Flakes/es: Difference between revisions

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== Flake file structure ==

Minimally, a flake file contains a description of the flake, a set of input dependencies and an output. You can generate a very basic flake file at any time using nix flake init. This will populate the current directory with a file called flake.nix that will contain something akin to:

{{File|3=<nowiki>{

   description = "A very basic flake";

inputs = {

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

   };

outputs = { self, nixpkgs }: {

packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hello;

packages.x86_64-linux.default = self.packages.x86_64-linux.hello;

}</nowiki>|name=flake.nix|lang=nix}}

In the example above, you can see the description, the input specified as a GitHub repository with a specific branch (here <code>nixos/nixpkgs</code> on the <code>nixos-unstable</code> branch), and an output that makes use of the input. The output simply specifies that the flake contains one package for the x86_64 architecture called <code>hello</code>. Even if your flake's output wouldn't use its input (however, in practice, that is highly unlikely), the output still needs to be a Nix function.

{{Note|Flakes require you to specify its outputs for each architecture separately. For more information, read the related section below.}}

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=== Nix configuration ===

It is possible to override the global Nix configuration set in your <code>nix.conf</code> file for the purposes of evaluating a flake. This can be useful, for example, for setting up binary caches specific to certain projects, while keeping the global configuration untouched. The flake file can contain a nixConfig attribute with any relevant configuration settings supplied. For example, enabling the nix-community binary cache would be achieved by:

{{File|3=<nowiki>{

   ...

     ];

   }

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

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  --experimental-features 'nix-command flakes'

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=== Enabling flakes permanently ===

experimental-features = nix-command flakes

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== Usage ==

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=== The nix flakes command ===

{{Main|Nix (command)}}

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$ nix flake show

         └───hello: package 'hello-2.12.2'

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{

   description = "Example flake with a devShell";

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

outputs = { self, nixpkgs}:

     let

}

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$ nix develop

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$ nix build .#hello

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<code>inputs.nixpkgs.url = "github:NixOS/nixpkgs/<branch name>";</code>

Nixpkgs can alternatively also point to an url cached by the NixOS organization:

<code>inputs.nixpkgs.url = "<nowiki>https://nixos.org/channels/nixpkgs-unstable/nixexprs.tar.xz</nowiki>";</code>

In this example the input would point to the `nixpkgs-unstable` channel.

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   inputs.self.submodules = true;

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{

   description = "A flake targeting multiple architectures";

inputs = {

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

   };

outputs = { self, nixpkgs }: let

     systems = [ "x86_64-linux" "aarch64-linux" ];

}

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{

     };

}

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# Output should show ~/libdep-src-checkout/ so you know it worked

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* [https://github.com/nix-community/todomvc-nix building Rust and Haskell flakes]

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