From c8b82d46ba36851fc6ef2710397091b88ae71bdd Mon Sep 17 00:00:00 2001
From: Marien Zwart <marien.zwart@gmail.com>
Date: Sat, 4 May 2024 22:48:11 +1000
Subject: [PATCH] Use emacs-overlay directly, not as overlay

Slight hack to avoid instantiating an additional nixpkgs unnecessarily.
---
 flake.nix        | 21 ++++++++++++++-------
 home-manager.nix |  6 ++++--
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/flake.nix b/flake.nix
index 1cce51f..0faaa3b 100644
--- a/flake.nix
+++ b/flake.nix
@@ -30,6 +30,13 @@
   outputs = { doomemacs, nixpkgs, emacs-overlay, ... }: let
     systems = [ "x86_64-linux" ];
     perSystemPackages = f: nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
+    # Hack to avoid pkgs.extend having to instantiate an additional nixpkgs.
+    #
+    # We need emacsPackagesFor from the overlay, but neither the overlay itself
+    # (it only uses "super", not "self") nor us actually needs anything overlaid
+    # on nixpkgs. So we can call the overlay and pass emacsPackagesFor through
+    # directly instead of having pkgs.callPackage do it.
+    emacsPackagesForFromOverlay = pkgs: (emacs-overlay.overlays.package {} pkgs).emacsPackagesFor;
     in {
       packages = perSystemPackages (pkgs:
         let
@@ -38,25 +45,25 @@
             # TODO: drop after NixOS 24.05 release.
             emacs = pkgs.emacs29;
             doomLocalDir = "~/.local/share/nix-doom-unstraightened";
+            emacsPackagesFor = emacsPackagesForFromOverlay pkgs;
           };
-          pkgsWithEmacsOverlay = pkgs.extend emacs-overlay.overlays.package;
         in {
           # Current Doom + NixOS 23.11 requires emacs-overlay: Doom pins
           # emacs-fish-completion, which moved from gitlab to github recently
           # enough stable nixpkgs pulls it from the wrong source.
-          doom-minimal = (pkgsWithEmacsOverlay.callPackages ./doom.nix (common // { doomDir = ./doomdirs/minimal; })).doomEmacs;
-          doom-full = (pkgsWithEmacsOverlay.callPackages ./doom.nix (common // { full = true; doomDir = ./doomdirs/minimal; })).doomEmacs;
-          doom-example = (pkgsWithEmacsOverlay.callPackages ./doom.nix (common // { doomDir = ./doomdirs/example; })).doomEmacs;
-          doom-example-without-loader = (pkgsWithEmacsOverlay.callPackages ./doom.nix (common // {
+          doom-minimal = (pkgs.callPackages ./doom.nix (common // { doomDir = ./doomdirs/minimal; })).doomEmacs;
+          doom-full = (pkgs.callPackages ./doom.nix (common // { full = true; doomDir = ./doomdirs/minimal; })).doomEmacs;
+          doom-example = (pkgs.callPackages ./doom.nix (common // { doomDir = ./doomdirs/example; })).doomEmacs;
+          doom-example-without-loader = (pkgs.callPackages ./doom.nix (common // {
             doomDir = ./doomdirs/example;
             profileName = "";
           })).doomEmacs;
         });
       overlays.default = final: prev:
         let
-          pkgs = final.extend emacs-overlay.overlays.package;
-          callPackages = args: (pkgs.callPackages ./doom.nix ({
+          callPackages = args: (final.callPackages ./doom.nix ({
             doomSource = doomemacs;
+            emacsPackagesFor = emacsPackagesForFromOverlay final;
           } // args));
         in {
           doomEmacs = args: (callPackages args).doomEmacs;
diff --git a/home-manager.nix b/home-manager.nix
index db8bf11..589bea0 100644
--- a/home-manager.nix
+++ b/home-manager.nix
@@ -99,8 +99,10 @@ in {
 
   config = mkIf cfg.enable (mkMerge [
     (let
-      doomPackages = (pkgs.extend emacsOverlay).callPackages ./doom.nix {
-        inherit doomSource;
+      # Hack to avoid pkgs.extend (see flake.nix).
+      emacsPackagesFor = (emacsOverlay {} pkgs).emacsPackagesFor;
+      doomPackages = pkgs.callPackages ./doom.nix {
+        inherit doomSource emacsPackagesFor;
         inherit (cfg) emacs doomDir doomLocalDir profileName noProfileHack;
       };
     in