NixOS 与 Flakes

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在 NixOS 上进行开发工作 ​

由于 NixOS 自身可复现的特性，它非常适合用于搭建开发环境。 但是如果你想直接将在其他发行版上的环境搭建经验用在 NixOS 上，可能会遇到许多问题，因为 NixOS 有自己的一套逻辑在，下面我们先对此稍作说明。

在 NixOS 上，全局环境中只建议安装一些通用的工具，比如 git、vim、emacs、tmux、zsh 等等，而各语言的开发环境，最好是每个项目都有一个独立的环境。 为了简便，你也可以考虑提前为常用语言创建一些通用的开发环境，在需要时切换进去。

总而言之，NixOS 上的开发环境不应该装在全局，应该是一个个独立的项目环境，或许还带有一些通用的语言环境，但是它们都是完全隔离的，不会相互影响。

在本章中我们先学习一下 Nix Flakes 开发环境的实现原理，后面的章节再按使用场景介绍一些更具体的内容。

创建与使用开发环境 ​

在 Nix Flakes 中，我们可以通过 pkgs.mkShell { ... } 来定义一个项目环境，通过 nix develop 来打开一个该开发环境的交互式 Bash Shell.

为了更好的使用上述两个功能，我们先来看看它们的原理。

pkgs.mkShell 的源码如下：

nix
{ lib, stdenv, buildEnv }:

# A special kind of derivation that is only meant to be consumed by the
# nix-shell.
{ name ? "nix-shell"
, # a list of packages to add to the shell environment
  packages ? [ ]
, # propagate all the inputs from the given derivations
  inputsFrom ? [ ]
, buildInputs ? [ ]
, nativeBuildInputs ? [ ]
, propagatedBuildInputs ? [ ]
, propagatedNativeBuildInputs ? [ ]
, ...
}@attrs:
let
  mergeInputs = name:
    (attrs.${name} or [ ]) ++
    (lib.subtractLists inputsFrom (lib.flatten (lib.catAttrs name inputsFrom)));

  rest = builtins.removeAttrs attrs [
    "name"
    "packages"
    "inputsFrom"
    "buildInputs"
    "nativeBuildInputs"
    "propagatedBuildInputs"
    "propagatedNativeBuildInputs"
    "shellHook"
  ];
in

stdenv.mkDerivation ({
  inherit name;

  buildInputs = mergeInputs "buildInputs";
  nativeBuildInputs = packages ++ (mergeInputs "nativeBuildInputs");
  propagatedBuildInputs = mergeInputs "propagatedBuildInputs";
  propagatedNativeBuildInputs = mergeInputs "propagatedNativeBuildInputs";

  shellHook = lib.concatStringsSep "\n" (lib.catAttrs "shellHook"
    (lib.reverseList inputsFrom ++ [ attrs ]));

  phases = [ "buildPhase" ];

  # ......

  # when distributed building is enabled, prefer to build locally
  preferLocalBuild = true;
} // rest)
{ lib, stdenv, buildEnv }:

# A special kind of derivation that is only meant to be consumed by the
# nix-shell.
{ name ? "nix-shell"
, # a list of packages to add to the shell environment
  packages ? [ ]
, # propagate all the inputs from the given derivations
  inputsFrom ? [ ]
, buildInputs ? [ ]
, nativeBuildInputs ? [ ]
, propagatedBuildInputs ? [ ]
, propagatedNativeBuildInputs ? [ ]
, ...
}@attrs:
let
  mergeInputs = name:
    (attrs.${name} or [ ]) ++
    (lib.subtractLists inputsFrom (lib.flatten (lib.catAttrs name inputsFrom)));

  rest = builtins.removeAttrs attrs [
    "name"
    "packages"
    "inputsFrom"
    "buildInputs"
    "nativeBuildInputs"
    "propagatedBuildInputs"
    "propagatedNativeBuildInputs"
    "shellHook"
  ];
in

stdenv.mkDerivation ({
  inherit name;

  buildInputs = mergeInputs "buildInputs";
  nativeBuildInputs = packages ++ (mergeInputs "nativeBuildInputs");
  propagatedBuildInputs = mergeInputs "propagatedBuildInputs";
  propagatedNativeBuildInputs = mergeInputs "propagatedNativeBuildInputs";

  shellHook = lib.concatStringsSep "\n" (lib.catAttrs "shellHook"
    (lib.reverseList inputsFrom ++ [ attrs ]));

  phases = [ "buildPhase" ];

