Address review comments

Author: markshannon

Include/internal/pycore_stackref.h

@@ -75,6 +75,8 @@ static const _PyStackRef PyStackRef_NULL = { .index = 0 };
 #define PyStackRef_False ((_PyStackRef){ .index = 2 })
 #define PyStackRef_True ((_PyStackRef){ .index = 3 })
 
+#define LAST_PREDEFINED_STACKREF_INDEX 3
+
 static inline int
 PyStackRef_IsNull(_PyStackRef ref)
 {

Misc/NEWS.d/next/Core_and_Builtins/2024-12-20-12-25-16.gh-issue-127705.WmCz1z.rst

@@ -1,2 +1,4 @@
 Adds stackref debugging when ``Py_STACKREF_DEBUG`` is set. Finds all
 double-closes and leaks, logging the origin and last borrow.
+
+Inspired by HPy's debug mode. https://docs.hpyproject.org/en/latest/debug-mode.html

Python/stackrefs.c

@@ -54,14 +54,15 @@ _Py_stackref_get_object(_PyStackRef ref)
     return entry->obj;
 }
 
-PyObject *_Py_stackref_close(_PyStackRef ref)
+PyObject *
+_Py_stackref_close(_PyStackRef ref)
 {
     PyInterpreterState *interp = PyInterpreterState_Get();
     if (ref.index >= interp->next_stackref) {
         _Py_FatalErrorFormat(__func__, "Garbled stack ref with ID %" PRIu64 "\n", ref.index);
     }
     PyObject *obj;
-    if (ref.index <= 3) {
+    if (ref.index <= LAST_PREDEFINED_STACKREF_INDEX) {
         // Pre-allocated reference to None, False or True -- Do not clear
         TableEntry *entry = _Py_hashtable_get(interp->stackref_debug_table, (void *)ref.index);
         obj = entry->obj;
@@ -98,7 +99,7 @@ _Py_stackref_create(PyObject *obj, const char *filename, int linenumber)
 void
 _Py_stackref_record_borrow(_PyStackRef ref, const char *filename, int linenumber)
 {
-    if (ref.index <= 3) {
+    if (ref.index <= LAST_PREDEFINED_STACKREF_INDEX) {
         return;
     }
     PyInterpreterState *interp = PyInterpreterState_Get();