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<div lang="en" dir="ltr" class="mw-content-ltr">
{{Cleanup}}
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
'''Nix flakes''' are an [[Experimental Nix features|experimental feature]] first introduced in the 2.4 [[Nix]] release,{{Cite manual|nix|development/experimental-features|number=13.8|title=Experimental Features|subsection=xp-feature-flakes|subtitle=flakes}}{{Cite manual|nix|release-notes/rl-2.4|number=14.27|title=Release 2.4 (2021-11-01)}} aiming to address a number of areas of improvement for the Nix ecosystem: they provide a uniform structure for Nix projects, allow for pinning specific versions of each dependencies, and sharing these dependencies via lock files, and overall make it more convenient to write reproducible Nix expressions.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
A flake is a directory which directly contains a Nix file called <code>flake.nix</code>, that follows a very specific structure. Flakes introduce a URL-like syntax{{Cite manual|nix|command-ref/new-cli/nix3-flake|number=8.5.17|title=nix flake|subsection=url-like-syntax|subtitle=URL-like syntax}} for specifying remote resources. To simplify the URL syntax, flakes use a registry of symbolic identifiers,{{Cite manual|nix|command-ref/new-cli/nix3-registry|number=8.5.62|title=nix registry}} allowing the direct specification of resources through syntax such as <code>github:NixOS/nixpkgs</code>.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Flakes also allow for locking references and versions, which can then be queried and updated programatically via the inputs {{cite manual|nix|command-ref/new-cli/nix3-flake-lock|number=7.5.19|title=nix flake lock}}{{cite manual|nix|command-ref/new-cli/nix3-flake-info|number=7.5.17|title=nix flake info}}. Additionally, an experimental CLI utility accepts flake references for expressions that build, run, and deploy packages.{{Cite manual|nix|command-ref/new-cli/nix|number=8.5.1|title=nix}}
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
== 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";
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
outputs = { self, nixpkgs }: {
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hello;
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
packages.x86_64-linux.default = self.packages.x86_64-linux.hello;
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
};
}</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.}}
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== 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>{
  ...
  nixConfig = {
    extra-substituters = [
      "https://nix-community.cachix.org"
    ];
    extra-trusted-public-keys = [
      "nix-community.cachix.org-1:...="
    ];
  }
}</nowiki>|name=flake.nix|lang=nix}}{{Note|If you are used to configuring your Nix settings via the NixOS configuration, these options are under <code>nix.settings</code> and not <code>nix</code>. For example, you cannot specify the automatic storage optimisation under <code>nix.optimisation.enable</code>.}}
</div>

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== Setup ==
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=== Enabling flakes temporarily ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
When using any [[Nix command|<code>nix</code> command]], add the following command-line options:
</div>
<syntaxhighlight lang="shell">
 --experimental-features 'nix-command flakes'
</syntaxhighlight>
<div lang="en" dir="ltr" class="mw-content-ltr">
=== Enabling flakes permanently ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
==== NixOS ====
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Add the following to the [[Overview_of_the_NixOS_Linux_distribution#Declarative_Configuration system configuration |NixOS configuration]]:
</div>

<syntaxHighlight lang=nix>
  nix.settings.experimental-features = [ "nix-command" "flakes" ];
</syntaxHighlight>

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====Home Manager====
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Add the following to your [[Home Manager|home manager]] config:
</div>

<syntaxhighlight lang="nix">
  nix.settings.experimental-features = [ "nix-command" "flakes" ];
</syntaxhighlight>

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====Nix standalone====
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
{{Note | The  [https://github.com/DeterminateSystems/nix-installer Determinate Nix Installer] enables flakes by default.}}
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Add the following to <code>~/.config/nix/nix.conf</code> or <code>/etc/nix/nix.conf</code>:
</div>

<syntaxHighlight lang=text>
experimental-features = nix-command flakes
</syntaxHighlight>
<div lang="en" dir="ltr" class="mw-content-ltr">
== Usage ==
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
{{Warning | Since contents of flake files are copied to the world-readable [[Nix_package_manager#Nix_store|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]].}}
</div>

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{{Note | For flakes in [[git]] repositories, only files in the working tree will be copied to the store.
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Therefore, if you use <code>git</code> for your flake, ensure to <code>git add</code> any project files after you first create them.}}
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=== The nix flakes command ===
{{Main|Nix (command)}}
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
The {{ic|nix flake}} subcommand is described in {{Nix Manual|name=command reference page of the Nix manual|anchor=command-ref/new-cli/nix3-flake}}.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
This flake produces a single flake output <code>packages</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:
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
<syntaxhighlight lang="console">
$ nix flake show
└───packages
    └───x86_64-linux
        ├───default: package 'hello-2.12.2'
        └───hello: package 'hello-2.12.2'
</syntaxhighlight>
</div>

