Extension type from documentation doesn't compile in C++20 mode #99202
Description
Bug report
C++20 added support for designated initializers and fails to compile if you mix named and unnamed initializers.
For demonstration I'll use the example from the documentation section "Defining Extension Types: Tutorial" with .tp_doc removed from CustomType so it builds on Python 3.10.
When building with C++ compiler in C++20 mode using
g++ $(python3-config --cflags) -std=c++20 -Wall -Wextra -Wno-missing-field-initializers -c pymod.cc
it fails with the following message:
pymod.cc:11:5: error: either all initializer clauses should be designated or none of them should be 11 | .tp_name = "custom.Custom", | ^ pymod.cc:20:5: error: either all initializer clauses should be designated or none of them should be 20 | .m_name = "custom", | ^ The problem is the macros that produce non-designated initializers here.
Additional information
The following compiles work flawlessly:
GNU C compiler:
gcc $(python3-config --cflags) -Wall -Wextra -Wno-missing-field-initializers -c pymod.cc
GNU C++ compiler with no C++ version specified:
g++ $(python3-config --cflags) -Wall -Wextra -Wno-missing-field-initializers -c pymod.cc
GNU C++ Compiler in C++17 mode:
g++ $(python3-config --cflags) -std=c++17 -Wall -Wextra -Wno-missing-field-initializers -c pymod.cc
Your environment
- Fedora 36 container with
python-devel,gccandgcc-c++installed - CPython: 3.10.7
- GCC: 12.2.1 20220819 (Red Hat 12.2.1-2)
The issue leading up to this was our build failing in C++20 mode on at least RHEL 7/8/9, Fedora 34 to 37, SLES 12, SLES 15, Debian 10/11, Ubuntu 16 to 22.
So I guess building with pretty much every GNU C++ compiler will break if you turn on C++20.
pymod.cc:
#define PY_SSIZE_T_CLEAN #include <Python.h> typedef struct { PyObject_HEAD /* Type-specific fields go here. */ } CustomObject; static PyTypeObject CustomType = { PyVarObject_HEAD_INIT(NULL, 0) .tp_name = "custom.Custom", .tp_basicsize = sizeof(CustomObject), .tp_itemsize = 0, .tp_flags = Py_TPFLAGS_DEFAULT, .tp_new = PyType_GenericNew, }; static PyModuleDef custommodule = { PyModuleDef_HEAD_INIT, .m_name = "custom", .m_doc = "Example module that creates an extension type.", .m_size = -1, }; PyMODINIT_FUNC PyInit_custom(void) { PyObject *m; if (PyType_Ready(&CustomType) < 0) return NULL; m = PyModule_Create(&custommodule); if (m == NULL) return NULL; Py_INCREF(&CustomType); if (PyModule_AddObject(m, "Custom", (PyObject *) &CustomType) < 0) { Py_DECREF(&CustomType); Py_DECREF(m); return NULL; } return m; }