Support Python 3.15 Free Threading

Author: vstinner

tests/extension.c

@@ -12,6 +12,44 @@
 #define _CONCAT(a, b) a ## b
 #define CONCAT(a, b) _CONCAT(a, b)
 
+// Use PySlot API on Python 3.15 and newer and on limited C API 3.15 and newer
+#if (PY_VERSION_HEX >= _Py_PACK_VERSION(3, 15) \
+     && (!defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= _Py_PACK_VERSION(3, 15)))
+
+PyABIInfo_VAR(abi_info);
+
+static PySlot module_slots[] = {
+    PySlot_PTR_STATIC(Py_mod_abi, &abi_info),
+    PySlot_PTR_STATIC(Py_mod_name, (void*)STR(MODULE_NAME)),
+    PySlot_PTR_STATIC(Py_mod_state_size, 0),
+    PySlot_PTR_STATIC(Py_mod_gil, Py_MOD_GIL_NOT_USED),
+    {0, 0, {0}, {0}}
+};
+
+#define EXPORT_FUNC CONCAT(PyModExport_, MODULE_NAME)
+
+PyMODEXPORT_FUNC
+EXPORT_FUNC(void)
+{
+    return module_slots;
+}
+
+#ifdef MS_WINDOWS
+#   define INIT_FUNC CONCAT(PyInit_, MODULE_NAME)
+
+// Workaround for https://github.com/pypa/distutils/issues/387
+// https://docs.python.org/3.16/howto/abi3t-migration.html#module-export-hook
+PyMODINIT_FUNC
+INIT_FUNC(void)
+{
+    PyErr_SetString(PyExc_SystemError,
+                    "PyInit_* called for module with PyModExport_*");
+    return NULL;
+}
+#endif
+
+#else
+
 // No method and no module exec method needed, most basic C extension
 
 static struct PyModuleDef module_def = {
@@ -34,3 +72,4 @@ INIT_FUNC(void)
 {
     return PyModule_Create(&module_def);
 }
+#endif