  # ......

  # when distributed building is enabled, prefer to build locally
  preferLocalBuild = true;
} // rest)

可以看到 pkgs.mkShell { ... } 本质上就是一个特殊的 Derivation（Nix 包），它的 name buildInputs 等参数都是可自定义的，而 shellHook 则是一个特殊的参数，它会在 nix develop 进入该环境时被执行。

如下是一份 flake.nix 文件，它定义了一个 nodejs 18 的开发环境：

nix
{
  description = "A Nix-flake-based Node.js development environment";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
  };

  outputs = { self , nixpkgs ,... }: let
    # system should match the system you are running on
    # system = "x86_64-linux";
    system = "x86_64-darwin";
  in {
    devShells."${system}".default = let
      pkgs = import nixpkgs {
        inherit system;
        overlays = [
          (self: super: rec {
            nodejs = super.nodejs-18_x;
            pnpm = super.nodePackages.pnpm;
            yarn = (super.yarn.override { inherit nodejs; });
          })
        ];
      };
    in pkgs.mkShell {
      # create an environment with nodejs-18_x, pnpm, and yarn
      packages = with pkgs; [
        node2nix
        nodejs
        pnpm
        yarn
      ];

      shellHook = ''
        echo "node `${pkgs.nodejs}/bin/node --version`"
      '';
    };
  };
}
{
  description = "A Nix-flake-based Node.js development environment";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
  };

  outputs = { self , nixpkgs ,... }: let
    # system should match the system you are running on
    # system = "x86_64-linux";
    system = "x86_64-darwin";
  in {
    devShells."${system}".default = let
      pkgs = import nixpkgs {
        inherit system;
        overlays = [
          (self: super: rec {
            nodejs = super.nodejs-18_x;
            pnpm = super.nodePackages.pnpm;
            yarn = (super.yarn.override { inherit nodejs; });
          })
        ];
      };
    in pkgs.mkShell {
      # create an environment with nodejs-18_x, pnpm, and yarn
      packages = with pkgs; [
        node2nix
        nodejs
        pnpm
        yarn
      ];

      shellHook = ''
        echo "node `${pkgs.nodejs}/bin/node --version`"
      '';
    };
  };
}

建个空文件夹，将上面的配置保存为 flake.nix，然后执行 nix develop（或者更精确点，可以用 nix develop .#default），你会发现你已经进入了一个 nodejs 18 的开发环境，可以使用 node npm pnpm yarn 等命令了。而且刚进入时，shellHook 也被执行了，输出了当前 nodejs 的版本。

在开发环境中使用 zsh/fish 等其他 shell ​

pkgs.mkShell 默认使用 bash，但是你也可以通过在 shellHook 中添加 exec <your-shell> 来使用 zsh 或者 fish 等其他 shell。

示例如下：

nix
{
  description = "A Nix-flake-based Node.js development environment";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
  };

  outputs = { self , nixpkgs ,... }: let
    # system should match the system you are running on
    # system = "x86_64-linux";
    system = "x86_64-darwin";
  in {
    devShells."${system}".default = let
      pkgs = import nixpkgs {
        inherit system;
        overlays = [
          (self: super: rec {
            nodejs = super.nodejs-18_x;
            pnpm = super.nodePackages.pnpm;
            yarn = (super.yarn.override { inherit nodejs; });
          })
        ];
      };
    in pkgs.mkShell {
      # create an environment with nodejs-18_x, pnpm, and yarn
      packages = with pkgs; [
        node2nix
        nodejs
        pnpm
        yarn
        nushell
      ];

