With a flake-parts flake

Suppose you have a flake-parts enabled flake that looks like:

{
  inputs = { # (A) So much inputs
    nixpkgs.url = "github:nixos/nixpkgs/unstable";
    flake-parts.url = "github:hercules-ci/flake-parts";
    foo.url = "github:coolguy/foo";
    bar.url = "github:coolguy/bar";
  };
  outputs = inputs:
    inputs.flake-parts.lib.mkFlake { inherit inputs; }
      # (B) flake-parts entry-point module.
      { systems = [ "aarch64-darwin" ]; ...  };
}

Your flake is already modular (in this case flake-parts modules), so your migration path is smoother here.

Split `flake.nix` in two

First step is moving the (B) flake-parts entry-point module outside of the flake.nix file into modules/default.nix.

{
  imports = [ ./inputs.nix ];
  systems = [ "aarch64-darwin" ];

  ...  # same code as before
}

Second is also moving the (A) inputs into ./modules

# This is now real Nix code, use let bindings, { lib, ... } etc.
# best practice is to split this inputs.nix into other modules
{
  flake-file.inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/unstable";
    flake-parts.url = "github:hercules-ci/flake-parts";
    # all your other inputs
  };
}

Boostraping using `./modules`

And now, lets replace flake.nix using bootstrapping magic step:

nix-shell https://github.com/vic/flake-file/archive/main.tar.gz \
  -A flake-file.sh --run write-flake \
  --arg modules ./modules --argstr outputs flake-parts

See also: all bootstrap command args

Run the same command whenever your input changes and they will be reflected into the static flake.nix.

Enabling `.#write-flake` app.

Edit ./modules/inputs.nix module to add in-flake flake-file.

 { inputs, lib, ... }: # resolved flake inputs as specialArgs
  {
    # same inputs code as before
    flake-file.inputs = {

      # make sure you add flake-file dependency.
     flake-file.url = lib.mkDefault "github:vic/flake-file";
    };

    imports = [
       # enable inside-flake and say goodbye to bootstrap
      inputs.flake-file.flakeModule

       # start splitting from inputs.nix into other files
    ];

    # generate the same output function we used at bootstrap
   flake-file.outputs = "flake-parts";
  }

Your flake is flake-file enabled

Commands for your daily life:

nix run .#write-flake # whenever you need to regen flake.nix

nix flake check # will make sure your flake.nix is up-to-date

Contribute Community Sponsor

With a flake-parts flake

Split flake.nix in two

Boostraping using ./modules

Enabling .#write-flake app.

Your flake is flake-file enabled

Split `flake.nix` in two

Boostraping using `./modules`

Enabling `.#write-flake` app.