New option to specify emacs package during build

default.nix

@@ -1,5 +1,7 @@
 { # Package set to build the Emacs environment from
   emacsPackages
+  # Emacs package to use during build
+, emacs ? emacsPackages.emacs
   # You may override to use your version of `straight`
 , straight ? null
   # Your `init.el` file to use for discovering and installing packages
@@ -14,7 +16,7 @@
 , abortOnNotFound ? false }:
 
 let
-  libstraight = epkgs.callPackage ./libstraight.nix { inherit abortOnNotFound epkgs; };
+  libstraight = epkgs.callPackage ./libstraight.nix { inherit abortOnNotFound epkgs emacs; };
   epkgs =
     if straight == null then
       emacsPackages.overrideScope' (self: super:

libstraight.nix

@@ -1,5 +1,5 @@
 { abortOnNotFound ? true,
-  lib, stdenv, epkgs, writeScript }:
+  lib, stdenv, epkgs, emacs, writeScript }:
 
 let
   inherit (builtins) filter trace;
@@ -45,7 +45,7 @@ let
 
   packagesJSON = { emacsInitFile, emacsLoadFiles, emacsArgs }: stdenv.mkDerivation {
     name = "emacs-straight-packages.json";
-    buildInputs = [ epkgs.emacs ];
+    buildInputs = [ emacs ];
     buildPhase = ":";
     installPhase = ''
       runHook preInstall
@@ -63,7 +63,7 @@ let
   emacsEnv = { emacsInitFile, emacsLoadFiles, emacsArgs }: { packages, straightDir }: stdenv.mkDerivation {
     name = "straight-emacs-env";
     buildPhase = ":";
-    buildInputs = [ epkgs.emacs ];
+    buildInputs = [ emacs ];
     installPhase = ''
       runHook preInstall