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==== Development shells ====
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
A <code>devShell</code> is a Nix-provided [[Development_environment_with_nix-shell#nix develop|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>.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
<syntaxhighlight lang="nix">
{
  description = "Example flake with a devShell";
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
outputs = { self, nixpkgs}:
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs { inherit system; };
    in {
      devShells.x86_64-linux.default = pkgs.mkShell {
        buildInputs = with pkgs; [
          hello
        ];
        shellHook = ''
          echo "Welcome to the devShell!"
        '';
      };
    };
}
</syntaxhighlight>
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
To enter the development shell environment:
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
<syntaxhighlight lang="console">
$ nix develop
</syntaxhighlight>
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
{{note|You don’t need to define a devShell to enter a development shell using nix develop.
If no devShell is defined, nix develop will drop you into an environment containing the default build dependencies of the flake (if any).}}
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
==== Build specific attributes in a flake repository ====
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
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:
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
<syntaxHighlight lang=console>
$ nix build .#hello
</syntaxHighlight>
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Likewise, you can specify an attribute with the run command: <code>nix run .#hello</code> and the develop command: <code>nix develop .#hello</code>.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
== Flake schema ==
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
The flake.nix file is a Nix file but that has special restrictions (more on that later).
</div>

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It has 4 top-level attributes:
</div>

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

<div lang="en" dir="ltr" class="mw-content-ltr">
* <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|binary cache]].
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Input schema ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
[https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-inputs The nix flake inputs manual].
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
[https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-references The nix flake references manual].
</div>

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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.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
[[Nixpkgs]] can be defined using the following code:
</div>

<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.

<div lang="en" dir="ltr" class="mw-content-ltr">
For any repository with its own flake.nix file, the website must also be defined. Nix knows where the nixpkgs repository is, so stating that it's on GitHub is unnecessary.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
For example, adding [[Hyprland]] as an input would look something like this:
</div>

<code>inputs.hyprland.url = "github:hyprwm/Hyprland";</code>

<div lang="en" dir="ltr" class="mw-content-ltr">
If you want to make Hyprland follow the nixpkgs input to avoid having multiple versions of nixpkgs, this can be done using the following code:
</div>

<code>inputs.hyprland.inputs.nixpkgs.follows = "nixpkgs";</code>

<div lang="en" dir="ltr" class="mw-content-ltr">
Using curly brackets({}), we can shorten all of this and put it in a table. The code will look something like this:
</div>

<syntaxhighlight lang="nix">
inputs = {
  nixpkgs.url = "github:NixOS/nixpkgs/<branch name>";
  hyprland = {
    url = "github:hyprwm/Hyprland";
    inputs.nixpkgs.follows = "nixpkgs";
  };
};
</syntaxhighlight>

<div lang="en" dir="ltr" class="mw-content-ltr">
By default, Git submodules in package <code>src</code>'s won't get copied to the nix store, this may cause the build to fail. Flakes in Git repositories can declare that they need Git submodules to be enabled. Since Nix version [https://discourse.nixos.org/t/nix-2-27-0-released/62003 2.27], you can enable submodules by:
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
<syntaxhighlight lang="nix">
  inputs.self.submodules = true;
</syntaxhighlight>
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Output schema ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
This is described in the nix package manager [https://github.com/NixOS/nix/blob/master/src/nix/flake-check.md src/nix/flake-check.md].
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Once the inputs are resolved, they're passed to the function `outputs` along with with `self`, which is the directory of this flake in the store. `outputs` returns the outputs of the flake, according to the following schema.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Where:
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
* <code><system></code> is something like "x86_64-linux", "aarch64-linux", "i686-linux", "x86_64-darwin"
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
* <code><name></code> is an attribute name like "hello".
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
* <code><flake></code> is a flake name like "nixpkgs".
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
* <code><store-path></code> is a <code>/nix/store..</code> path
</div>

<syntaxHighlight lang=nix>
{ self, ... }@inputs:
{
  # Executed by `nix flake check`
  checks."<system>"."<name>" = derivation;
  # Executed by `nix build .#<name>`
  packages."<system>"."<name>" = derivation;
  # Executed by `nix build .`
  packages."<system>".default = derivation;
  # Executed by `nix run .#<name>`
  apps."<system>"."<name>" = {
    type = "app";
    program = "<store-path>";
  };
  # Executed by `nix run . -- <args?>`
  apps."<system>".default = { type = "app"; program = "..."; };

