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/ruff/crates/ruff_benchmark/src
    
    the code of the file until where you have to start completion: pub mod criterion;

use std::fmt::{Display, Formatter};
use std::path::PathBuf;
use std::process::Command;

use url::Url;

/// Relative size of a test case. Benchmarks can use it to configure the time for how long a benchmark should run to get stable results.
#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)]
pub enum TestCaseSpeed {
    /// A test case that is fast to run
    Fast,

    /// A normal 
    
fn cargo_target_directory() -> Option<PathBuf> {
    #[derive(serde::Deserialize)]
    struct Metadata {
        target_directory: PathBuf,
    }

    std::env::var_os("CARGO_TARGET_DIR")
        .map(PathBuf::from)
        .or_else(|| {
            let output = Command::new(std::env::var_os("CARGO")?)
                .args(["metadata", "--format-version", "1"])
                .output()
                .ok()?;
            let metadata: Metadata = serde_json::from_slice(&output.stdout).ok()?;
            Some(metadata.target_directory)
        })
}