Nix

There is a way as was mentioned by @matrss in @distribits 2024 chat discussions, where on the example of https://atris.fz-juelich.de/m.risse/datalad-nix-demo/src/branch/main/flake.nix#L5 where for ` nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";` @matrss elaborates:

> Yes, you can also specify a specific commit hash (but I think it would be called `rev=` then, instead of `ref=`, it's documented here: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#flake-references). Of course it also doesn't have to be github, it can be gitlab or any git repository available over http, or even another local directory and stuff like that.
> I should add that nix flakes are still considered an experimental feature (but it has been working well for a long time now). All of this can be done with non-experimental nix as well, but it is a bit less standardized what it would look like.

Start by reading the linked flake.nix example at line 5 and the Nix flake reference documentation cited in the discussion. The issue does not specify what change to make or what completion should look like, so its scope and acceptance criteria need to be clarified first.

Written by the indexing model from the issue text.