Developing an Elixir Phoenix application

In this tutorial, you will learn how to add flake.nix to an Elixir Phoenix project.

Initialize a new project

Note

If you are adding flake.nix to an existing project, you can skip this section.

1. Make mix executable available:

   nix shell nixpkgs#elixir

2. Install the scaffolder for Phoenix using mix archive.install command. You need to do this only once per machine:

   mix archive.install hex phx_new

3. Use mix phx.new to scaffold a new project with your preferred options:

   mix phx.new 'your_new_project' --no-ecto

   Tip

   Phoenix provides various options for initializing a project. Check out the help:

   mix help phx.new

4. Enter the directory:

   cd 'your_new_project'

Add flake.nix to the project

1. Initialize the template from the root directory of the project:

   nix flake init -t github:akirak/flake-templates#elixir-app

2. Open flake.nix and choose the BEAM package set and Elixir version:

   let
     # Select the Erlang/OTP package set from nixpkgs
      beamVersion = "beam27Packages";
      beamVersion = "beam28Packages";
     # Set the Elixir version
      elixirVersion = "elixir_1_19";
      elixirVersion = "elixir_1_20";
   in

   The template maintains Erlang and Elixir versions through nixpkgs BEAM packages:

   • beamVersion selects a BEAM package set such as beam28Packages. erlang is taken from that package set, so the exact Erlang/OTP release is maintained by the pinned nixpkgs revision in your flake.lock.
   • elixirVersion selects the Elixir package from the same BEAM package set, such as elixir_1_20.

   When you update nixpkgs, the concrete patch versions of Erlang and Elixir can change even if these attribute names stay the same. To move to a newer major Erlang line, update beamVersion. To move to a newer Elixir release, update elixirVersion to an attribute available in that BEAM package set.

3. Add .envrc:

   use flake

4. Allow direnv:

   direnv allow

Switch the language server

Lexical is the default language server for Elixir, but you can change it to a different one:

[
  erlang
  elixir
  # You are likely to need Node.js if you develop a Phoenix
  # application.
  nodejs
  # Add the language server of your choice.
  inputs.lexical.packages.${system}.default
  elixir-ls
  # I once added Hex via a Nix development shell, but now I install
  # and upgrade it using Mix. Hex installed using Nix can cause an
  # issue if you manage Elixir dependencies using Mix.
]