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 rename_source(self):
        """This is fairly horrible.
        The github tarfiles have weird names that do not correspond to the
        canonical name. We need to rename these, but leave a symlink for
        spack to work with.
        """
        # Note that this particular OpenFOAM requires absolute directories
        # to build correctly!
        parent   = os.path.dirname(self.stage.source_path)
        original = os.path.basename(self.stage.source_path)
        target   = 'OpenFOAM-{0}'.format(self.version)
        # Could also grep through etc/bashrc for WM_PROJECT_VERSION
        with working_dir(parent):
            if original != target and not os.path.lexists(target):
                os.rename(original, target)
                os.symlink(target, original)
                tty.info('renamed {0} -> {1}'.format(original, target))