Unclear at what level you're asking, but Mitchell's comment identified it as a nix-darwin feature, and you can see how he's using it in the config he linked at https://github.com/mitchellh/nixos-config/blob/b73a16fc918c5...

nix-darwin supports managing your Brewfile.

The docs[2] are very helpful!

[1]: https://github.com/Homebrew/homebrew-bundle

[2]: https://daiderd.com/nix-darwin/manual/index.html#opt-homebre...

Here's my flake that does it: https://github.com/dustinlyons/nixos-config/blob/main/flake....