wip: feat: Emacs config (from scratch }:3)

Working:
  - The daemon
  - Mutable config — well, kinda. I'm not yet sure how it will interact with
    `emacsWithPackagesFromUsePackage`.
  - Packages via Nixpkgs

README.org

@@ -97,7 +97,24 @@ sydnix-cli is a command-line utility written in Clojure wrapping various sydnix-
 
 * Tasks
 
-** Emacs
+** Begin setting up doomless Emacs
+
+*** DONE Daemon
+CLOSED: [2025-01-03 Fri 20:00]
+
+*** DONE Mutable config
+CLOSED: [2025-01-03 Fri 20:01]
+
+Path is currently hardcoded to =/persist/dots/users/crumb/programs/emacs=. An immutable file (created by home-manager's =programs.emacs.extraConfig=) loads =init.el= from the hardcoded path.
+
+*** DONE Packages via Nixpkgs
+CLOSED: [2025-01-03 Fri 20:40]
+
+*** TODO =map!= macro
+
+*** TODO Module system?
+
+** Emacs config
 
 *** [#A] One-off environment changes without direnv
 
@@ -329,6 +346,10 @@ https://discourse.nixos.org/t/what-to-do-with-a-full-boot-partition/2049
 
 Remove a given host from =~/.ssh/known_hosts=. Something like =sed -i -e '/192.168.122.54/d' .ssh/known_hosts=.
 
+*** TODO =lets-temp [NAME]=
+
+Create a new tempdir called ~[NAME]~, and cd into it.
+
 * References
 
 Following is a subset of the many places I've learnt from.
@@ -341,3 +362,5 @@ Following is a subset of the many places I've learnt from.
 - [cite:@christensen2020erase]
 - [cite:@ayats2024dropping]
 - [cite:@zaynetdinov2024you]
+- [[https://prelude.emacsredux.com/en/stable/][Emacs Prelude]]
+- [[https://github.com/doomemacs/doomemacs][Doom Emacs]]

flake.nix

@@ -56,4 +56,13 @@
 
       homeConfigurations = import ./outputs/homeConfigurations.nix inputs;
     };
+
+  nixConfig = {
+    extra-substituters = [
+      "https://nix-community.cachix.org"
+    ];
+    extra-trusted-public-keys = [
+      "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+    ];
+  };
 }

users/crumb/programs/emacs.nix

@@ -0,0 +1,49 @@
+{ config, lib, pkgs, inputs, ... }@args:
+
+# NOTE: Remember to wrap `programs.emacs.finalPackage` rather than pass a
+# wrapped package to `programs.emacs.package`, lest some unexpected behaviour
+# occur when home-manager calls emacs during the build process.
+
+let
+  emacsPackage = pkgs.emacs30-pgtk;
+  emacsConfigDir = "/persist/dots/users/crumb/programs/emacs";
+
+  emacs-overlay =
+    import (builtins.fetchTarball {
+      url =
+        "https://github.com/nix-community/emacs-overlay/archive/master.tar.gz";
+      sha256 = "sha256:02aln37ch9isz8h7dlm9v6jkl60g923z0dij0rjsxq7xi61fas2j";
+    });
+
+  # Create a new instance of nixpkgs with emacs-overlay applied. This is a
+  # little unorthodox, but we do it
+  #   1. for the sake of organisation — For pure aesthetics and a clean codebase, I want
+  #      everything Emacs to stay in this file;
+  #   2. and, there's simply no need to leak emacs-overlay's packages into the
+  #      global nixpkgs instance when nothing else is using it!
+  pkgs' = import inputs.nixpkgs {
+    system = args.system;
+    overlays = [ emacs-overlay ];
+  };
+
+  my-emacs = pkgs'.emacsWithPackagesFromUsePackage {
+    config = ./emacs/init.el;
+    defaultInitFile = false;
+    package = emacsPackage;
+    alwaysEnsure = true;
+  };
+in {
+  programs.emacs = {
+    enable = true;
+    package = my-emacs;
+    extraConfig = ''
+      (load (file-name-concat "${emacsConfigDir}" "init"))
+    '';
+  };
+
+  services.emacs = {
+    enable = true;
+    # Generate a desktop entry for emacsclient.
+    client.enable = true;
+  };
+}

users/crumb/programs/emacs/init.el

@@ -0,0 +1,6 @@
+;; -*- lexical-binding: t; -*-
+
+(require 'use-package-ensure)
+(setq use-package-always-ensure t)
+
+(use-package evil)