diff --git a/Doc/c-api/type.rst b/Doc/c-api/type.rst index 99b3845237d..fece3e6e642 100644 --- a/Doc/c-api/type.rst +++ b/Doc/c-api/type.rst @@ -193,11 +193,12 @@ The following functions and structs are used to create .. c:function:: PyObject* PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, PyType_Spec *spec, PyObject *bases) Create and return a :ref:`heap type ` from the *spec* - (:const:`Py_TPFLAGS_HEAPTYPE`). + (see :const:`Py_TPFLAGS_HEAPTYPE`). The metaclass *metaclass* is used to construct the resulting type object. - When *metaclass* is ``NULL``, the default :c:type:`PyType_Type` is used - instead. Note that metaclasses that override + When *metaclass* is ``NULL``, the metaclass is derived from *bases* + (or *Py_tp_base[s]* slots if *bases* is ``NULL``, see below). + Note that metaclasses that override :c:member:`~PyTypeObject.tp_new` are not supported. The *bases* argument can be used to specify base classes; it can either @@ -215,6 +216,19 @@ The following functions and structs are used to create This function calls :c:func:`PyType_Ready` on the new type. + Note that this function does *not* fully match the behavior of + calling :py:class:`type() ` or using the :keyword:`class` statement. + With user-provided base types or metaclasses, prefer + :ref:`calling ` :py:class:`type` (or the metaclass) + over ``PyType_From*`` functions. + Specifically: + + * :py:meth:`~object.__new__` is not called on the new class + (and it must be set to ``type.__new__``). + * :py:meth:`~object.__init__` is not called on the new class. + * :py:meth:`~object.__init_subclass__` is not called on any bases. + * :py:meth:`~object.__set_name__` is not called on new descriptors. + .. versionadded:: 3.12 .. c:function:: PyObject* PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases) @@ -228,6 +242,11 @@ The following functions and structs are used to create The function now accepts a single class as the *bases* argument and ``NULL`` as the ``tp_doc`` slot. + .. versionchanged:: 3.12 + + The function now finds and uses a metaclass corresponding to the provided + base classes. Previously, only :class:`type` instances were returned. + .. c:function:: PyObject* PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases) @@ -235,10 +254,21 @@ The following functions and structs are used to create .. versionadded:: 3.3 + .. versionchanged:: 3.12 + + The function now finds and uses a metaclass corresponding to the provided + base classes. Previously, only :class:`type` instances were returned. + .. c:function:: PyObject* PyType_FromSpec(PyType_Spec *spec) Equivalent to ``PyType_FromMetaclass(NULL, NULL, spec, NULL)``. + .. versionchanged:: 3.12 + + The function now finds and uses a metaclass corresponding to the + base classes provided in *Py_tp_base[s]* slots. + Previously, only :class:`type` instances were returned. + .. c:type:: PyType_Spec Structure defining a type's behavior. diff --git a/Misc/NEWS.d/next/C API/2021-10-05-21-59-43.bpo-45383.TVClgf.rst b/Misc/NEWS.d/next/C API/2021-10-05-21-59-43.bpo-45383.TVClgf.rst new file mode 100644 index 00000000000..ca1b7a43d29 --- /dev/null +++ b/Misc/NEWS.d/next/C API/2021-10-05-21-59-43.bpo-45383.TVClgf.rst @@ -0,0 +1,3 @@ +The :c:func:`PyType_FromSpec` API will now find and use a metaclass +based on the provided bases. +An error will be raised if there is a metaclass conflict. diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c index ac0c96a11d3..b75e03c0c06 100644 --- a/Modules/_testcapimodule.c +++ b/Modules/_testcapimodule.c @@ -1208,6 +1208,161 @@ test_get_type_name(PyObject *self, PyObject *Py_UNUSED(ignored)) } +static PyType_Slot empty_type_slots[] = { + {0, 0}, +}; + +static PyType_Spec MinimalMetaclass_spec = { + .name = "_testcapi.MinimalMetaclass", + .basicsize = sizeof(PyHeapTypeObject), + .