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298 lines
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298 lines
15 KiB
Org Mode
:PROPERTIES:
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:ID: 6873de22-9eac-492c-93a8-6cdf8cbfc0f8
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:END:
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#+title: Nix flakes
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#+date: 2021-07-18 22:34:11 +08:00
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#+date_modified: 2022-01-07 13:58:21 +08:00
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#+language: en
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#+begin_note
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As of 2021-06-30, the version used for this note is at v2.3 so it needs to be invoked with the unstable version.
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#+end_note
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What are Nix flakes?
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A self-contained Nix module that takes inputs (can be from other flakes) and create outputs.
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It is comparable to [[https://guix.gnu.org/manual/en/html_node/Channels.html][Guix channels]] (or the NUR) in the way any arbitrary value can be exported, thus extending a Nix module in any direction the author can make it to.
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Also, it supercedes Nix channels as a way to manage your system.
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So, why use flakes?
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- Since it is self-contained, it is easier to compose and develop environments for projects.
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- It is more declarative compared to Nix channels.
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- Provides a structure for discoverability through exploring the output.
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- In case you're using roam:NixOS, it also provides an easier way to extend it with third-party custom modules.
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* Exploring a Nix flake
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To get started with a flake, you can quickly create one with =nix flake init=.
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This will create =flake.nix= which is also required for Nix to recognize the project as a flake.
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Here's the skeleton of a flake.
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#+begin_src nix
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{
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description = "A basic flake.";
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inputs = {};
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outputs = {};
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}
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#+end_src
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It is really just an attribute set that mainly deals with three attributes:
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- =description= which is self-descriptive enough to see what's it for. ;p
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- =inputs= which contains inputs (that are other flakes) to be used for...
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- ...the =outputs= which is a set or a function that returns an attribute set to be exported.
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Here's a real example of a basic flake.
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#+begin_src nix
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{
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description = "A basic flake with some real inputs this time.";
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inputs = {
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nixpkgs.url = "github:NixOS/nixpkgs";
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home-manager.url = "github:nix-community/home-manager";
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home-manager.inputs.nixpkgs.follows = "nixpkgs";
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};
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outputs = attrs@{ self, nixpkgs, home-manager, ... }: {
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homeManagerConfiguration = import ./hmUsers;
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packages.x86_64-linux = {
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hello = nixpkgs.pkgs.hello;
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};
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};
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}
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#+end_src
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The flake requires other flakes from the nixpkgs and home-manager as indicated from the URL.
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This will get the latest revision of both inputs.
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This is not ideal as it will get the latest revisions every time it requests the inputs.
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While you can pin the version by adding more information (e.g., =nixpkgs.url = "github:NixOS/nixpkgs/nixos-21.11"=, =home-manager.url = "github:nix-community/home-manager/781d25b315def05cd7ede3765226c54216f0b1fe"=), this isn't really necessary for the most part as we have lockfiles to secure our dependencies version.
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These lockfiles can be found at =flake.lock= where complete metadata for the flakes are found.
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* Selected list of attributes for outputs
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While you can export attributes of any type, there are common attributes you'll mostly see.
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As an example, here's the flake of my NixOS configuration.
