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: diff.rs
    path of file: ./repos/cargo/crates/cargo-test-support/src
    
    the code of the file until where you have to start completion: //! A simple Myers diff implementation.
//!
//! This focuses on being short and simple, and the expense of being
//! inefficient. A key characteristic here is that this supports cargotest's
//! `[..]` wildcard matching. That means things like hashing can't be used.
//! Since Cargo's output tends to be small, this should be sufficient.

use std::fmt;
use std::io::Write;

/// A single line change to be applied to the original.
#[derive(Debug, Eq, PartialEq)]
pub enum Change<T> {
    Add(usize, T),
    Remove(usize, T),
    Keep(usize, usize, T),
}

pub fn diff<'a, T>(a: &'a [T], b: &'a [T]) -> Vec<Change<&'a T>>
where
    T: PartialEq,
{
    if a.is_empty() && b.is_empty() {
        return vec![];
    }
    let mut diff = vec![];
    for (prev_x, prev_y, x, y
    
pub fn render_colored_changes<T: fmt::Display>(changes: &[Change<T>]) -> String {
    // anstyle is not very ergonomic, but I don't want to bring in another dependency.
    let red = anstyle::AnsiColor::Red.on_default().render();
    let green = anstyle::AnsiColor::Green.on_default().render();
    let dim = (anstyle::Style::new() | anstyle::Effects::DIMMED).render();
    let bold = (anstyle::Style::new() | anstyle::Effects::BOLD).render();
    let reset = anstyle::Reset.render();

    let choice = if crate::is_ci() {
        // Don't use color on CI. Even though GitHub can display colors, it
        // makes reading the raw logs more difficult.
        anstream::ColorChoice::Never
    } else {
        anstream::AutoStream::choice(&std::io::stdout())
    };
    let mut buffer = anstream::AutoStream::new(Vec::new(), choice);

    for change in changes {
        let (nums, sign, color, text) = match change {
            Change::Add(i, s) => (format!("    {:<4} ", i), '+', green, s),
            Change::Remove(i, s) => (format!("{:<4}     ", i), '-', red, s),
            Change::Keep(x, y, s) => (format!("{:<4}{:<4} ", x, y), ' ', dim, s),
        };
        writeln!(
            buffer,
            "{dim}{nums}{reset}{bold}{sign}{reset}{color}{text}{reset}"
        )
        .unwrap();
    }
    String::from_utf8(buffer.into_inner()).unwrap()
}