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: case.rs
    path of file: ./repos/serde/serde_derive/src/internals
    
    the code of the file until where you have to start completion: //! Code to convert the Rust-styled field/variant (e.g. `my_field`, `MyType`) to the
//! case of the source (e.g. `my-field`, `MY_FIELD`).

use self::RenameRule::*;
use std::fmt::{self, Debug, Display};

/// The different possible ways to change case of fields in a struct, or variants in an e
    
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str("unknown rename rule `rename_all = ")?;
        Debug::fmt(self.unknown, f)?;
        f.write_str("`, expected one of ")?;
        for (i, (name, _rule)) in RENAME_RULES.iter().enumerate() {
            if i > 0 {
                f.write_str(", ")?;
            }
            Debug::fmt(name, f)?;
        }
        Ok(())
    }