Configuring Aspell with Custom Dictionaries in Nix

Updates Since 2016 Link to heading

Configuration Method Changes:

• packageOverrides deprecated in favor of overlays (still works but generates warnings)
• User config location changed from ~/.nixpkgs/config.nix to ~/.config/nixpkgs/config.nix
• Home Manager integration now preferred for user-level package management

Modern Nix Ecosystem:

• Flakes widely adopted for reproducible configurations
• nix-env discouraged in favor of declarative approaches
• New Nix commands available (nix profile, nix shell)

Technical Updates:

• aspellWithDicts function remains stable and unchanged
• Dictionary packaging and availability unchanged
• Environment variable handling (ASPELL_CONF) remains the same

Recommended Modern Approach:

• Use Home Manager for user-level package management
• Consider flakes for project-specific environments
• Use overlays instead of packageOverrides
• Replace nix-env with declarative configuration

This setup ensures reliable spell checking across your development tools while maintaining the reproducibility that makes Nix powerful for development environments.

The following is the original post content with some updates to the writing style to (hopefully) make it easier to read:

Need spell checking in your development environment? Here’s how to configure aspell dictionaries through Nix for tools like flyspell in Emacs or Spacemacs.

Configuration Approaches Link to heading

You can configure aspell dictionaries in three ways:

System Level Configuration Add aspell to your NixOS system configuration for server deployments or multi-user systems.

User Level Configuration Install through your user profile for development machines and portable configurations.

Environment Variable Method Set ASPELL_CONF with the dict-dir path in your shell configuration.

For development environments, user-level configuration works best. It keeps system configuration minimal while allowing you to copy your setup to remote development machines.

User Level Nix Setup Link to heading

Create or modify ${HOME}/.config/nixpkgs/config.nix with your aspell configuration:

{ pkgs }:
let
  inherit (pkgs) aspellWithDicts buildEnv;

  # Configure aspell with desired dictionaries
  myaspell = aspellWithDicts (d: [d.en]);
  # Add more dictionaries: [d.en d.es d.fr]
in {
  allowUnfree = true;

  packageOverrides = pkgs: rec {
    myDevenv = buildEnv {
      name = "my-devenv";
      paths = with pkgs; [
        mtr
        tcpdump
        inetutils
        
        # Your custom aspell configuration
        myaspell
      ];
    };
  };
}

Testing the Configuration Link to heading

Install and verify your custom aspell setup:

$ nix-env -i myaspell

$ env | grep ASPELL
ASPELL_CONF=dict-dir /home/username/.nix-profile/lib/aspell

$ ls "$(readlink -f ~/.nix-profile/lib/aspell)/en_US*"
/nix/store/...-aspell-env/lib/aspell/en_US.multi
/nix/store/...-aspell-env/lib/aspell/en_US-variant_0.multi
/nix/store/...-aspell-env/lib/aspell/en_US-wo_accents-only.rws

$ aspell list <<<"some words one of which will be mispelledk"
mispelledk

Modern Overlay Alternative Link to heading

For newer nixpkgs versions, consider using overlays instead of packageOverrides:

{
  nixpkgs.overlays = [
    (self: super: {
      myaspell = super.aspellWithDicts (d: [d.en]);
    })
  ];
}

Key Benefits Link to heading

Reproducible Development Environment Your aspell configuration follows you across machines and survives system rebuilds.

Portable Configuration Copy your config.nix to any Nix-enabled system for consistent spell checking.

Isolation from System Changes User-level configuration won’t break when system packages change.

This setup ensures reliable spell checking across your development tools while maintaining the reproducibility that makes Nix powerful for development environments.