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gh-127902: Backport test_cext from the main branch
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‎Lib/test/test_cext/__init__.py

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# gh-116869: Build a basic C test extension to check that the Python C API
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# does not emit C compiler warnings.
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#
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# The Python C API must be compatible with building
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# with the -Werror=declaration-after-statement compiler flag.
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import os.path
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import shlex
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import shutil
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import subprocess
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import unittest
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from test import support
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SOURCE = os.path.join(os.path.dirname(__file__), 'extension.c')
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SETUP = os.path.join(os.path.dirname(__file__), 'setup.py')
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# With MSVC on a debug build, the linker fails with: cannot open file
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# 'python311.lib', it should look 'python311_d.lib'.
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@unittest.skipIf(support.MS_WINDOWS and support.Py_DEBUG,
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'test fails on Windows debug build')
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# Building and running an extension in clang sanitizing mode is not
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# straightforward
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@support.skip_if_sanitizer('test does not work with analyzing builds',
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address=True, memory=True, ub=True, thread=True)
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# the test uses venv+pip: skip if it's not available
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@support.requires_venv_with_pip()
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@support.requires_subprocess()
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@support.requires_resource('cpu')
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class TestExt(unittest.TestCase):
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# Default build with no options
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def test_build(self):
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self.check_build('_test_cext')
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def test_build_c11(self):
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self.check_build('_test_c11_cext', std='c11')
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@unittest.skipIf(support.MS_WINDOWS, "MSVC doesn't support /std:c99")
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def test_build_c99(self):
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self.check_build('_test_c99_cext', std='c99')
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def test_build_limited(self):
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self.check_build('_test_limited_cext', limited=True)
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def test_build_limited_c11(self):
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self.check_build('_test_limited_c11_cext', limited=True, std='c11')
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def check_build(self, extension_name, std=None, limited=False):
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venv_dir = 'env'
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with support.setup_venv_with_pip_setuptools_wheel(venv_dir) as python_exe:
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self._check_build(extension_name, python_exe,
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std=std, limited=limited)
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def _check_build(self, extension_name, python_exe, std, limited):
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pkg_dir = 'pkg'
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os.mkdir(pkg_dir)
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shutil.copy(SETUP, os.path.join(pkg_dir, os.path.basename(SETUP)))
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shutil.copy(SOURCE, os.path.join(pkg_dir, os.path.basename(SOURCE)))
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def run_cmd(operation, cmd):
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env = os.environ.copy()
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if std:
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env['CPYTHON_TEST_STD'] = std
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if limited:
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env['CPYTHON_TEST_LIMITED'] = '1'
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env['CPYTHON_TEST_EXT_NAME'] = extension_name
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if support.verbose:
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print('Run:', ' '.join(map(shlex.quote, cmd)))
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subprocess.run(cmd, check=True, env=env)
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else:
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proc = subprocess.run(cmd,
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env=env,
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stdout=subprocess.PIPE,
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stderr=subprocess.STDOUT,
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text=True)
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if proc.returncode:
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print('Run:', ' '.join(map(shlex.quote, cmd)))
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print(proc.stdout, end='')
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self.fail(
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f"{operation} failed with exit code {proc.returncode}")
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# Build and install the C extension
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cmd = [python_exe, '-X', 'dev',
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'-m', 'pip', 'install', '--no-build-isolation',
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os.path.abspath(pkg_dir)]
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if support.verbose:
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cmd.append('-v')
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run_cmd('Install', cmd)
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# Do a reference run. Until we test that running python
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# doesn't leak references (gh-94755), run it so one can manually check
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# -X showrefcount results against this baseline.
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cmd = [python_exe,
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'-X', 'dev',
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'-X', 'showrefcount',
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'-c', 'pass']
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run_cmd('Reference run', cmd)
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# Import the C extension
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cmd = [python_exe,
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'-X', 'dev',
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'-X', 'showrefcount',
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'-c', f"import {extension_name}"]
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run_cmd('Import', cmd)
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if __name__ == "__main__":
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unittest.main()

