From f1b3c94826f58607b8a75f4d88955185d9e50fc7 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 7 Oct 2025 20:01:21 +0300
Subject: [PATCH 01/22] First variant of stackref tests

---
 Lib/test/test_stackrefs.py  | 83 +++++++++++++++++++++++++++++++
 Modules/_testinternalcapi.c | 98 +++++++++++++++++++++++++++++++++++++
 2 files changed, 181 insertions(+)
 create mode 100644 Lib/test/test_stackrefs.py

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
new file mode 100644
index 00000000000000..2aabc0d82c0d7c
--- /dev/null
+++ b/Lib/test/test_stackrefs.py
@@ -0,0 +1,83 @@
+import unittest
+import sys
+from test.support import cpython_only
+try:
+    import _testinternalcapi
+except ImportError:
+    _testinternalcapi = None
+
+
+class StackRef:
+    def __init__(self, obj, flags):
+        self.obj = obj
+        self.flags = flags
+        self.refcount = sys.getrefcount(obj)
+
+    def __str__(self):
+        return f"StackRef(obj={self.obj}, flags={self.flags}, refcount={self.refcount})"
+
+    def __eq__(self, other):
+        return (
+            self.obj is other.obj
+            and self.flags == other.flags
+            and self.refcount == other.refcount
+        )
+
+    def __hash__(self):
+        return tuple.__hash__((self.obj, self.flags, self.refcount))
+
+
+@cpython_only
+class TestStackRef(unittest.TestCase):
+
+    def test_equivalent(self):
+        def run_with_refcount_check(self, func, obj):
+            refcount = sys.getrefcount(obj)
+            res = func(obj)
+            self.assertEqual(sys.getrefcount(obj), refcount)
+            return res
+
+        def stackref_from_object_borrow(obj):
+            return _testinternalcapi.stackref_from_object_borrow(obj)
+
+        funcs = [
+            _testinternalcapi.stackref_from_object_new,
+            _testinternalcapi.stackref_from_object_new2,
+            _testinternalcapi.stackref_from_object_steal_with_incref,
+            _testinternalcapi.stackref_make_heap_safe,
+            _testinternalcapi.stackref_make_heap_safe_with_borrow,
+            _testinternalcapi.stackref_strong_reference,
+        ]
+
+        funcs2 = [
+            _testinternalcapi.stackref_from_object_borrow,
+            _testinternalcapi.stackref_dup_borrowed_with_close,
+        ]
+
+        for obj in (None, True, False, 42, '1'):
+            results = set()
+            for func in funcs + funcs2:
+                res = run_with_refcount_check(self, func, obj)
+                #print(func.__name__, obj, res)
+                results.add(res)
+            self.assertEqual(len(results), 1)
+
+        for obj in (5000, range(10)):
+            results = set()
+            for func in funcs:
+                res = run_with_refcount_check(self, func, obj)
+                #print(func.__name__, obj, res)
+                results.add(res)
+            self.assertEqual(len(results), 1)
+
+            results = set()
+            for func in funcs2:
+                res = run_with_refcount_check(self, func, obj)
+                #print(func.__name__, obj, res)
+                results.add(res)
+            self.assertEqual(len(results), 1)
+
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index c2647d405e25bc..64c52d44c50e44 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -35,6 +35,7 @@
 #include "pycore_pylifecycle.h"   // _PyInterpreterConfig_InitFromDict()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
 #include "pycore_runtime_structs.h" // _PY_NSMALLPOSINTS
+#include "pycore_stackref.h"      // PyStackRef_FunctionCheck()
 #include "pycore_unicodeobject.h" // _PyUnicode_TransformDecimalAndSpaceToASCII()
 
 #include "clinic/_testinternalcapi.c.h"
@@ -2418,6 +2419,95 @@ set_vectorcall_nop(PyObject *self, PyObject *func)
     Py_RETURN_NONE;
 }
 