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#+begin_src shell :cache yes :results output
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nix flake show github:foo-dogsquared/nixos-config | nix run nixpkgs#gnused -- 's/\x1b\[[0-9;]*m//g'
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#+end_src
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#+results[cf6df0202da35fbba99f7581b2655fb75d9eef8a]:
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#+begin_example
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github:foo-dogsquared/nixos-config/12077bfc601e5465e343e590a830e8d3cb6a1a59
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├───devShells
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│ ├───aarch64-darwin
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│ │ ├───flatpak: development environment 'nix-shell'
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│ │ ├───hugo: development environment 'nix-shell'
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│ │ └───rust: development environment 'nix-shell'
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│ ├───aarch64-linux
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│ │ ├───flatpak: development environment 'nix-shell'
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│ │ ├───hugo: development environment 'nix-shell'
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│ │ └───rust: development environment 'nix-shell'
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│ ├───i686-linux
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│ │ ├───flatpak: development environment 'nix-shell'
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│ │ ├───hugo: development environment 'nix-shell'
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│ │ └───rust: development environment 'nix-shell'
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│ ├───x86_64-darwin
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│ │ ├───flatpak: development environment 'nix-shell'
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│ │ ├───hugo: development environment 'nix-shell'
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│ │ └───rust: development environment 'nix-shell'
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│ └───x86_64-linux
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│ ├───flatpak: development environment 'nix-shell'
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│ ├───hugo: development environment 'nix-shell'
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│ └───rust: development environment 'nix-shell'
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├───homeManagerConfigurations: unknown
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├───homeManagerModules: unknown
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├───lib: unknown
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├───nixosConfigurations
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│ └───ni: NixOS configuration
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├───nixosModules
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│ ├───agenix: NixOS module
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│ ├───archiving: NixOS module
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│ ├───desktop: NixOS module
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│ ├───dev: NixOS module
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│ ├───hardware-setup: NixOS module
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│ ├───themes: NixOS module
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│ └───users: NixOS module
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└───packages
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├───aarch64-darwin
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│ ├───doggo: package 'doggo-0.4.1'
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│ ├───gnome-shell-extension-burn-my-windows: package 'gnome-shell-extension-burn-my-windows-2'
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│ ├───gnome-shell-extension-desktop-cube: package 'gnome-shell-extension-desktop-cube-5'
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│ ├───gnome-shell-extension-fly-pie: package 'gnome-shell-extension-fly-pie-12'
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│ ├───gnome-shell-extension-pop-shell: package 'gnome-shell-extension-pop-shell-unstable-2021-11-30'
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│ ├───libcs50: package 'libcs50-10.1.1'
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│ ├───llama: package 'llama-1.0.2'
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│ ├───neo: package 'neo-0.6'
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│ ├───pop-launcher: package 'pop-launcher-1.1.0'
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│ ├───pop-launcher-plugin-duckduckgo-bangs: package 'pop-launcher-plugin-duckduckgo-bangs-1.3.0'
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│ ├───sioyek: package 'sioyek-1.0.0'
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│ └───tic-80: package 'tic-80-unstable-2021-12-18'
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├───aarch64-linux
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│ ├───doggo: package 'doggo-0.4.1'
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│ ├───gnome-shell-extension-burn-my-windows: package 'gnome-shell-extension-burn-my-windows-2'
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│ ├───gnome-shell-extension-desktop-cube: package 'gnome-shell-extension-desktop-cube-5'
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│ ├───gnome-shell-extension-fly-pie: package 'gnome-shell-extension-fly-pie-12'
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│ ├───gnome-shell-extension-pop-shell: package 'gnome-shell-extension-pop-shell-unstable-2021-11-30'
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│ ├───libcs50: package 'libcs50-10.1.1'
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│ ├───llama: package 'llama-1.0.2'
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│ ├───neo: package 'neo-0.6'
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│ ├───pop-launcher: package 'pop-launcher-1.1.0'
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│ ├───pop-launcher-plugin-duckduckgo-bangs: package 'pop-launcher-plugin-duckduckgo-bangs-1.3.0'
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│ ├───sioyek: package 'sioyek-1.0.0'
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│ └───tic-80: package 'tic-80-unstable-2021-12-18'
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├───i686-linux
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│ ├───doggo: package 'doggo-0.4.1'
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│ ├───gnome-shell-extension-burn-my-windows: package 'gnome-shell-extension-burn-my-windows-2'
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│ ├───gnome-shell-extension-desktop-cube: package 'gnome-shell-extension-desktop-cube-5'
