Emacs

Emacs is a versatile and powerful software application, valued for its exceptional extensibility, allowing users to tailor the editor to their specific needs. It boasts an automatic self-documenting behavior, providing users with readily accessible information about functions, variables, and keybindings. The flexibility of Emacs enables it to adapt to various workflows and programming styles, while its syntax awareness enhances coding efficiency across multiple languages. Its extensive package repository surpasses many of its competitors, including Vim and its fork Neovim, making it one of the most customizable and feature-rich editors available.

For those seeking a more approachable entry point to the Emacs ecosystem, the Doom Emacs project offers a framework with a beginner-friendly default configuration. Doom Emacs comes pre-configured with popular modules for features such as IDE-like functionality, note-taking, and time management.

There is an official Matrix room for Nix/Emacs: #emacs:nixos.org.

Installation

Using nix-shell

nix-shell -p emacs

Using Global Configuration

environment.systemPackages = [
  pkgs.emacs
];

After modifying your configuration, apply the changes by running:

sudo nixos-rebuild switch

Using Home Configuration

home.packages = [ 
  pkgs.emacs 
];

After updating your configuration, apply the changes by running:

home-manager switch

Configuration

Note: Currently, configuring Emacs is possible by using Home Manager. A workaround for a global configuration is highlighted in the advanced section.

Basic

programs.emacs = {
   enable = true;
   defaultEditor = true;
};

Advanced

# Global Configuration
# Emacs is running as a daemon here, accesible via the "emacsclient" command
services.emacs = {
  enable = true;
  package = pkgs.emacs; 
};

# Home Configuration
programs.emacs = {
  enable = true;
  package = pkgs.emacs;  # replace with pkgs.emacs-gtk if desired
  defaultEditor = true;
  extraConfig = ''
    (setq standard-indent 2)
  '';
};

Tips and Tricks

Location of Options

The home manager options are defined in the following Home Manager Options Manual.

The global options are listed on MyNixOS.

Installing Packages

Tip

Emacs, much like NixOS can rebuild and re-fetch all of its packages based on its initialization file alone, if one chooses to use an extension called (use-package). Such a configuration file can be version controlled and used in all compatible operating systems.

One can mix and match whether Emacs packages are installed by Nix or Emacs. This can be particularly useful for Emacs packages that need to be built, such as vterm. One way to install Emacs packages through Nix is by the following, replacing emacsPgtkNativeComp with the variant in use:

environment.systemPackages = with pkgs;
[ ...
  ((emacsPackagesFor emacsPgtkNativeComp).emacsWithPackages (
    epkgs: [ epkgs.vterm ]
  ))
  ...
];

# To make the packages available to emacsclient, one can do the following:
services.emacs.package = with pkgs; (
  (emacsPackagesFor emacsPgtkNativeComp).emacsWithPackages (
    epkgs: [ epkgs.vterm ]
  )
);

# Some packages have characters like + that Nix considers a syntax error. 
# To fix this, write the package name in quotes and specify the package set, even if using with epkgs;. 
# For example, use epkgs."ido-completing-read+".

Tree-sitter

Emacs 29 supports Tree-sitter parsers when built with the --with-tree-sitter option. The emacsPackages.treesit-grammars fake package makes them accessible to Emacs when using emacs29.pkgs.withPackages:

{
  pkgs ? import <nixpkgs> { },
}:
pkgs.emacs29.pkgs.withPackages (epkgs: [
  (epkgs.treesit-grammars.with-grammars (grammars: [ grammars.tree-sitter-bash ]))
])

When using Emacs with tree-sitter support, it's recommended to install both epkgs.tree-sitter-langs and epkgs.treesit-grammars. While treesit-grammars handles the registration of grammars with Emacs's native tree-sitter interface, the actual grammar files will come from tree-sitter-langs. tree-sitter-langs being a MELPA package means it receives regular updates when new grammar versions are released, whereas the grammars in the tree-sitter-grammars package may lag behind in nixpkgs. The combination ensures you get both up-to-date grammars and proper integration with Emacs's built-in tree-sitter support.

