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https://github.com/ryan4yin/nixos-and-flakes-book
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294 lines
11 KiB
Markdown
294 lines
11 KiB
Markdown
# 在 NixOS 上进行开发工作
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由于 NixOS 自身可复现的特性，它非常适合用于搭建开发环境。
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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。
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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。
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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。
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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。
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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。
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## 创建与使用开发环境
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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.
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为了更好的使用上述两个功能，我们先来看看它们的原理。
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[`pkgs.mkShell` 的源码](https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/mkshell/default.nix)如下：
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```nix
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{ lib, stdenv, buildEnv }:
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# A special kind of derivation that is only meant to be consumed by the
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# nix-shell.
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{ name ? "nix-shell"
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, # a list of packages to add to the shell environment
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packages ? [ ]
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, # propagate all the inputs from the given derivations
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inputsFrom ? [ ]
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, buildInputs ? [ ]
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, nativeBuildInputs ? [ ]
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, propagatedBuildInputs ? [ ]
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, propagatedNativeBuildInputs ? [ ]
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, ...
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}@attrs:
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let
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mergeInputs = name:
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(attrs.${name} or [ ]) ++
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(lib.subtractLists inputsFrom (lib.flatten (lib.catAttrs name inputsFrom)));
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rest = builtins.removeAttrs attrs [
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"name"
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"packages"
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"inputsFrom"
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"buildInputs"
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"nativeBuildInputs"
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"propagatedBuildInputs"
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"propagatedNativeBuildInputs"
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"shellHook"
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];
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in
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stdenv.mkDerivation ({
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inherit name;
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buildInputs = mergeInputs "buildInputs";
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nativeBuildInputs = packages ++ (mergeInputs "nativeBuildInputs");
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propagatedBuildInputs = mergeInputs "propagatedBuildInputs";
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propagatedNativeBuildInputs = mergeInputs "propagatedNativeBuildInputs";
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shellHook = lib.concatStringsSep "\n" (lib.catAttrs "shellHook"
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(lib.reverseList inputsFrom ++ [ attrs ]));
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phases = [ "buildPhase" ];
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# ......
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# when distributed building is enabled, prefer to build locally
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preferLocalBuild = true;
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} // rest)
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```
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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。
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如下是一份 `flake.nix` 文件，它定义了一个 nodejs 18 的开发环境：
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```nix
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{
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description = "A Nix-flake-based Node.js development environment";
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inputs = {
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nixpkgs.url = "github:nixos/nixpkgs/nixos-23.05";
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};
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outputs = { self , nixpkgs ,... }: let
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# system should match the system you are running on
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# system = "x86_64-linux";
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system = "x86_64-darwin";
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in {
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devShells."${system}".default = let
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pkgs = import nixpkgs {
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inherit system;
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overlays = [
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(self: super: rec {
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nodejs = super.nodejs-18_x;
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pnpm = super.nodePackages.pnpm;
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yarn = (super.yarn.override { inherit nodejs; });
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})
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];
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};
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in pkgs.mkShell {
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# create an environment with nodejs-18_x, pnpm, and yarn
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packages = with pkgs; [
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node2nix
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nodejs
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pnpm
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yarn
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];
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shellHook = ''
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echo "node `${pkgs.nodejs}/bin/node --version`"
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'';
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};
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};
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}
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```
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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。
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## 进入任何 Nix 包的构建环境
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现在再来看看 `nix develop`，先读下 `nix develop --help` 输出的帮助文档：
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```
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Name
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nix develop - run a bash shell that provides the build environment of a derivation
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Synopsis
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nix develop [option...] installable
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# ......
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```
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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。
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默认情况下，`nix develop` 命令会尝试 flake outputs 中的如下属性：
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- `devShells.<system>.default`
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- `packages.<system>.default`
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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：
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- `devShells.<system>.<name>`
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- `packages.<system>.<name>`
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- `legacyPackages.<system>.<name>`
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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：
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```shell
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ryan in 🌐 aquamarine in ~
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› c++
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c++: command not found
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ryan in 🌐 aquamarine in ~
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› g++
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g++: command not found
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```
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现在通过 `nix develop` 进入到 `hello` 的构建环境，然后再次测试下：
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```shell
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# login to the build environment of the package `hello`
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ryan in 🌐 aquamarine in ~
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› nix develop nixpkgs#hello
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ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
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› env | grep CXX
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CXX=g++
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ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
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› c++ --version
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g++ (GCC) 12.3.0
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Copyright (C) 2022 Free Software Foundation, Inc.