# Formatter (alejandra, nixfmt or nixpkgs-fmt)
  formatter."<system>" = derivation;
  # Used for nixpkgs packages, also accessible via `nix build .#<name>`
  legacyPackages."<system>"."<name>" = derivation;
  # Overlay, consumed by other flakes
  overlays."<name>" = final: prev: { };
  # Default overlay
  overlays.default = final: prev: { };
  # Nixos module, consumed by other flakes
  nixosModules."<name>" = { config, ... }: { options = {}; config = {}; };
  # Default module
  nixosModules.default = { config, ... }: { options = {}; config = {}; };
  # Used with `nixos-rebuild switch --flake .#<hostname>`
  # nixosConfigurations."<hostname>".config.system.build.toplevel must be a derivation
  nixosConfigurations."<hostname>" = {};
  # Used by `nix develop .#<name>`
  devShells."<system>"."<name>" = derivation;
  # Used by `nix develop`
  devShells."<system>".default = derivation;
  # Hydra build jobs
  hydraJobs."<attr>"."<system>" = derivation;
  # Used by `nix flake init -t <flake>#<name>`
  templates."<name>" = {
    path = "<store-path>";
    description = "template description goes here?";
  };
  # Used by `nix flake init -t <flake>`
  templates.default = { path = "<store-path>"; description = ""; };
}
</syntaxHighlight>

<div lang="en" dir="ltr" class="mw-content-ltr">
You can also define additional arbitrary attributes, but these are the outputs that Nix knows about.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
== Core usage patterns ==
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Making your evaluations pure ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Nix flakes are evaluated in a pure evaluation mode, meaning that access to the external environment is restricted to ensure reproducibility. To maintain purity when working with flakes, consider the following:
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
* {{Nixpkgs Manual|name=fetchurl|anchor=#sec-pkgs-fetchers-fetchurl-inputs}} and {{Nixpkgs Manual|name=fetchzip|anchor=#sec-pkgs-fetchers-fetchzip-inputs}} require a <code>sha256</code> argument to be considered pure.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
* <code>builtins.currentSystem</code> is non-hermetic and impure as it reflects the host system performing the evauluation. This can usually be avoided by passing the system (i.e., x86_64-linux) explicitly to derivations requiring it.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
*  <code>builtins.getEnv</code> is also impure. Avoid reading from environment variables and likewise, do not reference files outside of the flake's directory.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Defining a flake for multiple architectures ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Flakes force you to specify a program for each supported architecture. An example below shows how to write a flake that targets multiple architectures.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
<syntaxhighlight lang="nix">
{
  description = "A flake targeting multiple architectures";
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
outputs = { self, nixpkgs }: let
    systems = [ "x86_64-linux" "aarch64-linux" ];
    forAllSystems = f: builtins.listToAttrs (map (system: {
      name = system;
      value = f system;
    }) systems);
  in {
    packages = forAllSystems (system: let
      pkgs = nixpkgs.legacyPackages.${system};
    in {
      hello = pkgs.hello;
      default = pkgs.hello;
    });
  };
}
</syntaxhighlight>
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
You can also use third-parties projects like [[Flake Utils|flake-utils]] or [[Flake Parts|flake-parts]] that automatically provide code to avoid this boilerplate. To avoid re-defining the program multiple times, refer to [[Flake Utils#Defining a flake for multiple architectures]]
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Using overlays ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
To use [[Overlays]] with flakes, refer to [[Overlays#In a Nix flake]] page.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Enable unfree software ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
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.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
<syntaxhighlight lang="nix">
{
  inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  outputs = { self, nixpkgs, flake-compat }:
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs { inherit system; config.allowUnfree = true;};
    in {
      ...
    };
}
</syntaxhighlight>
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
== NixOS configuration with flakes ==
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
It is possible to manage a [[NixOS]] system configuration using flakes, gaining the benefits of reproducible, declarative inputs and streamlined updates.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
For details and examples, see [[NixOS system configuration#Defining NixOS as a flake]].
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
== Development tricks ==
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Automatically switch nix shells with direnv ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
It is possible to automatically activate different Nix shells when navigating between project directories by using [[Direnv]]. Additional Nix integration with Direnv can be achieved with [https://github.com/nix-community/nix-direnv nix-direnv].
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Pushing Flakes to Cachix ===
</div>

https://docs.cachix.org/pushing#flakes

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Flake support in projects without flakes ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
The [https://github.com/edolstra/flake-compat flake-compat] library provides a compatibility layer that allows projects using traditional <code>default.nix</code> and <code>shell.nix</code> files to operate with flakes. For more details and usage examples, see the [[Flake Compat]] page.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
Another project that allows consuming flakes from non-flake projects is [https://github.com/fricklerhandwerk/flake-inputs flake-inputs].
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Accessing flakes from Nix expressions ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
If you want to access a flake from within a regular Nix expression on a system that has flakes enabled, you can use something like <code>(builtins.getFlake "/path/to/directory").packages.x86_64-linux.default</code>, where 'directory' is the directory that contains your <code>flake.nix</code>.
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Efficiently build multiple flake outputs ===
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
To push ''all'' flake outputs automatically, checkout [https://github.com/srid/devour-flake#usage devour-flake].
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
=== Build a package added in a PR ===
</div>