+static PyObject *
+stackref_to_tuple(_PyStackRef ref, PyObject *op)
+{
+    int flags = ref.bits & Py_TAG_BITS;
+    return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
+}
+
+static PyObject *
+stackref_from_object_new(PyObject *self, PyObject *op)
+{
+    _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
+    PyObject *obj = stackref_to_tuple(ref, op);
+    PyStackRef_CLOSE(ref);
+    return obj;
+}
+
+static PyObject *
+stackref_from_object_new2(PyObject *self, PyObject *op)
+{
+    _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
+    PyObject *obj = stackref_to_tuple(ref, op);
+    PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
+    Py_DECREF(op2);
+    return obj;
+}
+
+static PyObject *
+stackref_from_object_steal_with_incref(PyObject *self, PyObject *op)
+{
+    Py_INCREF(op);
+    _PyStackRef ref = PyStackRef_FromPyObjectSteal(op);
+    PyObject *obj = stackref_to_tuple(ref, op);
+    PyStackRef_CLOSE(ref);
+    return obj;
+}
+
+static PyObject *
+stackref_make_heap_safe(PyObject *self, PyObject *op)
+{
+    _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
+    _PyStackRef ref2 = PyStackRef_MakeHeapSafe(ref);
+    PyObject *obj = stackref_to_tuple(ref2, op);
+    PyStackRef_CLOSE(ref2);
+    return obj;
+}
+
+static PyObject *
+stackref_make_heap_safe_with_borrow(PyObject *self, PyObject *op)
+{
+    _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
+    _PyStackRef ref2 = PyStackRef_Borrow(ref);
+    _PyStackRef ref3 = PyStackRef_MakeHeapSafe(ref2);
+    PyStackRef_CLOSE(ref);
+    PyObject *obj = stackref_to_tuple(ref3, op);
+    PyStackRef_CLOSE(ref3);
+    return obj;
+}
+
+static PyObject *
+stackref_strong_reference(PyObject *self, PyObject *op)
+{
+    _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
+    PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
+    _PyStackRef ref2 = PyStackRef_FromPyObjectSteal(op2);
+    PyObject *obj = stackref_to_tuple(ref2, op);
+    PyStackRef_CLOSE(ref2);
+    return obj;
+}
+
+static PyObject *
+stackref_from_object_borrow(PyObject *self, PyObject *op)
+{
+    _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
+    PyObject *obj = stackref_to_tuple(ref, op);
+    PyStackRef_CLOSE(ref);
+    return obj;
+}
+
+static PyObject *
+stackref_dup_borrowed_with_close(PyObject *self, PyObject *op)
+{
+    _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
+    _PyStackRef ref2 = PyStackRef_DUP(ref);
+    PyStackRef_XCLOSE(ref);
+    PyObject *obj = stackref_to_tuple(ref2, op);
+    PyStackRef_XCLOSE(ref2);
+    return obj;
+}
+
 static PyMethodDef module_functions[] = {
     {"get_configs", get_configs, METH_NOARGS},
     {"get_recursion_depth", get_recursion_depth, METH_NOARGS},
@@ -2527,6 +2617,14 @@ static PyMethodDef module_functions[] = {
 #endif
     {"simple_pending_call", simple_pending_call, METH_O},
     {"set_vectorcall_nop", set_vectorcall_nop, METH_O},
+    {"stackref_from_object_new", stackref_from_object_new, METH_O},
+    {"stackref_from_object_new2", stackref_from_object_new2, METH_O},
+    {"stackref_from_object_steal_with_incref", stackref_from_object_steal_with_incref, METH_O},
+    {"stackref_make_heap_safe", stackref_make_heap_safe, METH_O},
+    {"stackref_make_heap_safe_with_borrow", stackref_make_heap_safe_with_borrow, METH_O},
+    {"stackref_strong_reference", stackref_strong_reference, METH_O},
+    {"stackref_from_object_borrow", stackref_from_object_borrow, METH_O},
+    {"stackref_dup_borrowed_with_close", stackref_dup_borrowed_with_close, METH_O},
     {NULL, NULL} /* sentinel */
 };
 

From 871c013d76a542ec1c2cb2b1523b655a999a4d26 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 7 Oct 2025 20:50:16 +0300
Subject: [PATCH 02/22] Fixes for Py_STACKREF_DEBUG build

---
 Modules/_testinternalcapi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 64c52d44c50e44..873970884830b8 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2422,7 +2422,11 @@ set_vectorcall_nop(PyObject *self, PyObject *func)
 static PyObject *
 stackref_to_tuple(_PyStackRef ref, PyObject *op)
 {
+#if !defined(Py_GIL_DISABLED) && defined(Py_STACKREF_DEBUG)
+    int flags = ref.index & Py_TAG_BITS;
+#else
     int flags = ref.bits & Py_TAG_BITS;
+#endif
     return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
 }
 

From 0a82e96a668fdc3f715c6f53851b91a46b7c1e56 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 7 Oct 2025 21:16:38 +0300
Subject: [PATCH 03/22] Improvements

---
 Lib/test/test_stackrefs.py  | 50 ++++++++++---------------------------
 Modules/_testinternalcapi.c | 14 ++---------
 2 files changed, 15 insertions(+), 49 deletions(-)

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 2aabc0d82c0d7c..227deff8cb1114 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -6,74 +6,50 @@
 except ImportError:
     _testinternalcapi = None
 
-
-class StackRef:
-    def __init__(self, obj, flags):
-        self.obj = obj
-        self.flags = flags
-        self.refcount = sys.getrefcount(obj)
-
-    def __str__(self):
-        return f"StackRef(obj={self.obj}, flags={self.flags}, refcount={self.refcount})"
-
-    def __eq__(self, other):
-        return (
-            self.obj is other.obj
-            and self.flags == other.flags
-            and self.refcount == other.refcount
-        )
-
-    def __hash__(self):
-        return tuple.__hash__((self.obj, self.flags, self.refcount))
-
-
 @cpython_only
-class TestStackRef(unittest.TestCase):
+class TestDefinition(unittest.TestCase):
 
-    def test_equivalent(self):
+    def test_equivalence(self):
         def run_with_refcount_check(self, func, obj):
             refcount = sys.getrefcount(obj)
             res = func(obj)
             self.assertEqual(sys.getrefcount(obj), refcount)
             return res
 
-        def stackref_from_object_borrow(obj):
-            return _testinternalcapi.stackref_from_object_borrow(obj)
-
-        funcs = [
+        funcs_with_incref = [
             _testinternalcapi.stackref_from_object_new,
-            _testinternalcapi.stackref_from_object_new2,
             _testinternalcapi.stackref_from_object_steal_with_incref,
             _testinternalcapi.stackref_make_heap_safe,
             _testinternalcapi.stackref_make_heap_safe_with_borrow,
             _testinternalcapi.stackref_strong_reference,
         ]
 
-        funcs2 = [
+        funcs_with_borrow = [
             _testinternalcapi.stackref_from_object_borrow,
             _testinternalcapi.stackref_dup_borrowed_with_close,
         ]
 
-        for obj in (None, True, False, 42, '1'):
+        immortal_objs = (None, True, False, 42, '1')
+
+        for obj in immortal_objs:
             results = set()
-            for func in funcs + funcs2:
+            for func in funcs_with_incref + funcs_with_borrow:
                 res = run_with_refcount_check(self, func, obj)
-                #print(func.__name__, obj, res)
                 results.add(res)
             self.assertEqual(len(results), 1)
 
-        for obj in (5000, range(10)):
+        mortal_objs = (5000, 3+2j, range(10))
+
+        for obj in mortal_objs:
             results = set()
-            for func in funcs:
+            for func in funcs_with_incref:
                 res = run_with_refcount_check(self, func, obj)
-                #print(func.__name__, obj, res)
                 results.add(res)
             self.assertEqual(len(results), 1)
 
             results = set()
-            for func in funcs2:
+            for func in funcs_with_borrow:
                 res = run_with_refcount_check(self, func, obj)
-                #print(func.__name__, obj, res)
                 results.add(res)
             self.assertEqual(len(results), 1)
 
