Modify noxfile.py::_cmake so it works with nox --install-only

[dhermes]

The usage of session.run

    session.run(
        "cmake",
        "--build",
        build_dir,
        "--config",
        build_type,
        "--target",
        "install",
        external=cmake_external,
    )

means the later session.install(".", env=env) in install_bezier() doesn't work as expected when --install-only is used.

[dhermes]

I'm (sort of) happy to see that the --install-only check is hyper-isolated to Session.run():

if self._runner.global_config.install_only:
    logger.info("Skipping {} run, as --install-only is set.".format(args[0]))
    return None

[dhermes]

I can think of at least two options here:

1. Just invoke session._run() directly
2. Use a context manager (probably via @contextlib.contextmanager) to temporarily set self._runner.global_config.install_only to False

I don't like either one. Both assume some level of knowledge of implementation details, so they can bitrot over time if nox internals change.

The second one somehow seems more appealing, however by monkey-patching a global value, we ruin the ability for the config to be used concurrently by other nox sessions.

@theacodes WDYT?

[theacodes]

tbh I'd be happy to see a run_always for this exact use case.

[dhermes]

@theacodes Good idea. I love when teamwork works (i.e. my brain didn't go there at all)! Will send a PR soon.

[dhermes]

Sent: wntrblm/nox#331