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│ ├───gnome-shell-extension-fly-pie: package 'gnome-shell-extension-fly-pie-12'
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│ ├───gnome-shell-extension-pop-shell: package 'gnome-shell-extension-pop-shell-unstable-2021-11-30'
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│ ├───libcs50: package 'libcs50-10.1.1'
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│ ├───llama: package 'llama-1.0.2'
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│ ├───neo: package 'neo-0.6'
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│ ├───pop-launcher: package 'pop-launcher-1.1.0'
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│ ├───pop-launcher-plugin-duckduckgo-bangs: package 'pop-launcher-plugin-duckduckgo-bangs-1.3.0'
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│ ├───sioyek: package 'sioyek-1.0.0'
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│ └───tic-80: package 'tic-80-unstable-2021-12-18'
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├───x86_64-darwin
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│ ├───doggo: package 'doggo-0.4.1'
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│ ├───gnome-shell-extension-burn-my-windows: package 'gnome-shell-extension-burn-my-windows-2'
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│ ├───gnome-shell-extension-desktop-cube: package 'gnome-shell-extension-desktop-cube-5'
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│ ├───gnome-shell-extension-fly-pie: package 'gnome-shell-extension-fly-pie-12'
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│ ├───gnome-shell-extension-pop-shell: package 'gnome-shell-extension-pop-shell-unstable-2021-11-30'
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│ ├───libcs50: package 'libcs50-10.1.1'
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│ ├───llama: package 'llama-1.0.2'
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│ ├───neo: package 'neo-0.6'
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│ ├───pop-launcher: package 'pop-launcher-1.1.0'
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│ ├───pop-launcher-plugin-duckduckgo-bangs: package 'pop-launcher-plugin-duckduckgo-bangs-1.3.0'
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│ ├───sioyek: package 'sioyek-1.0.0'
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│ └───tic-80: package 'tic-80-unstable-2021-12-18'
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└───x86_64-linux
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├───doggo: package 'doggo-0.4.1'
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├───gnome-shell-extension-burn-my-windows: package 'gnome-shell-extension-burn-my-windows-2'
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├───gnome-shell-extension-desktop-cube: package 'gnome-shell-extension-desktop-cube-5'
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├───gnome-shell-extension-fly-pie: package 'gnome-shell-extension-fly-pie-12'
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├───gnome-shell-extension-pop-shell: package 'gnome-shell-extension-pop-shell-unstable-2021-11-30'
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├───libcs50: package 'libcs50-10.1.1'
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├───llama: package 'llama-1.0.2'
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├───neo: package 'neo-0.6'
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├───pop-launcher: package 'pop-launcher-1.1.0'
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├───pop-launcher-plugin-duckduckgo-bangs: package 'pop-launcher-plugin-duckduckgo-bangs-1.3.0'
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├───sioyek: package 'sioyek-1.0.0'
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└───tic-80: package 'tic-80-unstable-2021-12-18'
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#+end_example
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- =defaultPackage.${system}.${package}= (or =packages.${system}.${package}=) is mainly expected for packages.
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This allows for easy building — e.g., =nix build nixpkgs#hello= will refer to =defaultPackage.${system}.hello=.
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Another command that expects this is =nix run ${PACKAGE}= (e.g., =nix run nixpkgs#hello=).
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- =nixosConfigurations.${host}= is a NixOS host configuration.
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Each attribute contain a set similar to the traditional set from =/etc/nixos/configuration.nix=.
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This is very beneficial for quickly installing only with flakes — e.g., =nixos-install --flake github:foo-dogsquared/nixos-config#zilch= will install with =nixosConfigurations.zilch=.
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However, attributes should be created with =lib.nixosSystem= from =nixpkgs= flake.
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- =nixosModules.${module}= is a [[roam:NixOS modules]], allowing you to extend NixOS further.
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These are expected to be similar NixOS modules from nixpkgs.
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- =templates.${name}= is a template that has the attribute =path= and =description=.
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See [[Flake templates]] for more details about how it's used.
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- =devShell.${system}= is expected to be a derivation (mostly with =mkShell=).
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This is the default development environment to be used.
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This is mostly expected for projects providing an easy way to bootstrap for development (e.g., with =nix develop ${FLAKE}=).
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- =devShells.${system}.${name}= is an attribute set of derivations (mostly from =mkShell=).
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This is similar to =devShell= except this is where =nix develop= subcommand finds if an attribute name is given.
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* Flake templates
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- Flakes can have templates to get started with.
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They can be used with =nix flake init ${TEMPLATE}=.
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- You can export it in your flakes through the =templates= attribute. =templates= is expected to be an attribute set with each attribute representing a template.
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- By default, we have the =templates= flake from the global registry pointed to [[https://github.com/NixOS/templates][NixOS/templates]] Git repo.
