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gh-91321: Fix compatibility with C++ older than C++11 (#93784) (#93802)
* Fix the compatibility of the Python C API with C++ older than C++11. * _Py_NULL is only defined as nullptr on C++11 and newer. (cherry picked from commit 4caf5c2) * test_cppext now builds the C++ extension with setuptools. * Add @test.support.requires_venv_with_pip. (cherry picked from commit ca0cc9c)
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-88
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7 files changed

+156
-88
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‎Include/pyport.h

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -36,10 +36,12 @@ extern "C++" {
3636
inline type _Py_CAST_impl(int ptr) {
3737
return reinterpret_cast<type>(ptr);
3838
}
39+
#if __cplusplus >= 201103
3940
template <typename type>
4041
inline type _Py_CAST_impl(std::nullptr_t) {
4142
return static_cast<type>(nullptr);
4243
}
44+
#endif
4345

4446
template <typename type, typename expr_type>
4547
inline type _Py_CAST_impl(expr_type *expr) {
@@ -70,8 +72,9 @@ extern "C++" {
7072
#endif
7173

7274
// Static inline functions should use _Py_NULL rather than using directly NULL
73-
// to prevent C++ compiler warnings. In C++, _Py_NULL uses nullptr.
74-
#ifdef __cplusplus
75+
// to prevent C++ compiler warnings. On C++11 and newer, _Py_NULL is defined as
76+
// nullptr.
77+
#if defined(__cplusplus) && __cplusplus >= 201103
7578
# define _Py_NULL nullptr
7679
#else
7780
# define _Py_NULL NULL

‎Lib/test/_testcppext.cpp

Lines changed: 30 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -6,6 +6,12 @@
66

77
#include "Python.h"
88

9+
#if __cplusplus >= 201103
10+
# define NAME _testcpp11ext
11+
#else
12+
# define NAME _testcpp03ext
13+
#endif
14+
915
PyDoc_STRVAR(_testcppext_add_doc,
1016
"add(x, y)\n"
1117
"\n"
@@ -16,7 +22,7 @@ _testcppext_add(PyObject *Py_UNUSED(module), PyObject *args)
1622
{
1723
long i, j;
1824
if (!PyArg_ParseTuple(args, "ll:foo", &i, &j)) {
19-
return nullptr;
25+
return _Py_NULL;
2026
}
2127
long res = i + j;
2228
return PyLong_FromLong(res);
@@ -47,8 +53,8 @@ static PyObject *
4753
test_api_casts(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
4854
{
4955
PyObject *obj = Py_BuildValue("(ii)", 1, 2);
50-
if (obj == nullptr) {
51-
return nullptr;
56+
if (obj == _Py_NULL) {
57+
return _Py_NULL;
5258
}
5359
Py_ssize_t refcnt = Py_REFCNT(obj);
5460
assert(refcnt >= 1);
@@ -77,9 +83,11 @@ test_api_casts(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
7783
// gh-93442: Pass 0 as NULL for PyObject*
7884
Py_XINCREF(0);
7985
Py_XDECREF(0);
80-
// ensure that nullptr works too
86+
#if _cplusplus >= 201103
87+
// Test nullptr passed as PyObject*
8188
Py_XINCREF(nullptr);
8289
Py_XDECREF(nullptr);
90+
#endif
8391

8492
Py_DECREF(obj);
8593
Py_RETURN_NONE;
@@ -90,16 +98,16 @@ static PyObject *
9098
test_unicode(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
9199
{
92100
PyObject *str = PyUnicode_FromString("abc");
93-
if (str == nullptr) {
94-
return nullptr;
101+
if (str == _Py_NULL) {
102+
return _Py_NULL;
95103
}
96104

97105
assert(PyUnicode_Check(str));
98106
assert(PyUnicode_GET_LENGTH(str) == 3);
99107