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 873970884830b8..6dea8e23a61624 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2439,23 +2439,14 @@ stackref_from_object_new(PyObject *self, PyObject *op)
     return obj;
 }
 
-static PyObject *
-stackref_from_object_new2(PyObject *self, PyObject *op)
-{
-    _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
-    PyObject *obj = stackref_to_tuple(ref, op);
-    PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
-    Py_DECREF(op2);
-    return obj;
-}
-
 static PyObject *
 stackref_from_object_steal_with_incref(PyObject *self, PyObject *op)
 {
     Py_INCREF(op);
     _PyStackRef ref = PyStackRef_FromPyObjectSteal(op);
     PyObject *obj = stackref_to_tuple(ref, op);
-    PyStackRef_CLOSE(ref);
+    PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
+    Py_DECREF(op2);
     return obj;
 }
 
@@ -2622,7 +2613,6 @@ static PyMethodDef module_functions[] = {
     {"simple_pending_call", simple_pending_call, METH_O},
     {"set_vectorcall_nop", set_vectorcall_nop, METH_O},
     {"stackref_from_object_new", stackref_from_object_new, METH_O},
-    {"stackref_from_object_new2", stackref_from_object_new2, METH_O},
     {"stackref_from_object_steal_with_incref", stackref_from_object_steal_with_incref, METH_O},
     {"stackref_make_heap_safe", stackref_make_heap_safe, METH_O},
     {"stackref_make_heap_safe_with_borrow", stackref_make_heap_safe_with_borrow, METH_O},

From a5e39e8911ad406d008689a91372b98eb62f26eb Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 7 Oct 2025 22:09:52 +0300
Subject: [PATCH 04/22] Do not check flags on FT build

---
 Modules/_testinternalcapi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 6dea8e23a61624..525935f70c148f 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2424,6 +2424,8 @@ stackref_to_tuple(_PyStackRef ref, PyObject *op)
 {
 #if !defined(Py_GIL_DISABLED) && defined(Py_STACKREF_DEBUG)
     int flags = ref.index & Py_TAG_BITS;
+#elif defined(Py_GIL_DISABLED)
+    int flags = 0;
 #else
     int flags = ref.bits & Py_TAG_BITS;
 #endif

From 6feef7a7be2646c337be30ab1ca0f1232531ab06 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 27 Oct 2025 19:28:06 +0300
Subject: [PATCH 05/22] Review addressed

---
 Include/internal/pycore_stackref.h | 20 ++++++++++++++++++++
 Lib/test/test_stackrefs.py         |  2 +-
 Modules/_testinternalcapi.c        | 27 +++++++--------------------
 3 files changed, 28 insertions(+), 21 deletions(-)

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index 94fcb1d8aee52b..7d7254d16f6b03 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -74,6 +74,13 @@ static const _PyStackRef PyStackRef_ERROR = { .index = (1 << Py_TAGGED_SHIFT) };
 
 #define INITIAL_STACKREF_INDEX (5 << Py_TAGGED_SHIFT)
 
+static inline PyObject *
+_PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
+{
+    int flags = ref.index & Py_TAG_BITS;
+    return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
+}
+
 static inline _PyStackRef
 PyStackRef_Wrap(void *ptr)
 {
@@ -447,6 +454,12 @@ static const _PyStackRef PyStackRef_NULL = { .bits = Py_TAG_DEFERRED};
 
 #define PyStackRef_IsNullOrInt(stackref) (PyStackRef_IsNull(stackref) || PyStackRef_IsTaggedInt(stackref))
 
+static inline PyObject *
+_PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
+{
+    return Py_BuildValue("(Ii)", Py_REFCNT(op), 0);
+}
+
 static inline PyObject *
 PyStackRef_AsPyObjectBorrow(_PyStackRef stackref)
 {
@@ -633,6 +646,13 @@ static const _PyStackRef PyStackRef_NULL = { .bits = PyStackRef_NULL_BITS };
 
 #ifdef Py_DEBUG
 
+static inline PyObject *
+_PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
+{
+    int flags = ref.bits & Py_TAG_BITS;
+    return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
+}
+
 static inline void PyStackRef_CheckValid(_PyStackRef ref) {
     assert(ref.bits != 0);
     int tag = ref.bits & Py_TAG_BITS;
diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 227deff8cb1114..955a5e7b5b0a45 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -38,7 +38,7 @@ def run_with_refcount_check(self, func, obj):
                 results.add(res)
             self.assertEqual(len(results), 1)
 
-        mortal_objs = (5000, 3+2j, range(10))
+        mortal_objs = (5000, 3+2j, range(10), object())
 
         for obj in mortal_objs:
             results = set()
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 525935f70c148f..6594506b5a349f 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2419,24 +2419,11 @@ set_vectorcall_nop(PyObject *self, PyObject *func)
     Py_RETURN_NONE;
 }
 
