def clean_file(c_source, virtualenv_dirname):
    """Strip trailing whitespace and clean up "local" names in C source.

    These source files are autogenerated from the ``cython`` CLI.

    Args:
        c_source (str): Path to a ``.c`` source file.
        virtualenv_dirname (str): The name of the ``virtualenv``
            directory where Cython is installed (this is part of a
            relative path ``.nox/{NAME}/lib/...``).
    """
    with open(c_source, "r") as file_obj:
        contents = file_obj.read().rstrip()
    # Replace the path to the Cython include files.
    py_version = "python{}.{}".format(*sys.version_info[:2])
    lib_path = os.path.join(
        ".nox", virtualenv_dirname, "lib", py_version, "site-packages", ""
    )
    contents = contents.replace(lib_path, "")
    # Write the files back, but strip all trailing whitespace.
    lines = contents.split("\n")
    with open(c_source, "w") as file_obj:
        for line in lines:
            file_obj.write(line.rstrip() + "\n")