nix-buffer: nix-shell in Emacs

Shea Levy has a wonderful package out for users of Nix and Emacs. It’s called nix-buffer and it greatly improves working on Nix stuff in Emacs. To try it just get it from MELPA by running M-x package-install<RET>nix-buffer.

To use it in a project you need to create a new file in your project directory called dir-locals.nix. It works a lot like .dir-locals.el but it allows you to evaluate Nix expressions.

To setup, just create dir-locals.nix that looks like this:

let pkgs = import <nixpkgs> {};
in with pkgs; nixBufferBuilders.withPackages [ … ]

You can put anything from Nixpkgs inside of withPackages. That path is added to your exec-path in Emacs. Using this you can wrap your project in a container and avoid conflicts between project configurations!

There’s lot of future extensions for this. Ideally we could skip and the dir-locals.nix configuration and automatically detect what dependencies you need based on your default.nix file.