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: custom_files.rs
    path of file: ./repos/codespan/codespan-reporting/examples
    
    the code of the file until where you have to start completion: //! An example that shows how to implement a simple custom file database.
//! The database uses 32-bit file-ids, which could be useful for optimizing
//! memory usage.
//!
//! To run this example, execute the fol
    
fn main() -> anyhow::Result<()> {
    let mut files = files::Files::new();

    let file_id0 = files.add("0.greeting", "hello world!").unwrap();
    let file_id1 = files.add("1.greeting", "bye world").unwrap();

    let messages = vec![
        Message::UnwantedGreetings {
            greetings: vec![(file_id0, 0..5), (file_id1, 0..3)],
        },
        Message::OverTheTopExclamations {
            exclamations: vec![(file_id0, 11..12)],
        },
    ];

    let writer = StandardStream::stderr(ColorChoice::Always);
    let config = term::Config::default();
    for message in &messages {
        let writer = &mut writer.lock();
        term::emit(writer, &config, &files, &message.to_diagnostic())?;
    }

    Ok(())
}