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* Nix registry
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Per the Nix manual:
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#+begin_quote
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Flake registries are a convenience feature that allows you to refer to flakes using symbolic identifiers such as =nixpkgs=, rather than full URLs such as =git://github.com/NixOS/nixpkgs=.
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#+end_quote
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Here's an example of the registry list with some overriden flakes such as the =nixpkgs= flake following from my [[https://github.com/foo-dogsquared/nixos-config][NixOS configuration]].
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#+begin_src shell :cache yes
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nix registry list
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#+end_src
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#+results[2e793be4dcc8dcc2f0c921da5dffa1544455d14e]:
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#+begin_example
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system flake:agenix path:/nix/store/yka795vkb7ny5fnybf8dafbypcjfmi9n-source?lastModified=1638837456&narHash=sha256-WHLOxthAGx%2fwXw3QUa%2flFE3mr6cQtnXfFYZ0DNyYwt4=&rev=57806bf7e340f4cae705c91748d4fdf8519293a9
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system flake:config path:/nix/store/3nlagaj6748w4ffxx4vp5jss2k571f8i-source?lastModified=1640442672&narHash=sha256-Gkt2On9szrFlOo6QiYMOA90qTp4PICd7STHFhGA4bCs=
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system flake:home-manager path:/nix/store/ijh6v700kpssfyw44v4awbm2gmjx26qs-source?lastModified=1640296831&narHash=sha256-Mu32vTcfZru4VrvgnpvQKmwC4uY0oF3vnnC2o9SgnRU=&rev=f15b151ca1c4aea23515c241051d71f1b5cf97c8
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system flake:nixpkgs path:/nix/store/lgfhg4n6445yizgf0xjirb4bc4j86fr9-source?lastModified=1640269308&narHash=sha256-vBVwv3+kPrxbNyfo48cB5cc5%2f4tq5zlJGas%2fqw8XNBE=&rev=0c408a087b4751c887e463e3848512c12017be25
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global flake:agda github:agda/agda
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global flake:blender-bin github:edolstra/nix-warez?dir=blender
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global flake:dreampkgs github:nix-community/dreampkgs
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global flake:dwarffs github:edolstra/dwarffs
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global flake:fenix github:nix-community/fenix
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global flake:flake-utils github:flake-utils/numtide
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global flake:gemini github:nix-community/flake-gemini
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global flake:home-manager github:nix-community/home-manager
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global flake:hydra github:NixOS/hydra
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global flake:mach-nix github:DavHau/mach-nix
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global flake:nimble github:nix-community/flake-nimble
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global flake:nix github:NixOS/nix
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global flake:nixops github:NixOS/nixops
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global flake:nixos-hardware github:NixOS/nixos-hardware
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global flake:nixos-homepage github:NixOS/nixos-homepage/flake
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global flake:nur github:nix-community/NUR
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global flake:nixpkgs github:NixOS/nixpkgs/nixpkgs-unstable
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global flake:templates github:NixOS/templates
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global flake:patchelf github:NixOS/patchelf
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global flake:nix-serve github:edolstra/nix-serve
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global flake:nickel github:tweag/nickel
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#+end_example
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So how does a flake registry work?
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- It is managed through =nix registry= subcommand or set =nix.registry= in your system configuration.
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- Registries are primarily written as JSON files in certain files (e.g., =$XDG_CONFIG_HOME/nix/registry=, =/etc/nix/registry.json=).
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For more information, see the [[https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-registry.html#registry-format][registry format from the manual]].
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Unlike the traditional Nix channels, the inclusion of arbitrary files and their locations doesn't seem to affect the reproducibility since it is mostly used as a convenience feature after all.
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- The flakes from default registry are mostly getting the latest revisions of the flake per invocation so it is best practice to pin them (e.g., =nix registry pin=, through =nix.registry= while setting the NixOS systems in =flake.nix=).
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- There are primarily three registries to worry about: user, system, and global.
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- This is also the reason it downloads something why each time you invoke a Nix-related command (e.g., =nix search=, =nix edit=).
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[fn:: I think pinning the flakes from the global registry will simply resolve this issue.]
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* More information about flakes
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- We can modify our inputs.
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In the above example, we made =home-manager= to use our version of =nixpkgs= which will make it easier to sync.
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