为什么 home-manager 无法使用函数builtins.getEnv读取环境变量？

Question

为什么home-manager无法使用

$USER

中的Nix函数

$HOME

读取环境变量

builtins.getEnv

和

~/.config/home-manager/home.nix

？

# Excerpt from ~/.config/home-manager/home.nix
...
# Home Manager needs a bit of information about you and the paths it should
# manage.
#home.username = "derek";
home.username = builtins.getEnv "USER";
home.homeDirectory = "/home/derek";
#home.homeDirectory = builtins.getEnv "HOME";
...

alpine-2:~$ home-manager switch

error:
       … while evaluating a branch condition

         at /nix/store/z6w242l49pbrdawkz5vdhfxh2mvsj36c-source/lib/lists.nix:57:9:

           56|       fold' = n:
           57|         if n == len
             |         ^
           58|         then nul

       … while calling the 'length' builtin

         at /nix/store/z6w242l49pbrdawkz5vdhfxh2mvsj36c-source/lib/lists.nix:55:13:

           54|     let
           55|       len = length list;
             |             ^
           56|       fold' = n:

       (stack trace truncated; use '--show-trace' to show the full trace)

       error:
       Failed assertions:
       - Username could not be determined
alpine-2:~$ echo $USER
derek

Answer 1

使用命令

home-manager switch --impure

，家庭管理器能够读取环境变量

$USER

和

$HOME

。

--impure

将 home-manager 置于“不纯”模式，这允许 Nix 表达式包含不尊重引用完整性的“不纯”函数引用（即，可能针对不同的输入值或环境返回不同的结果）。