gh-94751: Install, import and run the test C++ extension (MVP)

[encukou]

This is a quick-and-dirty way to run the C++ tests. It can definitely be improved in the future, but it should fail when things go wrong.

• Run test functions on import (yes, this can definitely be improved)
• Fudge setuptools metadata (name & version) to make the extension installable
• Install and import the extension in test_cppext

• Issue: test_cppext does not import/run the C++ extension #94751

[da-woods]

It looks good to me as based on a quick read through. I think it's definitely worth running the tests rather than assuming that it's fine if it compiles.

It looks like '-X', 'showrefcount', is just going to require inspecting by eye? That's probably reasonable to defer for a future improvement, but it obviously reduces the chance of it catching any issues.

[encukou]

Thank you!

It looks like '-X', 'showrefcount', is just going to require inspecting by eye? That's probably reasonable to defer for a future improvement

Yes. I filed #94755 for the future improvement.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @encukou for commit a615602 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[miss-islington]

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[bedevere-bot]

GH-94780 is a backport of this pull request to the 3.11 branch.

[da-woods]

I'm seeing segfaults on from test_cppext on what should be an unrelated PR https://github.com/python/cpython/runs/7316060423?check_suite_focus=true

======================================================================
ERROR: test_build_cpp03 (test.test_cppext.TestCPPExt.test_build_cpp03)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/test_cppext.py", line 23, in test_build_cpp03
    self.check_build(True, '_testcpp03ext')
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/test_cppext.py", line 33, in check_build
    self._check_build(std_cpp03, extension_name)
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/test_cppext.py", line 95, in _check_build
    run_cmd('Import', cmd)
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/test_cppext.py", line 58, in run_cmd
    subprocess.run(cmd, check=True)
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/subprocess.py", line 558, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['env/bin/python', '-X', 'dev', '-X', 'showrefcount', '-c', 'import _testcpp03ext']' died with <Signals.SIGSEGV: 11>.

[encukou]

You've accidentally included the failing reproducer in that unrelated PR.

Context switching is hard! Thanks for doing it to come up with the reproducer :)