<syntaxHighlight>
nix build github:nixos/nixpkgs?ref=pull/<PR_NUMBER>/head#<PACKAGE>
</syntaxHighlight>

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this allows building a package that has not yet been added to nixpkgs.
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note that this will download a full source tarball of nixpkgs.  if you already have a local clone, using that may be faster due to delta compression:
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git fetch upstream pull/<PR_NUMBER>/head && git checkout FETCH_HEAD && nix build .#PACKAGE
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this allows building a package that has not yet been added to nixpkgs.
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=== How to add a file locally in git but not include it in commits ===
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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>):
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git add --intent-to-add extra/flake.nix
git update-index --skip-worktree --assume-unchanged extra/flake.nix
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=== Rapid iteration of a direct dependency ===
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One common pain point with using Nix as a development environment is the need to completely rebuild dependencies and re-enter the dev shell every time they are updated. The <code>nix develop --redirect <flake> <directory></code> command allows you to provide a mutable dependency to your shell as if it were built by Nix.
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Consider a situation where your executable, <code>consumexe</code>, depends on a library, <code>libdep</code>. You're trying to work on both at the same time, where changes to <code>libdep</code> are reflected in real time for <code>consumexe</code>. This workflow can be achieved like so:
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cd ~/libdep-src-checkout/
nix develop # Or `nix-shell` if applicable.
export prefix="./install" # configure nix to install it here
buildPhase   # build it like nix does
installPhase # install it like nix does
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Now that you've built the dependency, <code>consumexe</code> can take it as an input. '''In another terminal''':
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cd ~/consumexe-src-checkout/
nix develop --redirect libdep ~/libdep-src-checkout/install
echo $buildInputs | tr " " "\n" | grep libdep
# Output should show ~/libdep-src-checkout/ so you know it worked
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If Nix warns you that your redirected flake isn't actually used as an input to the evaluated flake, try using the <code>--inputs-from .</code> flag. If all worked well you should be able to <code>buildPhase && installPhase</code> when the dependency changes and rebuild your consumer with the new version ''without'' exiting the development shell.
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=== Official sources ===
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* [https://nix.dev/concepts/flakes Flakes] - nix.dev
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* [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.
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* [https://github.com/NixOS/nix/blob/master/src/nix/flake.md spec describing flake inputs in more detail]
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* [https://github.com/NixOS/rfcs/pull/49 RFC 49] (2019) - Original flakes specification
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=== Guides ===
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* [https://jade.fyi/blog/flakes-arent-real/ Flakes aren't real and can't hurt you] (Jade Lovelace, 2024)
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* [https://github.com/ryan4yin/nixos-and-flakes-book NixOS & Flakes Book](Ryan4yin, 2023) - 🛠️ ❤️ An unofficial NixOS & Flakes book for beginners.
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* [https://xeiaso.net/blog/nix-flakes-1-2022-02-21 Nix Flakes: an Introduction] (Xe Iaso, 2022)
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* [https://serokell.io/blog/practical-nix-flakes Practical Nix Flakes] (Alexander Bantyev, 2021) - Intro article on working with Nix and Flakes
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* [https://www.tweag.io/blog/2020-05-25-flakes/ Nix Flakes, Part 1: An introduction and tutorial] (Eelco Dolstra, 2020)
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* [https://www.tweag.io/blog/2020-06-25-eval-cache/ Nix Flakes, Part 2: Evaluation caching] (Eelco Dolstra, 2020)
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* [https://www.tweag.io/blog/2020-07-31-nixos-flakes/ Nix Flakes, Part 3: Managing NixOS systems] (Eelco Dolstra, 2020)
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* [https://www.youtube.com/watch?v=QXUlhnhuRX4&list=PLgknCdxP89RcGPTjngfNR9WmBgvD_xW0l Nix flakes 101: Introduction to nix flakes] (Jörg Thalheim, 2020) YouTube video
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=== Useful flake modules ===
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* [[Flake Utils|flake-utils]]: Library to avoid some boiler-code when writing flakes
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* [[Flake Parts|flake-parts]]: Library to help write modular and organized flakes
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* [[Flake Compat|flake-compat]]: A compatibility layer for flakes
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* [https://github.com/nix-community/todomvc-nix building Rust and Haskell flakes]
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{{references}}
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[[Category:Software]]
[[Category:Nix]]
[[Category:Nix Language]]
[[Category:Flakes]]