code: func (s Storage) moduleVersions(source string) ([]moduleRecord, error) {
  	manifest, err := s.loadManifest()
  	if err != nil {
  		return manifest.Modules, err
  	}
  
  	var matching []moduleRecord
  
  	for _, m := range manifest.Modules {
  		if m.Source == source && m.Version != "" {
  			log.Printf("[DEBUG] found local version %q for module %s", m.Version, m.Source)
  			matching = append(matching, m)
  		}
  	}
  
  	return matching, nil
  }
docs: // load the manifest from dir, and return all module versions matching the
  // provided source. Records with no version info will be skipped, as they need
  // to be uniquely identified by other means.