Add a method to make Emacs closures from use-package declarations

README.org

@@ -14,6 +14,32 @@ is updated daily.
 
 This package is named =emacsGit= in the overlay.
 
+** Extra library functionality
+This overlay comes with an extra function to generate an Emacs closure from =use-package= declarations.
+This is an abstraction on top of =emacsWithPackages=.
+#+BEGIN_SRC nix
+{
+  environment.systemPackages = [
+    (emacsWithPackagesUsePackage {
+      config = builtins.readFile ./emacs.el;
+      # Package is optional, defaults to pkgs.emacs
+      package = pkgs.emacsGit;
+      # Optionally provide extra packages not in the configuration file
+      extraEmacsPackages = epkgs: [
+        epkgs.cask
+      ];
+      # Optionally override derivations
+      override = epkgs: epkgs // {
+        weechat = epkgs.melpaPackages.weechat.overrideAttrs(old: {
+          patches = [ ./weechat-el.patch ];
+        });
+      };
+    })
+  ];
+}
+#+END_SRC
+
+
 ** Usage of the overlay
 *** Latest master each rebuild
 One way, and probably the most convenient way to pull in this overlay is by
@@ -28,11 +54,13 @@ package =emacsGit= available. These of course change quite rapidly and will
 cause compilation time.
 
 #+BEGIN_SRC nix
+{
   nixpkgs.overlays = [
     (import (builtins.fetchTarball {
       url = https://github.com/nix-community/emacs-overlay/archive/master.tar.gz;
     }))
   ];
+}
 #+END_SRC
 
 #  LocalWords:  EXWM NixOS emacsGit

default.nix

@@ -37,6 +37,8 @@ in {
     ];
   });
 
+  emacsWithPackagesFromUsePackage = import ./elisp.nix { pkgs = self; };
+
   emacsPackagesNgFor = emacs: (
     (super.emacsPackagesNgFor emacs).overrideScope'(eself: esuper: let
 

elisp.nix

@@ -0,0 +1,44 @@
+/*
+Parse an emacs lisp configuration file to derive packages from
+use-package declarations.
+*/
+
+{ pkgs }:
+
+let
+  isStrEmpty = s: (builtins.replaceStrings [" "] [""] s) == "";
+
+  splitString = _sep: _s: builtins.filter
+    (x: builtins.typeOf x == "string")
+    (builtins.split _sep _s);
+
+  stripComments = dotEmacs: let
+    lines = splitString "\n" dotEmacs;
+    stripped = builtins.map (l:
+      builtins.elemAt (splitString ";;" l) 0) lines;
+  in builtins.concatStringsSep " " stripped;
+
+  parsePackages = dotEmacs: let
+    strippedComments = stripComments dotEmacs;
+    tokens = builtins.filter (t: !(isStrEmpty t)) (builtins.map
+      (t: if builtins.typeOf t == "list" then builtins.elemAt t 0 else t)
+      (builtins.split "([\(\)])" strippedComments));
+    matches = builtins.map (t:
+      builtins.match "^use-package[[:space:]]+([A-Za-z0-9_-]+).*" t) tokens;
+  in builtins.map (m: builtins.elemAt m 0)
+      (builtins.filter (m: m != null) matches);
+
+in {
+  config,
+  extraEmacsPackages ? epkgs: [],
+  package ? pkgs.emacs,
+  override ? (epkgs: epkgs)
+}: let
+  packages = parsePackages config;
+  emacsPackages = pkgs.emacsPackagesNgGen package;
+  emacsWithPackages = emacsPackages.emacsWithPackages;
+in emacsWithPackages (epkgs: let
+  overriden = override epkgs;
+  usePkgs = builtins.map (name: overriden.${name}) packages;
+  extraPkgs = extraEmacsPackages overriden;
+in [ overriden.use-package ] ++ usePkgs ++ extraPkgs)