code: func (d *deployerImpl) readDescription(ctx context.Context, pkgDir string) (desc *description, err error) {
  	descriptionPath := filepath.Join(pkgDir, descriptionName)
  	r, err := os.Open(descriptionPath)
  	switch {
  	case os.IsNotExist(err):
  		// try fixup
  		break
  	case err == nil:
  		defer r.Close()
  		return readDescription(r)
  	default:
  		return
  	}
  
  	// see if this is a pre 1.4 directory
  	currentID, err := d.getCurrentInstanceID(pkgDir)
  	if err != nil {
  		return
  	}
  
  	if currentID == "" {
  		logging.Warningf(ctx, "No current instance id in %s", pkgDir)
  		err = nil
  		return
  	}
  
  	manifest, err := d.readManifest(ctx, filepath.Join(pkgDir, currentID))
  	if err != nil {
  		return
  	}
  
  	desc = &description{
  		PackageName: manifest.PackageName,
  	}
  	// To handle the case where some other user owns these directories, all errors
  	// from here to the end are treated as warnings.
  	err = d.fs.EnsureFile(ctx, descriptionPath, func(f *os.File) error {
  		return writeDescription(desc, f)
  	})
  	if err != nil {
  		logging.Warningf(ctx, "Unable to create description.json: %s", err)
  		err = nil
  	}
  	return
  }
docs: // readDescription reads the package description.json given a path to a package
  // directory.
  //
  // As a backwards-compatibility measure, it will also upgrade CIPD < 1.4 folders
  // to contain a description.json. Previous to 1.4, package folders only had
  // instance subfolders, and the current instances' manifest was used to
  // determine the package name. Versions prior to 1.4 also installed all packages
  // at the base (subdir ""), hence the implied subdir location here.
  //
  // Returns (nil, nil) if no description.json exists and there are no instance
  // folders present.