      shellHook = ''
        echo "node `${pkgs.nodejs}/bin/node --version`"
        exec nu
      '';
    };
  };
}
{
  description = "A Nix-flake-based Node.js development environment";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
  };

  outputs = { self , nixpkgs ,... }: let
    # system should match the system you are running on
    # system = "x86_64-linux";
    system = "x86_64-darwin";
  in {
    devShells."${system}".default = let
      pkgs = import nixpkgs {
        inherit system;
        overlays = [
          (self: super: rec {
            nodejs = super.nodejs-18_x;
            pnpm = super.nodePackages.pnpm;
            yarn = (super.yarn.override { inherit nodejs; });
          })
        ];
      };
    in pkgs.mkShell {
      # create an environment with nodejs-18_x, pnpm, and yarn
      packages = with pkgs; [
        node2nix
        nodejs
        pnpm
        yarn
        nushell
      ];

      shellHook = ''
        echo "node `${pkgs.nodejs}/bin/node --version`"
        exec nu
      '';
    };
  };
}

使用上面的 flake.nix 配置，nix develop 将进入一个 nodejs 18 的开发环境，同时使用 nushell 作为交互式 shell.

进入任何 Nix 包的构建环境 ​

现在再来看看 nix develop，先读下 nix develop --help 输出的帮助文档：

Name
    nix develop - run a bash shell that provides the build environment of a derivation

Synopsis
    nix develop [option...] installable
# ......
Name
    nix develop - run a bash shell that provides the build environment of a derivation

Synopsis
    nix develop [option...] installable
# ......

可以看到 nix develop 接受的参数是 installable，这说明我们可以通过它进入任何一个 installable 的 Nix 包的开发环境，而不仅仅是 pkgs.mkShell 创建的环境。

默认情况下，nix develop 命令会尝试 flake outputs 中的如下属性：

  • devShells.<system>.default
  • packages.<system>.default

而如果我们通过 nix develop /path/to/flake#<name> 来指定了 flake 包地址以及 flake output name，那么 nix develop 命令会尝试 flake outputs 中的如下属性：

  • devShells.<system>.<name>
  • packages.<system>.<name>
  • legacyPackages.<system>.<name>

现在来尝试一下，首先测试下，确认我当前环境中没有 c++ g++ 这这些编译相关的命令：

shell
ryan in 🌐 aquamarine in ~
› c++
c++: command not found

ryan in 🌐 aquamarine in ~
› g++
g++: command not found
ryan in 🌐 aquamarine in ~
› c++
c++: command not found

ryan in 🌐 aquamarine in ~
› g++
g++: command not found

现在通过 nix develop 进入到 hello 的构建环境，然后再次测试下：

shell
# login to the build environment of the package `hello`
ryan in 🌐 aquamarine in ~
› nix develop nixpkgs#hello

ryan in 🌐 aquamarine in ~ via ❄️  impure (hello-2.12.1-env)
› env | grep CXX
CXX=g++

ryan in 🌐 aquamarine in ~ via ❄️  impure (hello-2.12.1-env)
› c++ --version
g++ (GCC) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

ryan in 🌐 aquamarine in ~ via ❄️  impure (hello-2.12.1-env)
› g++ --version
g++ (GCC) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# login to the build environment of the package `hello`
ryan in 🌐 aquamarine in ~
› nix develop nixpkgs#hello

ryan in 🌐 aquamarine in ~ via ❄️  impure (hello-2.12.1-env)
› env | grep CXX
CXX=g++

ryan in 🌐 aquamarine in ~ via ❄️  impure (hello-2.12.1-env)
› c++ --version
g++ (GCC) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

ryan in 🌐 aquamarine in ~ via ❄️  impure (hello-2.12.1-env)
› g++ --version
g++ (GCC) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