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, + .slots = empty_type_slots, +}; + +static PyType_Spec MinimalType_spec = { + .name = "_testcapi.MinimalSpecType", + .basicsize = sizeof(PyObject), + .flags = Py_TPFLAGS_DEFAULT, + .slots = empty_type_slots, +}; + +static PyObject * +test_from_spec_metatype_inheritance(PyObject *self, PyObject *Py_UNUSED(ignored)) +{ + PyObject *metaclass = NULL; + PyObject *class = NULL; + PyObject *new = NULL; + PyObject *subclasses = NULL; + PyObject *result = NULL; + int r; + + metaclass = PyType_FromSpecWithBases(&MinimalMetaclass_spec, (PyObject*)&PyType_Type); + if (metaclass == NULL) { + goto finally; + } + class = PyObject_CallFunction(metaclass, "s(){}", "TestClass"); + if (class == NULL) { + goto finally; + } + + new = PyType_FromSpecWithBases(&MinimalType_spec, class); + if (new == NULL) { + goto finally; + } + if (Py_TYPE(new) != (PyTypeObject*)metaclass) { + PyErr_SetString(PyExc_AssertionError, + "Metaclass not set properly!"); + goto finally; + } + + /* Assert that __subclasses__ is updated */ + subclasses = PyObject_CallMethod(class, "__subclasses__", ""); + if (!subclasses) { + goto finally; + } + r = PySequence_Contains(subclasses, new); + if (r < 0) { + goto finally; + } + if (r == 0) { + PyErr_SetString(PyExc_AssertionError, + "subclasses not set properly!"); + goto finally; + } + + result = Py_NewRef(Py_None); + +finally: + Py_XDECREF(metaclass); + Py_XDECREF(class); + Py_XDECREF(new); + Py_XDECREF(subclasses); + return result; +} + + +static PyObject * +test_from_spec_invalid_metatype_inheritance(PyObject *self, PyObject *Py_UNUSED(ignored)) +{ + PyObject *metaclass_a = NULL; + PyObject *metaclass_b = NULL; + PyObject *class_a = NULL; + PyObject *class_b = NULL; + PyObject *bases = NULL; + PyObject *new = NULL; + PyObject *meta_error_string = NULL; + PyObject *exc_type = NULL; + PyObject *exc_value = NULL; + PyObject *exc_traceback = NULL; + PyObject *result = NULL; + + metaclass_a = PyType_FromSpecWithBases(&MinimalMetaclass_spec, (PyObject*)&PyType_Type); + if (metaclass_a == NULL) { + goto finally; + } + metaclass_b = PyType_FromSpecWithBases(&MinimalMetaclass_spec, (PyObject*)&PyType_Type); + if (metaclass_b == NULL) { + goto finally; + } + class_a = PyObject_CallFunction(metaclass_a, "s(){}", "TestClassA"); + if (class_a == NULL) { + goto finally; + } + + class_b = PyObject_CallFunction(metaclass_b, "s(){}", "TestClassB"); + if (class_b == NULL) { + goto finally; + } + + bases = PyTuple_Pack(2, class_a, class_b); + if (bases == NULL) { + goto finally; + } + + /* + * The following should raise a TypeError due to a MetaClass conflict. + */ + new = PyType_FromSpecWithBases(&MinimalType_spec, bases); + if (new != NULL) { + PyErr_SetString(PyExc_AssertionError, + "MetaType conflict not recognized by PyType_FromSpecWithBases"); + goto finally; + } + + // Assert that the correct exception was