def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def build(self, spec, prefix):
        """Build using the OpenFOAM Allwmake script, with a wrapper to source
        its environment first.
        Only build if the compiler is known to be supported.
        """
        self.foam_arch.has_rule(self.stage.source_path)
        self.foam_arch.create_rules(self.stage.source_path, self)

        args = []
        if self.parallel:  # Build in parallel? - pass via the environment
            os.environ['WM_NCOMPPROCS'] = str(make_jobs)
        builder = Executable(self.build_script)
        builder(*args)