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This is free software; see the source for copying conditions. There is NO
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warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
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› g++ --version
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g++ (GCC) 12.3.0
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Copyright (C) 2022 Free Software Foundation, Inc.
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This is free software; see the source for copying conditions. There is NO
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warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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```
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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。
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此外我们还可以正常调用 `hello` 这个 Nix 包的各构建阶段命令：
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> 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`
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```shell
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# 解压源码包
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ryan in 🌐 aquamarine in /tmp/xxx via ❄️ impure (hello-2.12.1-env)
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› unpackPhase
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unpacking source archive /nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz
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source root is hello-2.12.1
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setting SOURCE_DATE_EPOCH to timestamp 1653865426 of file hello-2.12.1/ChangeLog
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ryan in 🌐 aquamarine in /tmp/xxx via ❄️ impure (hello-2.12.1-env)
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› ls
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hello-2.12.1
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ryan in 🌐 aquamarine in /tmp/xxx via ❄️ impure (hello-2.12.1-env)
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› cd hello-2.12.1/
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# generate Makefile
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ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via ❄️ impure (hello-2.12.1-env)
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› configurePhase
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configure flags: --prefix=/tmp/xxx/outputs/out --prefix=/tmp/xxx/outputs/out
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checking for a BSD-compatible install... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/install -c
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checking whether build environment is sane... yes
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checking for a thread-safe mkdir -p... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/mkdir -p
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checking for gawk... gawk
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checking whether make sets $(MAKE)... yes
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checking whether make supports nested variables... yes
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checking for gcc... gcc
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# ......
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checking that generated files are newer than configure... done
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configure: creating ./config.status
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config.status: creating Makefile
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config.status: creating po/Makefile.in
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config.status: creating config.h
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config.status: config.h is unchanged
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config.status: executing depfiles commands
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config.status: executing po-directories commands
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config.status: creating po/POTFILES
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config.status: creating po/Makefile
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# build the package
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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
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› buildPhase
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build flags: SHELL=/run/current-system/sw/bin/bash
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make all-recursive
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make[1]: Entering directory '/tmp/xxx/hello-2.12.1'
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# ......
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ranlib lib/libhello.a
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gcc -g -O2 -o hello src/hello.o ./lib/libhello.a
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make[2]: Leaving directory '/tmp/xxx/hello-2.12.1'
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make[1]: Leaving directory '/tmp/xxx/hello-2.12.1'
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# run the built program
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ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via C v12.3.0-gcc via ❄️ impure (hello-2.12.1-env)
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› ./hello
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Hello, world!
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```
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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。
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## `nix shell` 与 `nix run`
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与 `nix develop` 相比，这两个命令就简单且好理解很多了。
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`nix shell` 用于进入到一个含有指定 Nix 包的环境并为它打开一个交互式 shell：
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```shell
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# hello 不存在
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› hello
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hello: command not found
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# 进入到一个含有 hello 的 shell 环境
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› nix shell nixpkgs#hello
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# hello 可以用了
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› hello
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Hello, world!
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```
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`nix run` 则是创建一个含有指定 Nix 包的环境，并在该环境中直接运行该 Nix 包（临时运行该程序，不将它安装到系统环境中）：
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```shell
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# hello 不存在
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› hello
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hello: command not found
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# 创建一个含有 hello 的环境并运行它
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› nix run nixpkgs#hello
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Hello, world!
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```
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因为 `nix run` 会直接将 Nix 包运行起来，所以作为其参数的 Nix 包必须能生成一个可执行程序。
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根据 `nix run --help` 的说明，`nix run` 会执行 `<out>/bin/<name>` 这个命令，其中 `<out>` 是一个 Derivation 的根目录，`<name>` 则按如下顺序进行选择尝试：
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- Derivation 的 `meta.mainProgram` 属性
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- Derivation 的 `pname` 属性
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- Derivation 的 `name` 属性中去掉版本号后的内容
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比如说我们上面测试的包 hello，`nix run` 实际会执行 `$out/bin/hello` 这个程序。
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## References
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- [pkgs.mkShell - nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-mkShell)
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- [A minimal nix-shell](https://fzakaria.com/2021/08/02/a-minimal-nix-shell.html)
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- [One too many shell, Clearing up with nix' shells nix shell and nix-shell - Yannik Sander](https://blog.ysndr.de/posts/guides/2021-12-01-nix-shells/)
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