I would like to see a way to specify additional arguments to pip wheel.

pip wheel acts as the build frontend here and the only "official" way to pass on arguments to the backend, e.g. a setuptools powered setup.py, is through the --build-option and --global-option flags.

More importantly, pip wheel builds the wheel in an isolated environment as suggested in PEP 517 ("Recommendations for build frontends"). In order to have any custom (i.e. not specified in pyproject.toml) build-time dependencies the --no-build-isolation argument of pip wheel has to be used.

I don't understand how the CIBW_BEFORE_BUILD can even be used to install build requirements as suggested in the documentation. pip wheel will creates a new virtualenv where the installed packages should not be available. Perhaps somebody can clarify?

(I'm currently looking into cibuildwheel in order to prepare wheels for a Cython-based package of mine. It looks like a great way to save boilerplate build scripts!)

EDIT: Fixed paragraph related to build isolation; Added second pip wheel option flag.