gh-108303: Add Lib/test/test_cppext/ sub-directory (#108325)

* Move test_cppext to its own directory
* Rename setup_testcppext.py to setup.py
* Rename _testcppext.cpp to extension.cpp
* The source (extension.cpp) is now also copied by the test.

Lib/test/test_cppext.py

@@ -1,88 +0,0 @@
-# gh-91321: Build a basic C++ test extension to check that the Python C API is
-# compatible with C++ and does not emit C++ compiler warnings.
-import os.path
-import shutil
-import sys
-import unittest
-import subprocess
-import sysconfig
-from test import support
-
-
-MS_WINDOWS = (sys.platform == 'win32')
-
-
-SETUP_TESTCPPEXT = support.findfile('setup_testcppext.py')
-
-
-@support.requires_subprocess()
-class TestCPPExt(unittest.TestCase):
-    def test_build_cpp11(self):
-        self.check_build(False, '_testcpp11ext')
-
-    def test_build_cpp03(self):
-        self.check_build(True, '_testcpp03ext')
-
-    # With MSVC, the linker fails with: cannot open file 'python311.lib'
-    # https://github.com/python/cpython/pull/32175#issuecomment-1111175897
-    @unittest.skipIf(MS_WINDOWS, 'test fails on Windows')
-    # Building and running an extension in clang sanitizing mode is not
-    # straightforward
-    @unittest.skipIf(
-        '-fsanitize' in (sysconfig.get_config_var('PY_CFLAGS') or ''),
-        'test does not work with analyzing builds')
-    # the test uses venv+pip: skip if it's not available
-    @support.requires_venv_with_pip()
-    def check_build(self, std_cpp03, extension_name):
-        venv_dir = 'env'
-        with support.setup_venv_with_pip_setuptools_wheel(venv_dir) as python_exe:
-            self._check_build(std_cpp03, extension_name, python_exe)
-
-    def _check_build(self, std_cpp03, extension_name, python_exe):
-        pkg_dir = 'pkg'
-        os.mkdir(pkg_dir)
-        shutil.copy(SETUP_TESTCPPEXT, os.path.join(pkg_dir, "setup.py"))
-
-        def run_cmd(operation, cmd):
-            env = os.environ.copy()
-            env['CPYTHON_TEST_CPP_STD'] = 'c++03' if std_cpp03 else 'c++11'
-            env['CPYTHON_TEST_EXT_NAME'] = extension_name
-            if support.verbose:
-                print('Run:', ' '.join(cmd))
-                subprocess.run(cmd, check=True, env=env)
-            else:
-                proc = subprocess.run(cmd,
-                                      env=env,
-                                      stdout=subprocess.PIPE,
-                                      stderr=subprocess.STDOUT,
-                                      text=True)
-                if proc.returncode:
-                    print(proc.stdout, end='')
-                    self.fail(
-                        f"{operation} failed with exit code {proc.returncode}")
-
-        # Build and install the C++ extension
-        cmd = [python_exe, '-X', 'dev',
-               '-m', 'pip', 'install', '--no-build-isolation',
-               os.path.abspath(pkg_dir)]
-        run_cmd('Install', cmd)
-
-        # Do a reference run. Until we test that running python
-        # doesn't leak references (gh-94755), run it so one can manually check
-        # -X showrefcount results against this baseline.
-        cmd = [python_exe,
-               '-X', 'dev',
-               '-X', 'showrefcount',
-               '-c', 'pass']
-        run_cmd('Reference run', cmd)
-
-        # Import the C++ extension
-        cmd = [python_exe,
-               '-X', 'dev',
-               '-X', 'showrefcount',
-               '-c', f"import {extension_name}"]
-        run_cmd('Import', cmd)
-
-
-if __name__ == "__main__":
-    unittest.main()