‎Lib/test/test_cext/extension.c

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// gh-116869: Basic C test extension to check that the Python C API
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// does not emit C compiler warnings.
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// Always enable assertions
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#undef NDEBUG
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#include "Python.h"
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#ifndef MODULE_NAME
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# error "MODULE_NAME macro must be defined"
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#endif
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#define _STR(NAME) #NAME
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#define STR(NAME) _STR(NAME)
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PyDoc_STRVAR(_testcext_add_doc,
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"add(x, y)\n"
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"\n"
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"Return the sum of two integers: x + y.");
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static PyObject *
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_testcext_add(PyObject *Py_UNUSED(module), PyObject *args)
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{
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long i, j, res;
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if (!PyArg_ParseTuple(args, "ll:foo", &i, &j)) {
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return NULL;
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}
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res = i + j;
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return PyLong_FromLong(res);
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}
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static PyMethodDef _testcext_methods[] = {
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{"add", _testcext_add, METH_VARARGS, _testcext_add_doc},
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{NULL, NULL, 0, NULL} // sentinel
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};
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static int
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_testcext_exec(
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#ifdef __STDC_VERSION__
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PyObject *module
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#else
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PyObject *Py_UNUSED(module)
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#endif
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)
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{
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#ifdef __STDC_VERSION__
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if (PyModule_AddIntMacro(module, __STDC_VERSION__) < 0) {
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return -1;
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}
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#endif
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// test Py_BUILD_ASSERT() and Py_BUILD_ASSERT_EXPR()
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Py_BUILD_ASSERT(sizeof(int) == sizeof(unsigned int));
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assert(Py_BUILD_ASSERT_EXPR(sizeof(int) == sizeof(unsigned int)) == 0);
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return 0;
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}
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static PyModuleDef_Slot _testcext_slots[] = {
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{Py_mod_exec, (void*)_testcext_exec},
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{0, NULL}
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};
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PyDoc_STRVAR(_testcext_doc, "C test extension.");
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static struct PyModuleDef _testcext_module = {
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PyModuleDef_HEAD_INIT, // m_base
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STR(MODULE_NAME), // m_name
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_testcext_doc, // m_doc
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0, // m_size
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_testcext_methods, // m_methods
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_testcext_slots, // m_slots
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NULL, // m_traverse
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NULL, // m_clear
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NULL, // m_free
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};
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#define _FUNC_NAME(NAME) PyInit_ ## NAME
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#define FUNC_NAME(NAME) _FUNC_NAME(NAME)
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PyMODINIT_FUNC
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FUNC_NAME(MODULE_NAME)(void)
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{
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return PyModuleDef_Init(&_testcext_module);
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}

‎Lib/test/test_cext/setup.py

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# gh-91321: Build a basic C test extension to check that the Python C API is
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# compatible with C and does not emit C compiler warnings.
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import os
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import platform
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import shlex
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import sys
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import sysconfig
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from test import support
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from setuptools import setup, Extension
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SOURCE = 'extension.c'
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if not support.MS_WINDOWS:
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# C compiler flags for GCC and clang
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CFLAGS = [
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# The purpose of test_cext extension is to check that building a C
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# extension using the Python C API does not emit C compiler warnings.
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'-Werror',
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# gh-120593: Check the 'const' qualifier
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'-Wcast-qual',
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# gh-116869: The Python C API must be compatible with building
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# with the -Werror=declaration-after-statement compiler flag.
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'-Werror=declaration-after-statement',
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]
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else:
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# MSVC compiler flags
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CFLAGS = [
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# Display warnings level 1 to 4
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'/W4',
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# Treat all compiler warnings as compiler errors
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'/WX',
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]
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def main():
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std = os.environ.get("CPYTHON_TEST_STD", "")
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module_name = os.environ["CPYTHON_TEST_EXT_NAME"]
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limited = bool(os.environ.get("CPYTHON_TEST_LIMITED", ""))
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cflags = list(CFLAGS)
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cflags.append(f'-DMODULE_NAME={module_name}')
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# Add -std=STD or /std:STD (MSVC) compiler flag
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if std:
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if support.MS_WINDOWS:
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cflags.append(f'/std:{std}')
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else:
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cflags.append(f'-std={std}')
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# Remove existing -std or /std options from CC command line.
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# Python adds -std=c11 option.
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cmd = (sysconfig.get_config_var('CC') or '')
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if cmd is not None:
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if support.MS_WINDOWS:
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std_prefix = '/std'
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else:
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std_prefix = '-std'
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cmd = shlex.split(cmd)
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cmd = [arg for arg in cmd if not arg.startswith(std_prefix)]
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cmd = shlex.join(cmd)
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# CC env var overrides sysconfig CC variable in setuptools
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os.environ['CC'] = cmd
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# Define Py_LIMITED_API macro
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if limited:
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version = sys.hexversion
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cflags.append(f'-DPy_LIMITED_API={version:#x}')
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# On Windows, add PCbuild\amd64\ to include and library directories
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include_dirs = []
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library_dirs = []
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if support.MS_WINDOWS:
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srcdir = sysconfig.get_config_var('srcdir')
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machine = platform.uname().machine
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pcbuild = os.path.join(srcdir, 'PCbuild', machine)
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if os.path.exists(pcbuild):
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# pyconfig.h is generated in PCbuild\amd64\
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include_dirs.append(pcbuild)
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# python313.lib is generated in PCbuild\amd64\
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library_dirs.append(pcbuild)
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print(f"Add PCbuild directory: {pcbuild}")
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# Display information to help debugging
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for env_name in ('CC', 'CFLAGS'):
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if env_name in os.environ:
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print(f"{env_name} env var: {os.environ[env_name]!r}")
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else:
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print(f"{env_name} env var: <missing>")
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print(f"extra_compile_args: {cflags!r}")
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ext = Extension(
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module_name,
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sources=[SOURCE],
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extra_compile_args=cflags,
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include_dirs=include_dirs,
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library_dirs=library_dirs)
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setup(name=f'internal_{module_name}',
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version='0.0',
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ext_modules=[ext])
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if __name__ == "__main__":
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main()

‎Misc/NEWS.d/next/Tests/2024-12-13-13-16-43.gh-issue-127902.wsZJ29.rst

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Backport test_cext from the main branch. Patch by Victor Stinner.

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