-static PyObject *
-stackref_to_tuple(_PyStackRef ref, PyObject *op)
-{
-#if !defined(Py_GIL_DISABLED) && defined(Py_STACKREF_DEBUG)
-    int flags = ref.index & Py_TAG_BITS;
-#elif defined(Py_GIL_DISABLED)
-    int flags = 0;
-#else
-    int flags = ref.bits & Py_TAG_BITS;
-#endif
-    return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
-}
-
 static PyObject *
 stackref_from_object_new(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
-    PyObject *obj = stackref_to_tuple(ref, op);
+    PyObject *obj = _PyStackRef_AsTuple(ref, op);
     PyStackRef_CLOSE(ref);
     return obj;
 }
@@ -2446,7 +2433,7 @@ stackref_from_object_steal_with_incref(PyObject *self, PyObject *op)
 {
     Py_INCREF(op);
     _PyStackRef ref = PyStackRef_FromPyObjectSteal(op);
-    PyObject *obj = stackref_to_tuple(ref, op);
+    PyObject *obj = _PyStackRef_AsTuple(ref, op);
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     Py_DECREF(op2);
     return obj;
@@ -2457,7 +2444,7 @@ stackref_make_heap_safe(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
     _PyStackRef ref2 = PyStackRef_MakeHeapSafe(ref);
-    PyObject *obj = stackref_to_tuple(ref2, op);
+    PyObject *obj = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_CLOSE(ref2);
     return obj;
 }
@@ -2469,7 +2456,7 @@ stackref_make_heap_safe_with_borrow(PyObject *self, PyObject *op)
     _PyStackRef ref2 = PyStackRef_Borrow(ref);
     _PyStackRef ref3 = PyStackRef_MakeHeapSafe(ref2);
     PyStackRef_CLOSE(ref);
-    PyObject *obj = stackref_to_tuple(ref3, op);
+    PyObject *obj = _PyStackRef_AsTuple(ref3, op);
     PyStackRef_CLOSE(ref3);
     return obj;
 }
@@ -2480,7 +2467,7 @@ stackref_strong_reference(PyObject *self, PyObject *op)
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     _PyStackRef ref2 = PyStackRef_FromPyObjectSteal(op2);
-    PyObject *obj = stackref_to_tuple(ref2, op);
+    PyObject *obj = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_CLOSE(ref2);
     return obj;
 }
@@ -2489,7 +2476,7 @@ static PyObject *
 stackref_from_object_borrow(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
-    PyObject *obj = stackref_to_tuple(ref, op);
+    PyObject *obj = _PyStackRef_AsTuple(ref, op);
     PyStackRef_CLOSE(ref);
     return obj;
 }
@@ -2500,7 +2487,7 @@ stackref_dup_borrowed_with_close(PyObject *self, PyObject *op)
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
     _PyStackRef ref2 = PyStackRef_DUP(ref);
     PyStackRef_XCLOSE(ref);
-    PyObject *obj = stackref_to_tuple(ref2, op);
+    PyObject *obj = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_XCLOSE(ref2);
     return obj;
 }

From 6390e57bc8b6f71e66b03ae370f1b2ebb6b6fb84 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 27 Oct 2025 22:13:45 +0300
Subject: [PATCH 06/22] Build fix

---
 Include/internal/pycore_stackref.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index 7d7254d16f6b03..fdbe1bd1e32f0e 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -644,8 +644,6 @@ static const _PyStackRef PyStackRef_NULL = { .bits = PyStackRef_NULL_BITS };
 #define PyStackRef_IsFalse(REF) ((REF).bits == (((uintptr_t)&_Py_FalseStruct) | Py_TAG_REFCNT))
 #define PyStackRef_IsNone(REF) ((REF).bits == (((uintptr_t)&_Py_NoneStruct) | Py_TAG_REFCNT))
 
-#ifdef Py_DEBUG
-
 static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {
@@ -653,6 +651,8 @@ _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
     return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
 }
 
+#ifdef Py_DEBUG
+
 static inline void PyStackRef_CheckValid(_PyStackRef ref) {
     assert(ref.bits != 0);
     int tag = ref.bits & Py_TAG_BITS;

From f0a09c34505722b2e6bc9fc5c3ac70a511ac4d4f Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 28 Oct 2025 10:40:49 +0300
Subject: [PATCH 07/22] Review addressed

---
 Include/internal/pycore_stackref.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index fdbe1bd1e32f0e..dd04a3f78caaf1 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -457,7 +457,8 @@ static const _PyStackRef PyStackRef_NULL = { .bits = Py_TAG_DEFERRED};
 static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {
-    return Py_BuildValue("(Ii)", Py_REFCNT(op), 0);
+    // Do not check StackRef flags in the free threading build.
+    return Py_BuildValue("(Ii)", Py_REFCNT(op), -1);
 }
 
 static inline PyObject *

From bf076549c79e65df4cd73cfd779be2bb31db680c Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 28 Oct 2025 11:15:04 +0300
Subject: [PATCH 08/22] Some comments are added

---
 Modules/_testinternalcapi.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 6594506b5a349f..1b7e97f336686e 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2431,9 +2431,11 @@ stackref_from_object_new(PyObject *self, PyObject *op)
 static PyObject *
 stackref_from_object_steal_with_incref(PyObject *self, PyObject *op)
 {
+    // The next two lines are equivalent to PyStackRef_FromPyObjectNew.
     Py_INCREF(op);
     _PyStackRef ref = PyStackRef_FromPyObjectSteal(op);
     PyObject *obj = _PyStackRef_AsTuple(ref, op);
+    // The next two lines are equivalent to PyStackRef_CLOSE.
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     Py_DECREF(op2);
     return obj;
@@ -2443,6 +2445,7 @@ static PyObject *
 stackref_make_heap_safe(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
+    // In no-GIL production build ref2 is equal to ref.
     _PyStackRef ref2 = PyStackRef_MakeHeapSafe(ref);
     PyObject *obj = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_CLOSE(ref2);
@@ -2455,6 +2458,7 @@ stackref_make_heap_safe_with_borrow(PyObject *self, PyObject *op)
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
     _PyStackRef ref2 = PyStackRef_Borrow(ref);
     _PyStackRef ref3 = PyStackRef_MakeHeapSafe(ref2);
+    // We can close ref, since ref3 is heap safe.
     PyStackRef_CLOSE(ref);
     PyObject *obj = _PyStackRef_AsTuple(ref3, op);
     PyStackRef_CLOSE(ref3);
@@ -2464,6 +2468,7 @@ stackref_make_heap_safe_with_borrow(PyObject *self, PyObject *op)
 static PyObject *
 stackref_strong_reference(PyObject *self, PyObject *op)
 {
+    // The next two lines are equivalent to op2 = Py_NewRef(op).
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     _PyStackRef ref2 = PyStackRef_FromPyObjectSteal(op2);
@@ -2485,7 +2490,9 @@ static PyObject *
 stackref_dup_borrowed_with_close(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
+    // In no-GIL production build ref2 is equal to ref.
     _PyStackRef ref2 = PyStackRef_DUP(ref);
+    // In production build closing borrowed ref is no-op.
     PyStackRef_XCLOSE(ref);
     PyObject *obj = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_XCLOSE(ref2);

