Flakes: Difference between revisions

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'''Nix flakes''' is an [https://nixos.org/manual/nix/stable/development/experimental-features.html experimental feature] that was introduced with Nix 2.4 ([https://nixos.org/manual/nix/unstable/release-notes/rl-2.4.html see release notes]).

====Introduction==== <!--T:2-->

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Nix flakes enforce a uniform structure for Nix projects, pin versions of their dependencies in a lock file, and make it more convenient to write reproducible Nix expressions.

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* A [https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-flake.html#description flake] refers to a file-system tree whose root directory contains the Nix file specification called <code>flake.nix</code>.

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* The contents of <code>flake.nix</code> file follow a uniform naming schema for declaring packages and their dependencies in the Nix language.

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* To simplify the long URL syntax with shorter names, [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-registry.html flakes uses a registry] of symbolic identifiers.

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* Flakes also allow for locking references and versions that can then be queried and updated programmatically.

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* 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.

=== Enabling flakes ===

====Enable flakes temporarily==== <!--T:5-->

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

====Enable flakes permanently in NixOS==== <!--T:7-->

 

====With Home Manager==== <!--T:10-->

 

====Other Distros, without Home Manager==== <!--T:13-->

 

===Basic Usage of Flake=== <!--T:17-->

{{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]].}}

====Generate flake.nix file==== <!--T:24-->

 

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This flake produces a single flake output <code>packagage</code>. And within that, <code>x86_64-linux</code> is a system-specifc attribute set. And within that, two package derivations <code>default</code> and <code>hello</code>. You can find outputs with the {{Nix Manual|name=show command|anchor=command-ref/new-cli/nix3-flake-show}} of a flake as shown below:

==== Development shells ====

A <code>devShell</code> is a Nix-provided development environment defined within a flake. It lets you declare a reproducible shell environment with the tools, libraries, and environment variables you need for the development of a specific project. This is flake equivalent to defining a <code>nix-shell</code>.

  inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";

  outputs = { self, nixpkgs}:

           pkgs.hello

Running <code>nix build</code> will look in the <code>legacyPackages</code> and <code>packages</code> output attributes for the corresponding derivation and then your system architecture and build the default output. If you want to specify a build attribute in a flake repository, you can run <code>nix build .#<attr></code>. In the example above, if you wanted to build the <code>packages.x86_64-linux.hello</code> attribute, run:

* <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.

Nixpkgs can be defined using the following code:

Using curly brackets({}), we can shorten all of this and put it in a table. The code will look something like this:

 

</translate>

<syntaxHighlight lang=nix>

   apps."<system>".default = { type = "app"; program = "..."; };

   # Formatter (alejandra, nixfmt or nixpkgs-fmt)

</syntaxHighlight>

== Core usage patterns ==

=== Defining a flake for multiple architectures ===

  inputs = {

  outputs = { self, nixpkgs }: let

=== Using overlays ===  

To allow for [Unfree software|unfree software]] in a flake project, you need to explicitly allow it by setting <code>config.allowUnree = true;</code> when importing Nixpkgs.

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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.

 

</translate>

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

in [

];

=== Efficiently build multiple flake outputs ===

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>):

=== Official sources ===

=== Guides ===

=== Useful flake modules ===