nixos/systemd-boot: atomically update copied destination files (#444960)

import shutil

import subprocess

import sys

import tempfile

import warnings

import json

from typing import NamedTuple, Any, Sequence

def copy_if_not_exists(source: Path, dest: Path) -> None:

    if not dest.exists():

        shutil.copyfile(source, dest)

        tmpfd, tmppath = tempfile.mkstemp(dir=dest.parent, prefix=dest.name, suffix='.tmp.')

        shutil.copyfile(source, tmppath)

        os.fsync(tmpfd)

        shutil.move(tmppath, dest)

def generation_dir(profile: str | None, generation: int) -> Path: