def _build_paths(self, name, spec_path_lists, exists):
        """
        Given an environment variable name and specified paths,
        return a pathsep-separated string of paths containing
        unique, extant, directories from those paths and from
        the environment variable. Raise an error if no paths
        are resolved.

        Parameters
        ----------
        name: str
            Environment variable name
        spec_path_lists: list of str
            Paths
        exists: bool
            It True, only return existing paths.

        Return
        ------
        str
            Pathsep-separated paths
        """
        # flatten spec_path_lists
        spec_paths = itertools.chain.from_iterable(spec_path_lists)
        env_paths = environ.get(name, '').split(pathsep)
        paths = itertools.chain(spec_paths, env_paths)
        extant_paths = list(filter(isdir, paths)) if exists else paths
        if not extant_paths:
            msg = "%s environment variable is empty" % name.upper()
            raise distutils.errors.DistutilsPlatformError(msg)
        unique_paths = unique_everseen(extant_paths)
        return pathsep.join(unique_paths)

        Given an environment variable name and specified paths,
        return a pathsep-separated string of paths containing
        unique, extant, directories from those paths and from
        the environment variable. Raise an error if no paths
        are resolved.

        Parameters
        ----------
        name: str
            Environment variable name
        spec_path_lists: list of str
            Paths
        exists: bool
            It True, only return existing paths.

        Return
        ------
        str
            Pathsep-separated paths
        
product/gradle-plugin/src/main/python/setuptools/msvc.py