100108
// gh-92800: test PyUnicode_READ()
101109
const void* data = PyUnicode_DATA(str);
102-
assert(data != nullptr);
110+
assert(data != _Py_NULL);
103111
int kind = PyUnicode_KIND(str);
104112
assert(kind == PyUnicode_1BYTE_KIND);
105113
assert(PyUnicode_READ(kind, data, 0) == 'a');
@@ -118,9 +126,9 @@ test_unicode(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
118126

119127
static PyMethodDef _testcppext_methods[] = {
120128
{"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
121-
{"test_api_casts", test_api_casts, METH_NOARGS, nullptr},
122-
{"test_unicode", test_unicode, METH_NOARGS, nullptr},
123-
{nullptr, nullptr, 0, nullptr} /* sentinel */
129+
{"test_api_casts", test_api_casts, METH_NOARGS, _Py_NULL},
130+
{"test_unicode", test_unicode, METH_NOARGS, _Py_NULL},
131+
{_Py_NULL, _Py_NULL, 0, _Py_NULL} /* sentinel */
124132
};
125133

126134

@@ -135,26 +143,32 @@ _testcppext_exec(PyObject *module)
135143

136144
static PyModuleDef_Slot _testcppext_slots[] = {
137145
{Py_mod_exec, reinterpret_cast<void*>(_testcppext_exec)},
138-
{0, nullptr}
146+
{0, _Py_NULL}
139147
};
140148

141149

142150
PyDoc_STRVAR(_testcppext_doc, "C++ test extension.");
143151

152+
#define _STR(NAME) #NAME
153+
#define STR(NAME) _STR(NAME)
154+
144155
static struct PyModuleDef _testcppext_module = {
145156
PyModuleDef_HEAD_INIT, // m_base
146-
"_testcppext", // m_name
157+
STR(NAME), // m_name
147158
_testcppext_doc, // m_doc
148159
0, // m_size
149160
_testcppext_methods, // m_methods
150161
_testcppext_slots, // m_slots
151-
nullptr, // m_traverse
152-
nullptr, // m_clear
153-
nullptr, // m_free
162+
_Py_NULL, // m_traverse
163+
_Py_NULL, // m_clear
164+
_Py_NULL, // m_free
154165
};
155166

167+
#define _FUNC_NAME(NAME) PyInit_ ## NAME
168+
#define FUNC_NAME(NAME) _FUNC_NAME(NAME)
169+
156170
PyMODINIT_FUNC
157-
PyInit__testcppext(void)
171+
FUNC_NAME(NAME)(void)
158172
{
159173
return PyModuleDef_Init(&_testcppext_module);
160174
}

‎Lib/test/setup_testcppext.py

Lines changed: 51 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,51 @@
1+
# gh-91321: Build a basic C++ test extension to check that the Python C API is
2+
# compatible with C++ and does not emit C++ compiler warnings.
3+
import sys
4+
from test import support
5+
6+
from setuptools import setup, Extension
7+
8+
9+
MS_WINDOWS = (sys.platform == 'win32')
10+
11+
12+
SOURCE = support.findfile('_testcppext.cpp')
13+
if not MS_WINDOWS:
14+
# C++ compiler flags for GCC and clang
15+
CPPFLAGS = [
16+
# gh-91321: The purpose of _testcppext extension is to check that building
17+
# a C++ extension using the Python C API does not emit C++ compiler
18+
# warnings
19+
'-Werror',
20+
# Warn on old-style cast (C cast) like: (PyObject*)op
21+
'-Wold-style-cast',
22+
# Warn when using NULL rather than _Py_NULL in static inline functions
23+
'-Wzero-as-null-pointer-constant',
24+
]
25+
else:
26+
# Don't pass any compiler flag to MSVC
27+
CPPFLAGS = []
28+
29+
30+
def main():
31+
cppflags = list(CPPFLAGS)
32+
if '-std=c++03' in sys.argv:
33+
sys.argv.remove('-std=c++03')
34+
std = 'c++03'
35+
name = '_testcpp03ext'
36+
else:
37+
# Python currently targets C++11
38+
std = 'c++11'
39+
name = '_testcpp11ext'
40+
41+
cppflags = [*CPPFLAGS, f'-std={std}']
42+
cpp_ext = Extension(
43+
name,
44+
sources=[SOURCE],
45+
language='c++',
46+
extra_compile_args=cppflags)
47+
setup(name=name, ext_modules=[cpp_ext])
48+
49+
50+
if __name__ == "__main__":
51+
main()

