gh-140550: Enable limited C API tests on Free Threading in test_cext

Enable limited C API tests on Free Threading in test_cext and
test_cppext: test Py_TARGET_ABI3T macro.

* Convert test_cppext to PySlot API using PySlot_PTR_STATIC().
* Define Py_MOD_GIL_NOT_USED in test_cext and test_cppext.
* Disable C++ test_virtual_object() if Py_TARGET_ABI3T is defined.
* Remove ";" from PyABIInfo_VAR macro definition, since
  "PyABIInfo_VAR(abi_info);" added two ";;" which is illegal in
  C++03.

Author: vstinner

Include/modsupport.h

@@ -140,7 +140,7 @@ PyAPI_FUNC(int) PyABIInfo_Check(PyABIInfo *info, const char *module_name);
     /////////////////////////////////////////////////////////
 
 #define PyABIInfo_VAR(NAME) \
-    static PyABIInfo NAME = _PyABIInfo_DEFAULT;
+    static PyABIInfo NAME = _PyABIInfo_DEFAULT
 
 #undef _PyABIInfo_DEFAULT_STABLE
 #undef _PyABIInfo_DEFAULT_FT

Lib/test/test_cext/__init__.py

@@ -110,11 +110,9 @@ def run_cmd(operation, cmd):
 
 
 class TestPublicCAPI(BaseTests, unittest.TestCase):
-    @support.requires_gil_enabled('incompatible with Free Threading')
     def test_build_limited(self):
         self.check_build('_test_limited_cext', limited=True)
 
-    @support.requires_gil_enabled('broken for now with Free Threading')
     def test_build_limited_c11(self):
         self.check_build('_test_limited_c11_cext', limited=True, std='c11')
 

Lib/test/test_cext/extension.c

@@ -139,6 +139,7 @@ static PySlot _testcext_slots[] = {
     PySlot_STATIC_DATA(Py_mod_doc, (void*)(char*)_testcext_doc),
     PySlot_FUNC(Py_mod_exec, (void*)_testcext_exec),
     PySlot_STATIC_DATA(Py_mod_methods, _testcext_methods),
+    PySlot_DATA(Py_mod_gil, Py_MOD_GIL_NOT_USED),
     PySlot_END,
 };
 

Lib/test/test_cppext/__init__.py

@@ -102,11 +102,9 @@ class TestPublicCAPI(BaseTests, unittest.TestCase):
     def test_build(self):
         self.check_build('_testcppext')
 
-    @support.requires_gil_enabled('incompatible with Free Threading')
     def test_build_limited_cpp03(self):
         self.check_build('_test_limited_cpp03ext', std='c++03', limited=True)
 
-    @support.requires_gil_enabled('incompatible with Free Threading')
     def test_build_limited(self):
         self.check_build('_testcppext_limited', limited=True)
 

Lib/test/test_cppext/extension.cpp

@@ -1,4 +1,4 @@
-// gh-91321: Very basic C++ test extension to check that the Python C API is
+// gh-91321: Basic C++ test extension to check that the Python C API is
 // compatible with C++ and does not emit C++ compiler warnings.
 //
 // The code is only built, not executed.
@@ -159,6 +159,8 @@ test_unicode(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     Py_RETURN_NONE;
 }
 
+// VirtualPyObject is incompatible with opaque PyObject
+#ifndef Py_TARGET_ABI3T
 /* Test a `new`-allocated object with a virtual method.
  * (https://github.com/python/cpython/issues/94731) */
 
@@ -237,6 +239,8 @@ test_virtual_object(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     }
     Py_RETURN_NONE;
 }
+#endif  // Py_TARGET_ABI3T
+
 
 static PyObject *
 test_datetime(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
@@ -256,7 +260,9 @@ static PyMethodDef _testcppext_methods[] = {
     {"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
     {"test_api_casts", test_api_casts, METH_NOARGS, _Py_NULL},
     {"test_unicode", test_unicode, METH_NOARGS, _Py_NULL},
+#ifndef Py_TARGET_ABI3T
     {"test_virtual_object", test_virtual_object, METH_NOARGS, _Py_NULL},
+#endif
     {"test_datetime", test_datetime, METH_NOARGS, _Py_NULL},
     // Note: _testcppext_exec currently runs all test functions directly.
     // When adding a new one, add a call there.
@@ -282,9 +288,11 @@ _testcppext_exec(PyObject *module)
     if (!result) return -1;
     Py_DECREF(result);
 
