From 05c132486d8cfae600bbfe8c9ac5d799b298afed Mon Sep 17 00:00:00 2001
From: Shea Levy <shea@shealevy.com>
Date: Mon, 5 Sep 2016 12:01:26 -0400
Subject: [PATCH] Initial version of nixBufferBuilders.withPackages.

This builds elisp to setup an emacs buffer with the packages given
available. See shlevy/nix-buffer for more information.

Currently only modifies $PATH.
---
 pkgs/build-support/emacs/buffer.nix | 20 ++++++++++++++++++++
 pkgs/top-level/all-packages.nix     |  2 ++
 2 files changed, 22 insertions(+)
 create mode 100644 pkgs/build-support/emacs/buffer.nix

diff --git a/pkgs/build-support/emacs/buffer.nix b/pkgs/build-support/emacs/buffer.nix
new file mode 100644
index 00000000000..2f7f536d5e7
--- /dev/null
+++ b/pkgs/build-support/emacs/buffer.nix
@@ -0,0 +1,20 @@
+# Functions to build elisp files to locally configure emcas buffers.
+# See https://github.com/shlevy/nix-buffer
+
+{ runCommand }:
+
+{
+  withPackages = pkgs: runCommand "dir-locals.el" { inherit pkgs; } ''
+    echo        "(make-local-variable 'process-environment)" >> $out
+    echo        "(setenv \"PATH\" (concat" >> $out
+    for pkg in $pkgs; do
+      echo        "                \"$pkg/bin:$pkg/sbin\"" >> $out
+    done
+    echo          "                (getenv \"PATH\")))" >> $out
+    echo -n       "(setq-local exec-path (append '(" >> $out
+    for pkg in $pkgs; do
+      echo -en  "\n                                \"$pkg/bin\" \"$pkg/sbin\"" >> $out
+    done
+    echo -e   ")\\n                              exec-path))" >> $out
+  '';
+}
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index c33dc33e6db..9023d33704c 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -285,6 +285,8 @@ in
       inherit kernel rootModules allowMissing;
     };
 
+  nixBufferBuilders = import ../build-support/emacs/buffer.nix { inherit (pkgs) runCommand; };
+
   pathsFromGraph = ../build-support/kernel/paths-from-graph.pl;
 
   srcOnly = args: callPackage ../build-support/src-only args;