Flakes/fr: Difference between revisions

====Introduction====

Les flocons Nix appliquent une structure uniforme pour les projets Nix, épinglent les versions de leurs dépendances dans un fichier de verrouillage et facilitent l'écriture d'expressions Nix reproductibles.

* Un [https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-flake.html#description flocon] fait référence à une arborescence de système de fichiers dont le répertoire racine contient la spécification de fichier Nix appelée

<code>flake.nix</code>.

* Le contenu d'un fichier <code>flake.nix</code> suit un schéma de dénomination uniforme pour déclarer les paquets et leurs dépendances dans le langage Nix

* Les flocons introduisent une [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-references syntaxe de type URL] pour spécifier des sources distantes.

* Pour simplifier la syntaxe des URL longues avec des noms plus courts, [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-registry.html les flocons utilisent des registres] d'identifiants symbolique.

* Pour simplifier la syntaxe des URL longues avec des noms plus courts, [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-registry.html flakes utilise un registre] d'identifiants symboliques.

* Les flocons permettent également de verrouiller des références et des versions, qui peuvent ensuite être interrogées et mises à jour de manière programmatique.

* An [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html experimental command-line interface] accepts flake references for expressions that build, run, and deploy packages.

====Enable flakes temporarily====

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When using any <code>nix</code> command, add the following command-line options:

====Enable flakes permanently in NixOS====

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Add the following to the [[Overview_of_the_NixOS_Linux_distribution#Declarative_Configuration system configuration |NixOS configuration]]:

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=====Other Distros, with Home-Manager=====

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Add the following to your home-manager config:

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=====Other Distros, without Home-Manager=====

Add the following to <code>~/.config/nix/nix.conf</code> or <code>/etc/nix/nix.conf</code>:

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===Basic Usage of Flake===

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Before running any nix commands at this point, please note the two warnings below: one for encryption and the other for git.

{{Warning | Since contents of flake files are copied to the world-readable Nix store folder, do not put any unencrypted secrets in flake files. You should instead use a [[Comparison of secret managing schemes|secret managing scheme]].}}

====Git WARNING====

For flakes in git repos, only files in the working tree will be copied to the store.

Therefore, if you use <code>git</code> for your flake, ensure to <code>git add</code> any project files after you first create them.

====Generate flake.nix file====

To start the basic usage of flake, run the flake command in the project directory:

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== Flake schema ==

* <code>description</code> is a string describing the flake.

* <code>inputs</code> is an attribute set of all the dependencies of the flake. The schema is described below.

* <code>outputs</code> is a function of one argument that takes an attribute set of all the realized inputs, and outputs another attribute set whose schema is described below.

* <code>nixConfig</code> is an attribute set of values which reflect the [https://nixos.org/manual/nix/stable/command-ref/conf-file.html values given to nix.conf]. This can extend the normal behavior of a user's nix experience by adding flake-specific configuration, such as a binary cache.

[https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-inputs The nix flake inputs manual].

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[https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-references The nix flake references manual].

The inputs attribute defines the dependencies of the flake. For example, nixpkgs has to be defined as a dependency for a system flake in order for the system to build properly.

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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 {{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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<syntaxhighlight lang="nix">

{

  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]