❯ nix run github:fzakaria/nix-auto-follow -- --help
usage: auto-follow [-h] [--in-place] [filename]

Update nix flake.lock file to autofollow.

positional arguments:
  filename        The path to the flake.lock file.

options:
  -h, --help      show this help message and exit
  --in-place, -i  Write the output back to the same file.

A (python) script to achieve automatically following all flake inputs for Nix.

If you have used Nix flakes, you likely encountered something like this 🤢

std.url = "github:divnix/std";
std.inputs.devshell.follows = "devshell";
std.inputs.nixago.follows = "nixago";
std.inputs.nixpkgs.follows = "nixpkgs";

hive.url = "github:divnix/hive";
hive.inputs.colmena.follows = "colmena";
hive.inputs.disko.follows = "disko";
hive.inputs.nixos-generators.follows = "nixos-generators";
hive.inputs.nixpkgs.follows = "nixpkgs";

Why is this follows necessary?

It's in fact not necessary but it makes the Nix evaluation simpler.

Rather than using the exact Nix flake commit your dependency desires, we are overriding it, with one we have likely already declared.

This has the effect of making our graph smaller, which is faster to evaluate and likely build.

Note: Although it's faster it's less correct since we are deviating from what the authors of the flake desired.

Writing all those follows can get real teadious, and it's tough to even know you did it all... surely there has to be a better way!

There is with this script 🥳

Simply run the script which will modify your flake.lock file. Commit the change and voila!

❯ auto-follow -i

The auto-follow tool includes a check mode ; so that you can validate you are correctly following everything.

❯ auto-follow -c
All ok!

This will fail (exit code 1) if not everything can be deduped.

❯ auto-follow -c
Node a has input nixpkgs pointing to nixpkgs_2 which is not the same as b's nixpkgs which is nixpkgs_3 in the lockfile.
Please add 'nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11"' or 'nixpkgs.url = "github:nixos/nixpkgs/nixos-23.05'

Note: This can still happen even after modifying your lock file. The reason for this is that if the top-level Nix expression (your application flake.nix) does not include all possible flakes, then there is no way for us to know which of the two choices we should consolidate to. The tool prints a friendly message showing some of the possible options to select amongst.

Running the development shell should drop you into a shell with all the required dependencies and the editable installation already done.

❯ nix develop