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: mod.rs
    path of file: ./repos/crates.io/src/sentry
    
    the code of the file until where you have to start completion: use crate::config::SentryConfig;
use sentry::{ClientInitGuard, ClientOptions, TransactionContext};
use std::sync::Arc;

/// Initializes the Sentry SDK from the environment variables.
///
/// If `SENTRY_DSN_API` is not set then Sentry will not be initialized,
/// otherwise it is required to be a valid DSN string. `SENTRY_ENV_API` must
/// be set if a DSN is provided.
///
/// `HEROKU_SLUG_COMMIT`, if present, will be used as the `release` property
/// on all events.
pub fn init() -> Option<ClientInitGuard> {
    let conf
    
pub fn init() -> Option<ClientInitGuard> {
    let config = match SentryConfig::from_environment() {
        Ok(config) => config,
        Err(error) => {
            warn!(%error, "Failed to read Sentry configuration from environment");
            return None;
        }
    };

    let traces_sampler = move |ctx: &TransactionContext| -> f32 {
        if let Some(sampled) = ctx.sampled() {
            return if sampled { 1.0 } else { 0.0 };
        }

        let op = ctx.operation();
        if op == "http.server" {
            let is_download_endpoint =
                ctx.name().starts_with("GET /api/v1/crates/") && ctx.name().ends_with("/download");

            if is_download_endpoint {
                // Reduce the sample rate for the download endpoint, since we have significantly
                // more traffic on that endpoint compared to the rest
                return config.traces_sample_rate / 100.;
            } else if ctx.name() == "PUT /api/v1/crates/new" {
                // Record all traces for crate publishing
                return 1.;
            } else if ctx.name().starts_with("GET /api/private/metrics/") {
                // Ignore all traces for internal metrics collection
                return 0.;
            }
        } else if op == "swirl.perform" || op == "admin.command" {
            // Record all traces for background tasks and admin commands
            return 1.;
        } else if op == "swirl.run" || op == "server.run" {
            // Ignore top-level span from the background worker and http server
            return 0.;
        }

        config.traces_sample_rate
    };

    let opts = ClientOptions {
        auto_session_tracking: true,
        dsn: config.dsn,
        environment: config.environment.map(Into::into),
        release: config.release.map(Into::into),
        session_mode: sentry::SessionMode::Request,
        traces_sampler: Some(Arc::new(traces_sampler)),
        ..Default::default()
    };

    Some(sentry::init(opts))
}