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gh-116869: Add test_cext test: build a C extension
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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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import os.path
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import shutil
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import subprocess
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import sysconfig
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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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# gh-110119: pip does not currently support 't' in the ABI flag use by
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# --disable-gil builds. Once it does, we can remove this skip.
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@unittest.skipIf(support.Py_GIL_DISABLED,
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'test does not work with --disable-gil')
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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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def test_build_c99(self):
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self.check_build('c99', '_test_c99_ext')
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def test_build_c11(self):
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self.check_build('c11', '_test_c11_ext')
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# With MSVC, the linker fails with: cannot open file 'python311.lib'
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# https://github.com/python/cpython/pull/32175#issuecomment-1111175897
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@unittest.skipIf(support.MS_WINDOWS, 'test fails on Windows')
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# Building and running an extension in clang sanitizing mode is not
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# straightforward
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@unittest.skipIf(
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'-fsanitize' in (sysconfig.get_config_var('PY_CFLAGS') or ''),
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'test does not work with analyzing builds')
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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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def check_build(self, clang_std, extension_name):
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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(clang_std, extension_name, python_exe)
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def _check_build(self, clang_std, extension_name, python_exe):
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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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env['CPYTHON_TEST_STD'] = clang_std
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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(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(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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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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#if defined (__STDC_VERSION__) && __STDC_VERSION__ > 201710L
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# define NAME _test_c2x_ext
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#elif defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
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# define NAME _test_c11_ext
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#else
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# define NAME _test_c99_ext
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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;
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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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long 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(PyObject *module)
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{
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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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return 0;
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}
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static PyModuleDef_Slot _testcext_slots[] = {
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{Py_mod_exec, _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(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(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 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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]
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else:
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# Don't pass any compiler flag to MSVC
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CFLAGS = []
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def main():
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std = os.environ["CPYTHON_TEST_STD"]
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name = os.environ["CPYTHON_TEST_EXT_NAME"]
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cflags = [*CFLAGS, f'-std={std}']
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# Remove existing -std options to only test ours
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cmd = (sysconfig.get_config_var('CC') or '')
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if cmd is not None:
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cmd = shlex.split(cmd)
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cmd = [arg for arg in cmd if not arg.startswith('-std=')]
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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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ext = Extension(
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name,
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sources=[SOURCE],
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extra_compile_args=cflags)
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setup(name='internal' + name, version='0.0', ext_modules=[ext])
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if __name__ == "__main__":
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main()

‎Misc/NEWS.d/next/C API/2024-03-18-10-58-47.gh-issue-116869.lN0GBl.rst‎

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Add ``test_cext`` test: build a C extension to check if the Python C API
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emits C compiler warnings. Patch by Victor Stinner.

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