Refactor PyType_LookupRef to return version

Include/internal/pycore_object.h

@@ -816,6 +816,8 @@ extern int _PyObject_StoreInstanceAttribute(PyObject *obj,
                                             PyObject *name, PyObject *value);
 extern bool _PyObject_TryGetInstanceAttribute(PyObject *obj, PyObject *name,
                                               PyObject **attr);
+extern PyObject *_PyType_LookupRefAndVersion(PyTypeObject *, PyObject *,
+                                             unsigned int *);
 
 #ifdef Py_GIL_DISABLED
 #  define MANAGED_DICT_OFFSET    (((Py_ssize_t)sizeof(PyObject *))*-1)

Objects/typeobject.c

@@ -5527,9 +5527,12 @@ _PyTypes_AfterFork(void)
 }
 
 /* Internal API to look for a name through the MRO.
-   This returns a borrowed reference, and doesn't set an exception! */
+   This returns a strong reference, and doesn't set an exception!
+   If nonzero, version is set to the value of type->tp_version at the time of
+   the lookup.
+*/
 PyObject *
-_PyType_LookupRef(PyTypeObject *type, PyObject *name)
+_PyType_LookupRefAndVersion(PyTypeObject *type, PyObject *name, unsigned int *version)
 {
     PyObject *res;
     int error;
@@ -5552,6 +5555,9 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name)
             // If the sequence is still valid then we're done
             if (value == NULL || _Py_TryIncref(value)) {
                 if (_PySeqLock_EndRead(&entry->sequence, sequence)) {
+                    if (version != NULL) {
+                        *version = entry_version;
+                    }
                     return value;
                 }
                 Py_XDECREF(value);
@@ -5573,6 +5579,9 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name)
         OBJECT_STAT_INC_COND(type_cache_hits, !is_dunder_name(name));
         OBJECT_STAT_INC_COND(type_cache_dunder_hits, is_dunder_name(name));
         Py_XINCREF(entry->value);
+        if (version != NULL) {
+            *version = entry->version;
+        }
         return entry->value;
     }
 #endif
@@ -5586,12 +5595,12 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name)
     // anyone else can modify our mro or mutate the type.
 
     int has_version = 0;
-    int version = 0;
+    unsigned int assigned_version = 0;
     BEGIN_TYPE_LOCK();
     res = find_name_in_mro(type, name, &error);
     if (MCACHE_CACHEABLE_NAME(name)) {
         has_version = assign_version_tag(interp, type);
-        version = type->tp_version_tag;
+        assigned_version = type->tp_version_tag;
     }
     END_TYPE_LOCK();
 
@@ -5608,24 +5617,43 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name)
         if (error == -1) {
             PyErr_Clear();
         }
+        if (version != NULL) {
+            // 0 is not a valid version
+            *version = 0;
+        }
         return NULL;
     }
 
     if (has_version) {
 #if Py_GIL_DISABLED
-        update_cache_gil_disabled(entry, name, version, res);
+        update_cache_gil_disabled(entry, name, assigned_version, res);
 #else
-        PyObject *old_value = update_cache(entry, name, version, res);
+        PyObject *old_value = update_cache(entry, name, assigned_version, res);
         Py_DECREF(old_value);
 #endif
     }
+    if (version != NULL) {
+        // 0 is not a valid version
+        *version = has_version ? assigned_version : 0;
+    }
     return res;
 }
 
+/* Internal API to look for a name through the MRO.
+   This returns a strong reference, and doesn't set an exception!
+*/
+PyObject *
+_PyType_LookupRef(PyTypeObject *type, PyObject *name)
+{
+    return _PyType_LookupRefAndVersion(type, name, NULL);
+}
+
+/* Internal API to look for a name through the MRO.
+   This returns a borrowed reference, and doesn't set an exception! */
 PyObject *
 _PyType_Lookup(PyTypeObject *type, PyObject *name)
 {
-    PyObject *res = _PyType_LookupRef(type, name);
+    PyObject *res = _PyType_LookupRefAndVersion(type, name, NULL);
     Py_XDECREF(res);
     return res;
 }