A compatibility shim to use Nix flakes with versions of Nix that don't have native flake support.

Given a source tree containing flake.nix and flake.lock, it fetches the flake inputs and calls the flake's outputs function. This allows you to use flake-based projects with:

• Stable Nix without experimental-features = nix-command flakes
• Nix versions before 2.4 (insecure, please upgrade)
• Tooling that doesn't support flakes natively

The flake-compat function returns

• defaultNix for use in default.nix,
• shellNix for shell.nix) attributes,
• outputs for simple access to the flake outputs.

This project was originally at edolstra/flake-compat and is now maintained at NixOS/flake-compat.

To use, add the following to your flake.nix:

inputs.flake-compat = {
  url = "github:NixOS/flake-compat";
  flake = false;
};

Afterwards, create a default.nix file containing the following:

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

If you would like a shell.nix file, create one containing the above, replacing defaultNix with shellNix.

You can access any flake output via the outputs attribute returned by flake-compat, e.g.

(import ... { src = ./.; }).outputs.packages.x86_64-linux.default

Improvements are welcomed. Some tips to make that a success:

• Check the issue tracker.

• Chat in the Nix Package Manager development matrix channel.

• We're writing a test suite, tests.nix. Science shows that PRs with tests are more likely to be merged!

• Update the documentation.

flake-compat is part of the Nix/NixOS community, which is supported by the NixOS Foundation.

Here's how you can help out financially.