After reading a bunch of stuff on the internet of how to replace Homebrew with Nix, I decided to finally take the plunge. This post outlines my efforts to get up and running with the Nix package manager and Nix Darwin.

Installing Nix

Nix gives you two installation options; single user or multi-user. Let's go with the recommended multi-user install.

Executing the following

$ sh <(curl -L https://nixos.org/nix/install) --daemon

gives me the following output

...
Note: a multi-user installation is possible. See https://nixos.org/nix/manual/#sect-multi-user-installation

Installing on macOS >=10.15 requires relocating the store to an apfs volume.
Use sh <(curl https://nixos.org/nix/install) --darwin-use-unencrypted-nix-store-volume or run the preparation steps manually.
See https://nixos.org/nix/manual/#sect-macos-installation

Starting with macOS 10.15 (Catalina), the root filesystem is read-only. This means that /nix can no longer live on you system volume. Thankfully, there exists a workaraound for this. Instead of installing Nix using the command we just executed, we run 

$ sh <(curl https://nixos.org/nix/install) --darwin-use-unencrypted-nix-store-volume

This should create an unencrypted APFS volume for your Nix store and a "synthetic" empty directory to mount it over at /nix.

I actually had some trouble executing the script using curl and I didn't feel like finding out why so I decided to just wget it and then run it. Anyways. Progress.

     ------------------------------------------------------------------ 
    | This installer will create a volume for the nix store and        |
    | configure it to mount at /nix.  Follow these steps to uninstall. |
     ------------------------------------------------------------------ 

  1. Remove the entry from fstab using 'sudo vifs'
  2. Destroy the data volume using 'diskutil apfs deleteVolume'
  3. Remove the 'nix' line from /etc/synthetic.conf or the file
  ...

This installer will go on and ask for sudo password and do it's thing.

Installing Nix Darwin

Backup a few files first

$ sudo mv /etc/zprofile /etc/zprofile.orig
$ sudo mv /etc/nix/nix.conf /etc/nix/nix.conf.orig
$ sudo mv /etc/zshrc /etc/zshrc.orig

Install Nix Darwin

$ nix-build https://github.com/LnL7/nix-darwin/archive/master.tar.gz -A installer
$ ./result/bin/darwin-installer

During the installation, we're presented with some options.

Would you like edit the default configuration.nix before starting? [y/n] n
Would you like to manage <darwin> with nix-channel? [y/n] y
Would you like to load darwin configuration in /etc/bashrc? [y/n] y
Would you like to load darwin configuration in /etc/zshrc? [y/n] y
Would you like to create /run? [y/n] y

Nice. The installation finishes up and gives us some helpful instructions

    Open '/Users/martin/.nixpkgs/darwin-configuration.nix' to get started.
    See the README for more information: https://github.com/LnL7/nix-darwin/blob/master/README.md

    Don't forget to start a new shell or source /etc/static/bashrc.

Installing packages

Now that we have nix-darwin installed, we can start installing packages.

Vim

Naturally, I want to start by installing vim. Let's look for it

$ nix-env -qaP vim

The result of the query is

nixpkgs.vim  vim-8.2.0701

Alright. So I guess we just add it to our darwin-configuration.nix then.

  environment.systemPackages = [
    pkgs.vim
  ];

Save, run darwin-rebuild switch, and wait for the result. Once the installation finishes we should have Vim installed.

Depending on how your PATH is set up, and if you installed vim with homebrew, you might still be on your previous version. Go ahead and check

$ which vim
# Alt 1: /usr/local/bin/vim
# Alt 2: /run/current-system/sw/bin/vim

If you get something like Alt 1, you can run brew unlink vim and log in again. Run which vim again and you should get something that looks like the second path.

When I fired up Vim I quickly realized that the package wasn't compiled with +python3. In my personal vim setup I have a plugin that depends on that, so I needed to figure out how to solve that issue. After I did some digging around, I found that there's a Nix package callen vim_configurable that I could use.

To install a Vim with Python 3 support, we need to edit our darwin-configuration.nix a little bit.

{
  ...

  environment.systemPackages = [
    config.programs.vim.package
  ];

  ...

  programs.vim.package = pkgs.vim_configurable.override {
    python = pkgs.python3
  };

  ...
}

Now run

$ darwin-rebuild switch

again, and you should see Vim being compiled. This takes a while, but once it finishes up you have Vim working with +python3. Neat!

Moving the rest of the packages

Moving the rest of the packages should be a pretty straight-forward process. Up until now, I have used a Brewfile to keep inventory of all installed packages.

To update my Brewfile with everything that's installed using Homebrew, I run

$ brew bundle dump --force

Then I move packages from Homebrew into darwin-configuration.nix, as described in Sala Rahmainan's article.

Occasionally, I run

$ brew bundle cleanup --force

to remove any garbage left from uninstalled Homebrew packages.

References