可以看到 CXX CXXCPP 环境变量已经被设置好了，而且 c++ g++ 等命令也可以正常使用了。

此外我们还可以正常调用 hello 这个 Nix 包的各构建阶段命令：

提前说明下，一个 Nix 包的所有构建阶段及其默认的执行顺序为：$prePhases unpackPhase patchPhase $preConfigurePhases configurePhase $preBuildPhases buildPhase checkPhase $preInstallPhases installPhase fixupPhase installCheckPhase $preDistPhases distPhase $postPhases

shell
# 解压源码包
ryan in 🌐 aquamarine in /tmp/xxx via ❄️  impure (hello-2.12.1-env)
› unpackPhase
unpacking source archive /nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz
source root is hello-2.12.1
setting SOURCE_DATE_EPOCH to timestamp 1653865426 of file hello-2.12.1/ChangeLog

ryan in 🌐 aquamarine in /tmp/xxx via ❄️  impure (hello-2.12.1-env)
› ls
hello-2.12.1

ryan in 🌐 aquamarine in /tmp/xxx via ❄️  impure (hello-2.12.1-env)
› cd hello-2.12.1/

# generate Makefile
ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via ❄️  impure (hello-2.12.1-env)
› configurePhase
configure flags: --prefix=/tmp/xxx/outputs/out --prefix=/tmp/xxx/outputs/out
checking for a BSD-compatible install... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking for gcc... gcc
# ......
checking that generated files are newer than configure... done
configure: creating ./config.status
config.status: creating Makefile
config.status: creating po/Makefile.in
config.status: creating config.h
config.status: config.h is unchanged
config.status: executing depfiles commands
config.status: executing po-directories commands
config.status: creating po/POTFILES
config.status: creating po/Makefile

# build the package
ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via C v12.3.0-gcc via ❄️  impure (hello-2.12.1-env) took 2s
› buildPhase
build flags: SHELL=/run/current-system/sw/bin/bash
make  all-recursive
make[1]: Entering directory '/tmp/xxx/hello-2.12.1'
# ......
ranlib lib/libhello.a
gcc  -g -O2   -o hello src/hello.o  ./lib/libhello.a
make[2]: Leaving directory '/tmp/xxx/hello-2.12.1'
make[1]: Leaving directory '/tmp/xxx/hello-2.12.1'

# run the built program
ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via C v12.3.0-gcc via ❄️  impure (hello-2.12.1-env)
› ./hello
Hello, world!
# 解压源码包
ryan in 🌐 aquamarine in /tmp/xxx via ❄️  impure (hello-2.12.1-env)
› unpackPhase
unpacking source archive /nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz
source root is hello-2.12.1
setting SOURCE_DATE_EPOCH to timestamp 1653865426 of file hello-2.12.1/ChangeLog

ryan in 🌐 aquamarine in /tmp/xxx via ❄️  impure (hello-2.12.1-env)
› ls
hello-2.12.1

ryan in 🌐 aquamarine in /tmp/xxx via ❄️  impure (hello-2.12.1-env)
› cd hello-2.12.1/

# generate Makefile
ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via ❄️  impure (hello-2.12.1-env)
› configurePhase
configure flags: --prefix=/tmp/xxx/outputs/out --prefix=/tmp/xxx/outputs/out
checking for a BSD-compatible install... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking for gcc... gcc
# ......
checking that generated files are newer than configure... done
configure: creating ./config.status
config.status: creating Makefile
config.status: creating po/Makefile.in
config.status: creating config.h
config.status: config.h is unchanged
config.status: executing depfiles commands
config.status: executing po-directories commands
config.status: creating po/POTFILES
config.status: creating po/Makefile

# build the package
ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via C v12.3.0-gcc via ❄️  impure (hello-2.12.1-env) took 2s
› buildPhase
build flags: SHELL=/run/current-system/sw/bin/bash
make  all-recursive
make[1]: Entering directory '/tmp/xxx/hello-2.12.1'
# ......
ranlib lib/libhello.a
gcc  -g -O2   -o hello src/hello.o  ./lib/libhello.a
make[2]: Leaving directory '/tmp/xxx/hello-2.12.1'
make[1]: Leaving directory '/tmp/xxx/hello-2.12.1'

# run the built program
ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via C v12.3.0-gcc via ❄️  impure (hello-2.12.1-env)
› ./hello
Hello, world!

