gh-140232: Do not track frozenset objects with immutables

Lib/test/test_sys.py

@@ -1876,7 +1876,10 @@ class S(set):
         check(S(), set(), '3P')
         class FS(frozenset):
             __slots__ = 'a', 'b', 'c'
-        check(FS(), frozenset(), '3P')
+
+        class mytuple(tuple):
+            pass
+        check(FS([mytuple()]), frozenset([mytuple()]), '3P')
         from collections import OrderedDict
         class OD(OrderedDict):
             __slots__ = 'a', 'b', 'c'

Misc/NEWS.d/next/Core_and_Builtins/2025-10-16-22-36-05.gh-issue-140232.u3srgv.rst

@@ -0,0 +1 @@
+Frozenset objects with immutable elements are no longer tracked by the garbage collector.

Objects/setobject.c

@@ -1174,6 +1174,23 @@ make_new_set_basetype(PyTypeObject *type, PyObject *iterable)
     return make_new_set(type, iterable);
 }
 
+void
+_PyFrozenSet_MaybeUntrack(PyObject *op)
+{
+    if ((op == NULL) || !(PyFrozenSet_CheckExact(op))) {
+        return;
+    }
+    // if all elements of a frozenset are not tracked, we untrack the object
+    Py_ssize_t pos = 0;
+    setentry *entry;
+    while (set_next((PySetObject *)op, &pos, &entry)) {
+        if (_PyObject_GC_MAY_BE_TRACKED(entry->key)) {
+            return;
+        }
+    }
+    _PyObject_GC_UNTRACK(op);
+}
+
 static PyObject *
 make_new_frozenset(PyTypeObject *type, PyObject *iterable)
 {
@@ -1185,7 +1202,9 @@ make_new_frozenset(PyTypeObject *type, PyObject *iterable)
         /* frozenset(f) is idempotent */
         return Py_NewRef(iterable);
     }
-    return make_new_set(type, iterable);
+    PyObject *obj = make_new_set(type, iterable);
+    _PyFrozenSet_MaybeUntrack(obj);
+    return obj;
 }
 
 static PyObject *
@@ -2710,7 +2729,9 @@ PySet_New(PyObject *iterable)
 PyObject *
 PyFrozenSet_New(PyObject *iterable)
 {
-    return make_new_set(&PyFrozenSet_Type, iterable);
+    PyObject *result = make_new_set(&PyFrozenSet_Type, iterable);
+    _PyFrozenSet_MaybeUntrack(result);
+    return result;
 }
 
 Py_ssize_t