def load_system(source_dir):
    """
    Load the build system from a source dir (pyproject.toml).
    """
    pyproject = os.path.join(source_dir, 'pyproject.toml')
    with open(pyproject) as f:
        pyproject_data = toml.load(f)
    return pyproject_data['build-system']

    Load the build system from a source dir (pyproject.toml).
    
product/gradle-plugin/src/main/python/pip/_vendor/pep517/build.py