def determine_version_specifier() -> str:
    """Determine the version of Black to install.

    The version can be specified either via the `with.version` input or via the
    pyproject.toml file if `with.use_pyproject` is set to `true`.
    """
    if USE_PYPROJECT and VERSION:
        print(
            "::error::'with.version' and 'with.use_pyproject' inputs are "
            "mutually exclusive.",
            file=sys.stderr,
            flush=True,
        )
        sys.exit(1)
    if USE_PYPROJECT:
        return read_version_specifier_from_pyproject()
    elif VERSION and VERSION[0] in "0123456789":
        return f"=={VERSION}"
    else:
        return VERSION
Determine the version of Black to install.

    The version can be specified either via the `with.version` input or via the
    pyproject.toml file if `with.use_pyproject` is set to `true`.
    
action/main.py