gh-105927: type_from_ref() uses _PyWeakref_GET_REF() (#105963)

type_from_ref() now returns a strong reference to the type, instead
of a borrowed reference: replace PyWeakref_GET_OBJECT() with
_PyWeakref_GET_REF().

Objects/typeobject.c

@@ -3,18 +3,19 @@
 #include "Python.h"
 #include "pycore_call.h"
 #include "pycore_code.h"          // CO_FAST_FREE
-#include "pycore_symtable.h"      // _Py_Mangle()
 #include "pycore_dict.h"          // _PyDict_KeysSize()
+#include "pycore_frame.h"         // _PyInterpreterFrame
 #include "pycore_initconfig.h"    // _PyStatus_OK()
+#include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_memoryobject.h"  // _PyMemoryView_FromBufferProc()
 #include "pycore_moduleobject.h"  // _PyModule_GetDef()
 #include "pycore_object.h"        // _PyType_HasFeature()
-#include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_pyerrors.h"      // _PyErr_Occurred()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
+#include "pycore_symtable.h"      // _Py_Mangle()
 #include "pycore_typeobject.h"    // struct type_cache
 #include "pycore_unionobject.h"   // _Py_union_type_or
-#include "pycore_frame.h"         // _PyInterpreterFrame
+#include "pycore_weakref.h"       // _PyWeakref_GET_REF()
 #include "opcode.h"               // MAKE_CELL
 #include "structmember.h"         // PyMemberDef
 
@@ -75,13 +76,10 @@ slot_tp_setattro(PyObject *self, PyObject *name, PyObject *value);
 static inline PyTypeObject *
 type_from_ref(PyObject *ref)
 {
-    assert(PyWeakref_CheckRef(ref));
-    PyObject *obj = PyWeakref_GET_OBJECT(ref);  // borrowed ref
-    assert(obj != NULL);
-    if (obj == Py_None) {
+    PyObject *obj = _PyWeakref_GET_REF(ref);
+    if (obj == NULL) {
         return NULL;
     }
-    assert(PyType_Check(obj));
     return _PyType_CAST(obj);
 }
 
@@ -450,15 +448,17 @@ _PyType_GetSubclasses(PyTypeObject *self)
     Py_ssize_t i = 0;
     PyObject *ref;  // borrowed ref
     while (PyDict_Next(subclasses, &i, NULL, &ref)) {
-        PyTypeObject *subclass = type_from_ref(ref);  // borrowed
+        PyTypeObject *subclass = type_from_ref(ref);
         if (subclass == NULL) {
             continue;
         }
 
         if (PyList_Append(list, _PyObject_CAST(subclass)) < 0) {
             Py_DECREF(list);
+            Py_DECREF(subclass);
             return NULL;
         }
+        Py_DECREF(subclass);
     }
     return list;
 }
@@ -778,11 +778,12 @@ PyType_Modified(PyTypeObject *type)
         Py_ssize_t i = 0;
         PyObject *ref;
         while (PyDict_Next(subclasses, &i, NULL, &ref)) {
-            PyTypeObject *subclass = type_from_ref(ref);  // borrowed
+            PyTypeObject *subclass = type_from_ref(ref);
             if (subclass == NULL) {
                 continue;
             }
             PyType_Modified(subclass);
+            Py_DECREF(subclass);
         }
     }
 
@@ -4989,12 +4990,13 @@ clear_static_tp_subclasses(PyTypeObject *type)
     Py_ssize_t i = 0;
     PyObject *key, *ref;  // borrowed ref
     while (PyDict_Next(subclasses, &i, &key, &ref)) {
-        PyTypeObject *subclass = type_from_ref(ref);  // borrowed
+        PyTypeObject *subclass = type_from_ref(ref);
         if (subclass == NULL) {
             continue;
         }
         // All static builtin subtypes should have been finalized already.
         assert(!(subclass->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN));
+        Py_DECREF(subclass);
     }
 
     clear_tp_subclasses(type);
@@ -7636,10 +7638,15 @@ get_subclasses_key(PyTypeObject *type, PyTypeObject *base)
     PyObject *subclasses = lookup_tp_subclasses(base);
     if (subclasses != NULL) {
         while (PyDict_Next(subclasses, &i, &key, &ref)) {
-            PyTypeObject *subclass = type_from_ref(ref);  // borrowed
+            PyTypeObject *subclass = type_from_ref(ref);
+            if (subclass == NULL) {
+                continue;
+            }
             if (subclass == type) {
+                Py_DECREF(subclass);
                 return Py_NewRef(key);
             }
+            Py_DECREF(subclass);
         }
     }
     /* It wasn't found. */
@@ -10035,7 +10042,7 @@ recurse_down_subclasses(PyTypeObject *type, PyObject *attr_name,
     Py_ssize_t i = 0;
     PyObject *ref;
     while (PyDict_Next(subclasses, &i, NULL, &ref)) {
-        PyTypeObject *subclass = type_from_ref(ref);  // borrowed
+        PyTypeObject *subclass = type_from_ref(ref);
         if (subclass == NULL) {
             continue;
         }
@@ -10045,16 +10052,20 @@ recurse_down_subclasses(PyTypeObject *type, PyObject *attr_name,
         if (dict != NULL && PyDict_Check(dict)) {
             int r = PyDict_Contains(dict, attr_name);
             if (r < 0) {
+                Py_DECREF(subclass);
                 return -1;
             }
             if (r > 0) {
+                Py_DECREF(subclass);
                 continue;
             }
         }
 
         if (update_subclasses(subclass, attr_name, callback, data) < 0) {
+            Py_DECREF(subclass);
             return -1;
         }
+        Py_DECREF(subclass);
     }
     return 0;
 }