If you’re looking for a way to add custom components to your Home Assistant setup, then NixOS has a good solution. NixOS is an open source Linux distribution that is designed to be functional. This can be a good alternative to have a more declarative configuration in contrast to HACS.

WARNING

This approach stopped working in NixOS 23.11, take a look at Home Assistant: Adding a custom_component in NixOS - revisited for a new and more native approach.

I’m using the hultenvp/solis-sensor HA component as an example here.

First of all declare a package

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{ stdenv, pkgs, fetchFromGitHub }:

stdenv.mkDerivation rec {
  name = "ha-solis-sensor";
  src = fetchFromGitHub {
    owner = "hultenvp";
    repo = "solis-sensor";
    rev = "v3.3.2";
    sha256 = "uPGqK6qyglz9aIU3iV/VQbwXXsaBw4HyW7LqtP/xnMg=";
  };

  
  installPhase = ''cp -a custom_components/solis $out'';
}

This package setup is very basic, it uses fetchFromGitHub to retrieve the latest release. We can retrieve the sha256 hash using the following cli nix-shell -p nix-prefetch-github --run "nix-prefetch-github --rev v3.3.2 hultenvp solis-sensor" which fetches the git repo, and figures out the sha256 of the repo.

By default the nix package will run make install to install to the correct location, however since we just want to copy the right files we can override this:

installPhase = ''cp -a custom_components/solis $out'';

Import the package

Home Assistant expects custom packages to be installed under /var/lib/hass/custom_components/{component_name}.

We can leverage an activationScript to install and symlink the package:

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  system.activationScripts.ha-solis.text = ''
    mkdir -p "/var/lib/hass/custom_components"
    ln -sfn "${(pkgs.callPackage ./apps/ha-solis-sensor.nix {})}" "/var/lib/hass/custom_components/solis"
  '';

We directly use callPackage to make sure it’s available, this will behind the scenes download and install the package in the nix store under /nix/store. Do note the ln -sfn, otherwise we won’t overwrite the symlink but add it to the directory.

Conclusions

Finally we apply our config using nixos-rebuild switch and we reload Home Assistant.

Your Home Assistant custom_component is now ready for use.

Part 2

In Part 2 we will take a look at adding an extra dependency which hasn’t been packed yet. ) we will take a look at adding an extra dependency which hasn’t been packed yet.

In the future

In the future this functionality will likely be fully integrated in the Home Assistant NixOS module, see the following PR NixOS/nixpkgs/pull/160346.