‎Lib/test/support/__init__.py

Lines changed: 17 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2196,3 +2196,20 @@ def clear_ignored_deprecations(*tokens: object) -> None:
21962196
if warnings.filters != new_filters:
21972197
warnings.filters[:] = new_filters
21982198
warnings._filters_mutated()
2199+
2200+
2201+
# Skip a test if venv with pip is known to not work.
2202+
def requires_venv_with_pip():
2203+
# ensurepip requires zlib to open ZIP archives (.whl binary wheel packages)
2204+
try:
2205+
import zlib
2206+
except ImportError:
2207+
return unittest.skipIf(True, "venv: ensurepip requires zlib")
2208+
2209+
# bpo-26610: pip/pep425tags.py requires ctypes.
2210+
# gh-92820: setuptools/windows_support.py uses ctypes (setuptools 58.1).
2211+
try:
2212+
import ctypes
2213+
except ImportError:
2214+
ctypes = None
2215+
return unittest.skipUnless(ctypes, 'venv: pip requires ctypes')

‎Lib/test/test_cppext.py

Lines changed: 48 additions & 66 deletions
Original file line numberDiff line numberDiff line change
@@ -1,91 +1,73 @@
11
# gh-91321: Build a basic C++ test extension to check that the Python C API is
22
# compatible with C++ and does not emit C++ compiler warnings.
3-
import contextlib
4-
import os
3+
import os.path
54
import sys
65
import unittest
7-
import warnings
6+
import subprocess
87
from test import support
98
from test.support import os_helper
109

11-
with warnings.catch_warnings():
12-
warnings.simplefilter('ignore', DeprecationWarning)
13-
from distutils.core import setup, Extension
14-
import distutils.sysconfig
15-
1610

1711
MS_WINDOWS = (sys.platform == 'win32')
1812

1913

20-
SOURCE = support.findfile('_testcppext.cpp')
21-
if not MS_WINDOWS:
22-
# C++ compiler flags for GCC and clang
23-
CPPFLAGS = [
24-
# Python currently targets C++11
25-
'-std=c++11',
26-
# gh-91321: The purpose of _testcppext extension is to check that building
27-
# a C++ extension using the Python C API does not emit C++ compiler
28-
# warnings
29-
'-Werror',
30-
# Warn on old-style cast (C cast) like: (PyObject*)op
31-
'-Wold-style-cast',
32-
# Warn when using NULL rather than _Py_NULL in static inline functions
33-
'-Wzero-as-null-pointer-constant',
34-
]
35-
else:
36-
# Don't pass any compiler flag to MSVC
37-
CPPFLAGS = []
14+
SETUP_TESTCPPEXT = support.findfile('setup_testcppext.py')
3815

3916

4017
@support.requires_subprocess()
4118
class TestCPPExt(unittest.TestCase):
42-
def build(self):
43-
cpp_ext = Extension(
44-
'_testcppext',
45-
sources=[SOURCE],
46-
language='c++',
47-
extra_compile_args=CPPFLAGS)
48-
capture_stdout = (not support.verbose)
19+
def test_build_cpp11(self):
20+
self.check_build(False)
4921

50-
try:
51-
try:
52-
if capture_stdout:
53-
stdout = support.captured_stdout()
54-
else:
55-
print()
56-
stdout = contextlib.nullcontext()
57-
with (stdout,
58-
support.swap_attr(sys, 'argv', ['setup.py', 'build_ext', '--verbose'])):
59-
setup(name="_testcppext", ext_modules=[cpp_ext])
60-
return
61-
except:
62-
if capture_stdout:
63-
# Show output on error
64-
print()
65-
print(stdout.getvalue())
66-
raise
67-
except SystemExit:
68-
self.fail("Build failed")
22+
def test_build_cpp03(self):
23+
self.check_build(True)
6924

