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: npm.rs
    path of file: ./repos/orogene/crates/nassun/src/fetch
    
    the code of the file until where you have to start completion: use std::collections::HashMap;
use std::path::Path;

use async_std::sync::Arc;
use async_trait::async_trait;
use dashmap::DashMap;
use oro_client::{self, OroClient};
use oro_common::{CorgiPackument, CorgiVersionMetadata, Packument, VersionMetadata};
use oro_package_spec::PackageSpec;
use url::Url;

use crate::error::{NassunError, Result};
use crate::fetch::PackageFetcher;
use crate::package::Package;
use crate::resolver::PackageResolution;

#[derive(Debug)
    
    async fn packument(&self, spec: &PackageSpec, _base_dir: &Path) -> Result<Arc<Packument>> {
        // When fetching the packument itself, we need the _package_ name, not
        // its alias! Hence these shenanigans.
        let pkg = match spec {
            PackageSpec::Alias { ref spec, .. } => spec,
            pkg @ PackageSpec::Npm { .. } => pkg,
            _ => unreachable!(),
        };
        if let PackageSpec::Npm {
            ref name,
            ref scope,
            ..
        } = pkg
        {
            if let Some(packument) = self.packuments.get(name) {
                if self.cache_packuments {
                    return Ok(packument.value().clone());
                }
            }
            let client = self.client.with_registry(self.pick_registry(scope));
            let packument = Arc::new(client.packument(&name).await?);
            if self.cache_packuments {
                self.packuments.insert(name.clone(), packument.clone());
            }
            Ok(packument)
        } else {
            unreachable!()
        }
    }