+#ifndef Py_TARGET_ABI3T
     result = PyObject_CallMethod(module, "test_virtual_object", "");
     if (!result) return -1;
     Py_DECREF(result);
+#endif
 
     result = PyObject_CallMethod(module, "test_datetime", "");
     if (!result) return -1;
@@ -313,40 +321,40 @@ _testcppext_exec(PyObject *module)
     return 0;
 }
 
-// Need to ignore "-Wpedantic" warnings; see VirtualPyObject_Slots above
-_Py_COMP_DIAG_PUSH
-#if defined(__GNUC__)
-#pragma GCC diagnostic ignored "-Wpedantic"
-#elif defined(__clang__)
-#pragma clang diagnostic ignored "-Wpedantic"
-#endif
 
-static PyModuleDef_Slot _testcppext_slots[] = {
-    {Py_mod_exec, reinterpret_cast<void*>(_testcppext_exec)},
-    {0, _Py_NULL}
+PyDoc_STRVAR(_testcppext_doc, "C++ test extension.");
+PyABIInfo_VAR(abi_info);
+
+static PySlot _testcppext_slots[] = {
+    PySlot_PTR_STATIC(Py_mod_abi, &abi_info),
+    PySlot_PTR_STATIC(Py_mod_name, (void*)STR(MODULE_NAME)),
+    PySlot_PTR_STATIC(Py_mod_doc, (void*)(char*)_testcppext_doc),
+    PySlot_PTR_STATIC(Py_mod_exec, (void*)_testcppext_exec),
+    PySlot_PTR_STATIC(Py_mod_methods, _testcppext_methods),
+    PySlot_PTR_STATIC(Py_mod_gil, Py_MOD_GIL_NOT_USED),
+    PySlot_END,
 };
 
-_Py_COMP_DIAG_POP
 
-PyDoc_STRVAR(_testcppext_doc, "C++ test extension.");
+#define _FUNC_NAME(NAME) PyModExport_ ## NAME
+#define FUNC_NAME(NAME) _FUNC_NAME(NAME)
 
-static struct PyModuleDef _testcppext_module = {
-    PyModuleDef_HEAD_INIT,  // m_base
-    STR(MODULE_NAME),  // m_name
-    _testcppext_doc,  // m_doc
-    0,  // m_size
-    _testcppext_methods,  // m_methods
-    _testcppext_slots,  // m_slots
-    _Py_NULL,  // m_traverse
-    _Py_NULL,  // m_clear
-    _Py_NULL,  // m_free
-};
+PyMODEXPORT_FUNC
+FUNC_NAME(MODULE_NAME)(void)
+{
+    return _testcppext_slots;
+}
 
-#define _FUNC_NAME(NAME) PyInit_ ## NAME
-#define FUNC_NAME(NAME) _FUNC_NAME(NAME)
+// Also define the soft-deprecated entrypoint to ensure it isn't called
+
+#define _INITFUNC_NAME(NAME) PyInit_ ## NAME
+#define INITFUNC_NAME(NAME) _INITFUNC_NAME(NAME)
 
 PyMODINIT_FUNC
-FUNC_NAME(MODULE_NAME)(void)
+INITFUNC_NAME(MODULE_NAME)(void)
 {
-    return PyModuleDef_Init(&_testcppext_module);
+    PyErr_SetString(
+        PyExc_AssertionError,
+        "PyInit_* function called while a PyModExport_* one is available");
+    return NULL;
 }

Misc/NEWS.d/next/Tests/2026-09-14-14-50-42.gh-issue-140550.7jirEN.rst

@@ -0,0 +1,2 @@
+Enable limited C API tests on Free Threading in test_cext and test_cppext:
+test the :c:macro:`Py_TARGET_ABI3T` macro. Patch by Victor Stinner.