use std::error::Error;

mod lua {
    use std::fmt;

    #[derive(Debug)]
    pub struct Error;

    impl fmt::Display for Error {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.write_str("Lua error")
        }
    }

    impl std::error::Error for Error {}
}

fn foo() -> Result<(), Box<dyn Error>> {
    bar()?;
    baz()?;
    Ok(())
}

fn bar() -> Result<(), url::ParseError> {
    Ok(())
}

fn baz() -> Result<(), lua::Error> {
    Ok(())
}