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

@@ -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
+  '';
+}

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;