Automatic Package Management

If you use use-package or leaf in your configuration, the community overlay can manage your Emacs packages automatically by using emacsWithPackagesFromUsePackage. First, install the overlay (instructions above), then add the following to your configuration.nix:

{
  environment.systemPackages = [
    (pkgs.emacsWithPackagesFromUsePackage {
      package = pkgs.emacsGit;  # replace with pkgs.emacsPgtk, or another version if desired.
      config = path/to/your/config.el;
      # config = path/to/your/config.org; # Org-Babel configs also supported

      # Optionally provide extra packages not in the configuration file.
      extraEmacsPackages = epkgs: [
        epkgs.use-package;
      ];

      # Optionally override derivations.
      override = epkgs: epkgs // {
        somePackage = epkgs.melpaPackages.somePackage.overrideAttrs(old: {
           # Apply fixes here
        });
      };
    })
  ];
}

See the overlay README for a full list of options.

Adding packages from outside ELPA / MELPA

Some packages may require more sophisticated derivation, but the following is a good starting point for adding external packages:

lambda-line.nix

{
  melpaBuild,
  fetchFromGitHub,
  all-the-icons,
}:
melpaBuild {
  pname = "lambda-line";
  version = "0-unstable-2022-11-23";
  src = fetchFromGitHub {
    owner = "Lambda-Emacs";
    repo = "lambda-line";
    rev = "22186321a7442f1bd3b121f739007bd809cb38f8";
    hash = "sha256-2tOXMqpmd14ohzmrRoV5Urf0HlnRPV1EVHm/d8OBSGE=";
  };
  # elisp dependencies
  packageRequires = [
    all-the-icons
  ];
}

You can then use the new package with automatic package management like so:

configuration.nix

{
  environment.systemPackages = [
    (pkgs.emacsWithPackagesFromUsePackage {
      ...
      override = epkgs: epkgs // {
        lambda-line = callPackage ./lambda-line.nix {
          inherit (pkgs) fetchFromGitHub;
          inherit (epkgs) melpaBuild all-the-icons;
        };
      };
    })
  ];
}

or manual package management like so:

configuration.nix

{
  environment.systemPackages = with pkgs;
    [ ...
      ((emacsPackagesFor emacsPgtkNativeComp).emacsWithPackages (epkgs: [ 
          epkgs.vterm 
          (callPackage ./lambda-line.nix {
            inherit (pkgs) fetchFromGitHub;
            inherit (epkgs) melpaBuild all-the-icons;
          };) 
       ]))
      ...
    ];
}

Packaging and testing emacs nixpkgs

Emacs packages can be defined and tested like other nixpkgs. They can be obtained from melpa, elpa or other sources such as github.

default.nix

{ melpaBuild
, lib
, fetchFromGitHub
...
}:

melpaBuild {
  pname = "...";
  version = "...";

  src = fetchFromGitHub {
    owner = "...";
    repo = "...";
    rev = "...";
    hash = "...";
  };

  packageRequires = [ ... ];

  patches = [ ... ];

  meta = {
    description = "...";
    license = lib.licenses.gpl3Plus;
  };
}

They are located at pkgs/applications/editors/emacs/elisp-packages/manual-packages/ and a new pkg must be added under pkgs/applications/editors/elisp-packages/manual-packages.nix. Once the nixpkg is ready, it can be tested using the following command. This inserts the nixpkg into the load-path of emacs.

 nix-shell -I nixpkgs=<path_to_nixpkgs_copy> -p "(emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [ epkgs.<package> ])"

Window Manager Integration

Out of the box, non-"Mac Port" versions of Emacs will not be picked up properly by window managers like Yabai because Emacs does not set the correct macOS window role. This can be fixed with a patch (e.g. the first patch in the example above). However, even with the patch, Yabai may not correctly pick up Emacs if you invoke the emacs binary directly from a shell. For Emacs to work properly with window managers you must invoke it by running the macOS app that is generated when you install Emacs with nix. You can setup an alias to do this like so (replace pkgs.emacs with the package you are using):

programs.zsh = {
  enable = true;
  shellAliases = {
    emacs = "${pkgs.emacs}/Applications/Emacs.app/Contents/MacOS/Emacs";
  };
};

Available Emacs Variants

Warning: Certain issues are possible, when mixing different versions of Emacs, in particular a configuration file tailored towards emacs with native compilation, may misbehave on non-native compiling versions, unless only the emacs lisp code is shared between them.

1. Stable (nixpkgs)

Emacs is available in nixpkgs under the names emacs and emacs-gtk. Since 2022-09, the package called emacs now installs the lucid toolkit instead of gtk. The reason is that emacs is less stable with gtk especially in daemon mode. However, the lucid flavor of emacs will not take into account the gtk theme (since it is not even gtk) and looks quite… ugly (see comparisons here). If you still prefer the gtk version of emacs, you can instead install emacs-gtk (before 2022-09 this package does not exist and emacs defaults to the gtk version).

