set_asyncgen_hooks(firstiter=firstiter)
         hooks = sys.get_asyncgen_hooks()
-        self.assertTrue(gc.is_tracked(hooks))
         self.assertIs(hooks.firstiter, firstiter)
         self.assertIs(hooks[0], firstiter)
         self.assertIs(hooks.finalizer, None)

Misc/NEWS.d/next/Core_and_Builtins/2026-09-08-15-55-00.gh-issue-157176.yZ8a1B.rst

@@ -1 +1 @@
-Track :func:`time.struct_time` and :func:`sys.get_asyncgen_hooks` objects in the garbage collector to prevent reference cycle leaks. Patch by Shamil Abdulaev.
+Make the :class:`time.struct_time` type immutable to prevent reference cycles between the type and its instances. Patch by Shamil Abdulaev.

Modules/timemodule.c

@@ -5,6 +5,7 @@
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 #include "pycore_namespace.h"     // _PyNamespace_New()
 #include "pycore_runtime.h"       // _Py_ID()
+#include "pycore_structseq.h"     // _PyStructSequence_NewType()
 #include "pycore_time.h"          // _PyTimeFraction
 
 #include <time.h>                 // clock()
@@ -497,7 +498,6 @@ tmtotuple(time_module_state *state, struct tm *p
 #undef SET
 #undef SET_ITEM
 
-    PyObject_GC_Track(v);
     return v;
 }
 
@@ -2111,7 +2111,8 @@ time_exec(PyObject *module)
     }
 
     // struct_time type
-    state->struct_time_type = PyStructSequence_NewType(&struct_time_type_desc);
+    state->struct_time_type = _PyStructSequence_NewType(
+        &struct_time_type_desc, Py_TPFLAGS_IMMUTABLETYPE);
     if (state->struct_time_type == NULL) {
         return -1;
     }

Python/sysmodule.c

@@ -1531,7 +1531,6 @@ sys_get_asyncgen_hooks_impl(PyObject *module)
     PyStructSequence_SET_ITEM(res, 0, Py_NewRef(firstiter));
     PyStructSequence_SET_ITEM(res, 1, Py_NewRef(finalizer));
 
-    PyObject_GC_Track(res);
     return res;
 }