7025
# With MSVC, the linker fails with: cannot open file 'python311.lib'
7126
# https://github.com/python/cpython/pull/32175#issuecomment-1111175897
7227
@unittest.skipIf(MS_WINDOWS, 'test fails on Windows')
73-
def test_build(self):
74-
# save/restore os.environ
75-
def restore_env(old_env):
76-
os.environ.clear()
77-
os.environ.update(old_env)
78-
self.addCleanup(restore_env, dict(os.environ))
79-
80-
def restore_sysconfig_vars(old_config_vars):
81-
distutils.sysconfig._config_vars.clear()
82-
distutils.sysconfig._config_vars.update(old_config_vars)
83-
self.addCleanup(restore_sysconfig_vars,
84-
dict(distutils.sysconfig._config_vars))
85-
28+
# the test uses venv+pip: skip if it's not available
29+
@support.requires_venv_with_pip()
30+
def check_build(self, std_cpp03):
8631
# Build in a temporary directory
8732
with os_helper.temp_cwd():
88-
self.build()
33+
self._check_build(std_cpp03)
34+
35+
def _check_build(self, std_cpp03):
36+
venv_dir = 'env'
37+
verbose = support.verbose
38+
39+
# Create virtual environment to get setuptools
40+
cmd = [sys.executable, '-X', 'dev', '-m', 'venv', venv_dir]
41+
if verbose:
42+
print()
43+
print('Run:', ' '.join(cmd))
44+
subprocess.run(cmd, check=True)
45+
46+
# Get the Python executable of the venv
47+
python_exe = 'python'
48+
if sys.executable.endswith('.exe'):
49+
python_exe += '.exe'
50+
if MS_WINDOWS:
51+
python = os.path.join(venv_dir, 'Scripts', python_exe)
52+
else:
53+
python = os.path.join(venv_dir, 'bin', python_exe)
54+
55+
# Build the C++ extension
56+
cmd = [python, '-X', 'dev',
57+
SETUP_TESTCPPEXT, 'build_ext', '--verbose']
58+
if std_cpp03:
59+
cmd.append('-std=c++03')
60+
if verbose:
61+
print('Run:', ' '.join(cmd))
62+
subprocess.run(cmd, check=True)
63+
else:
64+
proc = subprocess.run(cmd,
65+
stdout=subprocess.PIPE,
66+
stderr=subprocess.STDOUT,
67+
text=True)
68+
if proc.returncode:
69+
print(proc.stdout, end='')
70+
self.fail(f"Build failed with exit code {proc.returncode}")
8971

9072

9173
if __name__ == "__main__":

‎Lib/test/test_venv.py

Lines changed: 3 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -17,7 +17,8 @@
1717
import tempfile
1818
from test.support import (captured_stdout, captured_stderr, requires_zlib,
1919
skip_if_broken_multiprocessing_synchronize, verbose,
20-
requires_subprocess, is_emscripten, is_wasi)
20+
requires_subprocess, is_emscripten, is_wasi,
21+
requires_venv_with_pip)
2122
from test.support.os_helper import (can_symlink, EnvironmentVarGuard, rmtree)
2223
import unittest
2324
import venv
@@ -619,9 +620,7 @@ def do_test_with_pip(self, system_site_packages):
619620
if not system_site_packages:
620621
self.assert_pip_not_installed()
621622

622-
# Issue #26610: pip/pep425tags.py requires ctypes
623-
@unittest.skipUnless(ctypes, 'pip requires ctypes')
624-
@requires_zlib()
623+
@requires_venv_with_pip()
625624
def test_with_pip(self):
626625
self.do_test_with_pip(False)
627626
self.do_test_with_pip(True)

‎Misc/NEWS.d/next/C API/2022-06-13-21-37-31.gh-issue-91321.DgJFvS.rst

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Fix the compatibility of the Python C API with C++ older than C++11. Patch by
2+
Victor Stinner.

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