buck2-nix

NOTE: This repository is extremely experimental and may change radically. You probably don't want to be here unless you talk to me. Please see issue #1 for some design notes and feel free to provide input.

An experiment to integrate Buck2, Sapling, and Nix together in a harmonious way. Because this uses a pre-release Buck as well as our own Buck prelude to integrate with Nix, we're on our own.

You MUST have direnv installed. Everything else — including the correct tool versions — will be populated in your shell by direnv automatically when you move here.

There are some design notes in the buck/ directory. This is an experiment. Nothing is stable and everything is permitted. Do not taunt happy fun ball.

requirements

1. direnv installed into your shell
2. nix 2.14.0 or newer
3. trusted-users includes your $USER

direnv will warn you if either 2 or 3 are not satisfied when you move into this directory. See .envrc for details. The automated setup tool also warns you about these facts.

fully automated setup

Experiment: what if we used nix run as an "setup tool" to setup direnv and nix's configuration? In other words, use it to bootstrap the development environment? And what if I wrote it in Rust to learn more of it?

Run this command from your $HOME (or any directory, but it won't touch the current working dir):

nix run \
    --tarball-ttl 0 \
    --accept-flake-config \
    'github:thoughtpolice/buck2-nix?dir=buck/nix#setup'

This tool will set up everything to build this repository correctly, and (by default) clone a copy of the source code for you, under $HOME. I hope. The goal is that Nix along with the above command should be able to completely bootstrap your working environment. If it doesn't work, please let me know. Check out the source code under ./buck/nix/setup/

treading water

Assuming the setup tool worked with the default configuration to clone under $HOME:

cd $HOME/buck2-nix.sl

This will activate direnv automatically — assuming nothing exploded — and buck --version should now work. This early "bootstrap phase" is intended to be as lightweight as possible, with the minimal tooling needed for everything else to work; so only buck and other critical tools are installed into your shell environment at this point.

Now, build whole repo. The build is automatically configured (via flake configuration) to use my upstream binary cache — this is why you being a trusted user is so strongly emphasized, so it's fully automatic — to download all tools needed on demand.

buck build ... # equivalent to root//...

Much like how Nix works, in this design, Buck only commands Nix to downloads things as they're needed; e.g. rust-stable will only be downloaded through nix build the moment it's needed for a Buck rule, and a target using that rule was demanded. So if you only build one component of the repository, only a small subset of Nix paths are downloaded. This "lazy" design is a distinct difference from a typical direnv setup with Nix Flakes, which are "eager" to put things in your shell environment immediately.

And so, the very first time you run this, you'll see many Nix paths downloading into your store from the binary cache.

Now, clean buck-out/, then kill the buck2d daemon

buck clean

You can finally move out of the directory, and buck will go away:

cd $HOME