How to use the @parcel/fs.realpath function in @parcel/fs

async readPackage(dir) {
    let file = path.join(dir, 'package.json');
    if (this.packageCache.has(file)) {
      return this.packageCache.get(file);
    }

    let json = await fs.readFile(file, 'utf8');
    let pkg = JSON.parse(json);

    pkg.pkgfile = file;
    pkg.pkgdir = dir;

    // If the package has a `source` field, check if it is behind a symlink.
    // If so, we treat the module as source code rather than a pre-compiled module.
    if (pkg.source) {
      let realpath = await fs.realpath(file);
      if (realpath === file) {
        delete pkg.source;
      }
    }

    this.packageCache.set(file, pkg);
    return pkg;
  }

async readPackage(dir) {
    let file = path.join(dir, 'package.json');
    if (this.packageCache.has(file)) {
      return this.packageCache.get(file);
    }

    let json = await fs.readFile(file, 'utf8');
    let pkg = JSON.parse(json);

    pkg.pkgfile = file;
    pkg.pkgdir = dir;

    // If the package has a `source` field, check if it is behind a symlink.
    // If so, we treat the module as source code rather than a pre-compiled module.
    if (pkg.source) {
      let realpath = await fs.realpath(file);
      if (realpath === file) {
        delete pkg.source;
      }
    }

    this.packageCache.set(file, pkg);
    return pkg;
  }

let cached = this.packageCache.get(file);

    if (cached) {
      return cached;
    }

    let json = await fs.readFile(file, 'utf8');
    let pkg = JSON.parse(json);

    pkg.pkgfile = file;
    pkg.pkgdir = dir;

    // If the package has a `source` field, check if it is behind a symlink.
    // If so, we treat the module as source code rather than a pre-compiled module.
    if (pkg.source) {
      let realpath = await fs.realpath(file);
      if (realpath === file) {
        delete pkg.source;
      }
    }

    this.packageCache.set(file, pkg);
    return pkg;
  }

async function getBabelConfig(asset) {
  // Consider the module source code rather than precompiled if the resolver
  // used the `source` field, or it is not in node_modules.
  let pkg = await asset.getPackage();
  let isSource =
    !!(pkg && pkg.source && (await fs.realpath(asset.name)) !== asset.name) ||
    !asset.name.includes(NODE_MODULES);

  // Try to resolve a .babelrc file. If one is found, consider the module source code.
  let babelrc = await getBabelRc(asset, isSource);
  isSource = isSource || !!babelrc;

  let envConfig = await getEnvConfig(asset, isSource);
  let jsxConfig = await getJSXConfig(asset, isSource);
  let flowConfig = getFlowConfig(asset, isSource);

  if (babelrc && envConfig) {
    // Filter out presets that are already applied by @babel/preset-env
    if (Array.isArray(babelrc.config.presets)) {
      babelrc.config.presets = babelrc.config.presets.filter(preset => {
        return !ENV_PRESETS[getPluginName(preset)];
      });

async unwatch(path, asset) {
    path = await fs.realpath(path);
    if (!this.watchedAssets.has(path)) {
      return;
    }

    let watched = this.watchedAssets.get(path);
    watched.delete(asset);

    if (watched.size === 0) {
      this.watchedAssets.delete(path);
      this.watcher.unwatch(path);
    }
  }

async watch(path, asset) {
    if (!this.watcher) {
      return;
    }

    path = await fs.realpath(path);

    if (!this.watchedAssets.has(path)) {
      this.watcher.watch(path);
      this.watchedAssets.set(path, new Set());
    }
    this.watchedAssets.get(path).add(asset);
  }

async watch(path, asset) {
    if (!this.watcher) {
      return;
    }

    path = await fs.realpath(path);

    if (!this.watchedAssets.has(path)) {
      this.watcher.watch(path);
      this.watchedAssets.set(path, new Set());
    }
    this.watchedAssets.get(path).add(asset);
  }