From f53afa682aa9a099b39d842e3f40ce703b28553c Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 28 Oct 2025 11:20:06 +0300
Subject: [PATCH 09/22] Wording

---
 Modules/_testinternalcapi.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 1b7e97f336686e..d3f4158a40aac2 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2445,7 +2445,7 @@ static PyObject *
 stackref_make_heap_safe(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
-    // In no-GIL production build ref2 is equal to ref.
+    // For no-GIL release build ref2 is equal to ref.
     _PyStackRef ref2 = PyStackRef_MakeHeapSafe(ref);
     PyObject *obj = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_CLOSE(ref2);
@@ -2490,9 +2490,9 @@ static PyObject *
 stackref_dup_borrowed_with_close(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
-    // In no-GIL production build ref2 is equal to ref.
+    // For no-GIL release build ref2 is equal to ref.
     _PyStackRef ref2 = PyStackRef_DUP(ref);
-    // In production build closing borrowed ref is no-op.
+    // For release build closing borrowed ref is no-op.
     PyStackRef_XCLOSE(ref);
     PyObject *obj = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_XCLOSE(ref2);

From b1b3b2bb0cd4c188239da3a8f75fe3f9cb3d1284 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 17:06:15 +0300
Subject: [PATCH 10/22] Changes in Py_BuildValue calls

---
 Include/internal/pycore_stackref.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index 224398d5c6145a..b31d2a78f8fdc2 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -80,7 +80,7 @@ static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {
     int flags = ref.index & Py_TAG_BITS;
-    return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
+    return Py_BuildValue("(ni)", Py_REFCNT(op), flags);
 }
 
 static inline _PyStackRef
@@ -480,7 +480,7 @@ static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {
     // Do not check StackRef flags in the free threading build.
-    return Py_BuildValue("(Ii)", Py_REFCNT(op), -1);
+    return Py_BuildValue("(ni)", Py_REFCNT(op), flags);
 }
 
 static inline PyObject *
@@ -671,7 +671,7 @@ static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {
     int flags = ref.bits & Py_TAG_BITS;
-    return Py_BuildValue("(Ii)", Py_REFCNT(op), flags);
+    return Py_BuildValue("(ni)", Py_REFCNT(op), -1);
 }
 
 #ifdef Py_DEBUG

From d965529d0775668cf665bceed384fe744e50242a Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 17:09:17 +0300
Subject: [PATCH 11/22] Changes in Py_BuildValue calls 2

---
 Include/internal/pycore_stackref.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index b31d2a78f8fdc2..fddeb99ee204fe 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -480,7 +480,7 @@ static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {
     // Do not check StackRef flags in the free threading build.
-    return Py_BuildValue("(ni)", Py_REFCNT(op), flags);
+    return Py_BuildValue("(ni)", Py_REFCNT(op), -1);
 }
 
 static inline PyObject *
@@ -671,7 +671,7 @@ static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {
     int flags = ref.bits & Py_TAG_BITS;
-    return Py_BuildValue("(ni)", Py_REFCNT(op), -1);
+    return Py_BuildValue("(ni)", Py_REFCNT(op), flags);
 }
 
 #ifdef Py_DEBUG

From 77c88bbb4557e0a56b1229ff9b8d2558fd2b3b0a Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 18:48:40 +0300
Subject: [PATCH 12/22] Improvements in test

---
 Lib/test/test_stackrefs.py | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 955a5e7b5b0a45..0e5afc94331b33 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -9,6 +9,8 @@
 @cpython_only
 class TestDefinition(unittest.TestCase):
 
+    BIG_REFCOUNT = 1000
+
     def test_equivalence(self):
         def run_with_refcount_check(self, func, obj):
             refcount = sys.getrefcount(obj)
@@ -34,23 +36,30 @@ def run_with_refcount_check(self, func, obj):
         for obj in immortal_objs:
             results = set()
             for func in funcs_with_incref + funcs_with_borrow:
-                res = run_with_refcount_check(self, func, obj)
-                results.add(res)
+                refcount, flags = run_with_refcount_check(self, func, obj)
+                self.assertGreater(refcount, self.BIG_REFCOUNT)
+                self.assertIn(flags, (1, -1))
+                results.add((refcount, flags))
+
             self.assertEqual(len(results), 1)
 
-        mortal_objs = (5000, 3+2j, range(10), object())
+        mortal_objs = (object(), range(10), iter([1, 2, 3]))
 
         for obj in mortal_objs:
             results = set()
             for func in funcs_with_incref:
-                res = run_with_refcount_check(self, func, obj)
-                results.add(res)
+                refcount, flags = run_with_refcount_check(self, func, obj)
+                self.assertLess(refcount, self.BIG_REFCOUNT)
+                self.assertEqual(flags, 0)
+                results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 
             results = set()
             for func in funcs_with_borrow:
-                res = run_with_refcount_check(self, func, obj)
-                results.add(res)
+                refcount, flags = run_with_refcount_check(self, func, obj)
+                self.assertLess(refcount, self.BIG_REFCOUNT)
+                self.assertEqual(flags, 1)
+                results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 
 

From 06fe751a081c06541a0f28c629f00c19692147e1 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 18:50:05 +0300
Subject: [PATCH 13/22] Improvements in test 2