这种用法的主要应用场景是调试某个 Nix 包的构建过程，或者在某个 Nix 包的构建环境中执行一些命令。

nix build ​

nix build 用于构建一个软件包，并在当前目录下创建一个名为 result 的符号链接，链接到该构建结果。

一个示例：

bash
# 构建 `nixpkgs` flake 中的 `ponysay` 这个包
nix build "nixpkgs#ponysay"
# 使用构建出来的 ponysay 命令
› ./result/bin/ponysay 'hey buddy!'
 ____________ 
< hey buddy! >
 ------------ 
     \                                  
      \                                 
       \                                
       ▄▄  ▄▄ ▄ ▄                       
    ▀▄▄▄█▄▄▄▄▄█▄▄▄                      
   ▀▄███▄▄██▄██▄▄██                     
  ▄██▄███▄▄██▄▄▄█▄██                    
 █▄█▄██▄█████████▄██                    
  ▄▄█▄█▄▄▄▄▄████████                    
 ▀▀▀▄█▄█▄█▄▄▄▄▄█████         ▄   ▄      
    ▀▄████▄▄▄█▄█▄▄██       ▄▄▄▄▄█▄▄▄    
    █▄██▄▄▄▄███▄▄▄██    ▄▄▄▄▄▄▄▄▄█▄▄    
    ▀▄▄██████▄▄▄████    █████████████   
       ▀▀▀▀▀█████▄▄ ▄▄▄▄▄▄▄▄▄▄██▄█▄▄▀   
            ██▄███▄▄▄▄█▄▄▀  ███▄█▄▄▄█▀  
            █▄██▄▄▄▄▄████   ███████▄██  
            █▄███▄▄█████    ▀███▄█████▄ 
            ██████▀▄▄▄█▄█    █▄██▄▄█▄█▄ 
           ███████ ███████   ▀████▄████ 
           ▀▀█▄▄▄▀ ▀▀█▄▄▄▀     ▀██▄▄██▀█
                                ▀  ▀▀█
# 构建 `nixpkgs` flake 中的 `ponysay` 这个包
nix build "nixpkgs#ponysay"
# 使用构建出来的 ponysay 命令
› ./result/bin/ponysay 'hey buddy!'
 ____________ 
< hey buddy! >
 ------------ 
     \                                  
      \                                 
       \                                
       ▄▄  ▄▄ ▄ ▄                       
    ▀▄▄▄█▄▄▄▄▄█▄▄▄                      
   ▀▄███▄▄██▄██▄▄██                     
  ▄██▄███▄▄██▄▄▄█▄██                    
 █▄█▄██▄█████████▄██                    
  ▄▄█▄█▄▄▄▄▄████████                    
 ▀▀▀▄█▄█▄█▄▄▄▄▄█████         ▄   ▄      
    ▀▄████▄▄▄█▄█▄▄██       ▄▄▄▄▄█▄▄▄    
    █▄██▄▄▄▄███▄▄▄██    ▄▄▄▄▄▄▄▄▄█▄▄    
    ▀▄▄██████▄▄▄████    █████████████   
       ▀▀▀▀▀█████▄▄ ▄▄▄▄▄▄▄▄▄▄██▄█▄▄▀   
            ██▄███▄▄▄▄█▄▄▀  ███▄█▄▄▄█▀  
            █▄██▄▄▄▄▄████   ███████▄██  
            █▄███▄▄█████    ▀███▄█████▄ 
            ██████▀▄▄▄█▄█    █▄██▄▄█▄█▄ 
           ███████ ███████   ▀████▄████ 
           ▀▀█▄▄▄▀ ▀▀█▄▄▄▀     ▀██▄▄██▀█
                                ▀  ▀▀█

其他命令 ​

其他还有些 nix flake init 之类的命令，请自行查阅 New Nix Commands 学习研究，这里就不详细介绍了。

References ​

Released under the MIT License.

Copyright © 2023-present Ryan Yin