raised + if (PyErr_ExceptionMatches(PyExc_TypeError)) { + PyErr_Fetch(&exc_type, &exc_value, &exc_traceback); + + meta_error_string = PyUnicode_FromString("metaclass conflict:"); + if (meta_error_string == NULL) { + goto finally; + } + int res = PyUnicode_Contains(exc_value, meta_error_string); + if (res < 0) { + goto finally; + } + if (res == 0) { + PyErr_SetString(PyExc_AssertionError, + "TypeError did not inlclude expected message."); + goto finally; + } + result = Py_NewRef(Py_None); + } +finally: + Py_XDECREF(metaclass_a); + Py_XDECREF(metaclass_b); + Py_XDECREF(bases); + Py_XDECREF(new); + Py_XDECREF(meta_error_string); + Py_XDECREF(exc_type); + Py_XDECREF(exc_value); + Py_XDECREF(exc_traceback); + Py_XDECREF(class_a); + Py_XDECREF(class_b); + return result; +} + + static PyObject * simple_str(PyObject *self) { return PyUnicode_FromString(""); @@ -5952,6 +6107,11 @@ static PyMethodDef TestMethods[] = { {"test_get_type_name", test_get_type_name, METH_NOARGS}, {"test_get_type_qualname", test_get_type_qualname, METH_NOARGS}, {"test_type_from_ephemeral_spec", test_type_from_ephemeral_spec, METH_NOARGS}, + {"test_from_spec_metatype_inheritance", test_from_spec_metatype_inheritance, + METH_NOARGS}, + {"test_from_spec_invalid_metatype_inheritance", + test_from_spec_invalid_metatype_inheritance, + METH_NOARGS}, {"get_kwargs", _PyCFunction_CAST(get_kwargs), METH_VARARGS|METH_KEYWORDS}, {"getargs_tuple", getargs_tuple, METH_VARARGS}, diff --git a/Objects/typeobject.c b/Objects/typeobject.c index 2566d217a0f..51dc5e34c81 100644 --- a/Objects/typeobject.c +++ b/Objects/typeobject.c @@ -3361,13 +3361,51 @@ static const PySlot_Offset pyslot_offsets[] = { #include "typeslots.inc" }; +/* Given a PyType_FromMetaclass `bases` argument (NULL, type, or tuple of + * types), return a tuple of types. + */ +inline static PyObject * +get_bases_tuple(PyObject *bases_in, PyType_Spec *spec) +{ + if (!bases_in) { + /* Default: look in the spec, fall back to (type,). */ + PyTypeObject *base = &PyBaseObject_Type; // borrowed ref + PyObject *bases = NULL; // borrowed ref + const PyType_Slot *slot; + for (slot = spec->slots; slot->slot; slot++) { + switch (slot->slot) { + case Py_tp_base: + base = slot->pfunc; + break; + case Py_tp_bases: + bases = slot->pfunc; + break; + } + } + if (!bases) { + return PyTuple_Pack(1, base); + } + if (PyTuple_Check(bases)) { + return Py_NewRef(bases); + } + PyErr_SetString(PyExc_SystemError, "Py_tp_bases is not a tuple"); + return NULL; + } + if (PyTuple_Check(bases_in)) { + return Py_NewRef(bases_in); + } + // Not a tuple, should be a single type + return PyTuple_Pack(1, bases_in); +} + PyObject * PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, - PyType_Spec *spec, PyObject *bases) + PyType_Spec *spec, PyObject *bases_in) { - PyHeapTypeObject *res; - PyObject *modname; - PyTypeObject *type, *base; + PyHeapTypeObject *res = NULL; + PyObject *modname = NULL; + PyTypeObject *type; + PyObject *bases = NULL; int r; const PyType_Slot *slot; @@ -3375,16 +3413,6 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, char *res_start; short slot_offset, subslot_offset; - if (!metaclass) { - metaclass = &PyType_Type; - } - - if (metaclass->tp_new != PyType_Type.tp_new) { - PyErr_SetString(PyExc_TypeError, - "Metaclasses with custom tp_new are not supported."); - return NULL; - } - nmembers = weaklistoffset = dictoffset = vectorcalloffset = 0; for (slot = spec->slots; slot->slot; slot++) { if (slot->slot == Py_tp_members) { @@ -3413,17 +3441,58 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, } } - res = (PyHeapTypeObject*)metaclass->tp_alloc(metaclass, nmembers); - if (res == NULL) - return NULL; - res_start = (char*)res; - if (spec->name == NULL) { PyErr_SetString(PyExc_SystemError, "Type spec does not define the name field."); - goto fail; + goto finally; } + /* Get a tuple of bases. + * bases is a strong reference (unlike bases_in). + */ + bases = get_bases_tuple(bases_in, spec); + if (!bases) { + goto finally; + } + + /* Calculate the metaclass */ + + if (!metaclass) { + metaclass = &PyType_Type; + } + metaclass = _PyType_CalculateMetaclass(metaclass, bases); + if (metaclass == NULL) { + goto finally; + } + if (!PyType_Check(metaclass)) { + PyErr_Format(PyExc_TypeError, + "Metaclass '%R' is not a subclass of 'type'.", + metaclass); + goto finally; + } + if (metaclass->tp_new != PyType_Type.tp_new) { + PyErr_SetString(PyExc_TypeError, + "Metaclasses with custom tp_new are not supported."); + goto finally; + } + + /* Calculate best base, and check that all bases are type objects */ + PyTypeObject *base = best_base(bases); // borrowed ref + if (base == NULL) { + goto finally; + } + // best_base should check Py_TPFLAGS_BASETYPE & raise a proper exception, + // here we just check its work + assert(_PyType_HasFeature(base, Py_TPFLAGS_BASETYPE)); + + /* Allocate the new type */ + + res = (PyHeapTypeObject*)metaclass->tp_alloc(metaclass, nmembers); + if (res == NULL) { + goto finally; + } + res_start = (char*)res; + type = &res->ht_type; /* The flags must be initialized early, before the GC traverses us */ type->tp_flags = spec->flags | Py_TPFLAGS_HEAPTYPE; @@ -3439,7 +3508,7 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, res->ht_name = PyUnicode_FromString(s); if (!res->ht_name) { - goto fail; + goto finally; } res->ht_qualname = Py_NewRef(res->ht_name); @@ -3455,70 +3524,25 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, Py_ssize_t name_buf_len = strlen(spec->name) + 1; res->_ht_tpname = PyMem_Malloc(name_buf_len); if (res->_ht_tpname == NULL) { - goto fail; + goto finally; } type->tp_name = memcpy(res->_ht_tpname, spec->name, name_buf_len); res->ht_module = Py_XNewRef(module); - /* Adjust for empty tuple bases */ - if (!bases) { - base = &PyBaseObject_Type; - /* See whether Py_tp_base(s) was specified */ - for (slot = spec->slots; slot->slot; slot++) { - if (slot->slot == Py_tp_base) - base = slot->pfunc; - else if (slot->slot == Py_tp_bases) { - bases = slot->pfunc; - } - } - if (!bases) { - bases = PyTuple_Pack(1, base); - if (!bases) - goto fail; - } - else if (!PyTuple_Check(bases)) { - PyErr_SetString(PyExc_SystemError, "Py_tp_bases is not a tuple"); - goto fail; - } - else { - Py_INCREF(bases); - } - } - else if (!PyTuple_Check(bases)) { - bases = PyTuple_Pack(1, bases); - if (!bases) - goto fail; - } - else { - Py_INCREF(bases); - } - - /* Calculate best base, and check that all bases are type objects */ - base = best_base(bases); - if (base == NULL) { - Py_DECREF(bases); - goto fail; - } - if (!