I was wondering, what is the most painless way to get started with multiple elixir/erlang versions on nixos?
I’ve tried to install asdf, however when it comes to compiling OTP, I cannot configure correctly the dependencies required by OTP when building it from source, I am more than positive that the packages I’m using are the incorrect ones.
I also have zero idea how things like flakes, home-manager works (and I don’t have them set up yet), so it would be great to get a turnkey solution for the time being, until I get my head around all the concepts of nix.
You’ll have to enable flakes, but you can also do that temporarily by passing a cli argument as described here: https://nixos.wiki/wiki/flakes
I believe the following should work:
Inside your project directory run nix --experimental-features 'nix-command flakes' flake init --template github:c4710n/nix-dev-templates#elixir
Then you can change your version in flake.nix, you can search for available versions here: NixOS Search
Then run nix --experimental-features 'nix-command flakes' develop and you should have your version available.
I’m not sure about the enabling flakes temporarily part, so I hope that works.
Edit: It could be that the updated version is not picked up by nix because the old version is still in flake.lock, or when it’s not staged in git. I think I remember running into this at some point.
Once you exit the shell erlang_25 goes aways and everything is cleaned up. nix-shell is great to try different kind of software without messing anything up. You can find all the packages here https://search.nixos.org
Setting up erlang/elixir dev environments
To make the versions you use more convenient and bundle up other pieces of software I setup shell development environments.
Lets explore:
Create your project directory $ mkdir ~/tmp/g
Create a shell.nix file with content below
Enable shell environment with $ nix-shell
My standard simple shell.nix file for erlang/elixir development looks like this:
with import <nixpkgs> {};
let
basePackages = [
erlang_26
elixir_1_15
lexical
inotify-tools
];
PROJECT_ROOT = builtins.toString ./.;
## Hooks are not necessary but make things more convenient.
hooks = ''
mkdir -p .nix-mix
mkdir -p .nix-hex
export MIX_HOME=${PROJECT_ROOT}/.nix-mix
export HEX_HOME=${PROJECT_ROOT}/.nix-hex
export PATH=$MIX_HOME/bin:$PATH
export PATH=$HEX_HOME/bin:$PATH
export LANG=en_NZ.UTF-8
export ERL_AFLAGS="-kernel shell_history enabled"
'';
in mkShell {
buildInputs = basePackages;
shellHook = hooks;
}
I put this shell.nix file in the root of my project directory. I can the cd into the dir and run nix-shell
$ cd ~/tmp/g
$ nix-shell
$
And I have access to all the tools listed in the basePackages.
I am generally happy with using the erlang versions that come with NixOS. However, I often want to run a newer elixir version. Please look at the following shell.nix file for building elixir from github.
with import <nixpkgs> {};
## OVERCOURSE. The above statements uses Nix Channels and the channel named nixpkgs.
## If this channel is updated then your versions might change. This is one of the reasons I think
## flakes were introduced.
## However. If you want to pin your packages to a specific version of the nix repository then you can do it like
## This:
# # pkgs = import (builtins.fetchTarball {
## url = "https://github.com/NixOS/nixpkgs/archive/23c10dbe320e6957f2607d8a22f9e0e36f56a235.tar.gz";
## }) {};
## Once you get the hang of things I would recommend you to do this. Then it means, whoever uses your `shell.nix` file be it now or in the future will have the exact same setup.
let
# First I specify which beam packages base package I want to use to
# base my overrides on. In this case erlang_27
packages = beam.packagesWith beam.interpreters.erlang_27;
# Then I override the elixir package by fetching from github.
# If you try with a new version, make sure to change the sha256 slightly
# otherwise nix is "smart" enough to pick up the version which matches the hash
elixir = packages.elixir.overrideAttrs(old: {
name = "elixir-1.17.2";
src = fetchFromGitHub {
rev = "v1.17.2";
sha256 = "sha256-8rb2f4CvJzio3QgoxvCv1iz8HooXze0tWUJ4Sc13dxg=";
owner = "elixir-lang";
repo = "elixir";
};
});
# And often I also want to compile elixir-ls with the new elixir version
elixir_ls = packages.elixir-ls.override {
elixir = elixir;
mixRelease = packages.mixRelease.override { elixir = elixir; };
};
# Then I specify my development packages
basePackages = [
elixir
elixir_ls
lexical
packages.erlang
];
PROJECT_ROOT = builtins.toString ./.;
hooks = ''
mkdir -p .nix-mix
mkdir -p .nix-hex
export MIX_HOME=${PROJECT_ROOT}/.nix-mix
export HEX_HOME=${PROJECT_ROOT}/.nix-hex
export PATH=$MIX_HOME/bin:$PATH
export PATH=$HEX_HOME/bin:$PATH
export LANG=en_NZ.UTF-8
export ERL_AFLAGS="-kernel shell_history enabled"
'';
in mkShell {
buildInputs = basePackages;
shellHook = hooks;
}
For a setup with a separate postgresql database per project please check out the answer here:
I am a big fan of NixOS. WIth the development shells it makes it so easy for me to setup nearly all my projects development requirements and it has saved me so much time over the years I have been using it. And they just keep on working!
Sorry for the dumb question, but what is the difference between flake and nix-shell? I see people using either one or the second and I don’t fully understand the difference between them.
In my case I usually care about the opposite, there are a lot of times when I need a very specific OTP version, for example 26.2.5.4. Is it possible to do the same with erlang dependency as you did with the elixir one?
Yes, it is a bit unfortunate. From my understanding they are two different ways to do the same thing. I am sure flakes are great but I haven’t explored them much so cannot give any assistance regarding them.
nix-shell is the standard (or perhaps old?) way of specifying development shells. Flakes can also specify development shells but they can also do much more.
I should mention that my instructions above requires a channel named nixpkgs on your system. This is the default if you install nixos but if you have configured flakes for your system, the shell.nix might need to be adapted.
Yes. You should be able to do the same as well as modifying compiler flags if that is necessary. I had a quick look at the package so I think it should be enough to substitute elixir for version and then specify the correct revision, owner and repo in the src override.
Completely untested and more what I would try first:
I managed to get the project up and running using the sample shell.nix config, it is great how easy that was and how it worked out of the box. It will take some time to setup the language server (as I want to use elixir-ls), but having the initial configuration that works is the core thing I was searching for hours and couldn’t find.
For now I will stick to nix-shell, as it works and I actually understand at least partly what is going on there , but this doesn’t mean that @joelpaulkoch 's answer is not valid too, maybe I will try it later when I will have more time.
To keep maximum visibility for other people searching for this too I will leave both answers in this post and mark this post as the correct answer:
, but this doesn’t mean that 
