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dependency-management.md

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Managing your dependencies with Organist

Organist can be used to manage your development dependencies, and the whole environment.

Getting started

After running nix flake init, you should end-up with a project.ncl looking like:

let inputs = import "./nickel.lock.ncl" in
let organist = inputs.organist in

organist.contracts.OrganistExpression
& {
  Schema,
  config | Schema = {
    shells = organist.shells.Bash,

    shells.build = {
      packages = {},
    },

    shells.dev = {
      packages.hello = organist.lib.import_nix "nixpkgs#hello",
    },
  },
} | organist.modules.T

This defines two variants of the shell: build and dev, both of which inherit from organist.shells.Bash (more precisely, build inherits from organist.shells.Bash.build and dev inherits from organist.shells.Bash.dev).

You can enter the dev shell by running nix develop or nix develop .#dev and the build shell with nix develop .#build.

Customizing the base shell

You can use a different base for your shell by replacing shells = organist.shells.Bash but something else, like shells = organist.shells.Rust. You can even depend on multiple ones at the same time with

  shells = organist.shells.Nickel,
  shells = organist.shells.Rust,

The merging system will take care of combining their definitions.

Adding new Nix dependencies

Beyond these predefined generic environments, you can also customize the shells by adding some extra dependencies to them in the packages attribute.

Most of the time, these packages will come from nixpkgs through the nix_import function.

You can find the packages you need on https://search.nixos.org.

Setting environment variables

The shell options also take an env setting that can be used to declare arbitrary environment variables to be set. For instance setting

shells.dev.env.FASTBUILD = 1,

will make sure that the dev shells will have the FASTBUILD environment variable set to 1.

These variables can also refer to Nix inputs by using the special nix-s%" "% [symbolic string]. For instance, if you want your dev environment to use jemalloc as its malloc implementation, you can hook it with:

shells.build.env.LD_PRELOAD = nix-s%"%{organist.import_nix "nixpkgs#jemalloc"}/lib/libjemalloc.so}"%

Exposed options

flake

  • flake | FlakeOutputs

The raw flake outputs that will be passed to Nix.

These should follow the Nix flake outputs schema.

shells

  • shells | OrganistShells

The shells that will be entered by nix develop.

build

  • build | nix.derivation.NickelDerivation

Build shell.

Only contains the required dependencies to build the project.

Can be entered with nix develop .#build.

default

  • default | nix.derivation.NickelDerivation

Default shell.

This is the shell that gets entered by nix develop without any argument.

Defaults to the dev shell.

dev

  • dev | nix.derivation.NickelDerivation

Development shell.

Contains everything needed to build and work on the project.

Can be entered with nix develop .#dev.