You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lib.rs
    path of file: ./repos/clap/clap_lex/src
    
    the code of the file until where you have to start completion: //! Minimal, flexible command-line parser
//!
//! As opposed to a declarative parser, this processes arguments as a stream of tokens.  As lexing
//! a command-line is not context-free, we rel
    
    pub fn to_long(&self) -> Option<(Result<&str, &OsStr>, Option<&OsStr>)> {
        let raw = self.inner;
        let remainder = raw.strip_prefix("--")?;
        if remainder.is_empty() {
            debug_assert!(self.is_escape());
            return None;
        }

        let (flag, value) = if let Some((p0, p1)) = remainder.split_once("=") {
            (p0, Some(p1))
        } else {
            (remainder, None)
        };
        let flag = flag.to_str().ok_or(flag);
        Some((flag, value))
    }