---
 Lib/test/test_stackrefs.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 0e5afc94331b33..9d038b666f1bc6 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -50,7 +50,7 @@ def run_with_refcount_check(self, func, obj):
             for func in funcs_with_incref:
                 refcount, flags = run_with_refcount_check(self, func, obj)
                 self.assertLess(refcount, self.BIG_REFCOUNT)
-                self.assertEqual(flags, 0)
+                self.assertIn(flags, (0, -1))
                 results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 
@@ -58,7 +58,7 @@ def run_with_refcount_check(self, func, obj):
             for func in funcs_with_borrow:
                 refcount, flags = run_with_refcount_check(self, func, obj)
                 self.assertLess(refcount, self.BIG_REFCOUNT)
-                self.assertEqual(flags, 1)
+                self.assertIn(flags, (1, -1))
                 results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 

From c9ae051d8f2ae771ab2b80067d1aa774652cf958 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 19:09:23 +0300
Subject: [PATCH 14/22] Remove blank line

---
 Lib/test/test_stackrefs.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 9d038b666f1bc6..8143a710f1a57b 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -40,7 +40,6 @@ def run_with_refcount_check(self, func, obj):
                 self.assertGreater(refcount, self.BIG_REFCOUNT)
                 self.assertIn(flags, (1, -1))
                 results.add((refcount, flags))
-
             self.assertEqual(len(results), 1)
 
         mortal_objs = (object(), range(10), iter([1, 2, 3]))

From 474f650ced253ab97bd0666382ad2614a1d10ab0 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 21:07:44 +0300
Subject: [PATCH 15/22] Use -1 in flags only for immortal objects on ft build

---
 Include/internal/pycore_stackref.h | 27 +++++++++++++--------------
 Lib/test/test_stackrefs.py         |  4 ++--
 2 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index fddeb99ee204fe..4655b2e6024aa7 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -376,6 +376,19 @@ PyStackRef_IsNullOrInt(_PyStackRef ref);
 
 static const _PyStackRef PyStackRef_ERROR = { .bits = Py_TAG_INVALID };
 
+static inline PyObject *
+_PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
+{
+    int flags = ref.bits & Py_TAG_BITS;
+#ifdef Py_GIL_DISABLED
+    if (_Py_IsImmortal(op)) {
+        // Do not check flags on immortal objects in the free threading build.
+        flags = -1;
+    }
+#endif
+    return Py_BuildValue("(ni)", Py_REFCNT(op), flags);
+}
+
 /* Wrap a pointer in a stack ref.
  * The resulting stack reference is not safe and should only be used
  * in the interpreter to pass values from one uop to another.
@@ -476,13 +489,6 @@ static const _PyStackRef PyStackRef_NULL = { .bits = Py_TAG_DEFERRED};
 
 #define PyStackRef_IsNullOrInt(stackref) (PyStackRef_IsNull(stackref) || PyStackRef_IsTaggedInt(stackref))
 
-static inline PyObject *
-_PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
-{
-    // Do not check StackRef flags in the free threading build.
-    return Py_BuildValue("(ni)", Py_REFCNT(op), -1);
-}
-
 static inline PyObject *
 PyStackRef_AsPyObjectBorrow(_PyStackRef stackref)
 {
@@ -667,13 +673,6 @@ static const _PyStackRef PyStackRef_NULL = { .bits = PyStackRef_NULL_BITS };
 #define PyStackRef_IsFalse(REF) ((REF).bits == (((uintptr_t)&_Py_FalseStruct) | Py_TAG_REFCNT))
 #define PyStackRef_IsNone(REF) ((REF).bits == (((uintptr_t)&_Py_NoneStruct) | Py_TAG_REFCNT))
 
-static inline PyObject *
-_PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
-{
-    int flags = ref.bits & Py_TAG_BITS;
-    return Py_BuildValue("(ni)", Py_REFCNT(op), flags);
-}
-
 #ifdef Py_DEBUG
 
 static inline void PyStackRef_CheckValid(_PyStackRef ref) {
diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 8143a710f1a57b..4214f12d49c20e 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -49,7 +49,7 @@ def run_with_refcount_check(self, func, obj):
             for func in funcs_with_incref:
                 refcount, flags = run_with_refcount_check(self, func, obj)
                 self.assertLess(refcount, self.BIG_REFCOUNT)
-                self.assertIn(flags, (0, -1))
+                self.assertEqual(flags, 0)
                 results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 
@@ -57,7 +57,7 @@ def run_with_refcount_check(self, func, obj):
             for func in funcs_with_borrow:
                 refcount, flags = run_with_refcount_check(self, func, obj)
                 self.assertLess(refcount, self.BIG_REFCOUNT)
-                self.assertIn(flags, (1, -1))
+                self.assertEqual(flags, 1)
                 results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 

From 527412215e7fdaacdd9f804697170c8039a057d3 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 21:48:19 +0300
Subject: [PATCH 16/22] Rename obj -> res in aux functions

---
 Modules/_testinternalcapi.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 3a002bb317359c..4668243c760f8e 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2501,9 +2501,9 @@ static PyObject *
 stackref_from_object_new(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
-    PyObject *obj = _PyStackRef_AsTuple(ref, op);
+    PyObject *res = _PyStackRef_AsTuple(ref, op);
     PyStackRef_CLOSE(ref);
-    return obj;
+    return res;
 }
 
 static PyObject *
@@ -2512,11 +2512,11 @@ stackref_from_object_steal_with_incref(PyObject *self, PyObject *op)
     // The next two lines are equivalent to PyStackRef_FromPyObjectNew.
     Py_INCREF(op);
     _PyStackRef ref = PyStackRef_FromPyObjectSteal(op);
-    PyObject *obj = _PyStackRef_AsTuple(ref, op);
+    PyObject *res = _PyStackRef_AsTuple(ref, op);
     // The next two lines are equivalent to PyStackRef_CLOSE.
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     Py_DECREF(op2);
-    return obj;
+    return res;
 }
 
