Some comments are added

Author: efimov-mikhail

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);