Flakes/ja: Difference between revisions

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====概要====

Nix flakesはNixのプロジェクトに一定の構造を強制し、ロックファイルを用いて依存するプロジェクトのバージョンを指定することでより便利に再現可能なNix式を記述できるようにします。

* [https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-flake.html#description Flake]とは<code>flake.nix</code>というのNixファイルをルートに持つファイルシステムツリーを指します。

* <code>flake.nix</code>ファイルの内容は、Nix言語でパッケージとその依存関係を宣言するための統一された命名スキーマに従っています。

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*  Flakes introduce a [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-references URL-like syntax] for specifying remote sources.

* 長いURL構文を簡易にするために[https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-registry.html Flakeはレジストリを使用]して短い記号として登録できます。

* [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html 実験的なコマンドラインインタフェース]はFlakeの参照を受け取りパッケージのビルド、実行やべプロ医ができます。

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===基本的なFlakeの使用方法===

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====暗号化に関する警告====

{{Warning | flakeファイルの内容は世界的に読み取り可能なNix storeフォルダにコピーされるため、暗号化されていない機密情報はflakeファイルに置かないでください。代わりに[[Comparison of secret managing schemes|secret managing scheme]]を使うべきです。}}

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====Gitに関する警告====

したがって、flakeに<code>git</code>を使用する場合は、プロジェクトファイルを作成した後、必ず<code>git add</code>を実行してください。

See also https://www.tweag.io/blog/2020-05-25-flakes/

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nix flake init

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Nixpkgs can be defined using the following code:

==== nix run ====

 

 

 

 

 

 

 

 

 

 

 

== Making your evaluations pure ==

Nix flakes run in pure evaluation mode, which is underdocumented. Some tips for now:

* fetchurl and fetchtar [https://github.com/NixOS/nix/blob/36c4d6f59247826dde32ad2e6b5a9471a9a1c911/src/libexpr/primops/fetchTree.cc#L201 require] a sha256 argument to be considered pure.

* builtins.currentSystem is non-hermetic and impure. This can usually be avoided by passing the system (i.e., x86_64-linux) explicitly to derivations requiring it.

* Imports from channels like <code><nixpkgs></code> can be made pure by instead importing from the <code>output</code> function in <code>flake.nix</code>, where the arguments provide the store path to the flake's inputs:

== The nix flakes command ==

The {{ic|nix flake}} subcommand is described in [https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-flake.html command reference page of the unstable manual].

   inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-unstable;

 

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{

  inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-unstable;

 

    };

   ...

 

 

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{{Ic|nixos-rebuild}} also allows to specify different flake using the <code>--flake</code> flag (# is optional):

 

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$ sudo nixos-rebuild switch --flake .

 

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By default nixos-rebuild will use the currents system hostname to lookup the right nixos configuration in <code>nixosConfigurations</code>. You can also override this by using appending it to the flake parameter:

 

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   --target-host mymachine-hostname \

 

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{{warning|Remote building seems to have an issue that's [https://github.com/NixOS/nixpkgs/issues/134952#issuecomment-1367056358 resolved by setting the <code>--fast</code> flag].}}

 

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{ inputs, ... }:

{

nix.registry = {

     nixpkgs.flake = inputs.nixpkgs;

This has the unfortunate side-effect of requiring import-from-derivation and slowing down build times, however it may greatly speed up almost every eval. Full-time flakes users may be able to just use <code>narHash = pkgs.narHash</code>.

== Super fast nix-shell ==

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A feature of the nix Flake edition is that Nix evaluations are cached.

Running nix-shell can be a bit slow and take 1-3 seconds.

   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";

 

   outputs =

    { nixpkgs, ... }:

     {

       /*

        This example assumes your system is x86_64-linux

       devShells.x86_64-linux =

          pkgs = nixpkgs.legacyPackages.x86_64-linux;

        in

        {

          default = pkgs.mkShell {

            packages = [ pkgs.hello ];

And finally, run <code>nix develop</code>. This is what replaces the old nix-shell invocation.

Exit and run again, this command should now be super fast.

=== Automatically switch nix shells with nix-direnv ===

You can easily switch nix shells when you cd into different projects with [https://github.com/nix-community/nix-direnv nix-direnv].

== Pushing Flakes to Cachix ==

== Build specific attributes in a flake repository ==

When in the repository top-level, run <code>nix build .#<attr></code>. It will look in the <code>legacyPackages</code> and <code>packages</code> output attributes for the corresponding derivation.

=== Building flakes from a Git repo url with submodules ===

As per nix 2.9.1, git submodules in package <code>src</code>'s won't get copied to the nix store, this may cause the build to fail.  To workaround this, use:

 

 

 

 

 

 

 

 

 

== Getting ''Instant'' System Flakes Repl ==

 

How to get a nix repl out of your system flake:

 

 

 

 

 

However, this won't be instant upon evaluation if any file changes have been done since your last configuration rebuild. Instead, if one puts:

 

nix.nixPath = let path = toString ./.; in [ "repl=${path}/repl.nix" "nixpkgs=${inputs.nixpkgs}" ];

 

In their system <code>flake.nix</code> configuration file, and includes the following file in their root directory flake as <code>repl.nix</code>:

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  flake = builtins.getFlake (toString ./.);

// flake.nixosConfigurations

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(Don't forget to <code>git add repl.nix && nixos-rebuild  switch --flake "/etc/nixos"</code>)

 

source /etc/set-environment && nix repl $(echo $NIX_PATH | perl -pe 's|.*(/nix/store/.*-source/repl.nix).*|\1|')</syntaxHighlight>

 

This will launch a repl with access to <code>nixpkgs</code>, <code>lib</code>, and the <code>flake</code> options in a split of a second.

 

 

nix.nixPath = [ "nixpkgs=${inputs.nixpkgs}" ];

  my-nix-fast-repl = pkgs.writeShellScriptBin "my-nix-fast-repl" ''

 

 

 

When a git folder exists, flake will only copy files added in git to maximize reproducibility (this way if you forgot to add a local file in your repo, you will directly get an error when you try to compile it). However, for development purpose you may want to create an alternative flake file, for instance containing configuration for your preferred editors as described [https://discourse.nixos.org/t/local-personal-development-tools-with-flakes/22714/8 here]… of course without committing this file since it contains only your own preferred tools. You can do so by doing something like that (say for a file called <code>extra/flake.nix</code>):

* [https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-flake.html Nix flake command reference manual] - Many additional details about flakes, and their parts.

* [https://www.youtube.com/watch?v=QXUlhnhuRX4&list=PLgknCdxP89RcGPTjngfNR9WmBgvD_xW0l Nix flakes 101: Introduction to nix flakes] (Jörg Thalheim, 2020)

* [https://github.com/NixOS/nix/blob/master/src/nix/flake.md spec describing flake inputs in more detail]

* [https://github.com/numtide/flake-utils flake-utils: Library to avoid some boiler-code when writing flakes]

* [https://zimbatm.com/NixFlakes/#direnv-integration zimbat's direnv article]