Hooks

Overview

flake-file provides two hook lists:

• flake-file.write-hooks — commands executed after write-flake writes flake.nix.
• flake-file.check-hooks — commands executed during nix flake check.

Each hook is an attrset with an index (for ordering) and a program: a function from pkgs to a derivation with meta.mainProgram, such as one built by pkgs.writeShellApplication.

write-hooks

Use write-hooks to trigger follow-up actions whenever flake.nix is regenerated — for example, updating a lock file or reformatting.

Write hooks run from the flake root with no arguments.

{
  flake-file.write-hooks = [
    {
      index = 10;
      program =
        pkgs:
        pkgs.writeShellApplication {
          name = "update-lock";
          runtimeInputs = [ pkgs.nix ];
          text = "nix flake update";
        };
    }
  ];
}

Hooks run in ascending index order, so you can coordinate between modules without knowing the full list.

check-hooks

Use check-hooks to add extra validation during nix flake check — for example, checking that a derived file is up to date.

Check hooks receive a copy of the flake root containing only the files listed in flake-file.check-files (default: flake.nix and flake.lock), so that commits touching other files keep the check cacheable. Add any file your hook reads:

{ flake-file.check-files = [ "flake.nix" "flake.lock" "generated/inputs.nix" ]; }

Check hooks run inside the check derivation and receive the path of the flake root as their first argument.

{
  flake-file.check-hooks = [
    {
      index = 10;
      program =
        pkgs:
        pkgs.writeShellApplication {
          name = "lint";
          runtimeInputs = [ pkgs.my-linter ];
          text = ''my-linter --check "$1"'';
        };
    }
  ];
}

Practical uses

• Run nix flake update automatically after regeneration.
• Reformat flake.nix with a formatter (see flake-file.formatter).
• Validate generated files in CI via check-hooks.
• Trigger allfollow or nix-auto-follow to flatten the lock file.