 static PyObject *
@@ -2525,9 +2525,9 @@ stackref_make_heap_safe(PyObject *self, PyObject *op)
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
     // For no-GIL release build ref2 is equal to ref.
     _PyStackRef ref2 = PyStackRef_MakeHeapSafe(ref);
-    PyObject *obj = _PyStackRef_AsTuple(ref2, op);
+    PyObject *res = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_CLOSE(ref2);
-    return obj;
+    return res;
 }
 
 static PyObject *
@@ -2538,9 +2538,9 @@ stackref_make_heap_safe_with_borrow(PyObject *self, PyObject *op)
     _PyStackRef ref3 = PyStackRef_MakeHeapSafe(ref2);
     // We can close ref, since ref3 is heap safe.
     PyStackRef_CLOSE(ref);
-    PyObject *obj = _PyStackRef_AsTuple(ref3, op);
+    PyObject *res = _PyStackRef_AsTuple(ref3, op);
     PyStackRef_CLOSE(ref3);
-    return obj;
+    return res;
 }
 
 static PyObject *
@@ -2550,18 +2550,18 @@ stackref_strong_reference(PyObject *self, PyObject *op)
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     _PyStackRef ref2 = PyStackRef_FromPyObjectSteal(op2);
-    PyObject *obj = _PyStackRef_AsTuple(ref2, op);
+    PyObject *res = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_CLOSE(ref2);
-    return obj;
+    return res;
 }
 
 static PyObject *
 stackref_from_object_borrow(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
-    PyObject *obj = _PyStackRef_AsTuple(ref, op);
+    PyObject *res = _PyStackRef_AsTuple(ref, op);
     PyStackRef_CLOSE(ref);
-    return obj;
+    return res;
 }
 
 static PyObject *
@@ -2572,9 +2572,9 @@ stackref_dup_borrowed_with_close(PyObject *self, PyObject *op)
     _PyStackRef ref2 = PyStackRef_DUP(ref);
     // For release build closing borrowed ref is no-op.
     PyStackRef_XCLOSE(ref);
-    PyObject *obj = _PyStackRef_AsTuple(ref2, op);
+    PyObject *res = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_XCLOSE(ref2);
-    return obj;
+    return res;
 }
 
 

From 24716092f4b10f7573859fc7e6c2d5dbafb7b8e6 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 21:49:01 +0300
Subject: [PATCH 17/22] Use constants in test

---
 Lib/test/test_stackrefs.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 4214f12d49c20e..0ffc3e04ff4855 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -10,6 +10,9 @@
 class TestDefinition(unittest.TestCase):
 
     BIG_REFCOUNT = 1000
+    FLAGS_REFCOUNT = 1
+    FLAGS_NO_REFCOUNT = 0
+    FLAGS_INVALID = -1
 
     def test_equivalence(self):
         def run_with_refcount_check(self, func, obj):
@@ -38,7 +41,7 @@ def run_with_refcount_check(self, func, obj):
             for func in funcs_with_incref + funcs_with_borrow:
                 refcount, flags = run_with_refcount_check(self, func, obj)
                 self.assertGreater(refcount, self.BIG_REFCOUNT)
-                self.assertIn(flags, (1, -1))
+                self.assertIn(flags, (self.FLAGS_REFCOUNT, self.FLAGS_INVALID))
                 results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 
@@ -49,7 +52,7 @@ def run_with_refcount_check(self, func, obj):
             for func in funcs_with_incref:
                 refcount, flags = run_with_refcount_check(self, func, obj)
                 self.assertLess(refcount, self.BIG_REFCOUNT)
-                self.assertEqual(flags, 0)
+                self.assertEqual(flags, self.FLAGS_NO_REFCOUNT)
                 results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 
@@ -57,7 +60,7 @@ def run_with_refcount_check(self, func, obj):
             for func in funcs_with_borrow:
                 refcount, flags = run_with_refcount_check(self, func, obj)
                 self.assertLess(refcount, self.BIG_REFCOUNT)
-                self.assertEqual(flags, 1)
+                self.assertEqual(flags, self.FLAGS_REFCOUNT)
                 results.add((refcount, flags))
             self.assertEqual(len(results), 1)
 

From 36a2fb4780a385affcaf223a69fcbf302aee2c89 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 21:49:42 +0300
Subject: [PATCH 18/22] Remove blank line

---
 Lib/test/test_stackrefs.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index 0ffc3e04ff4855..e96d650bec7274 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -65,6 +65,5 @@ def run_with_refcount_check(self, func, obj):
             self.assertEqual(len(results), 1)
 
 
-
 if __name__ == "__main__":
     unittest.main()

From 14521a112df484d0182ecb77ef18aa87e2a5749e Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 21:52:27 +0300
Subject: [PATCH 19/22] Asserts on mortality

---
 Lib/test/test_stackrefs.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Lib/test/test_stackrefs.py b/Lib/test/test_stackrefs.py
index e96d650bec7274..e8855e7635d14c 100644
--- a/Lib/test/test_stackrefs.py
+++ b/Lib/test/test_stackrefs.py
@@ -37,6 +37,7 @@ def run_with_refcount_check(self, func, obj):
         immortal_objs = (None, True, False, 42, '1')
 
         for obj in immortal_objs:
+            self.assertTrue(sys._is_immortal(obj))
             results = set()
             for func in funcs_with_incref + funcs_with_borrow:
                 refcount, flags = run_with_refcount_check(self, func, obj)
@@ -48,6 +49,7 @@ def run_with_refcount_check(self, func, obj):
         mortal_objs = (object(), range(10), iter([1, 2, 3]))
 
         for obj in mortal_objs:
+            self.assertFalse(sys._is_immortal(obj))
             results = set()
             for func in funcs_with_incref:
                 refcount, flags = run_with_refcount_check(self, func, obj)

