View source for Flake Compat

[https://github.com/edolstra/flake-compat Flake Compat] is a compatibility layer for Nix [[Flakes]] that lets projects written in the old style Nix (<code>default.nix</code> and <code>shell.nix</code>) use inputs and outputs from flake style Nix setups.

The flake-compat library downloads the inputs of the flake, pass them to the flake’s <code>outputs</code> function and return an attribute set containing <code>defaultNix</code> and <code>shellNix</code> attributes. The attributes will contain the output attribute set with an extra <code>default</code> attribute pointing to current platform’s <code>defaultPackage</code> (resp. <code>devShell</code> for <code>shellNix</code>).

= Usage =

To integrate flake-compat into a project, place the following into <code>default.nix</code> (for <code>shell.nix</code>, replace <code>defaultNix</code> with <code>shellNix</code>) to use the shim:

{{file|default.nix|nix|
<nowiki>
(import
  (
    let
      lock = builtins.fromJSON (builtins.readFile ./flake.lock);
      nodeName = lock.nodes.root.inputs.flake-compat;
    in
    fetchTarball {
      url = lock.nodes.${nodeName}.locked.url or "https://github.com/edolstra/flake-compat/archive/${lock.nodes.${nodeName}.locked.rev}.tar.gz";
      sha256 = lock.nodes.${nodeName}.locked.narHash;
    }
  )
  { src = ./.; }
).defaultNix
</nowiki>
}}

Then in your <code>flake.nix</code>, add <code>flake-compat.url = "github:edolstra/flake-compat";</code> to your inputs.

== Example usage ==

An example flake.nix that packages a simple shell script:

{{file|flake.nix|nix|
<nowiki>
{
  description = "A very basic flake";
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
    flake-compat.url = "github:edolstra/flake-compat";
  };
  outputs = { self, nixpkgs, flake-compat }:
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs { inherit system; };
    in {
      packages.x86_64-linux.hello = pkgs.stdenv.mkDerivation {
        pname = "hello";
        version = "1.0";
        src = ./hello.sh;
        unpackPhase = "true";
        installPhase = ''
          mkdir -p $out/bin
          cp $src $out/bin/hello
          chmod +x $out/bin/hello
        '';
      };
      packages.x86_64-linux.default = self.packages.x86_64-linux.hello;
    };
}
</nowiki>
}}

The shell script being packaged:

{{file|hello.sh|nix|
<nowiki>
#!/usr/bin/env sh

echo "Hello"
</nowiki>
}}

With this setup, running <code>nix run</code> will build and execute the flake as expected. When using flake-compat, it becomes possible to run traditional commands like <code>nix-build</code> which will return a derivation using the flake’s output definitions.

[[Category:Flakes]]