code: def match_envs(declared_envs, desired_envs, passthru):
      
      matched = [
          declared for declared in declared_envs
          if any(env_matches(declared, desired) for desired in desired_envs)
      ]
      return desired_envs if not matched and passthru else matched
docs: Determine the envs that match the desired_envs.
  
      If ``passthru` is True, and none of the declared envs match the
      desired envs, then the desired envs will be used verbatim.
  
      :param declared_envs: The envs that are declared in the tox config.
      :param desired_envs: The envs desired from the tox-travis config.
      :param bool passthru: Whether to used the ``desired_envs`` as a
                            fallback if no declared envs match.