处于Git仓库内时nix-darwin rebuild执行失败的问题排查

正常情况（未加入Git） #

在~/x目录下执行命令无报错：

$ darwin-rebuild switch --dry-run --flake x/
building the system configuration...
Password:
user defaults...
setting up user launchd services...
setting up /Applications/Nix Apps...
setting up pam...
applying patches...
setting up /etc...
system defaults...
setting up launchd services...
reloading nix-daemon...
waiting for nix-daemon
configuring networking...
setting up /Library/Fonts/Nix Fonts...
setting nvram variables...

异常情况（加入Git后） #

复制目录并初始化Git提交后，执行命令出现错误：

$ cp -r x y
$ cd y
$ git init && git add . && git commit -am 'initial'

$ darwin-rebuild switch --dry-run --flake y/
building the system configuration...
these 9 derivations will be built:
  /nix/store/6q8gs4030fj613h1rc77qdd2vmsiydn7-options.json.drv
  /nix/store/6i4fwbq03hrbsvw9skl60zz8w82z9mzp-options.json.drv
  /nix/store/1213z7hj01zs50wsy3yjqsj6lcdvw4p7-darwin-manpages.drv
  /nix/store/xdby0n64ijkcmyl1wf9dby5fgvmin03a-darwin-manual-html.drv
  /nix/store/7m19k5gppfcbisdzk0rlyhqcq2kqsq88-darwin-help.drv
  /nix/store/b35vswyff9pfd2a57y85zc8r326fsdq9-system-path.drv
  /nix/store/ss6wmn08c1zp3snng97hs1qb7pl7x9my-system-applications.drv
  /nix/store/z5c666bd7d5lrhg879n46hyl7mvp7a0j-darwin-version.json.drv
  /nix/store/b1wjlf0rnzj84mv3w1yffqa1rph62jnc-darwin-system-24.05.20240621.201ed88+darwin4.29b3096.drv
don't know how to build these paths:
  /nix/store/a2j86yi5rbprnq9wis88pq5n4qyfm0gq-darwin-system-24.05.20240621.201ed88+darwin4.29b3096
error: build of '/nix/store/a2j86yi5rbprnq9wis88pq5n4qyfm0gq-darwin-system-24.05.20240621.201ed88+darwin4.29b3096' failed

用到的flake.nix代码 #

description = "Example Darwin system flake";

inputs = {
  nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-24.05-darwin";
  nix-darwin = {
    url = "github:LnL7/nix-darwin";
    inputs.nixpkgs.follows = "nixpkgs";
  };
  home-manager = {
    url = "github:nix-community/home-manager/release-24.05";
    inputs.nixpkgs.follows = "nixpkgs";
  };
};

outputs = inputs@{ self, nix-darwin, nixpkgs, home-manager }:
let
  configuration = { pkgs, ... }: {
    # List packages installed in system profile. To search by name, run:
    # $ nix-env -qaP | grep wget
    environment.systemPackages = [
        pkgs.vim
      ];
    system.stateVersion = 4;

    # The platform the configuration will be used on.
    nixpkgs.hostPlatform = "x86_64-darwin";
  };
in
{
  # Build darwin flake using:
  # $ darwin-rebuild build --flake .#xx
  darwinConfigurations = {
    "xx" = nix-darwin.lib.darwinSystem {
      modules = [
        configuration
        home-manager.darwinModules.home-manager {
          home-manager.useGlobalPkgs = true;
          home-manager.useUserPackages = true;
        }
      ];
    };
  };

  # Expose the package set, including overlays, for convenience.
  darwinPackages = self.darwinConfigurations."xx".pkgs;
};

问题本质 #

目录被Git初始化后，Nix Flake会自动识别为Git仓库，此时Flake的self引用会绑定到Git的版本状态（如commit哈希）。而你的flake.nix中darwinPackages直接通过self引用darwinConfigurations."xx".pkgs，触发了版本化Flake的构建逻辑——这种情况下Nix会尝试生成基于Git版本的派生，但依赖链出现不匹配，导致无法找到正确的构建路径。

简单来说：普通目录是"本地非版本化Flake"，Git仓库是"版本化Flake"，两者的self解析逻辑不同，你的输出定义直接通过self引用配置派生，引发了冲突。

解决方法 #

方法1：修改flake.nix，避免通过self引用 #

调整darwinPackages的定义，直接复用配置对象而非通过self引用：

outputs = inputs@{ self, nix-darwin, nixpkgs, home-manager }:
let
  configuration = { pkgs, ... }: {
    # 原有配置内容不变
    environment.systemPackages = [ pkgs.vim ];
    system.stateVersion = 4;
    nixpkgs.hostPlatform = "x86_64-darwin";
  };
  # 提前定义配置对象
  xxConfig = nix-darwin.lib.darwinSystem {
    modules = [
      configuration
      home-manager.darwinModules.home-manager {
        home-manager.useGlobalPkgs = true;
        home-manager.useUserPackages = true;
      }
    ];
  };
in
{
  darwinConfigurations = {
    "xx" = xxConfig;
  };

  # 直接使用提前定义的对象，绕过self引用
  darwinPackages = xxConfig.pkgs;
};

方法2：执行命令时明确指定配置名称 #

运行命令时加上配置标识，让Nix直接定位到你定义的配置，而非自动推断：

darwin-rebuild switch --dry-run --flake y/#xx

方法3：强制忽略Git版本化（不推荐） #

使用--impure参数让Nix将目录视为普通非版本化Flake：

darwin-rebuild switch --dry-run --flake y/ --impure

该方法会绕过Flake的纯模式检查，仅适合临时测试，不推荐长期使用。

内容的提问来源于stack exchange，提问作者ubi