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: plugin.rs
    path of file: ./repos/extism/runtime/src
    
    the code of the file until where you have to start completion: use std::{
    collections::{BTreeMap, BTreeSet},
    path::PathBuf,
};

use crate::*;

pub const EXTISM_ENV_MODULE: &str = "extism:host/env";
pub const EXTISM_USER_MODULE: &str = "extism:host/user";
pub(crate) const MAIN_KEY: &str = "main";

#[derive(Default, Clone)]
pub(crate) struct Output {
    pub(crate) offset: u64,
    pub(crate) length: u64,
    pub(crate) error_offset: u64,
    pub(crate) error_length: u64,
}

/// A `CancelHandle` can be used to cancel a running plugin from another thread
#[derive(Clone)]
pub struct CancelHandle {
    pub(crate) timer_tx: std::sync::mpsc::Sender<TimerAction>,
    pub id: uuid::Uuid,
}

unsafe impl Syn
    
    pub(crate) fn initialize_guest_runtime(&mut self) -> Result<(), Error> {
        let mut store = &mut self.store;
        if let Some(runtime) = &self.runtime {
            trace!(plugin = self.id.to_string(), "Plugin::initialize_runtime");
            match runtime {
                GuestRuntime::Haskell { init, reactor_init } => {
                    if let Some(reactor_init) = reactor_init {
                        reactor_init.call(&mut store, &[], &mut [])?;
                    }
                    let mut results = vec![Val::null(); init.ty(&store).results().len()];
                    init.call(
                        &mut store,
                        &[Val::I32(0), Val::I32(0)],
                        results.as_mut_slice(),
                    )?;
                    debug!(
                        plugin = self.id.to_string(),
                        "initialized Haskell language runtime"
                    );
                }
                GuestRuntime::Wasi { init } => {
                    init.call(&mut store, &[], &mut [])?;
                    debug!(plugin = self.id.to_string(), "initialied WASI runtime");
                }
            }
        }

        Ok(())
    }