bpo-41171: Added method "PyMetaType_FromSpec" to allow for specifying the metaclass for the type.

Doc/c-api/type.rst

@@ -142,7 +142,13 @@ The following functions and structs are used to create
 
 .. c:function:: PyObject* PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
 
-   Creates and returns a heap type object from the *spec*
+   Equivalent to ``PyMetaType_FromSpec(module, &PyType_Type, spec, bases)``.
+
+   .. versionadded:: 3.9
+
+.. c:function:: PyObject* PyMetaType_FromSpec(PyObject *module, PyTypeObject *meta_type, PyType_Spec *spec, PyObject *bases)
+
+   Creates and returns a heap type object from the *spec* whose's metaclass is *meta_type*
    (:const:`Py_TPFLAGS_HEAPTYPE`).
 
    If *bases* is a tuple, the created heap type contains all types contained
@@ -155,19 +161,23 @@ The following functions and structs are used to create
    If not ``NULL``, the module is associated with the new type and can later be
    retreived with :c:func:`PyType_GetModule`.
 
-   This function calls :c:func:`PyType_Ready` on the new type.
+   This function calls :c:func:`PyType_Ready` on the new type.'
 
-   .. versionadded:: 3.9
+   .. note::
+
+      This method DOES NOT invoke ``PyTypeObject.tp_new`` on 'meta_type'.
+
+   .. versionadded:: 3.10
 
 .. c:function:: PyObject* PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
 
-   Equivalent to ``PyType_FromModuleAndSpec(NULL, spec, bases)``.
+   Equivalent to ``PyMetaType_FromSpec(NULL, &PyType_Type, spec, bases)``.
 
    .. versionadded:: 3.3
 
 .. c:function:: PyObject* PyType_FromSpec(PyType_Spec *spec)
 
-   Equivalent to ``PyType_FromSpecWithBases(spec, NULL)``.
+   Equivalent to ``PyMetaType_FromSpec(NULL, &PyType_Type, spec, NULL)``.
 
 .. c:type:: PyType_Spec
 

Include/object.h

@@ -225,15 +225,16 @@ typedef struct{
     PyType_Slot *slots; /* terminated by slot==0. */
 } PyType_Spec;
 
-PyAPI_FUNC(PyObject*) PyType_FromSpec(PyType_Spec*);
+#define PyType_FromSpec(spec) PyMetaType_FromSpec(NULL, &PyType_Type, spec, NULL)
+PyAPI_FUNC(PyObject*) PyMetaType_FromSpec(PyObject*, PyTypeObject*, PyType_Spec*, PyObject*);
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03030000
-PyAPI_FUNC(PyObject*) PyType_FromSpecWithBases(PyType_Spec*, PyObject*);
+#define PyType_FromSpecWithBases(spec, bases) PyMetaType_FromSpec(NULL, &PyType_Type, spec, bases)
 #endif
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03040000
 PyAPI_FUNC(void*) PyType_GetSlot(PyTypeObject*, int);
 #endif
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03090000
-PyAPI_FUNC(PyObject*) PyType_FromModuleAndSpec(PyObject *, PyType_Spec *, PyObject *);
+#define PyType_FromModuleAndSpec(module, spec, bases) PyMetaType_FromSpec(module, &PyType_Type, spec, bases)
 PyAPI_FUNC(PyObject *) PyType_GetModule(struct _typeobject *);
 PyAPI_FUNC(void *) PyType_GetModuleState(struct _typeobject *);
 #endif

Misc/NEWS.d/next/C API/2020-06-30-16-31-15.bpo-41171.wFnoOM.rst

@@ -0,0 +1 @@
+Added method "PyMetaType_FromSpec" to allow for specifying the metaclass for the type.

Objects/typeobject.c

@@ -2880,14 +2880,13 @@ static const short slotoffsets[] = {
 };
 
 PyObject *
-PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
+PyMetaType_FromSpec(PyObject *module, PyTypeObject *meta_type, PyType_Spec *spec, PyObject *bases)
 {
-    return PyType_FromModuleAndSpec(NULL, spec, bases);
-}
+    if (meta_type == NULL) {
+        PyErr_BadArgument();
+        return NULL;
+    }
 
-PyObject *
-PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
-{
     PyHeapTypeObject *res;
     PyObject *modname;
     PyTypeObject *type, *base;
@@ -2924,7 +2923,7 @@ PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
         }
     }
 
-    res = (PyHeapTypeObject*)PyType_GenericAlloc(&PyType_Type, nmembers);
+    res = (PyHeapTypeObject*)PyType_GenericAlloc(meta_type, nmembers);
     if (res == NULL)
         return NULL;
     res_start = (char*)res;
@@ -3098,12 +3097,6 @@ PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
     return NULL;
 }
 
-PyObject *
-PyType_FromSpec(PyType_Spec *spec)
-{
-    return PyType_FromSpecWithBases(spec, NULL);
-}
-
 void *
 PyType_GetSlot(PyTypeObject *type, int slot)
 {

PC/python3dll.c

@@ -541,8 +541,7 @@ EXPORT_FUNC(PyTuple_Pack)
 EXPORT_FUNC(PyTuple_SetItem)
 EXPORT_FUNC(PyTuple_Size)
 EXPORT_FUNC(PyType_ClearCache)
-EXPORT_FUNC(PyType_FromSpec)
-EXPORT_FUNC(PyType_FromSpecWithBases)
+EXPORT_FUNC(PyMetaType_FromSpec)
 EXPORT_FUNC(PyType_GenericAlloc)
 EXPORT_FUNC(PyType_GenericNew)
 EXPORT_FUNC(PyType_GetFlags)