2. Unstable (community overlay)

The community overlay provides nightly versions of the Emacs unstable branches, ELPA / MELPA packages, and EXWM + its dependencies. To use these, first apply the overlay (instructions below), which will make the packages available in nixpkgs. Then you can follow the normal nixpkgs installation instructions (above), but use your package of choice from the overlay (e.g. pkgs.emacsGit) in place of pkgs.emacs. See the README for a complete list of packages provided, and their differences.

With flakes

Using a system flake, one can specify the specific revision of the overlay as a flake input, for example:

inputs.emacs-overlay.url = "github:nix-community/emacs-overlay/da2f552d133497abd434006e0cae996c0a282394";

This can then be used in the system configuration by using the self argument:

nixpkgs.overlays = [ (import self.inputs.emacs-overlay) ];

Without flakes

For installing one of the unstable branches of emacs, add the following lines to /etc/nixos/configuration.nix:

configuration.nix

{
  nixpkgs.overlays = [
    (import (builtins.fetchGit {
      url = "https://github.com/nix-community/emacs-overlay.git";
      ref = "master";
      rev = "bfc8f6edcb7bcf3cf24e4a7199b3f6fed96aaecf"; # change the revision
    }))
  ];
}

3. Darwin (macOS)

Nixpkgs provides several of the "Mac Port" versions of Emacs, which have been patched to provide better integration with macOS (see the NixOS manual entry for a full list of packages). However, those packages typically track the stable releases of Emacs.

If you would like to use the latest version of Emacs on Darwin, one option is to use a package like emacsPgkt from the community overlay (see above), and apply patches yourself via an override. For example, here is a derivation that applies the patches from the emacs-plus homebrew formula:

pkgs.emacsPgtk.overrideAttrs (old: {
      patches =
        (old.patches or [])
        ++ [
          # Fix OS window role (needed for window managers like yabai)
          (fetchpatch {
            url = "https://raw.githubusercontent.com/d12frosted/homebrew-emacs-plus/master/patches/emacs-28/fix-window-role.patch";
            sha256 = "0c41rgpi19vr9ai740g09lka3nkjk48ppqyqdnncjrkfgvm2710z";
          })
          # Use poll instead of select to get file descriptors
          (fetchpatch {
            url = "https://raw.githubusercontent.com/d12frosted/homebrew-emacs-plus/master/patches/emacs-29/poll.patch";
            sha256 = "0j26n6yma4n5wh4klikza6bjnzrmz6zihgcsdx36pn3vbfnaqbh5";
          })
          # Enable rounded window with no decoration
          (fetchpatch {
            url = "https://raw.githubusercontent.com/d12frosted/homebrew-emacs-plus/master/patches/emacs-29/round-undecorated-frame.patch";
            sha256 = "111i0r3ahs0f52z15aaa3chlq7ardqnzpwp8r57kfsmnmg6c2nhf";
          })
          # Make Emacs aware of OS-level light/dark mode
          (fetchpatch {
            url = "https://raw.githubusercontent.com/d12frosted/homebrew-emacs-plus/master/patches/emacs-28/system-appearance.patch";
            sha256 = "14ndp2fqqc95s70fwhpxq58y8qqj4gzvvffp77snm2xk76c1bvnn";
          })
        ];
    });
  };
}

Troubleshooting

Plasma taskbar grouping

To fix/workaround Plasma grouping emacs incorrectly (confusing emacs.desktop with emacsclient.desktop), perform the following: 1. open emacs 2. right click title bar 3. More Actions > Configure Special Window Settings 4. click Add Property > Desktop File Name 5. set desktop file name to "/home/<USERNAME>/.nix-profile/share/applications/emacs.desktop" 6. hit OK 7. restart emacs if need

all emacs instances should now be grouped together, allowing you to pin it and reliably switch to it with Super+<number>

Spell checking

Because emacs expects the dictionaries to be on the same directory as aspell, they won't be picked up. To fix it install the aspellWithDicts package, specifying the dictionaries you want to use:

configuration.nix

{
  environment.systemPackages = with pkgs; [
    (aspellWithDicts (dicts: with dicts; [ en en-computers en-science es]))
  ];
}

A list of official dictionaries for aspell can be found on Aspell Website