Issue #24254: Preserve class attribute definition order.

2 files changed, 80 insertions, 1 deletions

diff --git a/Objects/odictobject.c b/Objects/odictobject.c
index 14be1cd..f056074 100644
--- a/Objects/odictobject.c
+++ b/Objects/odictobject.c
@@ -1762,6 +1762,21 @@ PyODict_DelItem(PyObject *od, PyObject *key)
     return _PyDict_DelItem_KnownHash(od, key, hash);
 }
 
+PyObject *
+_PyODict_KeysAsTuple(PyObject *od) {
+    Py_ssize_t i = 0;
+    _ODictNode *node;
+    PyObject *keys = PyTuple_New(PyODict_Size(od));
+    if (keys == NULL)
+        return NULL;
+    _odict_FOREACH((PyODictObject *)od, node) {
+        Py_INCREF(_odictnode_KEY(node));
+        PyTuple_SET_ITEM(keys, i, _odictnode_KEY(node));
+        i++;
+    }
+    return keys;
+}
+
 
 /* -------------------------------------------
  * The OrderedDict views (keys/values/items)
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 5f0db2b..6cffb4e 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -48,6 +48,7 @@ static size_t method_cache_collisions = 0;
 _Py_IDENTIFIER(__abstractmethods__);
 _Py_IDENTIFIER(__class__);
 _Py_IDENTIFIER(__delitem__);
+_Py_IDENTIFIER(__definition_order__);
 _Py_IDENTIFIER(__dict__);
 _Py_IDENTIFIER(__doc__);
 _Py_IDENTIFIER(__getattribute__);
@@ -489,6 +490,23 @@ type_set_module(PyTypeObject *type, PyObject *value, void *context)
 }
 
 static PyObject *
+type_deforder(PyTypeObject *type, void *context)
+{
+    if (type->tp_deforder == NULL)
+        Py_RETURN_NONE;
+    Py_INCREF(type->tp_deforder);
+    return type->tp_deforder;
+}
+
+static int
+type_set_deforder(PyTypeObject *type, PyObject *value, void *context)
+{
+    Py_XINCREF(value);
+    Py_XSETREF(type->tp_deforder, value);
+    return 0;
+}
+
+static PyObject *
 type_abstractmethods(PyTypeObject *type, void *context)
 {
     PyObject *mod = NULL;
@@ -834,6 +852,8 @@ static PyGetSetDef type_getsets[] = {
     {"__qualname__", (getter)type_qualname, (setter)type_set_qualname, NULL},
     {"__bases__", (getter)type_get_bases, (setter)type_set_bases, NULL},
     {"__module__", (getter)type_module, (setter)type_set_module, NULL},
+    {"__definition_order__", (getter)type_deforder,
+     (setter)type_set_deforder, NULL},
     {"__abstractmethods__", (getter)type_abstractmethods,
      (setter)type_set_abstractmethods, NULL},
     {"__dict__",  (getter)type_dict,  NULL, NULL},
@@ -2351,6 +2371,7 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
         goto error;
     }
 
+    /* Copy the definition namespace into a new dict. */
     dict = PyDict_Copy(orig_dict);
     if (dict == NULL)
         goto error;
@@ -2559,6 +2580,48 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
     if (qualname != NULL && PyDict_DelItem(dict, PyId___qualname__.object) < 0)
         goto error;
 
+    /* Set tp_deforder to the extracted definition order, if any. */
+    type->tp_deforder = _PyDict_GetItemId(dict, &PyId___definition_order__);
+    if (type->tp_deforder != NULL) {
+        Py_INCREF(type->tp_deforder);
+
+        // Due to subclass lookup, __definition_order__ can't be in __dict__.
+        if (_PyDict_DelItemId(dict, &PyId___definition_order__) != 0) {
+            goto error;
+        }
+
+        if (type->tp_deforder != Py_None) {
+            Py_ssize_t numnames;
+
+            if (!PyTuple_Check(type->tp_deforder)) {
+                PyErr_SetString(PyExc_TypeError,
+                                "__definition_order__ must be a tuple or None");
+                goto error;
+            }
+
+            // Make sure they are identifers.
+            numnames = PyTuple_Size(type->tp_deforder);
+            for (i = 0; i < numnames; i++) {
+                PyObject *name = PyTuple_GET_ITEM(type->tp_deforder, i);
+                if (name == NULL) {
+                    goto error;
+                }
+                if (!PyUnicode_Check(name) || !PyUnicode_IsIdentifier(name)) {
+                    PyErr_Format(PyExc_TypeError,
+                                 "__definition_order__ must "
+                                 "contain only identifiers, got '%s'",
+                                 name);
+                    goto error;
+                }
+            }
+        }
+    }
+    else if (PyODict_Check(orig_dict)) {
+        type->tp_deforder = _PyODict_KeysAsTuple(orig_dict);
+        if (type->tp_deforder == NULL)
+            goto error;
+    }
+
     /* Set tp_doc to a copy of dict['__doc__'], if the latter is there
        and is a string.  The __doc__ accessor will first look for tp_doc;
        if that fails, it will still look into __dict__.
@@ -3073,6 +3136,7 @@ type_dealloc(PyTypeObject *type)
     Py_XDECREF(type->tp_mro);
     Py_XDECREF(type->tp_cache);
     Py_XDECREF(type->tp_subclasses);
+    Py_XDECREF(type->tp_deforder);
     /* A type's tp_doc is heap allocated, unlike the tp_doc slots
      * of most other objects.  It's okay to cast it to char *.
      */
@@ -3115,7 +3179,7 @@ type_subclasses(PyTypeObject *type, PyObject *args_ignored)
 static PyObject *
 type_prepare(PyObject *self, PyObject *args, PyObject *kwds)
 {
-    return PyDict_New();
+    return PyODict_New();
 }
 
 /*