_PyType_HasFeature(base, Py_TPFLAGS_BASETYPE)) { - PyErr_Format(PyExc_TypeError, - "type '%.100s' is not an acceptable base type", - base->tp_name); - Py_DECREF(bases); - goto fail; - } - /* Initialize essential fields */ type->tp_as_async = &res->as_async; type->tp_as_number = &res->as_number; type->tp_as_sequence = &res->as_sequence; type->tp_as_mapping = &res->as_mapping; type->tp_as_buffer = &res->as_buffer; - /* Set tp_base and tp_bases */ - type->tp_bases = bases; - Py_INCREF(base); - type->tp_base = base; + /* Set tp_base and tp_bases */ + type->tp_base = (PyTypeObject *)Py_NewRef(base); + type->tp_bases = bases; + bases = NULL; // We give our reference to bases to the type + + /* Copy the sizes */ type->tp_basicsize = spec->basicsize; type->tp_itemsize = spec->itemsize; @@ -3526,7 +3550,7 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, if (slot->slot < 0 || (size_t)slot->slot >= Py_ARRAY_LENGTH(pyslot_offsets)) { PyErr_SetString(PyExc_RuntimeError, "invalid slot offset"); - goto fail; + goto finally; } else if (slot->slot == Py_tp_base || slot->slot == Py_tp_bases) { /* Processed above */ @@ -3544,7 +3568,7 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, if (tp_doc == NULL) { type->tp_doc = NULL; PyErr_NoMemory(); - goto fail; + goto finally; } memcpy(tp_doc, slot->pfunc, len); type->tp_doc = tp_doc; @@ -3579,8 +3603,9 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, type->tp_vectorcall_offset = vectorcalloffset; } - if (PyType_Ready(type) < 0) - goto fail; + if (PyType_Ready(type) < 0) { + goto finally; + } if (type->tp_flags & Py_TPFLAGS_MANAGED_DICT) { res->ht_cached_keys = _PyDict_NewKeysForClass(); @@ -3588,29 +3613,33 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, if (type->tp_doc) { PyObject *__doc__ = PyUnicode_FromString(_PyType_DocWithoutSignature(type->tp_name, type->tp_doc)); - if (!__doc__) - goto fail; + if (!__doc__) { + goto finally; + } r = PyDict_SetItem(type->tp_dict, &_Py_ID(__doc__), __doc__); Py_DECREF(__doc__); - if (r < 0) - goto fail; + if (r < 0) { + goto finally; + } } if (weaklistoffset) { type->tp_weaklistoffset = weaklistoffset; - if (PyDict_DelItemString((PyObject *)type->tp_dict, "__weaklistoffset__") < 0) - goto fail; + if (PyDict_DelItemString((PyObject *)type->tp_dict, "__weaklistoffset__") < 0) { + goto finally; + } } if (dictoffset) { type->tp_dictoffset = dictoffset; - if (PyDict_DelItemString((PyObject *)type->tp_dict, "__dictoffset__") < 0) - goto fail; + if (PyDict_DelItemString((PyObject *)type->tp_dict, "__dictoffset__") < 0) { + goto finally; + } } /* Set type.__module__ */ r = PyDict_Contains(type->tp_dict, &_Py_ID(__module__)); if (r < 0) { - goto fail; + goto finally; } if (r == 0) { s = strrchr(spec->name, '.'); @@ -3618,26 +3647,30 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, modname = PyUnicode_FromStringAndSize( spec->name, (Py_ssize_t)(s - spec->name)); if (modname == NULL) { - goto fail; + goto finally; } r = PyDict_SetItem(type->tp_dict, &_Py_ID(__module__), modname); - Py_DECREF(modname); - if (r != 0) - goto fail; - } else { + if (r != 0) { + goto finally; + } + } + else { if (PyErr_WarnFormat(PyExc_DeprecationWarning, 1, "builtin type %.200s has no __module__ attribute", spec->name)) - goto fail; + goto finally; } } assert(_PyType_CheckConsistency(type)); - return (PyObject*)res; - fail: - Py_DECREF(res); - return NULL; + finally: + if (PyErr_Occurred()) { + Py_CLEAR(res); + } + Py_XDECREF(bases); + Py_XDECREF(modname); + return (PyObject*)res; } PyObject *