code: def _verify_app_source_dir(src_dir, mode, enforce=True):
      
      temp_dir = tempfile.mkdtemp(prefix='dx-build_tmp')
      try:
          _verify_app_source_dir_impl(src_dir, temp_dir, mode, enforce=enforce)
      finally:
          shutil.rmtree(temp_dir)
docs: Performs syntax and lint checks on the app source.
  
      Precondition: the dxapp.json file exists and can be parsed.