From db34b878f20d8a7359b711e59a826ab338fef327 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Mon, 17 Nov 2025 22:05:32 +0300
Subject: [PATCH 20/22] Comment change

---
 Modules/_testinternalcapi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 4668243c760f8e..e5438930e87b95 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2570,7 +2570,7 @@ stackref_dup_borrowed_with_close(PyObject *self, PyObject *op)
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
     // For no-GIL release build ref2 is equal to ref.
     _PyStackRef ref2 = PyStackRef_DUP(ref);
-    // For release build closing borrowed ref is no-op.
+    // Closing borrowed ref is no-op.
     PyStackRef_XCLOSE(ref);
     PyObject *res = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_XCLOSE(ref2);

From 63ea804e54d527a47794696d2c1d221d0929bb25 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Tue, 18 Nov 2025 16:27:06 +0300
Subject: [PATCH 21/22] Comments improvement

---
 Modules/_testinternalcapi.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index e5438930e87b95..4926429e1c5576 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -2500,8 +2500,10 @@ test_threadstate_set_stack_protection(PyObject *self, PyObject *Py_UNUSED(args))
 static PyObject *
 stackref_from_object_new(PyObject *self, PyObject *op)
 {
+    // Make a new strong reference and give ownership of it to ref.
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
     PyObject *res = _PyStackRef_AsTuple(ref, op);
+    // Remove a strong reference by closing ref.
     PyStackRef_CLOSE(ref);
     return res;
 }
@@ -2509,13 +2511,22 @@ stackref_from_object_new(PyObject *self, PyObject *op)
 static PyObject *
 stackref_from_object_steal_with_incref(PyObject *self, PyObject *op)
 {
-    // The next two lines are equivalent to PyStackRef_FromPyObjectNew.
+    // Combination of Py_INCREF and PyStackRef_FromPyObjectSteal
+    // is equivalent to PyStackRef_FromPyObjectNew.
+
     Py_INCREF(op);
+    // Transfer ownership of a strong reference from op to ref.
     _PyStackRef ref = PyStackRef_FromPyObjectSteal(op);
+
     PyObject *res = _PyStackRef_AsTuple(ref, op);
-    // The next two lines are equivalent to PyStackRef_CLOSE.
+
+    // Combination of PyStackRef_AsPyObjectSteal and Py_DECREF
+    // is equivalent to PyStackRef_CLOSE.
+
+    // Transfer ownership of a strong reference from ref to op2.
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     Py_DECREF(op2);
+
     return res;
 }
 
@@ -2523,7 +2534,8 @@ static PyObject *
 stackref_make_heap_safe(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
-    // For no-GIL release build ref2 is equal to ref.
+    // Transfer ownership of a strong reference to op from ref to ref2,
+    // ref shouldn't be used anymore.
     _PyStackRef ref2 = PyStackRef_MakeHeapSafe(ref);
     PyObject *res = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_CLOSE(ref2);
@@ -2534,7 +2546,10 @@ static PyObject *
 stackref_make_heap_safe_with_borrow(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectNew(op);
+    // Create a borrowed reference to op, ref keeps a strong reference.
     _PyStackRef ref2 = PyStackRef_Borrow(ref);
+    // Make a new strong reference to op from ref2,
+    // ref2 shouldn't be used anymore.
     _PyStackRef ref3 = PyStackRef_MakeHeapSafe(ref2);
     // We can close ref, since ref3 is heap safe.
     PyStackRef_CLOSE(ref);
@@ -2546,7 +2561,8 @@ stackref_make_heap_safe_with_borrow(PyObject *self, PyObject *op)
 static PyObject *
 stackref_strong_reference(PyObject *self, PyObject *op)
 {
-    // The next two lines are equivalent to op2 = Py_NewRef(op).
+    // Combination of PyStackRef_FromPyObjectBorrow and
+    // PyStackRef_AsPyObjectSteal is equivalent to Py_NewRef.
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
     PyObject *op2 = PyStackRef_AsPyObjectSteal(ref);
     _PyStackRef ref2 = PyStackRef_FromPyObjectSteal(op2);
@@ -2560,6 +2576,7 @@ stackref_from_object_borrow(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
     PyObject *res = _PyStackRef_AsTuple(ref, op);
+    // Closing borrowed ref is no-op.
     PyStackRef_CLOSE(ref);
     return res;
 }
@@ -2568,9 +2585,9 @@ static PyObject *
 stackref_dup_borrowed_with_close(PyObject *self, PyObject *op)
 {
     _PyStackRef ref = PyStackRef_FromPyObjectBorrow(op);
-    // For no-GIL release build ref2 is equal to ref.
+    // Duplicate reference, ref and ref2 both will be
+    // correct borrowed references from op.
     _PyStackRef ref2 = PyStackRef_DUP(ref);
-    // Closing borrowed ref is no-op.
     PyStackRef_XCLOSE(ref);
     PyObject *res = _PyStackRef_AsTuple(ref2, op);
     PyStackRef_XCLOSE(ref2);

From 2998fed1bd8839e89977d68bfab112eee4ad7e63 Mon Sep 17 00:00:00 2001
From: Mikhail Efimov <efimov.mikhail@gmail.com>
Date: Sat, 20 Dec 2025 15:27:05 +0300
Subject: [PATCH 22/22] Lint fix

---
 Include/internal/pycore_stackref.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index 7cc8ecc10f40d6..a042cfe38989a6 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -381,7 +381,7 @@ static const _PyStackRef PyStackRef_ERROR = { .bits = Py_TAG_INVALID };
 /* For use in the JIT to clear an unused value.
  * PyStackRef_ZERO_BITS has no meaning and should not be used other than by the JIT. */
 static const _PyStackRef PyStackRef_ZERO_BITS = { .bits = 0 };
-  
+
 static inline PyObject *
 _PyStackRef_AsTuple(_PyStackRef ref, PyObject *op)
 {