An Earthfile for installing and using Nix development shells

Nix is a popular package manager which boasts tens of thousands of packages. When combined with development shells, it provides reproducible development environments where dependencies can be easily identified and pinned.

Earthly provides a friendly UX on top of Docker and Buildkit. It allows defining targets (similar to make) which can be executed the same locally as they are in CI. Additionally, with Earthly satellites, caching is given first-class treatment resulting in a significant decrease in build times.

Why combine the two? Development shells are unmatched in terms of developer productivity, especially across large teams. However, utilizing them requires installing Nix on your local system, which can be very intrusive. By encapsulating the Nix development shell into Earthly, it's possible to gain the benefits of clearly identifying/locking development dependencies with very little modification of local systems (just Docker running and the Earthly CLI installed).

The additional layer of isolation provided by Earthly also makes it much easier to reason about what is going on in CI. The CI systems simply invoke Earthly targets which will run in the exact same manner as they would locally. With Earthly satellites, the whole process can be lifted to hosted runners with first class support for caching.

This repository provides two things:

1. A base image (debian slim) which installs the latest version of Nix
2. A UDC which loads the default development shell from a flake.nix

Additionally, it presumes the following structure in your local repository:

• nix/**
• flake.nix
• flake.lock

Where nix/** is a directory where dependent nix code is located. The UDT will automatically copy these files into the container and load the default development shell.

A typical Earthfile might look like:

VERSION 0.7

nix:
    FROM github.com/jmgilman/earthly-nix+nix
    DO github.com/jmgilman/earthly-nix+SETUP

test:
    FROM +nix
    RUN with_nix treefmt

In the first target, we inherit from the nix target which contains all of the Nix tooling. After that, we call the SETUP UDC which loads the default development shell from your local repository. Finally, it writes a with_nix script which can be used for calling nix dependencies. In the above example, we call the treefmt CLI which was supplied by our development shell.

Building with Nix is still very much possible. The benefit that Earthly provides is not requiring a Nix installation on your local system. For solo developers using Nix, the extra layer might not make sense. Where it excels is in an open-source project where external contributors might not be interested in setting up Nix.