code: def symlink_bundles(self, app, bundle_dir):
      
      for bundle_counter, bundle in enumerate(app.bundles):
        count = 0
        for path, relpath in bundle.filemap.items():
          bundle_path = os.path.join(bundle_dir, relpath)
          count += 1
          if os.path.exists(bundle_path):
            continue
  
          if os.path.isfile(path):
            safe_mkdir(os.path.dirname(bundle_path))
            os.symlink(path, bundle_path)
          elif os.path.isdir(path):
            safe_mkdir(bundle_path)
  
        if count == 0:
          raise TargetDefinitionException(app.target,
                                          'Bundle index {} of "bundles" field '
                                          'does not match any files.'.format(bundle_counter))
docs: For each bundle in the given app, symlinks relevant matched paths.
  
      Validates that at least one path was matched by a bundle.